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rfc:fyi:fyi36

Network Working Group R. Shirey Request for Comments: 4949 August 2007 FYI: 36 Obsoletes: 2828 Category: Informational

               Internet Security Glossary, Version 2

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The IETF Trust (2007).

RFC Editor Note

 This document is both a major revision and a major expansion of the
 Security Glossary in RFC 2828. This revised Glossary is an extensive
 reference that should help the Internet community to improve the
 clarity of documentation and discussion in an important area of
 Internet technology. However, readers should be aware of the
 following:
 (1) The recommendations and some particular interpretations in
 definitions are those of the author, not an official IETF position.
 The IETF has not taken a formal position either for or against
 recommendations made by this Glossary, and the use of RFC 2119
 language (e.g., SHOULD NOT) in the Glossary must be understood as
 unofficial. In other words, the usage rules, wording interpretations,
 and other recommendations that the Glossary offers are personal
 opinions of the Glossary's author. Readers must judge for themselves
 whether or not to follow his recommendations, based on their own
 knowledge combined with the reasoning presented in the Glossary.
 (2) The glossary is rich in the history of early network security
 work, but it may be somewhat incomplete in describing recent security
 work, which has been developing rapidly.

Shirey Informational [Page 1] RFC 4949 Internet Security Glossary, Version 2 August 2007

Abstract

 This Glossary provides definitions, abbreviations, and explanations
 of terminology for information system security. The 334 pages of
 entries offer recommendations to improve the comprehensibility of
 written material that is generated in the Internet Standards Process
 (RFC 2026). The recommendations follow the principles that such
 writing should (a) use the same term or definition whenever the same
 concept is mentioned; (b) use terms in their plainest, dictionary
 sense; (c) use terms that are already well-established in open
 publications; and (d) avoid terms that either favor a particular
 vendor or favor a particular technology or mechanism over other,
 competing techniques that already exist or could be developed.

Table of Contents

 1. Introduction ....................................................3
 2. Format of Entries ...............................................4
    2.1. Order of Entries ...........................................4
    2.2. Capitalization and Abbreviations ...........................5
    2.3. Support for Automated Searching ............................5
    2.4. Definition Type and Context ................................5
    2.5. Explanatory Notes ..........................................6
    2.6. Cross-References ...........................................6
    2.7. Trademarks .................................................6
    2.8. The New Punctuation ........................................6
 3. Types of Entries ................................................7
    3.1. Type "I": Recommended Definitions of Internet Origin .......7
    3.2. Type "N": Recommended Definitions of Non-Internet Origin ...8
    3.3. Type "O": Other Terms and Definitions To Be Noted ..........8
    3.4. Type "D": Deprecated Terms and Definitions .................8
    3.5. Definition Substitutions ...................................8
 4. Definitions .....................................................9
 5. Security Considerations .......................................343
 6. Normative Reference ...........................................343
 7. Informative References ........................................343
 8. Acknowledgments ...............................................364

Shirey Informational [Page 2] RFC 4949 Internet Security Glossary, Version 2 August 2007

1. Introduction

 This Glossary is *not* an Internet Standard, and its recommendations
 represent only the opinions of its author. However, this Glossary
 gives reasons for its recommendations -- especially for the SHOULD
 NOTs -- so that readers can judge for themselves what to do.
 This Glossary provides an internally consistent and self-contained
 set of terms, abbreviations, and definitions -- supported by
 explanations, recommendations, and references -- for terminology that
 concerns information system security. The intent of this Glossary is
 to improve the comprehensibility of written materials that are
 generated in the Internet Standards Process (RFC 2026) -- i.e., RFCs,
 Internet-Drafts, and other items of discourse -- which are referred
 to here as IDOCs. A few non-security, networking terms are included
 to make the Glossary self-contained, but more complete glossaries of
 such terms are available elsewhere [A1523, F1037, R1208, R1983].
 This Glossary supports the goals of the Internet Standards Process:
 o  Clear, Concise, Easily Understood Documentation
    This Glossary seeks to improve comprehensibility of security-
    related content of IDOCs. That requires wording to be clear and
    understandable, and requires the set of security-related terms and
    definitions to be consistent and self-supporting. Also,
    terminology needs to be uniform across all IDOCs; i.e., the same
    term or definition needs to be used whenever and wherever the same
    concept is mentioned. Harmonization of existing IDOCs need not be
    done immediately, but it is desirable to correct and standardize
    terminology when new versions are issued in the normal course of
    standards development and evolution.
 o  Technical Excellence
    Just as Internet Standard (STD) protocols should operate
    effectively, IDOCs should use terminology accurately, precisely,
    and unambiguously to enable standards to be implemented correctly.
 o  Prior Implementation and Testing
    Just as STD protocols require demonstrated experience and
    stability before adoption, IDOCs need to use well-established
    language; and the robustness principle for protocols -- "be
    liberal in what you accept, and conservative in what you send" --
    is also applicable to the language used in IDOCs that describe
    protocols. Using terms in their plainest, dictionary sense (when
    appropriate) helps to make them more easily understood by

Shirey Informational [Page 3] RFC 4949 Internet Security Glossary, Version 2 August 2007

    international readers. IDOCs need to avoid using private, newly
    invented terms in place of generally accepted terms from open
    publications. IDOCs need to avoid substituting new definitions
    that conflict with established ones. IDOCs need to avoid using
    "cute" synonyms (e.g., "Green Book"), because no matter how
    popular a nickname may be in one community, it is likely to cause
    confusion in another.
    However, although this Glossary strives for plain, internationally
    understood English language, its terms and definitions are biased
    toward English as used in the United States of America (U.S.).
    Also, with regard to terminology used by national governments and
    in national defense areas, the glossary addresses only U.S. usage.
 o  Openness, Fairness, and Timeliness
    IDOCs need to avoid using proprietary and trademarked terms for
    purposes other than referring to those particular systems. IDOCs
    also need to avoid terms that either favor a particular vendor or
    favor a particular security technology or mechanism over other,
    competing techniques that already exist or might be developed in
    the future. The set of terminology used across the set of IDOCs
    needs to be flexible and adaptable as the state of Internet
    security art evolves.
 In support of those goals, this Glossary offers guidance by marking
 terms and definitions as being either endorsed or deprecated for use
 in IDOCs. The key words "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
 and "OPTIONAL" are intended to be interpreted the same way as in an
 Internet Standard (i.e., as specified in RFC 2119 [R2119]). Other
 glossaries (e.g., [Raym]) list additional terms that deal with
 Internet security but have not been included in this Glossary because
 they are not appropriate for IDOCs.

2. Format of Entries

 Section 4 presents Glossary entries in the following manner:

2.1. Order of Entries

 Entries are sorted in lexicographic order, without regard to
 capitalization. Numeric digits are treated as preceding alphabetic
 characters, and special characters are treated as preceding digits.
 Blanks are treated as preceding non-blank characters, except that a
 hyphen or slash between the parts of a multiword entry (e.g.,
 "RED/BLACK separation") is treated like a blank.

Shirey Informational [Page 4] RFC 4949 Internet Security Glossary, Version 2 August 2007

 If an entry has multiple definitions (e.g., "domain"), they are
 numbered beginning with "1", and any of those multiple definitions
 that are RECOMMENDED for use in IDOCs are presented before other
 definitions for that entry. If definitions are closely related (e.g.,
 "threat"), they are denoted by adding letters to a number, such as
 "1a" and "1b".

2.2. Capitalization and Abbreviations

 Entries that are proper nouns are capitalized (e.g., "Data Encryption
 Algorithm"), as are other words derived from proper nouns (e.g.,
 "Caesar cipher"). All other entries are not capitalized (e.g.,
 "certification authority"). Each acronym or other abbreviation that
 appears in this Glossary, either as an entry or in a definition or
 explanation, is defined in this Glossary, except items of common
 English usage, such as "a.k.a.", "e.g.", "etc.", "i.e.", "vol.",
 "pp.", and "U.S.".

2.3. Support for Automated Searching

 Each entry is preceded by a dollar sign ($) and a space. This makes
 it possible to find the defining entry for an item "X" by searching
 for the character string "$ X", without stopping at other entries in
 which "X" is used in explanations.

2.4. Definition Type and Context

 Each entry is preceded by a character -- I, N, O, or D -- enclosed in
 parentheses, to indicate the type of definition (as is explained
 further in Section 3):
 -  "I" for a RECOMMENDED term or definition of Internet origin.
 -  "N" if RECOMMENDED but not of Internet origin.
 -  "O" for a term or definition that is NOT recommended for use in
    IDOCs but is something that authors of Internet documents should
    know about.
 -  "D" for a term or definition that is deprecated and SHOULD NOT be
    used in Internet documents.
 If a definition is valid only in a specific context (e.g.,
 "baggage"), that context is shown immediately following the
 definition type and is enclosed by a pair of slash symbols (/). If
 the definition is valid only for specific parts of speech, that is
 shown in the same way (e.g., "archive").

Shirey Informational [Page 5] RFC 4949 Internet Security Glossary, Version 2 August 2007

2.5. Explanatory Notes

 Some entries have explanatory text that is introduced by one or more
 of the following keywords:
 -  Deprecated Abbreviation (e.g., "AA")
 -  Deprecated Definition (e.g., "digital certification")
 -  Deprecated Usage (e.g., "authenticate")
 -  Deprecated Term (e.g., "certificate authority")
 -  Pronunciation (e.g., "*-property")
 -  Derivation (e.g., "discretionary access control")
 -  Tutorial (e.g., "accreditation")
 -  Example (e.g., "back door")
 -  Usage (e.g., "access")
 Explanatory text in this Glossary MAY be reused in IDOCs. However,
 this text is not intended to authoritatively supersede text of an
 IDOC in which the Glossary entry is already used.

2.6. Cross-References

 Some entries contain a parenthetical remark of the form "(See: X.)",
 where X is a list of other, related terms. Some entries contain a
 remark of the form "(Compare: X)", where X is a list of terms that
 either are antonyms of the entry or differ in some other manner worth
 noting.

2.7. Trademarks

 All servicemarks and trademarks that appear in this Glossary are used
 in an editorial fashion and to the benefit of the mark owner, without
 any intention of infringement.

2.8. The New Punctuation

 This Glossary uses the "new" or "logical" punctuation style favored
 by computer programmers, as described by Raymond [Raym]: Programmers
 use pairs of quotation marks the same way they use pairs of
 parentheses, i.e., as balanced delimiters. For example, if "Alice
 sends" is a phrase, and so are "Bill receives" and "Eve listens",
 then a programmer would write the following sentence:
    "Alice sends", "Bill receives", and "Eve listens".
 According to standard American usage, the punctuation in that
 sentence is incorrect; the continuation commas and the final period
 should go inside the string quotes, like this:
    "Alice sends," "Bill receives," and "Eve listens."

Shirey Informational [Page 6] RFC 4949 Internet Security Glossary, Version 2 August 2007

 However, a programmer would not include a character in a literal
 string if the character did not belong there, because that could
 cause an error. For example, suppose a sentence in a draft of a
 tutorial on the vi editing language looked like this:
    Then delete one line from the file by typing "dd".
 A book editor following standard usage might change the sentence to
 look like this:
    Then delete one line from the file by typing "dd."
 However, in the vi language, the dot character repeats the last
 command accepted. So, if a reader entered "dd.", two lines would be
 deleted instead of one.
 Similarly, use of standard American punctuation might cause
 misunderstanding in entries in this Glossary. Thus, the new
 punctuation is used here, and we recommend it for IDOCs.

3. Types of Entries

 Each entry in this Glossary is marked as type I, N, O, or D:

3.1. Type "I": Recommended Definitions of Internet Origin

 The marking "I" indicates two things:
 -  Origin: "I" (as opposed to "N") means either that the Internet
    Standards Process or Internet community is authoritative for the
    definition *or* that the term is sufficiently generic that this
    Glossary can freely state a definition without contradicting a
    non-Internet authority (e.g., "attack").
 -  Recommendation: "I" (as opposed to "O") means that the term and
    definition are RECOMMENDED for use in IDOCs. However, some "I"
    entries may be accompanied by a "Usage" note that states a
    limitation (e.g., "certification"), and IDOCs SHOULD NOT use the
    defined term outside that limited context.
 Many "I" entries are proper nouns (e.g., "Internet Protocol") for
 which the definition is intended only to provide basic information;
 i.e., the authoritative definition of such terms is found elsewhere.
 For a proper noun described as an "Internet protocol", please refer
 to the current edition of "Internet Official Protocol Standards"
 (Standard 1) for the standardization status of the protocol.

Shirey Informational [Page 7] RFC 4949 Internet Security Glossary, Version 2 August 2007

3.2. Type "N": Recommended Definitions of Non-Internet Origin

 The marking "N" indicates two things:
 -  Origin: "N" (as opposed to "I") means that the entry has a non-
    Internet basis or origin.
 -  Recommendation: "N" (as opposed to "O") means that the term and
    definition are RECOMMENDED for use in IDOCs, if they are needed at
    all in IDOCs. Many of these entries are accompanied by a label
    that states a context (e.g., "package") or a note that states a
    limitation (e.g., "data integrity"), and IDOCs SHOULD NOT use the
    defined term outside that context or limit. Some of the contexts
    are rarely if ever expected to occur in an IDOC (e.g., "baggage").
    In those cases, the listing exists to make Internet authors aware
    of the non-Internet usage so that they can avoid conflicts with
    non-Internet documents.

3.3. Type "O": Other Terms and Definitions To Be Noted

 The marking "O" means that the definition is of non-Internet origin
 and SHOULD NOT be used in IDOCs *except* in cases where the term is
 specifically identified as non-Internet.
 For example, an IDOC might mention "BCA" (see: brand certification
 authority) or "baggage" as an example of some concept; in that case,
 the document should specifically say "SET(trademark) BCA" or
 "SET(trademark) baggage" and include the definition of the term.

3.4. Type "D": Deprecated Terms and Definitions

 If this Glossary recommends that a term or definition SHOULD NOT be
 used in IDOCs, then the entry is marked as type "D", and an
 explanatory note -- "Deprecated Term", "Deprecated Abbreviation",
 "Deprecated Definition", or "Deprecated Usage" -- is provided.

3.5. Definition Substitutions

 Some terms have a definition published by a non-Internet authority --
 a government (e.g., "object reuse"), an industry (e.g., "Secure Data
 Exchange"), a national authority (e.g., "Data Encryption Standard"),
 or an international body (e.g., "data confidentiality") -- that is
 suitable for use in IDOCs. In those cases, this Glossary marks the
 definition "N", recommending its use in Internet documents.
 Other such terms have definitions that are inadequate or
 inappropriate for IDOCs. For example, a definition might be outdated
 or too narrow, or it might need clarification by substituting more
 careful wording (e.g., "authentication exchange") or explanations,
 using other terms that are defined in this Glossary. In those cases,

Shirey Informational [Page 8] RFC 4949 Internet Security Glossary, Version 2 August 2007

 this Glossary marks the entry "O", and provides an "I" or "N" entry
 that precedes, and is intended to supersede, the "O" entry.
 In some cases where this Glossary provides a definition to supersede
 an "O" definition, the substitute is intended to subsume the meaning
 of the "O" entry and not conflict with it. For the term "security
 service", for example, the "O" definition deals narrowly with only
 communication services provided by layers in the OSIRM and is
 inadequate for the full range of IDOC usage, while the new "I"
 definition provided by this Glossary can be used in more situations
 and for more kinds of service. However, the "O" definition is also
 listed so that IDOC authors will be aware of the context in which the
 term is used more narrowly.
 When making substitutions, this Glossary attempts to avoid
 contradicting any non-Internet authority. Still, terminology differs
 between authorities such as the American Bar Association, OSI, SET,
 the U.S. DoD, and other authorities; and this Glossary probably is
 not exactly aligned with any of them.

4. Definitions

 $ *-property
    (N) Synonym for "confinement property" in the context of the Bell-
    LaPadula model. Pronunciation: star property.
 $ 3DES
    (N) See: Triple Data Encryption Algorithm.
 $ A1 computer system
    (O) /TCSEC/ See: Tutorial under "Trusted Computer System
    Evaluation Criteria". (Compare: beyond A1.)
 $ AA
    (D) See: Deprecated Usage under "attribute authority".
 $ ABA Guidelines
    (N) "American Bar Association (ABA) Digital Signature Guidelines"
    [DSG], a framework of legal principles for using digital
    signatures and digital certificates in electronic commerce.
 $ Abstract Syntax Notation One (ASN.1)
    (N) A standard for describing data objects. [Larm, X680] (See:
    CMS.)
    Usage: IDOCs SHOULD use the term "ASN.1" narrowly to describe the
    notation or language called "Abstract Syntax Notation One". IDOCs
    MAY use the term more broadly to encompass the notation, its

Shirey Informational [Page 9] RFC 4949 Internet Security Glossary, Version 2 August 2007

    associated encoding rules (see: BER), and software tools that
    assist in its use, when the context makes this meaning clear.
    Tutorial: OSIRM defines computer network functionality in layers.
    Protocols and data objects at higher layers are abstractly defined
    to be implemented using protocols and data objects from lower
    layers. A higher layer may define transfers of abstract objects
    between computers, and a lower layer may define those transfers
    concretely as strings of bits. Syntax is needed to specify data
    formats of abstract objects, and encoding rules are needed to
    transform abstract objects into bit strings at lower layers. OSI
    standards use ASN.1 for those specifications and use various
    encoding rules for those transformations. (See: BER.)
    In ASN.1, formal names are written without spaces, and separate
    words in a name are indicated by capitalizing the first letter of
    each word except the first word. For example, the name of a CRL is
    "certificateRevocationList".
 $ ACC
    (I) See: access control center.
 $ acceptable risk
    (I) A risk that is understood and tolerated by a system's user,
    operator, owner, or accreditor, usually because the cost or
    difficulty of implementing an effective countermeasure for the
    associated vulnerability exceeds the expectation of loss. (See:
    adequate security, risk, "second law" under "Courtney's laws".)
 $ access
    1a. (I) The ability and means to communicate with or otherwise
    interact with a system to use system resources either to handle
    information or to gain knowledge of the information the system
    contains. (Compare: handle.)
    Usage: The definition is intended to include all types of
    communication with a system, including one-way communication in
    either direction. In actual practice, however, passive users might
    be treated as not having "access" and, therefore, be exempt from
    most requirements of the system's security policy. (See: "passive
    user" under "user".)
    1b. (O) "Opportunity to make use of an information system (IS)
    resource." [C4009]
    2. (O) /formal model/ "A specific type of interaction between a
    subject and an object that results in the flow of information from
    one to the other." [NCS04]

Shirey Informational [Page 10] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ Access Certificate for Electronic Services (ACES)
    (O) A PKI operated by the U.S. Government's General Services
    Administration in cooperation with industry partners. (See: CAM.)
 $ access control
    1. (I) Protection of system resources against unauthorized access.
    2. (I) A process by which use of system resources is regulated
    according to a security policy and is permitted only by authorized
    entities (users, programs, processes, or other systems) according
    to that policy. (See: access, access control service, computer
    security, discretionary access control, mandatory access control,
    role-based access control.)
    3. (I) /formal model/ Limitations on interactions between subjects
    and objects in an information system.
    4. (O) "The prevention of unauthorized use of a resource,
    including the prevention of use of a resource in an unauthorized
    manner." [I7498-2]
    5. (O) /U.S. Government/ A system using physical, electronic, or
    human controls to identify or admit personnel with properly
    authorized access to a SCIF.
 $ access control center (ACC)
    (I) A computer that maintains a database (possibly in the form of
    an access control matrix) defining the security policy for an
    access control service, and that acts as a server for clients
    requesting access control decisions.
    Tutorial: An ACC is sometimes used in conjunction with a key
    center to implement access control in a key-distribution system
    for symmetric cryptography. (See: BLACKER, Kerberos.)
 $ access control list (ACL)
    (I) /information system/ A mechanism that implements access
    control for a system resource by enumerating the system entities
    that are permitted to access the resource and stating, either
    implicitly or explicitly, the access modes granted to each entity.
    (Compare: access control matrix, access list, access profile,
    capability list.)
 $ access control matrix
    (I) A rectangular array of cells, with one row per subject and one
    column per object. The entry in a cell -- that is, the entry for a
    particular subject-object pair -- indicates the access mode that
    the subject is permitted to exercise on the object. Each column is

Shirey Informational [Page 11] RFC 4949 Internet Security Glossary, Version 2 August 2007

    equivalent to an "access control list" for the object; and each
    row is equivalent to an "access profile" for the subject.
 $ access control service
    (I) A security service that protects against a system entity using
    a system resource in a way not authorized by the system's security
    policy. (See: access control, discretionary access control,
    identity-based security policy, mandatory access control, rule-
    based security policy.)
    Tutorial: This service includes protecting against use of a
    resource in an unauthorized manner by an entity (i.e., a
    principal) that is authorized to use the resource in some other
    manner. (See: insider.) The two basic mechanisms for implementing
    this service are ACLs and tickets.
 $ access level
    1. (D) Synonym for the hierarchical "classification level" in a
    security level. [C4009] (See: security level.)
    2. (D) Synonym for "clearance level".
    Deprecated Definitions: IDOCs SHOULD NOT use this term with these
    definitions because they duplicate the meaning of more specific
    terms. Any IDOC that uses this term SHOULD provide a specific
    definition for it because access control may be based on many
    attributes other than classification level and clearance level.
 $ access list
    (I) /physical security/ Roster of persons who are authorized to
    enter a controlled area. (Compare: access control list.)
 $ access mode
    (I) A distinct type of data processing operation (e.g., read,
    write, append, or execute, or a combination of operations) that a
    subject can potentially perform on an object in an information
    system. [Huff] (See: read, write.)
 $ access policy
    (I) A kind of "security policy". (See: access, access control.)
 $ access profile
    (O) Synonym for "capability list".
    Usage: IDOCs that use this term SHOULD state a definition for it
    because the definition is not widely known.

Shirey Informational [Page 12] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ access right
    (I) Synonym for "authorization"; emphasizes the possession of the
    authorization by a system entity.
 $ accountability
    (I) The property of a system or system resource that ensures that
    the actions of a system entity may be traced uniquely to that
    entity, which can then be held responsible for its actions. [Huff]
    (See: audit service.)
    Tutorial: Accountability (a.k.a. individual accountability)
    typically requires a system ability to positively associate the
    identity of a user with the time, method, and mode of the user's
    access to the system. This ability supports detection and
    subsequent investigation of security breaches. Individual persons
    who are system users are held accountable for their actions after
    being notified of the rules of behavior for using the system and
    the penalties associated with violating those rules.
 $ accounting See: COMSEC accounting.
 $ accounting legend code (ALC)
    (O) /U.S. Government/ Numeric system used to indicate the minimum
    accounting controls required for items of COMSEC material within
    the CMCS. [C4009] (See: COMSEC accounting.)
 $ accreditation
    (N) An administrative action by which a designated authority
    declares that an information system is approved to operate in a
    particular security configuration with a prescribed set of
    safeguards. [FP102, SP37] (See: certification.)
    Tutorial: An accreditation is usually based on a technical
    certification of the system's security mechanisms. To accredit a
    system, the approving authority must determine that any residual
    risk is an acceptable risk. Although the terms "certification" and
    "accreditation" are used more in the U.S. DoD and other U.S.
    Government agencies than in commercial organizations, the concepts
    apply any place where managers are required to deal with and
    accept responsibility for security risks. For example, the
    American Bar Association is developing accreditation criteria for
    CAs.
 $ accreditation boundary
    (O) Synonym for "security perimeter". [C4009]

Shirey Informational [Page 13] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ accreditor
    (N) A management official who has been designated to have the
    formal authority to "accredit" an information system, i.e., to
    authorize the operation of, and the processing of sensitive data
    in, the system and to accept the residual risk associated with the
    system. (See: accreditation, residual risk.)
 $ ACES
    (O) See: Access Certificate for Electronic Services.
 $ ACL
    (I) See: access control list.
 $ acquirer
    1. (O) /SET/ "The financial institution that establishes an
    account with a merchant and processes payment card authorizations
    and payments." [SET1]
    2. (O) /SET/ "The institution (or its agent) that acquires from
    the card acceptor the financial data relating to the transaction
    and initiates that data into an interchange system." [SET2]
 $ activation data
    (N) Secret data, other than keys, that is required to access a
    cryptographic module. (See: CIK. Compare: initialization value.)
 $ active attack
    (I) See: secondary definition under "attack".
 $ active content
    1a. (I) Executable software that is bound to a document or other
    data file and that executes automatically when a user accesses the
    file, without explicit initiation by the user. (Compare: mobile
    code.)
    Tutorial: Active content can be mobile code when its associated
    file is transferred across a network.
    1b. (O) "Electronic documents that can carry out or trigger
    actions automatically on a computer platform without the
    intervention of a user. [This technology enables] mobile code
    associated with a document to execute as the document is
    rendered." [SP28]
 $ active user
    (I) See: secondary definition under "system user".

Shirey Informational [Page 14] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ active wiretapping
    (I) A wiretapping attack that attempts to alter data being
    communicated or otherwise affect data flow. (See: wiretapping.
    Compare: active attack, passive wiretapping.)
 $ add-on security
    (N) The retrofitting of protection mechanisms, implemented by
    hardware or software, in an information system after the system
    has become operational. [FP039] (Compare: baked-in security.)
 $ adequate security
    (O) /U.S. DoD/ "Security commensurate with the risk and magnitude
    of harm resulting from the loss, misuse, or unauthorized access to
    or modification of information." (See: acceptable risk, residual
    risk.)
 $ administrative security
    1. (I) Management procedures and constraints to prevent
    unauthorized access to a system. (See: "third law" under
    "Courtney's laws", manager, operational security, procedural
    security, security architecture. Compare: technical security.)
    Examples: Clear delineation and separation of duties;
    configuration control.
    Usage: Administrative security is usually understood to consist of
    methods and mechanisms that are implemented and executed primarily
    by people, rather than by automated systems.
    2. (O) "The management constraints, operational procedures,
    accountability procedures, and supplemental controls established
    to provide an acceptable level of protection for sensitive data."
    [FP039]
 $ administrator
    1. (O) /Common Criteria/ A person that is responsible for
    configuring, maintaining, and administering the TOE in a correct
    manner for maximum security. (See: administrative security.)
    2. (O) /ITSEC/ A person in contact with the TOE, who is
    responsible for maintaining its operational capability.
 $ Advanced Encryption Standard (AES)
    (N) A U.S. Government standard [FP197] (the successor to DES) that
    (a) specifies "the AES algorithm", which is a symmetric block
    cipher that is based on Rijndael and uses key sizes of 128, 192,
    or 256 bits to operate on a 128-bit block, and (b) states policy
    for using that algorithm to protect unclassified, sensitive data.

Shirey Informational [Page 15] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Tutorial: Rijndael was designed to handle additional block sizes
    and key lengths that were not adopted in the AES. Rijndael was
    selected by NIST through a public competition that was held to
    find a successor to the DEA; the other finalists were MARS, RC6,
    Serpent, and Twofish.
 $ adversary
    1. (I) An entity that attacks a system. (Compare: cracker,
    intruder, hacker.)
    2. (I) An entity that is a threat to a system.
 $ AES
    (N) See: Advanced Encryption Standard.
 $ Affirm
    (O) A formal methodology, language, and integrated set of software
    tools developed at the University of Southern California's
    Information Sciences Institute for specifying, coding, and
    verifying software to produce correct and reliable programs.
    [Cheh]
 $ aggregation
    (I) A circumstance in which a collection of information items is
    required to be classified at a higher security level than any of
    the items is classified individually. (See: classification.)
 $ AH
    (I) See: Authentication Header
 $ air gap
    (I) An interface between two systems at which (a) they are not
    connected physically and (b) any logical connection is not
    automated (i.e., data is transferred through the interface only
    manually, under human control). (See: sneaker net. Compare:
    gateway.)
    Example: Computer A and computer B are on opposite sides of a
    room. To move data from A to B, a person carries a disk across the
    room. If A and B operate in different security domains, then
    moving data across the air gap may involve an upgrade or downgrade
    operation.
 $ ALC
    (O) See: accounting legend code.

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 $ algorithm
    (I) A finite set of step-by-step instructions for a problem-
    solving or computation procedure, especially one that can be
    implemented by a computer. (See: cryptographic algorithm.)
 $ alias
    (I) A name that an entity uses in place of its real name, usually
    for the purpose of either anonymity or masquerade.
 $ Alice and Bob
    (I) The parties that are most often called upon to illustrate the
    operation of bipartite security protocols. These and other
    dramatis personae are listed by Schneier [Schn].
 $ American National Standards Institute (ANSI)
    (N) A private, not-for-profit association that administers U.S.
    private-sector voluntary standards.
    Tutorial: ANSI has approximately 1,000 member organizations,
    including equipment users, manufacturers, and others. These
    include commercial firms, governmental agencies, and other
    institutions and international entities.
    ANSI is the sole U.S. representative to (a) ISO and (b) (via the
    U.S. National Committee) the International Electrotechnical
    Commission (IEC), which are the two major, non-treaty,
    international standards organizations.
    ANSI provides a forum for ANSI-accredited standards development
    groups. Among those groups, the following are especially relevant
    to Internet security:
    -  International Committee for Information Technology
       Standardization (INCITS) (formerly X3): Primary U.S. focus of
       standardization in information and communications technologies,
       encompassing storage, processing, transfer, display,
       management, organization, and retrieval of information.
       Example: [A3092].
    -  Accredited Standards Committee X9: Develops, establishes,
       maintains, and promotes standards for the financial services
       industry. Example: [A9009].
    -  Alliance for Telecommunications Industry Solutions (ATIS):
       Develops standards, specifications, guidelines, requirements,
       technical reports, industry processes, and verification tests
       for interoperability and reliability of telecommunications
       networks, equipment, and software. Example: [A1523].

Shirey Informational [Page 17] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ American Standard Code for Information Interchange (ASCII)
    (N) A scheme that encodes 128 specified characters -- the numbers
    0-9, the letters a-z and A-Z, some basic punctuation symbols, some
    control codes that originated with Teletype machines, and a blank
    space -- into the 7-bit binary integers. Forms the basis of the
    character set representations used in most computers and many
    Internet standards. [FP001] (See: code.)
 $ Anderson report
    (O) A 1972 study of computer security that was written by James P.
    Anderson for the U.S. Air Force [Ande].
    Tutorial: Anderson collaborated with a panel of experts to study
    Air Force requirements for multilevel security. The study
    recommended research and development that was urgently needed to
    provide secure information processing for command and control
    systems and support systems. The report introduced the reference
    monitor concept and provided development impetus for computer and
    network security technology. However, many of the security
    problems that the 1972 report called "current" still plague
    information systems today.
 $ anomaly detection
    (I) An intrusion detection method that searches for activity that
    is different from the normal behavior of system entities and
    system resources. (See: IDS. Compare: misuse detection.)
 $ anonymity
    (I) The condition of an identity being unknown or concealed. (See:
    alias, anonymizer, anonymous credential, anonymous login,
    identity, onion routing, persona certificate. Compare: privacy.)
    Tutorial: An application may require security services that
    maintain anonymity of users or other system entities, perhaps to
    preserve their privacy or hide them from attack. To hide an
    entity's real name, an alias may be used; for example, a financial
    institution may assign account numbers. Parties to transactions
    can thus remain relatively anonymous, but can also accept the
    transactions as legitimate. Real names of the parties cannot be
    easily determined by observers of the transactions, but an
    authorized third party may be able to map an alias to a real name,
    such as by presenting the institution with a court order. In other
    applications, anonymous entities may be completely untraceable.
 $ anonymizer
    (I) An internetwork service, usually provided via a proxy server,
    that provides anonymity and privacy for clients. That is, the
    service enables a client to access servers (a) without allowing

Shirey Informational [Page 18] RFC 4949 Internet Security Glossary, Version 2 August 2007

    anyone to gather information about which servers the client
    accesses and (b) without allowing the accessed servers to gather
    information about the client, such as its IP address.
 $ anonymous credential
    (D) /U.S. Government/ A credential that (a) can be used to
    authenticate a person as having a specific attribute or being a
    member of a specific group (e.g., military veterans or U.S.
    citizens) but (b) does not reveal the individual identity of the
    person that presents the credential. [M0404] (See: anonymity.)
    Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
    in a potentially misleading way. For example, when the credential
    is an X.509 certificate, the term could be misunderstood to mean
    that the certificate was signed by a CA that has a persona
    certificate. Instead, use "attribute certificate", "organizational
    certificate", or "persona certificate" depending on what is meant,
    and provide additional explanations as needed.
 $ anonymous login
    (I) An access control feature (actually, an access control
    vulnerability) in many Internet hosts that enables users to gain
    access to general-purpose or public services and resources of a
    host (such as allowing any user to transfer data using FTP)
    without having a pre-established, identity-specific account (i.e.,
    user name and password). (See: anonymity.)
    Tutorial: This feature exposes a system to more threats than when
    all the users are known, pre-registered entities that are
    individually accountable for their actions. A user logs in using a
    special, publicly known user name (e.g., "anonymous", "guest", or
    "ftp"). To use the public login name, the user is not required to
    know a secret password and may not be required to input anything
    at all except the name. In other cases, to complete the normal
    sequence of steps in a login protocol, the system may require the
    user to input a matching, publicly known password (such as
    "anonymous") or may ask the user for an e-mail address or some
    other arbitrary character string.
 $ ANSI
    (N) See: American National Standards Institute.
 $ anti-jam
    (N) "Measures ensuring that transmitted information can be
    received despite deliberate jamming attempts." [C4009] (See:
    electronic security, frequency hopping, jam, spread spectrum.)

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 $ apex trust anchor
    (N) The trust anchor that is superior to all other trust anchors
    in a particular system or context. (See: trust anchor, top CA.)
 $ API
    (I) See: application programming interface.
 $ APOP
    (I) See: POP3 APOP.
 $ Application Layer
    See: Internet Protocol Suite, OSIRM.
 $ application program
    (I) A computer program that performs a specific function directly
    for a user (as opposed to a program that is part of a computer
    operating system and exists to perform functions in support of
    application programs).
 $ architecture
    (I) See: security architecture, system architecture.
 $ archive
    1a. (I) /noun/ A collection of data that is stored for a
    relatively long period of time for historical and other purposes,
    such as to support audit service, availability service, or system
    integrity service. (Compare: backup, repository.)
    1b. (I) /verb/ To store data in such a way as to create an
    archive. (Compare: back up.)
    Tutorial: A digital signature may need to be verified many years
    after the signing occurs. The CA -- the one that issued the
    certificate containing the public key needed to verify that
    signature -- may not stay in operation that long. So every CA
    needs to provide for long-term storage of the information needed
    to verify the signatures of those to whom it issues certificates.
 $ ARPANET
    (I) Advanced Research Projects Agency (ARPA) Network, a pioneer
    packet-switched network that (a) was designed, implemented,
    operated, and maintained by BBN from January 1969 until July 1975
    under contract to the U.S. Government; (b) led to the development
    of today's Internet; and (c) was decommissioned in June 1990.
    [B4799, Hafn]
 $ ASCII
    (N) See: American Standard Code for Information Interchange.

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 $ ASN.1
    (N) See: Abstract Syntax Notation One.
 $ asset
    (I) A system resource that is (a) required to be protected by an
    information system's security policy, (b) intended to be protected
    by a countermeasure, or (c) required for a system's mission.
 $ association
    (I) A cooperative relationship between system entities, usually
    for the purpose of transferring information between them. (See:
    security association.)
 $ assurance See: security assurance.
 $ assurance level
    (N) A rank on a hierarchical scale that judges the confidence
    someone can have that a TOE adequately fulfills stated security
    requirements. (See: assurance, certificate policy, EAL, TCSEC.)
    Example: U.S. Government guidance [M0404] describes four assurance
    levels for identity authentication, where each level "describes
    the [U.S. Federal Government] agency's degree of certainty that
    the user has presented [a credential] that refers to [the user's]
    identity." In that guidance, assurance is defined as (a) "the
    degree of confidence in the vetting process used to establish the
    identity of the individual to whom the credential was issued" and
    (b) "the degree of confidence that the individual who uses the
    credential is the individual to whom the credential was issued."
    The four levels are described as follows:
    -  Level 1: Little or no confidence in the asserted identity.
    -  Level 2: Some confidence in the asserted identity.
    -  Level 3: High confidence in the asserted identity.
    -  Level 4: Very high confidence in the asserted identity.
    Standards for determining these levels are provided in a NIST
    publication [SP12]. However, as noted there, an assurance level is
    "a degree of confidence, not a true measure of how secure the
    system actually is. This distinction is necessary because it is
    extremely difficult -- and in many cases, virtually impossible --
    to know exactly how secure a system is."
 $ asymmetric cryptography
    (I) A modern branch of cryptography (popularly known as "public-
    key cryptography") in which the algorithms use a pair of keys (a
    public key and a private key) and use a different component of the
    pair for each of two counterpart cryptographic operations (e.g.,

Shirey Informational [Page 21] RFC 4949 Internet Security Glossary, Version 2 August 2007

    encryption and decryption, or signature creation and signature
    verification). (See: key pair, symmetric cryptography.)
    Tutorial: Asymmetric algorithms have key management advantages
    over equivalently strong symmetric ones. First, one key of the
    pair need not be known by anyone but its owner; so it can more
    easily be kept secret. Second, although the other key is shared by
    all entities that use the algorithm, that key need not be kept
    secret from other, non-using entities; thus, the key-distribution
    part of key management can be done more easily.
    Asymmetric cryptography can be used to create algorithms for
    encryption, digital signature, and key agreement:
    -  In an asymmetric encryption algorithm (e.g., "RSA"), when Alice
       wants to ensure confidentiality for data she sends to Bob, she
       encrypts the data with a public key provided by Bob. Only Bob
       has the matching private key that is needed to decrypt the
       data. (Compare: seal.)
    -  In an asymmetric digital signature algorithm (e.g., "DSA"),
       when Alice wants to ensure data integrity or provide
       authentication for data she sends to Bob, she uses her private
       key to sign the data (i.e., create a digital signature based on
       the data). To verify the signature, Bob uses the matching
       public key that Alice has provided.
    -  In an asymmetric key-agreement algorithm (e.g., "Diffie-
       Hellman-Merkle"), Alice and Bob each send their own public key
       to the other party. Then each uses their own private key and
       the other's public key to compute the new key value.
 $ asymmetric key
    (I) A cryptographic key that is used in an asymmetric
    cryptographic algorithm. (See: asymmetric cryptography, private
    key, public key.)
 $ ATIS
    (N) See: "Alliance for Telecommunications Industry Solutions"
    under "ANSI".
 $ attack
    1. (I) An intentional act by which an entity attempts to evade
    security services and violate the security policy of a system.
    That is, an actual assault on system security that derives from an
    intelligent threat. (See: penetration, violation, vulnerability.)
    2. (I) A method or technique used in an assault (e.g.,
    masquerade). (See: blind attack, distributed attack.)

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    Tutorial: Attacks can be characterized according to intent:
    -  An "active attack" attempts to alter system resources or affect
       their operation.
    -  A "passive attack" attempts to learn or make use of information
       from a system but does not affect system resources of that
       system. (See: wiretapping.)
    The object of a passive attack might be to obtain data that is
    needed for an off-line attack.
    -  An "off-line attack" is one in which the attacker obtains data
       from the target system and then analyzes the data on a
       different system of the attacker's own choosing, possibly in
       preparation for a second stage of attack on the target.
    Attacks can be characterized according to point of initiation:
    -  An "inside attack" is one that is initiated by an entity inside
       the security perimeter (an "insider"), i.e., an entity that is
       authorized to access system resources but uses them in a way
       not approved by the party that granted the authorization.
    -  An "outside attack" is initiated from outside the security
       perimeter, by an unauthorized or illegitimate user of the
       system (an "outsider"). In the Internet, potential outside
       attackers range from amateur pranksters to organized criminals,
       international terrorists, and hostile governments.
    Attacks can be characterized according to method of delivery:
    -  In a "direct attack", the attacker addresses attacking packets
       to the intended victim(s).
    -  In an "indirect attack", the attacker addresses packets to a
       third party, and the packets either have the address(es) of the
       intended victim(s) as their source address(es) or indicate the
       intended victim(s) in some other way. The third party responds
       by sending one or more attacking packets to the intended
       victims. The attacker can use third parties as attack
       amplifiers by providing a broadcast address as the victim
       address (e.g., "smurf attack"). (See: reflector attack.
       Compare: reflection attack, replay attack.)

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    The term "attack" relates to some other basic security terms as
    shown in the following diagram:
    + - - - - - - - - - - - - +  + - - - - +  + - - - - - - - - - - -+
    | An Attack:              |  |Counter- |  | A System Resource:   |
    | i.e., A Threat Action   |  | measure |  | Target of the Attack |
    | +----------+            |  |         |  | +-----------------+  |
    | | Attacker |<==================||<=========                 |  |
    | |   i.e.,  |   Passive  |  |         |  | |  Vulnerability  |  |
    | | A Threat |<=================>||<========>                 |  |
    | |  Agent   |  or Active |  |         |  | +-------|||-------+  |
    | +----------+   Attack   |  |         |  |         VVV          |
    |                         |  |         |  | Threat Consequences  |
    + - - - - - - - - - - - - +  + - - - - +  + - - - - - - - - - - -+
 $ attack potential
    (I) The perceived likelihood of success should an attack be
    launched, expressed in terms of the attacker's ability (i.e.,
    expertise and resources) and motivation. (Compare: threat, risk.)
 $ attack sensing, warning, and response
    (I) A set of security services that cooperate with audit service
    to detect and react to indications of threat actions, including
    both inside and outside attacks. (See: indicator.)
 $ attack tree
    (I) A branching, hierarchical data structure that represents a set
    of potential approaches to achieving an event in which system
    security is penetrated or compromised in a specified way. [Moor]
    Tutorial: Attack trees are special cases of fault trees. The
    security incident that is the goal of the attack is represented as
    the root node of the tree, and the ways that an attacker could
    reach that goal are iteratively and incrementally represented as
    branches and subnodes of the tree. Each subnode defines a subgoal,
    and each subgoal may have its own set of further subgoals, etc.
    The final nodes on the paths outward from the root, i.e., the leaf
    nodes, represent different ways to initiate an attack. Each node
    other than a leaf is either an AND-node or an OR-node. To achieve
    the goal represented by an AND-node, the subgoals represented by
    all of that node's subnodes must be achieved; and for an OR-node,
    at least one of the subgoals must be achieved. Branches can be
    labeled with values representing difficulty, cost, or other attack
    attributes, so that alternative attacks can be compared.

Shirey Informational [Page 24] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ attribute
    (N) Information of a particular type concerning an identifiable
    system entity or object. An "attribute type" is the component of
    an attribute that indicates the class of information given by the
    attribute; and an "attribute value" is a particular instance of
    the class of information indicated by an attribute type. (See:
    attribute certificate.)
 $ attribute authority (AA)
    1. (N) A CA that issues attribute certificates.
    2. (O) "An authority [that] assigns privileges by issuing
    attribute certificates." [X509]
    Deprecated Usage: The abbreviation "AA" SHOULD NOT be used in an
    IDOC unless it is first defined in the IDOC.
 $ attribute certificate
    1. (I) A digital certificate that binds a set of descriptive data
    items, other than a public key, either directly to a subject name
    or to the identifier of another certificate that is a public-key
    certificate. (See: capability token.)
    2. (O) "A data structure, digitally signed by an [a]ttribute
    [a]uthority, that binds some attribute values with identification
    information about its holder." [X509]
    Tutorial: A public-key certificate binds a subject name to a
    public key value, along with information needed to perform certain
    cryptographic functions using that key. Other attributes of a
    subject, such as a security clearance, may be certified in a
    separate kind of digital certificate, called an attribute
    certificate. A subject may have multiple attribute certificates
    associated with its name or with each of its public-key
    certificates.
    An attribute certificate might be issued to a subject in the
    following situations:
    -  Different lifetimes: When the lifetime of an attribute binding
       is shorter than that of the related public-key certificate, or
       when it is desirable not to need to revoke a subject's public
       key just to revoke an attribute.
    -  Different authorities: When the authority responsible for the
       attributes is different than the one that issues the public-key
       certificate for the subject. (There is no requirement that an
       attribute certificate be issued by the same CA that issued the
       associated public-key certificate.)

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 $ audit
    See: security audit.
 $ audit log
    (I) Synonym for "security audit trail".
 $ audit service
    (I) A security service that records information needed to
    establish accountability for system events and for the actions of
    system entities that cause them. (See: security audit.)
 $ audit trail
    (I) See: security audit trail.
 $ AUTH
    (I) See: POP3 AUTH.
 $ authenticate
    (I) Verify (i.e., establish the truth of) an attribute value
    claimed by or for a system entity or system resource. (See:
    authentication, validate vs. verify, "relationship between data
    integrity service and authentication services" under "data
    integrity service".)
    Deprecated Usage: In general English usage, this term is used with
    the meaning "to prove genuine" (e.g., an art expert authenticates
    a Michelangelo painting); but IDOCs should restrict usage as
    follows:
    -  IDOCs SHOULD NOT use this term to refer to proving or checking
       that data has not been changed, destroyed, or lost in an
       unauthorized or accidental manner. Instead, use "verify".
    -  IDOCs SHOULD NOT use this term to refer to proving the truth or
       accuracy of a fact or value such as a digital signature.
       Instead, use "verify".
    -  IDOCs SHOULD NOT use this term to refer to establishing the
       soundness or correctness of a construct, such as a digital
       certificate. Instead, use "validate".
 $ authentication
    (I) The process of verifying a claim that a system entity or
    system resource has a certain attribute value. (See: attribute,
    authenticate, authentication exchange, authentication information,
    credential, data origin authentication, peer entity
    authentication, "relationship between data integrity service and
    authentication services" under "data integrity service", simple
    authentication, strong authentication, verification, X.509.)

Shirey Informational [Page 26] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Tutorial: Security services frequently depend on authentication of
    the identity of users, but authentication may involve any type of
    attribute that is recognized by a system. A claim may be made by a
    subject about itself (e.g., at login, a user typically asserts its
    identity) or a claim may be made on behalf of a subject or object
    by some other system entity (e.g., a user may claim that a data
    object originates from a specific source, or that a data object is
    classified at a specific security level).
    An authentication process consists of two basic steps:
    -  Identification step: Presenting the claimed attribute value
       (e.g., a user identifier) to the authentication subsystem.
    -  Verification step: Presenting or generating authentication
       information (e.g., a value signed with a private key) that acts
       as evidence to prove the binding between the attribute and that
       for which it is claimed. (See: verification.)
 $ authentication code
    (D) Synonym for a checksum based on cryptography. (Compare: Data
    Authentication Code, Message Authentication Code.)
    Deprecated Term: IDOCs SHOULD NOT use this uncapitalized term as a
    synonym for any kind of checksum, regardless of whether or not the
    checksum is cryptographic. Instead, use "checksum", "Data
    Authentication Code", "error detection code", "hash", "keyed
    hash", "Message Authentication Code", "protected checksum", or
    some other recommended term, depending on what is meant.
    The term mixes concepts in a potentially misleading way. The word
    "authentication" is misleading because the checksum may be used to
    perform a data integrity function rather than a data origin
    authentication function.
 $ authentication exchange
    1. (I) A mechanism to verify the identity of an entity by means of
    information exchange.
    2. (O) "A mechanism intended to ensure the identity of an entity
    by means of information exchange." [I7498-2]
 $ Authentication Header (AH)
    (I) An Internet protocol [R2402, R4302] designed to provide
    connectionless data integrity service and connectionless data
    origin authentication service for IP datagrams, and (optionally)
    to provide partial sequence integrity and protection against
    replay attacks. (See: IPsec. Compare: ESP.)

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    Tutorial: Replay protection may be selected by the receiver when a
    security association is established. AH authenticates the upper-
    layer PDU that is carried as an IP SDU, and also authenticates as
    much of the IP PCI (i.e., the IP header) as possible. However,
    some IP header fields may change in transit, and the value of
    these fields, when the packet arrives at the receiver, may not be
    predictable by the sender. Thus, the values of such fields cannot
    be protected end-to-end by AH; protection of the IP header by AH
    is only partial when such fields are present.
    AH may be used alone, or in combination with the ESP, or in a
    nested fashion with tunneling. Security services can be provided
    between a pair of communicating hosts, between a pair of
    communicating security gateways, or between a host and a gateway.
    ESP can provide nearly the same security services as AH, and ESP
    can also provide data confidentiality service. The main difference
    between authentication services provided by ESP and AH is the
    extent of the coverage; ESP does not protect IP header fields
    unless they are encapsulated by AH.
 $ authentication information
    (I) Information used to verify an identity claimed by or for an
    entity. (See: authentication, credential, user. Compare:
    identification information.)
    Tutorial: Authentication information may exist as, or be derived
    from, one of the following: (a) Something the entity knows (see:
    password); (b) something the entity possesses (see: token); (c)
    something the entity is (see: biometric authentication).
 $ authentication service
    (I) A security service that verifies an identity claimed by or for
    an entity. (See: authentication.)
    Tutorial: In a network, there are two general forms of
    authentication service: data origin authentication service and
    peer entity authentication service.
 $ authenticity
    (I) The property of being genuine and able to be verified and be
    trusted. (See: authenticate, authentication, validate vs. verify.)
 $ authority
    (D) /PKI/ "An entity [that is] responsible for the issuance of
    certificates." [X509]

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    Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
    attribute authority, certification authority, registration
    authority, or similar terms; the shortened form may cause
    confusion. Instead, use the full term at the first instance of
    usage and then, if it is necessary to shorten text, use AA, CA,
    RA, and other abbreviations defined in this Glossary.
 $ authority certificate
    (D) "A certificate issued to an authority (e.g. either to a
    certification authority or to an attribute authority)." [X509]
    (See: authority.)
    Deprecated Term: IDOCs SHOULD NOT use this term because it is
    ambiguous. Instead, use the full term "certification authority
    certificate", "attribute authority certificate", "registration
    authority certificate", etc. at the first instance of usage and
    then, if it is necessary to shorten text, use AA, CA, RA, and
    other abbreviations defined in this Glossary.
 $ Authority Information Access extension
    (I) The private extension defined by PKIX for X.509 certificates
    to indicate "how to access CA information and services for the
    issuer of the certificate in which the extension appears.
    Information and services may include on-line validation services
    and CA policy data." [R3280] (See: private extension.)
 $ authorization
    1a. (I) An approval that is granted to a system entity to access a
    system resource. (Compare: permission, privilege.)
    Usage: Some synonyms are "permission" and "privilege". Specific
    terms are preferred in certain contexts:
    -  /PKI/ "Authorization" SHOULD be used, to align with
       "certification authority" in the standard [X509].
    -  /role-based access control/ "Permission" SHOULD be used, to
       align with the standard [ANSI].
    -  /computer operating systems/ "Privilege" SHOULD be used, to
       align with the literature. (See: privileged process, privileged
       user.)
    Tutorial: The semantics and granularity of authorizations depend
    on the application and implementation (see: "first law" under
    "Courtney's laws"). An authorization may specify a particular
    access mode -- such as read, write, or execute -- for one or more
    system resources.
    1b. (I) A process for granting approval to a system entity to
    access a system resource.

Shirey Informational [Page 29] RFC 4949 Internet Security Glossary, Version 2 August 2007

    2. (O) /SET/ "The process by which a properly appointed person or
    persons grants permission to perform some action on behalf of an
    organization. This process assesses transaction risk, confirms
    that a given transaction does not raise the account holder's debt
    above the account's credit limit, and reserves the specified
    amount of credit. (When a merchant obtains authorization, payment
    for the authorized amount is guaranteed -- provided, of course,
    that the merchant followed the rules associated with the
    authorization process.)" [SET2]
 $ authorization credential
    (I) See: /access control/ under "credential".
 $ authorize
    (I) Grant an authorization to a system entity.
 $ authorized user
    (I) /access control/ A system entity that accesses a system
    resource for which the entity has received an authorization.
    (Compare: insider, outsider, unauthorized user.)
    Deprecated Usage: IDOCs that use this term SHOULD state a
    definition for it because the term is used in many ways and could
    easily be misunderstood.
 $ automated information system
    See: information system.
 $ availability
    1. (I) The property of a system or a system resource being
    accessible, or usable or operational upon demand, by an authorized
    system entity, according to performance specifications for the
    system; i.e., a system is available if it provides services
    according to the system design whenever users request them. (See:
    critical, denial of service. Compare: precedence, reliability,
    survivability.)
    2. (O) "The property of being accessible and usable upon demand by
    an authorized entity." [I7498-2]
    3. (D) "Timely, reliable access to data and information services
    for authorized users." [C4009]
    Deprecated Definition: IDOCs SHOULD NOT use the term with
    definition 3; the definition mixes "availability" with
    "reliability", which is a different property. (See: reliability.)

Shirey Informational [Page 30] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Tutorial: Availability requirements can be specified by
    quantitative metrics, but sometimes are stated qualitatively, such
    as in the following:
    -  "Flexible tolerance for delay" may mean that brief system
       outages do not endanger mission accomplishment, but extended
       outages may endanger the mission.
    -  "Minimum tolerance for delay" may mean that mission
       accomplishment requires the system to provide requested
       services in a short time.
 $ availability service
    (I) A security service that protects a system to ensure its
    availability.
    Tutorial: This service addresses the security concerns raised by
    denial-of-service attacks. It depends on proper management and
    control of system resources, and thus depends on access control
    service and other security services.
 $ avoidance
    (I) See: secondary definition under "security".
 $ B1, B2, or B3 computer system
    (O) /TCSEC/ See: Tutorial under "Trusted Computer System
    Evaluation Criteria".
 $ back door
    1. (I) /COMPUSEC/ A computer system feature -- which may be (a) an
    unintentional flaw, (b) a mechanism deliberately installed by the
    system's creator, or (c) a mechanism surreptitiously installed by
    an intruder -- that provides access to a system resource by other
    than the usual procedure and usually is hidden or otherwise not
    well-known. (See: maintenance hook. Compare: Trojan Horse.)
    Example: A way to access a computer other than through a normal
    login. Such an access path is not necessarily designed with
    malicious intent; operating systems sometimes are shipped by the
    manufacturer with hidden accounts intended for use by field
    service technicians or the vendor's maintenance programmers.
    2. (I) /cryptography/ A feature of a cryptographic system that
    makes it easily possible to break or circumvent the protection
    that the system is designed to provide.
    Example: A feature that makes it possible to decrypt cipher text
    much more quickly than by brute-force cryptanalysis, without
    having prior knowledge of the decryption key.

Shirey Informational [Page 31] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ back up
    (I) /verb/ Create a reserve copy of data or, more generally,
    provide alternate means to perform system functions despite loss
    of system resources. (See: contingency plan. Compare: archive.)
 $ backup
    (I) /noun or adjective/ Refers to alternate means of performing
    system functions despite loss of system resources. (See:
    contingency plan).
    Example: A reserve copy of data, preferably one that is stored
    separately from the original, for use if the original becomes lost
    or damaged. (Compare: archive.)
 $ bagbiter
    (D) /slang/ "An entity, such as a program or a computer, that
    fails to work or that works in a remarkably clumsy manner. A
    person who has caused some trouble, inadvertently or otherwise,
    typically by failing to program the computer properly." [NCSSG]
    (See: flaw.)
    Deprecated Term: It is likely that other cultures use different
    metaphors for these concepts. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
    Usage under "Green Book".)
 $ baggage
    (O) /SET/ An "opaque encrypted tuple, which is included in a SET
    message but appended as external data to the PKCS encapsulated
    data. This avoids superencryption of the previously encrypted
    tuple, but guarantees linkage with the PKCS portion of the
    message." [SET2]
    Deprecated Usage: IDOCs SHOULD NOT use this term to describe a
    data element, except in the form "SET(trademark) baggage" with the
    meaning given above.
 $ baked-in security
    (D) The inclusion of security mechanisms in an information system
    beginning at an early point in the system's lifecycle, i.e.,
    during the design phase, or at least early in the implementation
    phase. (Compare: add-on security.)
    Deprecated Term: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term (unless they also
    provide a definition like this one). (See: Deprecated Usage under
    "Green Book".)

Shirey Informational [Page 32] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ bandwidth
    (I) The total width of the frequency band that is available to or
    used by a communication channel; usually expressed in Hertz (Hz).
    (RFC 3753) (Compare: channel capacity.)
 $ bank identification number (BIN)
    1. (O) The digits of a credit card number that identify the
    issuing bank. (See: primary account number.)
    2. (O) /SET/ The first six digits of a primary account number.
 $ Basic Encoding Rules (BER)
    (I) A standard for representing ASN.1 data types as strings of
    octets. [X690] (See: Distinguished Encoding Rules.)
    Deprecated Usage: Sometimes incorrectly treated as part of ASN.1.
    However, ASN.1 properly refers only to a syntax description
    language, and not to the encoding rules for the language.
 $ Basic Security Option
    (I) See: secondary definition under "IPSO".
 $ bastion host
    (I) A strongly protected computer that is in a network protected
    by a firewall (or is part of a firewall) and is the only host (or
    one of only a few) in the network that can be directly accessed
    from networks on the other side of the firewall. (See: firewall.)
    Tutorial: Filtering routers in a firewall typically restrict
    traffic from the outside network to reaching just one host, the
    bastion host, which usually is part of the firewall. Since only
    this one host can be directly attacked, only this one host needs
    to be very strongly protected, so security can be maintained more
    easily and less expensively. However, to allow legitimate internal
    and external users to access application resources through the
    firewall, higher-layer protocols and services need to be relayed
    and forwarded by the bastion host. Some services (e.g., DNS and
    SMTP) have forwarding built in; other services (e.g., TELNET and
    FTP) require a proxy server on the bastion host.
 $ BBN Technologies Corp. (BBN)
    (O) The research-and-development company (originally called Bolt
    Baranek and Newman, Inc.) that built the ARPANET.
 $ BCA
    (O) See: brand certification authority.

Shirey Informational [Page 33] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ BCR
    (O) See: BLACK/Crypto/RED.
 $ BCI
    (O) See: brand CRL identifier.
 $ Bell-LaPadula model
    (N) A formal, mathematical, state-transition model of
    confidentiality policy for multilevel-secure computer systems
    [Bell]. (Compare: Biba model, Brewer-Nash model.)
    Tutorial: The model, devised by David Bell and Leonard LaPadula at
    The MITRE Corporation in 1973, characterizes computer system
    elements as subjects and objects. To determine whether or not a
    subject is authorized for a particular access mode on an object,
    the clearance of the subject is compared to the classification of
    the object. The model defines the notion of a "secure state", in
    which the only permitted access modes of subjects to objects are
    in accordance with a specified security policy. It is proven that
    each state transition preserves security by moving from secure
    state to secure state, thereby proving that the system is secure.
    In this model, a multilevel-secure system satisfies several rules,
    including the "confinement property" (a.k.a. the "*-property"),
    the "simple security property", and the "tranquility property".
 $ benign
    1. (N) /COMSEC/ "Condition of cryptographic data [such] that [the
    data] cannot be compromised by human access [to the data]."
    [C4009]
    2. (O) /COMPUSEC/ See: secondary definition under "trust".
 $ benign fill
    (N) Process by which keying material is generated, distributed,
    and placed into an ECU without exposure to any human or other
    system entity, except the cryptographic module that consumes and
    uses the material. (See: benign.)
 $ BER
    (I) See: Basic Encoding Rules.
 $ beyond A1
    1. (O) /formal/ A level of security assurance that is beyond the
    highest level (level A1) of criteria specified by the TCSEC. (See:
    Tutorial under "Trusted Computer System Evaluation Criteria".)

Shirey Informational [Page 34] RFC 4949 Internet Security Glossary, Version 2 August 2007

    2. (O) /informal/ A level of trust so high that it is beyond
    state-of-the-art technology; i.e., it cannot be provided or
    verified by currently available assurance methods, and especially
    not by currently available formal methods.
 $ Biba integrity
    (N) Synonym for "source integrity".
 $ Biba model
    (N) A formal, mathematical, state-transition model of integrity
    policy for multilevel-secure computer systems [Biba]. (See: source
    integrity. Compare: Bell-LaPadula model.)
    Tutorial: This model for integrity control is analogous to the
    Bell-LaPadula model for confidentiality control. Each subject and
    object is assigned an integrity level and, to determine whether or
    not a subject is authorized for a particular access mode on an
    object, the integrity level of the subject is compared to that of
    the object. The model prohibits the changing of information in an
    object by a subject with a lesser or incomparable level. The rules
    of the Biba model are duals of the corresponding rules in the
    Bell-LaPadula model.
 $ billet
    (N) "A personnel position or assignment that may be filled by one
    person." [JCP1] (Compare: principal, role, user.)
    Tutorial: In an organization, a "billet" is a populational
    position, of which there is exactly one instance; but a "role" is
    functional position, of which there can be multiple instances.
    System entities are in one-to-one relationships with their
    billets, but may be in many-to-one and one-to-many relationships
    with their roles.
 $ BIN
    (O) See: bank identification number.
 $ bind
    (I) To inseparably associate by applying some security mechanism.
    Example: A CA creates a public-key certificate by using a digital
    signature to bind together (a) a subject name, (b) a public key,
    and usually (c) some additional data items (e.g., "X.509 public-
    key certificate").
 $ biometric authentication
    (I) A method of generating authentication information for a person
    by digitizing measurements of a physical or behavioral

Shirey Informational [Page 35] RFC 4949 Internet Security Glossary, Version 2 August 2007

    characteristic, such as a fingerprint, hand shape, retina pattern,
    voiceprint, handwriting style, or face.
 $ birthday attack
    (I) A class of attacks against cryptographic functions, including
    both encryption functions and hash functions. The attacks take
    advantage of a statistical property: Given a cryptographic
    function having an N-bit output, the probability is greater than
    1/2 that for 2**(N/2) randomly chosen inputs, the function will
    produce at least two outputs that are identical. (See: Tutorial
    under "hash function".)
    Derivation: From the somewhat surprising fact (often called the
    "birthday paradox") that although there are 365 days in a year,
    the probability is greater than 1/2 that two of more people share
    the same birthday in any randomly chosen group of 23 people.
    Birthday attacks enable an adversary to find two inputs for which
    a cryptographic function produces the same cipher text (or find
    two inputs for which a hash functions produces the same hash
    result) much faster than a brute-force attack can; and a clever
    adversary can use such a capability to create considerable
    mischief. However, no birthday attack can enable an adversary to
    decrypt a given cipher text (or find a hash input that results in
    a given hash result) any faster than a brute-force attack can.
 $ bit
    (I) A contraction of the term "binary digit"; the smallest unit of
    information storage, which has two possible states or values. The
    values usually are represented by the symbols "0" (zero) and "1"
    (one). (See: block, byte, nibble, word.)
 $ bit string
    (I) A sequence of bits, each of which is either "0" or "1".
 $ BLACK
    1. (N) Designation for data that consists only of cipher text, and
    for information system equipment items or facilities that handle
    only cipher text. Example: "BLACK key". (See: BCR, color change,
    RED/BLACK separation. Compare: RED.)
    2. (O) /U.S. Government/ "Designation applied to information
    systems, and to associated areas, circuits, components, and
    equipment, in which national security information is encrypted or
    is not processed." [C4009]
    3. (D) Any data that can be disclosed without harm.

Shirey Informational [Page 36] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Deprecated Definition: IDOCs SHOULD NOT use the term with
    definition 3 because the definition is ambiguous with regard to
    whether or not the data is protected.
 $ BLACK/Crypto/RED (BCR)
    (N) An experimental, end-to-end, network packet encryption system
    developed in a working prototype form by BBN and the Collins Radio
    division of Rockwell Corporation in the 1975-1980 time frame for
    the U.S. DoD. BCR was the first network security system to support
    TCP/IP traffic, and it incorporated the first DES chips that were
    validated by the U.S. National Bureau of Standards (now called
    NIST). BCR also was the first to use a KDC and an ACC to manage
    connections.
 $ BLACK key
    (N) A key that is protected with a key-encrypting key and that
    must be decrypted before use. (See: BLACK. Compare: RED key.)
 $ BLACKER
    (O) An end-to-end encryption system for computer data networks
    that was developed by the U.S. DoD in the 1980s to provide host-
    to-host data confidentiality service for datagrams at OSIRM Layer
    3. [Weis] (Compare: CANEWARE, IPsec.)
    Tutorial: Each user host connects to its own bump-in-the-wire
    encryption device called a BLACKER Front End (BFE, TSEC/KI-111),
    through which the host connects to the subnetwork. The system also
    includes two types of centralized devices: one or more KDCs
    connect to the subnetwork and communicate with assigned sets of
    BFEs, and one or more ACCs connect to the subnetwork and
    communicate with assigned KDCs. BLACKER uses only symmetric
    encryption. A KDC distributes session keys to BFE pairs as
    authorized by an ACC. Each ACC maintains a database for a set of
    BFEs, and the database determines which pairs from that set (i.e.,
    which pairs of user hosts behind the BFEs) are authorized to
    communicate and at what security levels.
    The BLACKER system is MLS in three ways: (a) The BFEs form a
    security perimeter around a subnetwork, separating user hosts from
    the subnetwork, so that the subnetwork can operate at a different
    security level (possibly a lower, less expensive level) than the
    hosts. (b) The BLACKER components are trusted to separate
    datagrams of different security levels, so that each datagram of a
    given security level can be received only by a host that is
    authorized for that security level; and thus BLACKER can separate
    host communities that operate at different security levels. (c)
    The host side of a BFE is itself MLS and can recognize a security
    label on each packet, so that an MLS user host can be authorized

Shirey Informational [Page 37] RFC 4949 Internet Security Glossary, Version 2 August 2007

    to successively transmit datagrams that are labeled with different
    security levels.
 $ blind attack
    (I) A type of network-based attack method that does not require
    the attacking entity to receive data traffic from the attacked
    entity; i.e., the attacker does not need to "see" data packets
    sent by the victim. Example: SYN flood.
    Tutorial: If an attack method is blind, the attacker's packets can
    carry (a) a false IP source address (making it difficult for the
    victim to find the attacker) and (b) a different address on every
    packet (making it difficult for the victim to block the attack).
    If the attacker needs to receive traffic from the victim, the
    attacker must either (c) reveal its own IP address to the victim
    (which enables the victim to find the attacker or block the attack
    by filtering) or (d) provide a false address and also subvert
    network routing mechanisms to divert the returning packets to the
    attacker (which makes the attack more complex, more difficult, or
    more expensive). [R3552]
 $ block
    (I) A bit string or bit vector of finite length. (See: bit, block
    cipher. Compare: byte, word.)
    Usage: An "N-bit block" contains N bits, which usually are
    numbered from left to right as 1, 2, 3, ..., N.
 $ block cipher
    (I) An encryption algorithm that breaks plain text into fixed-size
    segments and uses the same key to transform each plaintext segment
    into a fixed-size segment of cipher text. Examples: AES, Blowfish,
    DEA, IDEA, RC2, and SKIPJACK. (See: block, mode. Compare: stream
    cipher.)
    Tutorial: A block cipher can be adapted to have a different
    external interface, such as that of a stream cipher, by using a
    mode of cryptographic operation to package the basic algorithm.
    (See: CBC, CCM, CFB, CMAC, CTR, DEA, ECB, OFB.)
 $ Blowfish
    (N) A symmetric block cipher with variable-length key (32 to 448
    bits) designed in 1993 by Bruce Schneier as an unpatented,
    license-free, royalty-free replacement for DES or IDEA. [Schn]
    (See: Twofish.)

Shirey Informational [Page 38] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ brain-damaged
    (D) /slang/ "Obviously wrong: extremely poorly designed. Calling
    something brain-damaged is very extreme. The word implies that the
    thing is completely unusable, and that its failure to work is due
    to poor design, not accident." [NCSSG] (See: flaw.)
    Deprecated Term: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
    Usage under "Green Book".)
 $ brand
    1. (I) A distinctive mark or name that identifies a product or
    business entity.
    2. (O) /SET/ The name of a payment card. (See: BCA.)
    Tutorial: Financial institutions and other companies have founded
    payment card brands, protect and advertise the brands, establish
    and enforce rules for use and acceptance of their payment cards,
    and provide networks to interconnect the financial institutions.
    These brands combine the roles of issuer and acquirer in
    interactions with cardholders and merchants. [SET1]
 $ brand certification authority (BCA)
    (O) /SET/ A CA owned by a payment card brand, such as MasterCard,
    Visa, or American Express. [SET2] (See: certification hierarchy,
    SET.)
 $ brand CRL identifier (BCI)
    (O) /SET/ A digitally signed list, issued by a BCA, of the names
    of CAs for which CRLs need to be processed when verifying
    signatures in SET messages. [SET2]
 $ break
    (I) /cryptography/ To successfully perform cryptanalysis and thus
    succeed in decrypting data or performing some other cryptographic
    function, without initially having knowledge of the key that the
    function requires. (See: penetrate, strength, work factor.)
    Usage: This term applies to encrypted data or, more generally, to
    a cryptographic algorithm or cryptographic system. Also, while the
    most common use is to refer to completely breaking an algorithm,
    the term is also used when a method is found that substantially
    reduces the work factor.

Shirey Informational [Page 39] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ Brewer-Nash model
    (N) A security model [BN89] to enforce the Chinese wall policy.
    (Compare: Bell-LaPadula model, Clark-Wilson model.)
    Tutorial: All proprietary information in the set of commercial
    firms F(1), F(2), ..., F(N) is categorized into mutually exclusive
    conflict-of-interest classes I(1), I(2), ..., I(M) that apply
    across all firms. Each firm belongs to exactly one class. The
    Brewer-Nash model has the following mandatory rules:
    -  Brewer-Nash Read Rule: Subject S can read information object O
       from firm F(i) only if either (a) O is from the same firm as
       some object previously read by S *or* (b) O belongs to a class
       I(i) from which S has not previously read any object. (See:
       object, subject.)
    -  Brewer-Nash Write Rule: Subject S can write information object
       O to firm F(i) only if (a) S can read O by the Brewer-Nash Read
       Rule *and* (b) no object can be read by S from a different firm
       F(j), no matter whether F(j) belongs to the same class as F(i)
       or to a different class.
 $ bridge
    (I) A gateway for traffic flowing at OSIRM Layer 2 between two
    networks (usually two LANs). (Compare: bridge CA, router.)
 $ bridge CA
    (I) A PKI consisting of only a CA that cross-certifies with CAs of
    some other PKIs. (See: cross-certification. Compare: bridge.)
    Tutorial: A bridge CA functions as a hub that enables a
    certificate user in any of the PKIs that attach to the bridge, to
    validate certificates issued in the other attached PKIs.
    For example, a bridge CA (BCA)                 CA1
    could cross-certify with four                   ^
    PKIs that have the roots CA1,                   |
    CA2, CA3, and CA4. The cross-                   v
    certificates that the roots            CA2 <-> BCA <-> CA3
    exchange with the BCA enable an                 ^
    end entity EE1 certified under                  |
    under CA1 in PK1 to construct                   v
    a certification path needed to                 CA4
    validate the certificate of
    end entity EE2 under CA2,           CA1 -> BCA -> CA2 -> EE2
    or vice versa.                     CA2 -> BCA -> CA1 -> EE1

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 $ British Standard 7799
    (N) Part 1 of the standard is a code of practice for how to secure
    an information system. Part 2 specifies the management framework,
    objectives, and control requirements for information security
    management systems. [BS7799] (See: ISO 17799.)
 $ browser
    (I) A client computer program that can retrieve and display
    information from servers on the World Wide Web. Examples: Netscape
    Navigator and Microsoft Internet Explorer.
 $ brute force
    (I) A cryptanalysis technique or other kind of attack method
    involving an exhaustive procedure that tries a large number of
    possible solutions to the problem. (See: impossible, strength,
    work factor.)
    Tutorial: In some cases, brute force involves trying all of the
    possibilities. For example, for cipher text where the analyst
    already knows the decryption algorithm, a brute-force technique
    for finding matching plain text is to decrypt the message with
    every possible key. In other cases, brute force involves trying a
    large number of possibilities but substantially fewer than all of
    them. For example, given a hash function that produces an N-bit
    hash result, the probability is greater than 1/2 that the analyst
    will find two inputs that have the same hash result after trying
    only 2**(N/2) randomly chosen inputs. (See: birthday attack.)
 $ BS7799
    (N) See: British Standard 7799.
 $ buffer overflow
    (I) Any attack technique that exploits a vulnerability resulting
    from computer software or hardware that does not check for
    exceeding the bounds of a storage area when data is written into a
    sequence of storage locations beginning in that area.
    Tutorial: By causing a normal system operation to write data
    beyond the bounds of a storage area, the attacker seeks to either
    disrupt system operation or cause the system to execute malicious
    software inserted by the attacker.
 $ buffer zone
    (I) A neutral internetwork segment used to connect other segments
    that each operate under a different security policy.

Shirey Informational [Page 41] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Tutorial: To connect a private network to the Internet or some
    other relatively public network, one could construct a small,
    separate, isolated LAN and connect it to both the private network
    and the public network; one or both of the connections would
    implement a firewall to limit the traffic that could pass through
    the buffer zone.
 $ bulk encryption
    1. (I) Encryption of multiple channels by aggregating them into a
    single transfer path and then encrypting that path. (See:
    channel.)
    2. (O) "Simultaneous encryption of all channels of a multichannel
    telecommunications link." [C4009] (Compare: bulk keying material.)
    Usage: The use of "simultaneous" in definition 2 could be
    interpreted to mean that multiple channels are encrypted
    separately but at the same time. However, the common meaning of
    the term is that multiple data flows are combined into a single
    stream and then that stream is encrypted as a whole.
 $ bulk key
    (D) In a few published descriptions of hybrid encryption for SSH,
    Windows 2000, and other applications, this term refers to a
    symmetric key that (a) is used to encrypt a relatively large
    amount of data and (b) is itself encrypted with a public key.
    (Compare: bulk keying material, session key.)
    Example: To send a large file to Bob, Alice (a) generates a
    symmetric key and uses it to encrypt the file (i.e., encrypt the
    bulk of the information that is to be sent) and then (b) encrypts
    that symmetric key (the "bulk key") with Bob's public key.
    Deprecated Term: IDOCs SHOULD NOT use this term or definition; the
    term is not well-established and could be confused with the
    established term "bulk keying material". Instead, use "symmetric
    key" and carefully explain how the key is applied.
 $ bulk keying material
    (N) Refers to handling keying material in large quantities, e.g.,
    as a dataset that contains many items of keying material. (See:
    type 0. Compare: bulk key, bulk encryption.)
 $ bump-in-the-stack
    (I) An implementation approach that places a network security
    mechanism inside the system that is to be protected. (Compare:
    bump-in-the-wire.)

Shirey Informational [Page 42] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Example: IPsec can be implemented inboard, in the protocol stack
    of an existing system or existing system design, by placing a new
    layer between the existing IP layer and the OSIRM Layer 3 drivers.
    Source code access for the existing stack is not required, but the
    system that contains the stack does need to be modified [R4301].
 $ bump-in-the-wire
    (I) An implementation approach that places a network security
    mechanism outside of the system that is to be protected. (Compare:
    bump-in-the-stack.)
    Example: IPsec can be implemented outboard, in a physically
    separate device, so that the system that receives the IPsec
    protection does not need to be modified at all [R4301]. Military-
    grade link encryption has mainly been implemented as bump-in-the-
    wire devices.
 $ business-case analysis
    (N) An extended form of cost-benefit analysis that considers
    factors beyond financial metrics, including security factors such
    as the requirement for security services, their technical and
    programmatic feasibility, their qualitative benefits, and
    associated risks. (See: risk analysis.)
 $ byte
    (I) A fundamental unit of computer storage; the smallest
    addressable unit in a computer's architecture. Usually holds one
    character of information and, today, usually means eight bits.
    (Compare: octet.)
    Usage: Understood to be larger than a "bit", but smaller than a
    "word". Although "byte" almost always means "octet" today, some
    computer architectures have had bytes in other sizes (e.g., six
    bits, nine bits). Therefore, an STD SHOULD state the number of
    bits in a byte where the term is first used in the STD.
 $ C field
    (D) See: Compartments field.
 $ C1 or C2 computer system
    (O) /TCSEC/ See: Tutorial under "Trusted Computer System
    Evaluation Criteria".
 $ CA
    (I) See: certification authority.

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 $ CA certificate
    (D) "A [digital] certificate for one CA issued by another CA."
    [X509]
    Deprecated Definition: IDOCs SHOULD NOT use the term with this
    definition; the definition is ambiguous with regard to how the
    certificate is constructed and how it is intended to be used.
    IDOCs that use this term SHOULD provide a technical definition for
    it. (See: certificate profile.)
    Tutorial: There is no single, obvious choice for a technical
    definition of this term. Different PKIs can use different
    certificate profiles, and X.509 provides several choices of how to
    issue certificates to CAs. For example, one possible definition is
    the following: A v3 X.509 public-key certificate that has a
    "basicConstraints" extension containing a "cA" value of "TRUE".
    That would specifically indicate that "the certified public key
    may be used to verify certificate signatures", i.e., that the
    private key may be used by a CA.
    However, there also are other ways to indicate such usage. The
    certificate may have a "key Usage" extension that indicates the
    purposes for which the public key may be used, and one of the
    values that X.509 defines for that extension is "keyCertSign", to
    indicate that the certificate may be used for verifying a CA's
    signature on certificates. If "keyCertSign" is present in a
    certificate that also has a "basicConstraints" extension, then
    "cA" is set to "TRUE" in that extension. Alternatively, a CA could
    be issued a certificate in which "keyCertSign" is asserted without
    "basicConstraints" being present; and an entity that acts as a CA
    could be issued a certificate with "keyUsage" set to other values,
    either with or without "keyCertSign".
 $ CA domain
    (N) /PKI/ A security policy domain that "consists of a CA and its
    subjects [i.e., the entities named in the certificates issued by
    the CA]. Sometimes referred to as a PKI domain." [PAG] (See:
    domain.)
 $ Caesar cipher
    (I) A cipher that is defined for an alphabet of N characters,
    A(1), A(2), ..., A(N), and creates cipher text by replacing each
    plaintext character A(i) by A(i+K, mod N) for some 0<K<N+1. [Schn]
    Examples: (a) During the Gallic wars, Julius Caesar used a cipher
    with K=3. In a Caesar cipher with K=3 for the English alphabet, A
    is replaced by D, B by E, C by F, ..., W by Z, X by A, Y by B, Z

Shirey Informational [Page 44] RFC 4949 Internet Security Glossary, Version 2 August 2007

    by C. (b) UNIX systems sometimes include "ROT13" software that
    implements a Caesar cipher with K=13 (i.e., ROTate by 13).
 $ call back
    (I) An authentication technique for terminals that remotely access
    a computer via telephone lines; the host system disconnects the
    caller and then reconnects on a telephone number that was
    previously authorized for that terminal.
 $ CAM
    (O) See: Certificate Arbitrator Module.
 $ CANEWARE
    (O) An end-to-end encryption system for computer data networks
    that was developed by the U.S. DoD in the 1980s to provide host-
    to-host data confidentiality service for datagrams in OSIRM Layer
    3. [Roge] (Compare: BLACKER, IPsec.)
    Tutorial: Each user host connects to its own bump-in-the-wire
    encryption device called a CANEWARE Front End (CFE), through which
    the host connects to the subnetwork. CANEWARE uses symmetric
    encryption for CFE-to-CFE traffic, but also uses FIREFLY to
    establish those session keys. The public-key certificates issued
    by the FIREFLY system include credentials for mandatory access
    control. For discretionary access control, the system also
    includes one or more centralized CANEWARE Control Processors
    (CCPs) that connect to the subnetwork, maintain a database for
    discretionary access control authorizations, and communicate those
    authorizations to assigned sets of CFEs.
    The CANEWARE system is MLS in only two of the three ways that
    BLACKER is MLS: (a) Like BLACKER BFEs, CFEs form a security
    perimeter around a subnetwork, separating user hosts from the
    subnetwork, so that the subnetwork can operate at a different
    security level than the hosts. (b) Like BLACKER, the CANEWARE
    components are trusted to separate datagrams of different security
    levels, so that each datagram of a given security level can be
    received only by a host that is authorized for that security
    level; and thus CANEWARE can separate host communities that
    operate at different security levels. (c) Unlike a BFE, the host
    side of a CFE is not MLS, and treats all packets received from a
    user host as being at the same mandatory security level.
 $ capability list
    (I) /information system/ A mechanism that implements access
    control for a system entity by enumerating the system resources
    that the entity is permitted to access and, either implicitly or
    explicitly, the access modes granted for each resource. (Compare:

Shirey Informational [Page 45] RFC 4949 Internet Security Glossary, Version 2 August 2007

    access control list, access control matrix, access profile,
    capability token.)
 $ capability token
    (I) A token (usually an unforgeable data object) that gives the
    bearer or holder the right to access a system resource. Possession
    of the token is accepted by a system as proof that the holder has
    been authorized to access the resource indicated by the token.
    (See: attribute certificate, capability list, credential, digital
    certificate, ticket, token.)
 $ Capability Maturity Model (CMM)
    (N) Method for judging the maturity of software processes in an
    organization and for identifying crucial practices needed to
    increase process maturity. [Chris] (Compare: Common Criteria.)
    Tutorial: The CMM does not specify security evaluation criteria
    (see: assurance level), but its use may improve security
    assurance. The CMM describes principles and practices that can
    improve software processes in terms of evolving from ad hoc
    processes to disciplined processes. The CMM has five levels:
    -  Initial: Software processes are ad hoc or chaotic, and few are
       well-defined. Success depends on individual effort and heroics.
    -  Repeatable: Basic project management processes are established
       to track cost, schedule, and functionality. Necessary process
       discipline is in place to repeat earlier successes on projects
       with similar applications.
    -  Defined: Software process for both management and engineering
       activities is documented, standardized, and integrated into a
       standard software process for the organization. Each project
       uses an approved, tailored version of the organization's
       standard process for developing and maintaining software.
    -  Managed: Detailed measures of software process and product
       quality are collected. Both software process and products are
       quantitatively understood and controlled.
    -  Optimizing: Continuous process improvement is enabled by
       quantitative feedback from the process and from piloting
       innovative ideas and technologies.
 $ CAPI
    (I) See: cryptographic application programming interface.
 $ CAPSTONE
    (N) An integrated microcircuit (in MYK-8x series manufactured by
    Mykotronx, Inc.) that implements SKIPJACK, KEA, DSA, SHA, and
    basic mathematical functions needed to support asymmetric
    cryptography; has a non-deterministic random number generator; and
    supports key escrow. (See: FORTEZZA. Compare: CLIPPER.)

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 $ card
    See: cryptographic card, FORTEZZA, payment card, PC card, smart
    card, token.
 $ card backup
    See: token backup.
 $ card copy
    See: token copy.
 $ card restore
    See: token restore.
 $ cardholder
    1. (I) An entity to whom or to which a card has been issued.
    Usage: Usually refers to a living human being, but might refer (a)
    to a position (see: billet, role) in an organization or (b) to an
    automated process. (Compare: user.)
    2. (O) /SET/ "The holder of a valid payment card account and user
    of software supporting electronic commerce." [SET2] A cardholder
    is issued a payment card by an issuer. SET ensures that in the
    cardholder's interactions with merchants, the payment card account
    information remains confidential. [SET1]
 $ cardholder certificate
    (O) /SET/ A digital certificate that is issued to a cardholder
    upon approval of the cardholder's issuing financial institution
    and that is transmitted to merchants with purchase requests and
    encrypted payment instructions, carrying assurance that the
    account number has been validated by the issuing financial
    institution and cannot be altered by a third party. [SET1]
 $ cardholder certification authority (CCA)
    (O) /SET/ A CA responsible for issuing digital certificates to
    cardholders and operated on behalf of a payment card brand, an
    issuer, or another party according to brand rules. A CCA maintains
    relationships with card issuers to allow for the verification of
    cardholder accounts. A CCA does not issue a CRL but does
    distribute CRLs issued by root CAs, brand CAs, geopolitical CAs,
    and payment gateway CAs. [SET2]
 $ CAST
    (N) A design procedure for symmetric encryption algorithms, and a
    resulting family of algorithms, invented by Carlisle Adams (C.A.)
    and Stafford Tavares (S.T.). [R2144, R2612]

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 $ category
    (I) A grouping of sensitive information items to which a non-
    hierarchical restrictive security label is applied to increase
    protection of the data. (See: formal access approval. Compare:
    compartment, classification.)
 $ CAW
    (N) See: certification authority workstation.
 $ CBC
    (N) See: cipher block chaining.
 $ CCA
    (O) See: cardholder certification authority.
 $ CCEP
    (O) See: Commercial COMSEC Endorsement Program.
 $ CCI
    (O) See: Controlled Cryptographic Item.
 $ CCITT
    (N) Acronym for French translation of International Telephone and
    Telegraph Consultative Committee. Now renamed ITU-T.
 $ CCM
    (N) See: Counter with Cipher Block Chaining-Message Authentication
    Code.
 $ CERIAS
    (O) Purdue University's Center for Education and Research in
    Information Assurance and Security, which includes faculty from
    multiple schools and departments and takes a multidisciplinary
    approach to security problems ranging from technical to ethical,
    legal, educational, communicational, linguistic, and economic.
 $ CERT
    (I) See: computer emergency response team.
 $ certificate
    1. (I) /general English/ A document that attests to the truth of
    something or the ownership of something.
    2. (I) /general security/ See: capability token, digital
    certificate.
    3. (I) /PKI/ See: attribute certificate, public-key certificate.

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 $ Certificate Arbitrator Module (CAM)
    (O) An open-source software module that is designed to be
    integrated with an application for routing, replying to, and
    otherwise managing and meditating certificate validation requests
    between that application and the CAs in the ACES PKI.
 $ certificate authority
    (D) Synonym for "certification authority".
    Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
    careless use of the term "certification authority", which is
    preferred in PKI standards (e.g., [X509, R3280]).
 $ certificate chain
    (D) Synonym for "certification path". (See: trust chain.)
    Deprecated Term: IDOCs SHOULD NOT use this term; it duplicates the
    meaning of a standardized term. Instead, use "certification path".
 $ certificate chain validation
    (D) Synonym for "certificate validation" or "path validation".
    Deprecated Term: IDOCs SHOULD NOT use this term; it duplicates the
    meaning of standardized terms and mixes concepts in a potentially
    misleading way. Instead, use "certificate validation" or "path
    validation", depending on what is meant. (See: validate vs.
    verify.)
 $ certificate creation
    (I) The act or process by which a CA sets the values of a digital
    certificate's data fields and signs it. (See: issue.)
 $ certificate expiration
    (I) The event that occurs when a certificate ceases to be valid
    because its assigned lifetime has been exceeded. (See: certificate
    revocation, expire.)
    Tutorial: The assigned lifetime of an X.509 certificate is stated
    in the certificate itself. (See: validity period.)
 $ certificate extension
    (I) See: extension.
 $ certificate holder
    (D) Synonym for the "subject" of a digital certificate. (Compare:
    certificate owner, certificate user.)

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    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for the subject of a digital certificate; the term is potentially
    ambiguous. For example, the term could be misunderstood as
    referring to a system entity or component, such as a repository,
    that simply has possession of a copy of the certificate.
 $ certificate management
    (I) The functions that a CA may perform during the lifecycle of a
    digital certificate, including the following:
    -  Acquire and verify data items to bind into the certificate.
    -  Encode and sign the certificate.
    -  Store the certificate in a directory or repository.
    -  Renew, rekey, and update the certificate.
    -  Revoke the certificate and issue a CRL.
    (See: archive management, certificate management, key management,
    security architecture, token management.)
 $ certificate management authority (CMA)
    (D) /U.S. DoD/ Used to mean either a CA or an RA. [DoD7, SP32]
    Deprecated Term: IDOCs SHOULD NOT use this term because it is
    potentially ambiguous, such as in a context involving ICRLs.
    Instead, use CA, RA, or both, depending on what is meant.
 $ certificate owner
    (D) Synonym for the "subject" of a digital certificate. (Compare:
    certificate holder, certificate user.)
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for the subject of a digital certificate; the term is potentially
    ambiguous. For example, the term could refer to a system entity,
    such as a corporation, that has purchased a certificate to operate
    equipment, such as a Web server.
 $ certificate path
    (D) Synonym for "certification path".
    Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
    careless use of "certification path", which is preferred in PKI
    standards (e.g., [X509, R3280]).
 $ certificate policy
    (I) "A named set of rules that indicates the applicability of a
    certificate to a particular community and/or class of application
    with common security requirements." [X509] (Compare: CPS, security
    policy.)

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    Example: U.S. DoD's certificate policy [DoD7] defined four classes
    (i.e., assurance levels) for X.509 public-key certificates and
    defines the applicability of those classes. (See: class 2.)
    Tutorial: A certificate policy can help a certificate user to
    decide whether a certificate should be trusted in a particular
    application. "For example, a particular certificate policy might
    indicate applicability of a type of certificate for the
    authentication of electronic data interchange transactions for the
    trading of goods within a given price range." [R3647]
    A v3 X.509 public-key certificate may have a "certificatePolicies"
    extension that lists certificate policies, recognized by the
    issuing CA, that apply to the certificate and govern its use. Each
    policy is denoted by an object identifier and may optionally have
    certificate policy qualifiers. (See: certificate profile.)
    Each SET certificate specifies at least one certificate policy,
    that of the SET root CA. SET uses certificate policy qualifiers to
    point to the actual policy statement and to add qualifying
    policies to the root policy. (See: SET qualifier.)
 $ certificate policy qualifier
    (I) Information that pertains to a certificate policy and is
    included in a "certificatePolicies" extension in a v3 X.509
    public-key certificate.
 $ certificate profile
    (I) A specification (e.g., [DoD7, R3280]) of the format and
    semantics of public-key certificates or attribute certificates,
    constructed for use in a specific application context by selecting
    from among options offered by a broader standard. (Compare:
    protection profile.)
 $ certificate reactivation
    (I) The act or process by which a digital certificate, that a CA
    has designated for revocation but not yet listed on a CRL, is
    returned to the valid state.
 $ certificate rekey
    1. (I) The act or process by which an existing public-key
    certificate has its key value changed by issuing a new certificate
    with a different (usually new) public key. (See: certificate
    renewal, certificate update, rekey.)
    Tutorial: For an X.509 public-key certificate, the essence of
    rekey is that the subject stays the same and a new public key is
    bound to that subject. Other changes are made, and the old

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    certificate is revoked, only as required by the PKI and CPS in
    support of the rekey. If changes go beyond that, the process is a
    "certificate update".
    2. (O) /MISSI/ The act or process by which a MISSI CA creates a
    new X.509 public-key certificate that is identical to the old one,
    except the new one has (a) a new, different KEA key or (b) a new,
    different DSS key or (c) new, different KEA and DSS keys. The new
    certificate also has a different serial number and may have a
    different validity period. A new key creation date and maximum key
    lifetime period are assigned to each newly generated key. If a new
    KEA key is generated, that key is assigned a new KMID. The old
    certificate remains valid until it expires, but may not be further
    renewed, rekeyed, or updated.
 $ certificate renewal
    (I) The act or process by which the validity of the binding
    asserted by an existing public-key certificate is extended in time
    by issuing a new certificate. (See: certificate rekey, certificate
    update.)
    Tutorial: For an X.509 public-key certificate, this term means
    that the validity period is extended (and, of course, a new serial
    number is assigned) but the binding of the public key to the
    subject and to other data items stays the same. The other data
    items are changed, and the old certificate is revoked, only as
    required by the PKI and CPS to support the renewal. If changes go
    beyond that, the process is a "certificate rekey" or "certificate
    update".
 $ certificate request
    (D) Synonym for "certification request".
    Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
    careless use of the term "certification request", which is
    preferred in PKI standards (e.g., see PKCS #10).
 $ certificate revocation
    (I) The event that occurs when a CA declares that a previously
    valid digital certificate issued by that CA has become invalid;
    usually stated with an effective date.
    Tutorial: In X.509, a revocation is announced to potential
    certificate users by issuing a CRL that mentions the certificate.
    Revocation and listing on a CRL is only necessary prior to the
    certificate's scheduled expiration.

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 $ certificate revocation list (CRL)
    1. (I) A data structure that enumerates digital certificates that
    have been invalidated by their issuer prior to when they were
    scheduled to expire. (See: certificate expiration, delta CRL,
    X.509 certificate revocation list.)
    2. (O) "A signed list indicating a set of certificates that are no
    longer considered valid by the certificate issuer. In addition to
    the generic term CRL, some specific CRL types are defined for CRLs
    that cover particular scopes." [X509]
 $ certificate revocation tree
    (N) A mechanism for distributing notices of certificate
    revocations; uses a tree of hash results that is signed by the
    tree's issuer. Offers an alternative to issuing a CRL, but is not
    supported in X.509. (See: certificate status responder.)
 $ certificate serial number
    1. (I) An integer value that (a) is associated with, and may be
    carried in, a digital certificate; (b) is assigned to the
    certificate by the certificate's issuer; and (c) is unique among
    all the certificates produced by that issuer.
    2. (O) "An integer value, unique within the issuing CA, [that] is
    unambiguously associated with a certificate issued by that CA."
    [X509]
 $ certificate status authority
    (D) /U.S. DoD/ "A trusted entity that provides on-line
    verification to a Relying Party of a subject certificate's
    trustworthiness [should instead say 'validity'], and may also
    provide additional attribute information for the subject
    certificate." [DoD7]
    Deprecated Term: IDOCs SHOULD NOT use this term because it is not
    widely accepted; instead, use "certificate status responder" or
    "OCSP server", or otherwise explain what is meant.
 $ certificate status responder
    (N) /FPKI/ A trusted online server that acts for a CA to provide
    authenticated certificate status information to certificate users
    [FPKI]. Offers an alternative to issuing a CR. (See: certificate
    revocation tree, OCSP.)
 $ certificate update
    (I) The act or process by which non-key data items bound in an
    existing public-key certificate, especially authorizations granted

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    to the subject, are changed by issuing a new certificate. (See:
    certificate rekey, certificate renewal.)
    Usage: For an X.509 public-key certificate, the essence of this
    process is that fundamental changes are made in the data that is
    bound to the public key, such that it is necessary to revoke the
    old certificate. (Otherwise, the process is only a "certificate
    rekey" or "certificate renewal".)
 $ certificate user
    1. (I) A system entity that depends on the validity of information
    (such as another entity's public key value) provided by a digital
    certificate. (See: relying party. Compare: /digital certificate/
    subject.)
    Usage: The depending entity may be a human being or an
    organization, or a device or process controlled by a human or
    organization. (See: user.)
    2. (O) "An entity that needs to know, with certainty, the public
    key of another entity." [X509]
    3. (D) Synonym for "subject" of a digital certificate.
    Deprecated Definition: IDOCs SHOULD NOT use this term with
    definition 3; the term could be confused with one of the other two
    definitions given above.
 $ certificate validation
    1. (I) An act or process by which a certificate user establishes
    that the assertions made by a digital certificate can be trusted.
    (See: valid certificate, validate vs. verify.)
    2. (O) "The process of ensuring that a certificate was valid at a
    given time, including possibly the construction and processing of
    a certification path [R4158], and ensuring that all certificates
    in that path were valid (i.e. were not expired or revoked) at that
    given time." [X509]
    Tutorial: To validate a certificate, a certificate user checks
    that the certificate is properly formed and signed and is
    currently in force:
    -  Checks the syntax and semantics: Parses the certificate's
       syntax and interprets its semantics, applying rules specified
       for and by its data fields, such as for critical extensions in
       an X.509 certificate.

Shirey Informational [Page 54] RFC 4949 Internet Security Glossary, Version 2 August 2007

  1. Checks the signature: Uses the issuer's public key to verify

the digital signature of the CA who issued the certificate in

       question. If the verifier obtains the issuer's public key from
       the issuer's own public-key certificate, that certificate
       should be validated, too. That validation may lead to yet
       another certificate to be validated, and so on. Thus, in
       general, certificate validation involves discovering and
       validating a certification path.
    -  Checks currency and revocation: Verifies that the certificate
       is currently in force by checking that the current date and
       time are within the validity period (if that is specified in
       the certificate) and that the certificate is not listed on a
       CRL or otherwise announced as invalid. (The CRLs also must be
       checked by a similar validation process.)
 $ certification
    1. (I) /information system/ Comprehensive evaluation (usually made
    in support of an accreditation action) of an information system's
    technical security features and other safeguards to establish the
    extent to which the system's design and implementation meet a set
    of specified security requirements. [C4009, FP102, SP37] (See:
    accreditation. Compare: evaluation.)
    2. (I) /digital certificate/ The act or process of vouching for
    the truth and accuracy of the binding between data items in a
    certificate. (See: certify.)
    3. (I) /PKI/ The act or process of vouching for the ownership of a
    public key by issuing a public-key certificate that binds the key
    to the name of the entity that possesses the matching private key.
    Besides binding a key with a name, a public-key certificate may
    bind those items with other restrictive or explanatory data items.
    (See: X.509 public-key certificate.)
    4. (O) /SET/ "The process of ascertaining that a set of
    requirements or criteria has been fulfilled and attesting to that
    fact to others, usually with some written instrument. A system
    that has been inspected and evaluated as fully compliant with the
    SET protocol by duly authorized parties and process would be said
    to have been certified compliant." [SET2]
 $ certification authority (CA)
    1. (I) An entity that issues digital certificates (especially
    X.509 certificates) and vouches for the binding between the data
    items in a certificate.

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    2. (O) "An authority trusted by one or more users to create and
    assign certificates. Optionally the certification authority may
    create the user's keys." [X509]
    Tutorial: Certificate users depend on the validity of information
    provided by a certificate. Thus, a CA should be someone that
    certificate users trust and that usually holds an official
    position created and granted power by a government, a corporation,
    or some other organization. A CA is responsible for managing the
    life cycle of certificates (see: certificate management) and,
    depending on the type of certificate and the CPS that applies, may
    be responsible for the lifecycle of key pairs associated with the
    certificates (see: key management).
 $ certification authority workstation (CAW)
    (N) A computer system that enables a CA to issue digital
    certificates and supports other certificate management functions
    as required.
 $ certification hierarchy
    1. (I) A tree-structured (loop-free) topology of relationships
    between CAs and the entities to whom the CAs issue public-key
    certificates. (See: hierarchical PKI, hierarchy management.)
    Tutorial: In this structure, one CA is the top CA, the highest
    level of the hierarchy. (See: root, top CA.) The top CA may issue
    public-key certificates to one or more additional CAs that form
    the second-highest level. Each of these CAs may issue certificates
    to more CAs at the third-highest level, and so on. The CAs at the
    second-lowest level issue certificates only to non-CA entities
    that form the lowest level (see: end entity). Thus, all
    certification paths begin at the top CA and descend through zero
    or more levels of other CAs. All certificate users base path
    validations on the top CA's public key.
    2. (I) /PEM/ A certification hierarchy for PEM has three levels of
    CAs [R1422]:
    -  The highest level is the "Internet Policy Registration
       Authority".
    -  A CA at the second-highest level is a "policy certification
       authority".
    -  A CA at the third-highest level is a "certification authority".
    3. (O) /MISSI/ A certification hierarchy for MISSI has three or
    four levels of CAs:
    -  A CA at the highest level, the top CA, is a "policy approving
       authority".

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  1. A CA at the second-highest level is a "policy creation

authority".

  1. A CA at the third-highest level is a local authority called a

"certification authority".

  1. A CA at the fourth-highest (optional) level is a "subordinate

certification authority".

    4. (O) /SET/ A certification hierarchy for SET has three or four
    levels of CAs:
    -  The highest level is a "SET root CA".
    -  A CA at the second-highest level is a "brand certification
       authority".
    -  A CA at the third-highest (optional) level is a "geopolitical
       certification authority".
    -  A CA at the fourth-highest level is a "cardholder CA", a
       "merchant CA", or a "payment gateway CA".
 $ certification path
    1. (I) A linked sequence of one or more public-key certificates,
    or one or more public-key certificates and one attribute
    certificate, that enables a certificate user to verify the
    signature on the last certificate in the path, and thus enables
    the user to obtain (from that last certificate) a certified public
    key, or certified attributes, of the system entity that is the
    subject of that last certificate. (See: trust anchor, certificate
    validation, valid certificate.)
    2. (O) "An ordered sequence of certificates of objects in the
    [X.500 Directory Information Tree] which, together with the public
    key of the initial object in the path, can be processed to obtain
    that of the final object in the path." [R3647, X509]
    Tutorial: The list is "linked" in the sense that the digital
    signature of each certificate (except possibly the first) is
    verified by the public key contained in the preceding certificate;
    i.e., the private key used to sign a certificate and the public
    key contained in the preceding certificate form a key pair that
    has previously been bound to the authority that signed.
    The path is the "list of certificates needed to [enable] a
    particular user to obtain the public key [or attributes] of
    another [user]." [X509] Here, the word "particular" points out
    that a certification path that can be validated by one certificate
    user might not be able to be validated by another. That is because
    either the first certificate needs to be a trusted certificate or
    the signature on the first certificate needs to be verifiable by a
    trusted key (e.g., a root key), but such trust is established only

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    relative to a "particular" (i.e., specific) user, not absolutely
    for all users.
 $ certification policy
    (D) Synonym for either "certificate policy" or "certification
    practice statement".
    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    either of those terms; that would be duplicative and would mix
    concepts in a potentially misleading way. Instead, use either
    "certificate policy" or "certification practice statement",
    depending on what is meant.
 $ certification practice statement (CPS)
    (I) "A statement of the practices which a certification authority
    employs in issuing certificates." [DSG, R3647] (See: certificate
    policy.)
    Tutorial: A CPS is a published security policy that can help a
    certificate user to decide whether a certificate issued by a
    particular CA can be trusted enough to use in a particular
    application. A CPS may be (a) a declaration by a CA of the details
    of the system and practices it uses in its certificate management
    operations, (b) part of a contract between the CA and an entity to
    whom a certificate is issued, (c) a statute or regulation
    applicable to the CA, or (d) a combination of these types
    involving multiple documents. [DSG]
    A CPS is usually more detailed and procedurally oriented than a
    certificate policy. A CPS applies to a particular CA or CA
    community, while a certificate policy applies across CAs or
    communities. A CA with its single CPS may support multiple
    certificate policies, which may be used for different application
    purposes or by different user communities. On the other hand,
    multiple CAs, each with a different CPS, may support the same
    certificate policy. [R3647]
 $ certification request
    (I) An algorithm-independent transaction format (e.g., PKCS #10,
    RFC 4211) that contains a DN, and a public key or, optionally, a
    set of attributes, collectively signed by the entity requesting
    certification, and sent to a CA, which transforms the request to
    an X.509 public-key certificate or another type of certificate.
 $ certify
    1. (I) Issue a digital certificate and thus vouch for the truth,
    accuracy, and binding between data items in the certificate (e.g.,
    "X.509 public-key certificate"), such as the identity of the

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    certificate's subject and the ownership of a public key. (See:
    certification.)
    Usage: To "certify a public key" means to issue a public-key
    certificate that vouches for the binding between the certificate's
    subject and the key.
    2. (I) The act by which a CA uses measures to verify the truth,
    accuracy, and binding between data items in a digital certificate.
    Tutorial: A description of the measures used for verification
    should be included in the CA's CPS.
 $ CFB
    (N) See: cipher feedback.
 $ chain
    (D) See: trust chain.
 $ Challenge Handshake Authentication Protocol (CHAP)
    (I) A peer entity authentication method (employed by PPP and other
    protocols, e.g., RFC 3720) that uses a randomly generated
    challenge and requires a matching response that depends on a
    cryptographic hash of some combination of the challenge and a
    secret key. [R1994] (See: challenge-response, PAP.)
 $ challenge-response
    (I) An authentication process that verifies an identity by
    requiring correct authentication information to be provided in
    response to a challenge. In a computer system, the authentication
    information is usually a value that is required to be computed in
    response to an unpredictable challenge value, but it might be just
    a password.
 $ Challenge-Response Authentication Mechanism (CRAM)
    (I) /IMAP4/ A mechanism [R2195], intended for use with IMAP4
    AUTHENTICATE, by which an IMAP4 client uses a keyed hash [R2104]
    to authenticate itself to an IMAP4 server. (See: POP3 APOP.)
    Tutorial: The server includes a unique time stamp in its ready
    response to the client. The client replies with the client's name
    and the hash result of applying MD5 to a string formed from
    concatenating the time stamp with a shared secret that is known
    only to the client and the server.
 $ channel
    1. (I) An information transfer path within a system. (See: covert
    channel.)

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    2. (O) "A subdivision of the physical medium allowing possibly
    shared independent uses of the medium." (RFC 3753)
 $ channel capacity
    (I) The total capacity of a link to carry information; usually
    expressed in bits per second. (RFC 3753) (Compare: bandwidth.)
    Tutorial: Within a given bandwidth, the theoretical maximum
    channel capacity is given by Shannon's Law. The actual channel
    capacity is determined by the bandwidth, the coding system used,
    and the signal-to-noise ratio.
 $ CHAP
    (I) See: Challenge Handshake Authentication Protocol.
 $ checksum
    (I) A value that (a) is computed by a function that is dependent
    on the contents of a data object and (b) is stored or transmitted
    together with the object, for detecting changes in the data. (See:
    cyclic redundancy check, data integrity service, error detection
    code, hash, keyed hash, parity bit, protected checksum.)
    Tutorial: To gain confidence that a data object has not been
    changed, an entity that later uses the data can independently
    recompute the checksum value and compare the result with the value
    that was stored or transmitted with the object.
    Computer systems and networks use checksums (and other mechanisms)
    to detect accidental changes in data. However, active wiretapping
    that changes data could also change an accompanying checksum to
    match the changed data. Thus, some checksum functions by
    themselves are not good countermeasures for active attacks. To
    protect against active attacks, the checksum function needs to be
    well-chosen (see: cryptographic hash), and the checksum result
    needs to be cryptographically protected (see: digital signature,
    keyed hash).
 $ Chinese wall policy
    (I) A security policy to prevent conflict of interest caused by an
    entity (e.g., a consultant) interacting with competing firms.
    (See: Brewer-Nash model.)
    Tutorial: All information is categorized into mutually exclusive
    conflict-of-interest classes I(1), I(2), ..., I(M), and each firm
    F(1), F(2), ..., F(N) belongs to exactly one class. The policy
    states that if a consultant has access to class I(i) information
    from a firm in that class, then the consultant may not access
    information from another firm in that same class, but may access

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    information from another firm that is in a different class. Thus,
    the policy creates a barrier to communication between firms that
    are in the same conflict-of-interest class. Brewer and Nash
    modeled enforcement of this policy [BN89], including dealing with
    policy violations that could occur because two or more consultants
    work for the same firm.
 $ chosen-ciphertext attack
    (I) A cryptanalysis technique in which the analyst tries to
    determine the key from knowledge of plain text that corresponds to
    cipher text selected (i.e., dictated) by the analyst.
 $ chosen-plaintext attack
    (I) A cryptanalysis technique in which the analyst tries to
    determine the key from knowledge of cipher text that corresponds
    to plain text selected (i.e., dictated) by the analyst.
 $ CIAC
    (O) See: Computer Incident Advisory Capability.
 $ CIK
    (N) See: cryptographic ignition key.
 $ cipher
    (I) A cryptographic algorithm for encryption and decryption.
 $ cipher block chaining (CBC)
    (N) A block cipher mode that enhances ECB mode by chaining
    together blocks of cipher text it produces. [FP081] (See: block
    cipher, [R1829], [R2405], [R2451], [SP38A].)
    Tutorial: This mode operates by combining (exclusive OR-ing) the
    algorithm's ciphertext output block with the next plaintext block
    to form the next input block for the algorithm.
 $ cipher feedback (CFB)
    (N) A block cipher mode that enhances ECB mode by chaining
    together the blocks of cipher text it produces and operating on
    plaintext segments of variable length less than or equal to the
    block length. [FP081] (See: block cipher, [SP38A].)
    Tutorial: This mode operates by using the previously generated
    ciphertext segment as the algorithm's input (i.e., by "feeding
    back" the cipher text) to generate an output block, and then
    combining (exclusive OR-ing) that output block with the next
    plaintext segment (block length or less) to form the next
    ciphertext segment.

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 $ cipher text
    1. (I) /noun/ Data that has been transformed by encryption so that
    its semantic information content (i.e., its meaning) is no longer
    intelligible or directly available. (See: ciphertext. Compare:
    clear text, plain text.)
    2. (O) "Data produced through the use of encipherment. The
    semantic content of the resulting data is not available."
    [I7498-2]
 $ ciphertext
    1. (O) /noun/ Synonym for "cipher text" [I7498-2].
    2. (I) /adjective/ Referring to cipher text. Usage: Commonly used
    instead of "cipher-text". (Compare: cleartext, plaintext.)
 $ ciphertext auto-key (CTAK)
    (D) "Cryptographic logic that uses previous cipher text to
    generate a key stream." [C4009, A1523] (See: KAK.)
    Deprecated Term: IDOCs SHOULD NOT use this term; it is neither
    well-known nor precisely defined. Instead, use terms associated
    with modes that are defined in standards, such as CBC, CFB, and
    OFB.
 $ ciphertext-only attack
    (I) A cryptanalysis technique in which the analyst tries to
    determine the key solely from knowledge of intercepted cipher text
    (although the analyst may also know other clues, such as the
    cryptographic algorithm, the language in which the plain text was
    written, the subject matter of the plain text, and some probable
    plaintext words.)
 $ ciphony
    (O) The process of encrypting audio information.
 $ CIPSO
    (I) See: Common IP Security Option.
 $ CKL
    (I) See: compromised key list.
 $ Clark-Wilson model
    (N) A security model [Clark] to maintain data integrity in the
    commercial world. (Compare: Bell-LaPadula model.)

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 $ class 2, 3, 4, 5
    (O) /U.S. DoD/ Assurance levels for PKIs, and for X.509 public-key
    certificates issued by a PKI. [DoD7] (See: "first law" under
    "Courtney's laws".)
    -  "Class 2": Intended for applications handling unclassified,
       low-value data in minimally or moderately protected
       environments.
    -  "Class 3": Intended for applications handling unclassified,
       medium-value data in moderately protected environments, or
       handling unclassified or high-value data in highly protected
       environments, and for discretionary access control of
       classified data in highly protected environments.
    -  "Class 4": Intended for applications handling unclassified,
       high-value data in minimally protected environments.
    -  "Class 5": Intended for applications handling classified data
       in minimally protected environments, and for authentication of
       material that would affect the security of classified systems.
    The environments are defined as follows:
    -  "Highly protected environment": Networks that are protected
       either with encryption devices approved by NSA for protection
       of classified data or via physical isolation, and that are
       certified for processing system-high classified data, where
       exposure of unencrypted data is limited to U.S. citizens
       holding appropriate security clearances.
    -  "Moderately protected environment":
       -- Physically isolated unclassified, unencrypted networks in
          which access is restricted based on legitimate need.
       -- Networks protected by NSA-approved, type 1 encryption,
          accessible by U.S.-authorized foreign nationals.
    -  "Minimally protected environments": Unencrypted networks
       connected to either the Internet or NIPRNET, either directly or
       via a firewall.
 $ Class A1, B3, B2, B1, C2, or C1 computer system
    (O) /TCSEC/ See: Tutorial under "Trusted Computer System
    Evaluation Criteria".
 $ classification
    1. (I) A grouping of classified information to which a
    hierarchical, restrictive security label is applied to increase
    protection of the data from unauthorized disclosure. (See:
    aggregation, classified, data confidentiality service. Compare:
    category, compartment.)
    2. (I) An authorized process by which information is determined to
    be classified and assigned to a security level. (Compare:
    declassification.)

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    Usage: Usually understood to involve data confidentiality, but
    IDOCs SHOULD make this clear when data also is sensitive in other
    ways and SHOULD use other terms for those other sensitivity
    concepts. (See: sensitive information, data integrity.)
 $ classification label
    (I) A security label that tells the degree of harm that will
    result from unauthorized disclosure of the labeled data, and may
    also tell what countermeasures are required to be applied to
    protect the data from unauthorized disclosure. Example: IPSO.
    (See: classified, data confidentiality service. Compare: integrity
    label.)
    Usage: Usually understood to involve data confidentiality, but
    IDOCs SHOULD make this clear when data also is sensitive in other
    ways and SHOULD use other terms for those other sensitivity
    concepts. (See: sensitive information, data integrity.)
 $ classification level
    (I) A hierarchical level of protection (against unauthorized
    disclosure) that is required to be applied to certain classified
    data. (See: classified. Compare: security level.)
    Usage: Usually understood to involve data confidentiality, but
    IDOCs SHOULD make this clear when data also is sensitive in other
    ways and SHOULD use other terms for those other sensitivity
    concepts. (See: sensitive information, data integrity.)
 $ classified
    1. (I) Refers to information (stored or conveyed, in any form)
    that is formally required by a security policy to receive data
    confidentiality service and to be marked with a security label
    (which, in some cases, might be implicit) to indicate its
    protected status. (See: classify, collateral information, SAP,
    security level. Compare: unclassified.)
    Usage: Usually understood to involve data confidentiality, but
    IDOCs SHOULD make this clear when data also is sensitive in other
    ways and SHOULD use other terms for those other sensitivity
    concepts. (See: sensitive information, data integrity.)
    Mainly used by national governments, especially by the military,
    but the underlying concept also applies outside of governments.
    2. (O) /U.S. Government/ "Information that has been determined
    pursuant to Executive Order 12958 or any predecessor Order, or by
    the Atomic Energy Act of 1954, as amended, to require protection

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    against unauthorized disclosure and is marked to indicate its
    classified status." [C4009]
 $ classify
    (I) To officially designate an information item or type of
    information as being classified and assigned to a specific
    security level. (See: classified, declassify, security level.)
 $ clean system
    (I) A computer system in which the operating system and
    application system software and files have been freshly installed
    from trusted software distribution media. (Compare: secure state.)
 $ clear
    (D) /verb/ Synonym for "erase". [C4009]
    Deprecated Definition: IDOCs SHOULD NOT use the term with this
    definition; that could be confused with "clear text" in which
    information is directly recoverable.
 $ clear text
    1. (I) /noun/ Data in which the semantic information content
    (i.e., the meaning) is intelligible or is directly available,
    i.e., not encrypted. (See: cleartext, in the clear. Compare:
    cipher text, plain text.)
    2. (O) /noun/ "Intelligible data, the semantic content of which is
    available." [I7498-2]
    3. (D) /noun/ Synonym for "plain text".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "plain text", because the plain text that is input to an
    encryption operation may itself be cipher text that was output
    from a previous encryption operation. (See: superencryption.)
 $ clearance
    See: security clearance.
 $ clearance level
    (I) The security level of information to which a security
    clearance authorizes a person to have access.
 $ cleartext
    1. (O) /noun/ Synonym for "clear text" [I7498-2].
    2. (I) /adjective/ Referring to clear text. Usage: Commonly used
    instead of "clear-text". (Compare: ciphertext, plaintext.)

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    3. (D) /adjective/ Synonym for "plaintext".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "plaintext", because the plaintext data that is input to an
    encryption operation may itself be ciphertext data that was output
    from a previous encryption operation. (See: superencryption.)
 $ CLEF
    (N) See: commercially licensed evaluation facility.
 $ client
    (I) A system entity that requests and uses a service provided by
    another system entity, called a "server". (See: server.)
    Tutorial: Usually, it is understood that the client and server are
    automated components of the system, and the client makes the
    request on behalf of a human user. In some cases, the server may
    itself be a client of some other server.
 $ client-server system
    (I) A distributed system in which one or more entities, called
    clients, request a specific service from one or more other
    entities, called servers, that provide the service to the clients.
    Example: The Word Wide Web, in which component servers provide
    information that is requested by component clients called
    "browsers".
 $ CLIPPER
    (N) An integrated microcircuit (in MYK-7x series manufactured by
    Mykotronx, Inc.) that implements SKIPJACK, has a non-deterministic
    random number generator, and supports key escrow. (See: Escrowed
    Encryption Standard. Compare: CLIPPER.)
    Tutorial: The chip was mainly intended for protecting
    telecommunications over the public switched network. The key
    escrow scheme for the chip involves a SKIPJACK key that is common
    to all chips and that protects the unique serial number of the
    chip, and a second SKIPJACK key unique to the chip that protects
    all data encrypted by the chip. The second key is escrowed as
    split key components held by NIST and the U.S. Treasury
    Department.
 $ closed security environment
    (O) /U.S. DoD/ A system environment that meets both of the
    following conditions: (a) Application developers (including
    maintainers) have sufficient clearances and authorizations to
    provide an acceptable presumption that they have not introduced

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    malicious logic. (b) Configuration control provides sufficient
    assurance that system applications and the equipment they run on
    are protected against the introduction of malicious logic prior to
    and during the operation of applications. [NCS04] (See: "first
    law" under "Courtney's laws". Compare: open security environment.)
 $ CMA
    (D) See: certificate management authority.
 $ CMAC
    (N) A message authentication code [SP38B] that is based on a
    symmetric block cipher. (See: block cipher.)
    Derivation: Cipher-based MAC. (Compare: HMAC.)
    Tutorial: Because CMAC is based on approved, symmetric-key block
    ciphers, such as AES, CMAC can be considered a mode of operation
    for those block ciphers. (See: mode of operation.)
 $ CMCS
    (O) See: COMSEC Material Control System.
 $ CMM
    (N) See: Capability Maturity Model.
 $ CMS
    (I) See: Cryptographic Message Syntax.
 $ code
    1. (I) A system of symbols used to represent information, which
    might originally have some other representation. Examples: ASCII,
    BER, country code, Morse code. (See: encode, object code, source
    code.)
    Deprecated Abbreviation: To avoid confusion with definition 1,
    IDOCs SHOULD NOT use "code" as an abbreviation of "country code",
    "cyclic redundancy code", "Data Authentication Code", "error
    detection code", or "Message Authentication Code". To avoid
    misunderstanding, use the fully qualified term in these other
    cases, at least at the point of first usage.
    2. (I) /cryptography/ An encryption algorithm based on
    substitution; i.e., a system for providing data confidentiality by
    using arbitrary groups (called "code groups") of letters, numbers,
    or symbols to represent units of plain text of varying length.
    (See: codebook, cryptography.)

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    Deprecated Usage: To avoid confusion with definition 1, IDOCs
    SHOULD NOT use "code" as a synonym for any of the following terms:
    (a) "cipher", "hash", or other words that mean "a cryptographic
    algorithm"; (b) "cipher text"; or (c) "encrypt", "hash", or other
    words that refer to applying a cryptographic algorithm.
    3. (I) An algorithm based on substitution, but used to shorten
    messages rather than to conceal their content.
    4. (I) /computer programming/ To write computer software. (See:
    object code, source code.)
    Deprecated Abbreviation: To avoid confusion with definition 1,
    IDOCs SHOULD NOT use "code" as an abbreviation of "object code" or
    "source code". To avoid misunderstanding, use the fully qualified
    term in these other cases, at least at the point of first usage.
 $ code book
    1. (I) Document containing a systematically arranged list of
    plaintext units and their ciphertext equivalents. [C4009]
    2. (I) An encryption algorithm that uses a word substitution
    technique. [C4009] (See: code, ECB.)
 $ code signing
    (I) A security mechanism that uses a digital signature to provide
    data integrity and data origin authentication for software that is
    being distributed for use. (See: mobile code, trusted
    distribution.)
    Tutorial: In some cases, the signature on a software module may
    imply some assertion that the signer makes about the software. For
    example, a signature may imply that the software has been
    designed, developed, or tested according to some criterion.
 $ code word
    (O) /U.S. Government/ A single word that is used as a security
    label (usually applied to classified information) but which itself
    has a classified meaning. (See: classified, /U.S. Government/
    security label.)
 $ COI
    (I) See: community of interest.
 $ cold start
    (N) /cryptographic module/ A procedure for initially keying
    cryptographic equipment. [C4009]

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 $ collateral information
    (O) /U.S. Government/ Information that is classified but is not
    required to be protected by an SAP. (See: /U.S. Government/
    classified.)
 $ color change
    (I) In a system being operated in periods-processing mode, the act
    of purging all information from one processing period and then
    changing over to the next processing period. (See: BLACK, RED.)
 $ Commercial COMSEC Evaluation Program (CCEP)
    (O) "Relationship between NSA and industry in which NSA provides
    the COMSEC expertise (i.e., standards, algorithms, evaluations,
    and guidance) and industry provides design, development, and
    production capabilities to produce a type 1 or type 2 product."
    [C4009]
 $ commercially licensed evaluation facility (CLEF)
    (N) An organization that has official approval to evaluate the
    security of products and systems under the Common Criteria, ITSEC,
    or some other standard. (Compare: KLIF.)
 $ Committee on National Security Systems (CNSS)
    (O) /U.S. Government/ A Government, interagency, standing
    committee of the President's Critical Infrastructure Protection
    Board. The CNSS is chaired by the Secretary of Defense and
    provides a forum for the discussion of policy issues, sets
    national policy, and promulgates direction, operational
    procedures, and guidance for the security of national security
    systems. The Secretary of Defense and the Director of Central
    Intelligence are responsible for developing and overseeing the
    implementation of Government-wide policies, principles, standards,
    and guidelines for the security of systems that handle national
    security information.
 $ Common Criteria for Information Technology Security
    (N) A standard for evaluating information technology (IT) products
    and systems. It states requirements for security functions and for
    assurance measures. [CCIB] (See: CLEF, EAL, packages, protection
    profile, security target, TOE. Compare: CMM.)
    Tutorial: Canada, France, Germany, the Netherlands, the United
    Kingdom, and the United States (NIST and NSA) began developing
    this standard in 1993, based on the European ITSEC, the Canadian
    Trusted Computer Product Evaluation Criteria (CTCPEC), and the
    U.S. "Federal Criteria for Information Technology Security" and
    its precursor, the TCSEC. Work was done in cooperation with
    ISO/IEC Joint Technical Committee 1 (Information Technology),

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    Subcommittee 27 (Security Techniques), Working Group 3 (Security
    Criteria). Version 2.0 of the Criteria has been issued as ISO's
    International Standard 15408. The U.S. Government intends this
    standard to supersede both the TCSEC and FIPS PUB 140. (See:
    NIAP.)
    The standard addresses data confidentiality, data integrity, and
    availability and may apply to other aspects of security. It
    focuses on threats to information arising from human activities,
    malicious or otherwise, but may apply to non-human threats. It
    applies to security measures implemented in hardware, firmware, or
    software. It does not apply to (a) administrative security not
    related directly to technical security, (b) technical physical
    aspects of security such as electromagnetic emanation control, (c)
    evaluation methodology or administrative and legal framework under
    which the criteria may be applied, (d) procedures for use of
    evaluation results, or (e) assessment of inherent qualities of
    cryptographic algorithms.
    Part 1, Introduction and General Model, defines general concepts
    and principles of IT security evaluation; presents a general model
    of evaluation; and defines constructs for expressing IT security
    objectives, for selecting and defining IT security requirements,
    and for writing high-level specifications for products and
    systems.
    Part 2, Security Functional Requirements, contains a catalog of
    well-defined and well-understood functional requirement statements
    that are intended to be used as a standard way of expressing the
    security requirements for IT products and systems.
    Part 3, Security Assurance Requirements, contains a catalog of
    assurance components for use as a standard way of expressing such
    requirements for IT products and systems, and defines evaluation
    criteria for protection profiles and security targets.
 $ Common IP Security Option (CIPSO)
    (I) See: secondary definition under "IPSO".
 $ common name
    (N) A character string that (a) may be a part of the X.500 DN of a
    Directory object ("commonName" attribute), (b) is a (possibly
    ambiguous) name by which the object is commonly known in some
    limited scope (such as an organization), and (c) conforms to the
    naming conventions of the country or culture with which it is
    associated. [X520] (See: "subject" and "issuer" under "X.509
    public-key certificate".)

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    Examples: "Dr. Albert Einstein", "The United Nations", and "12-th
    Floor Laser Printer".
 $ communications cover
    (N) "Concealing or altering of characteristic communications
    patterns to hide information that could be of value to an
    adversary." [C4009] (See: operations security, traffic-flow
    confidentiality, TRANSEC.)
 $ communication security (COMSEC)
    (I) Measures that implement and assure security services in a
    communication system, particularly those that provide data
    confidentiality and data integrity and that authenticate
    communicating entities.
    Usage: COMSEC is usually understood to include (a) cryptography
    and its related algorithms and key management methods and
    processes, devices that implement those algorithms and processes,
    and the lifecycle management of the devices and keying material.
    Also, COMSEC is sometimes more broadly understood as further
    including (b) traffic-flow confidentiality, (c) TRANSEC, and (d)
    steganography [Kahn]. (See: cryptology, signal security.)
 $ community of interest (COI)
    1. (I) A set of entities that operate under a common security
    policy. (Compare: domain.)
    2. (I) A set of entities that exchange information collaboratively
    for some purpose.
 $ community risk
    (N) Probability that a particular vulnerability will be exploited
    within an interacting population and adversely affect some members
    of that population. [C4009] (See: Morris worm, risk.)
 $ community string
    (I) A community name in the form of an octet string that serves as
    a cleartext password in SNMP version 1 (RFC 1157) and version 2
    (RFC 1901). (See: password, Simple Network Management Protocol.)
    Tutorial: The SNMPv1 and SNMPv2 protocols have been declared
    "historic" and have been replaced by the more secure SNMPv3
    standard (RFCs 3410-3418), which does not use cleartext passwords.

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 $ compartment
    1. (I) A grouping of sensitive information items that require
    special access controls beyond those normally provided for the
    basic classification level of the information. (See: compartmented
    security mode. Compare: category, classification.)
    Usage: The term is usually understood to include the special
    handling procedures to be used for the information.
    2. (I) Synonym for "category".
    Deprecated Usage: This Glossary defines "category" with a slightly
    narrower meaning than "compartment". That is, a security label is
    assigned to a category because the data owner needs to handle the
    data as a compartment. However, a compartment could receive
    special protection in a system without being assigned a category
    label.
 $ compartmented security mode
    (N) A mode of system operation wherein all users having access to
    the system have the necessary security clearance for the single,
    hierarchical classification level of all data handled by the
    system, but some users do not have the clearance for a non-
    hierarchical category of some data handled by the system. (See:
    category, /system operation/ under "mode", protection level,
    security clearance.)
    Usage: Usually abbreviated as "compartmented mode". This term was
    defined in U.S. Government policy on system accreditation. In this
    mode, a system may handle (a) a single hierarchical classification
    level and (b) multiple non-hierarchical categories within that
    level.
 $ Compartments field
    (I) A 16-bit field (the "C field") that specifies compartment
    values in the security option (option type 130) of version 4 IP's
    datagram header format. The valid field values are assigned by the
    U.S. Government, as specified in RFC 791.
    Deprecated Abbreviation: IDOCs SHOULD NOT use the abbreviation "C
    field"; the abbreviation is potentially ambiguous. Instead, use
    "Compartments field".
 $ component
    See: system component.

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 $ compression
    (I) A process that encodes information in a way that minimizes the
    number of resulting code symbols and thus reduces storage space or
    transmission time.
    Tutorial: A data compression algorithm may be "lossless", i.e.,
    retain all information that was encoded in the data, so that
    decompression can recover all the information; or an algorithm may
    be "lossy". Text usually needs to be compressed losslessly, but
    images are often compressed with lossy schemes.
    Not all schemes that encode information losslessly for machine
    processing are efficient in terms of minimizing the number of
    output bits. For example, ASCII encoding is lossless, but ASCII
    data can often be losslessly reencoded in fewer bits with other
    schemes. These more efficient schemes take advantage of some sort
    of inherent imbalance, redundancy, or repetition in the data, such
    as by replacing a character string in which all characters are the
    same by a shorter string consisting of only the single character
    and a character count.
    Lossless compression schemes cannot effectively reduce the number
    of bits in cipher text produced by a strong encryption algorithm,
    because the cipher text is essentially a pseudorandom bit string
    that does not contain patterns susceptible to reencoding.
    Therefore, protocols that offer both encryption and compression
    services (e.g., SSL) need to perform the compression operation
    before the encryption operation.
 $ compromise
    See: data compromise, security compromise.
 $ compromise recovery
    (I) The process of regaining a secure state for a system after
    detecting that the system has experienced a security compromise.
 $ compromised key list (CKL)
    (N) /MISSI/ A list that identifies keys for which unauthorized
    disclosure or alteration may have occurred. (See: compromise.)
    Tutorial: A CKL is issued by a CA, like a CRL is issued. But a CKL
    lists only KMIDs, not subjects that hold the keys, and not
    certificates in which the keys are bound.
 $ COMPUSEC
    (I) See: computer security.

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 $ computer emergency response team (CERT)
    (I) An organization that studies computer and network INFOSEC in
    order to provide incident response services to victims of attacks,
    publish alerts concerning vulnerabilities and threats, and offer
    other information to help improve computer and network security.
    (See: CSIRT, security incident.)
    Examples: CERT Coordination Center at Carnegie Mellon University
    (sometimes called "the" CERT); CIAC.
 $ Computer Incident Advisory Capability (CIAC)
    (O) The centralized CSIRT of the U.S. Department of Energy; a
    member of FIRST.
 $ computer network
    (I) A collection of host computers together with the subnetwork or
    internetwork through which they can exchange data.
    Usage: This definition is intended to cover systems of all sizes
    and types, ranging from the complex Internet to a simple system
    composed of a personal computer dialing in as a remote terminal of
    another computer.
 $ computer platform
    (I) A combination of computer hardware and an operating system
    (which may consist of software, firmware, or both) for that
    hardware. (Compare: computer system.)
 $ computer security (COMPUSEC)
    1. (I) Measures to implement and assure security services in a
    computer system, particularly those that assure access control
    service.
    Usage: Usually refers to internal controls (functions, features,
    and technical characteristics) that are implemented in software
    (especially in operating systems); sometimes refers to internal
    controls implemented in hardware; rarely used to refer to external
    controls.
    2. (O) "The protection afforded to an automated information system
    in order to attain the applicable objectives of preserving the
    integrity, availability and confidentiality of information system
    resources (includes hardware, software, firmware,
    information/data, and telecommunications)." [SP12]

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 $ computer security incident response team (CSIRT)
    (I) An organization "that coordinates and supports the response to
    security incidents that involve sites within a defined
    constituency." [R2350] (See: CERT, FIRST, security incident.)
    Tutorial: To be considered a CSIRT, an organization must do as
    follows: (a) Provide a (secure) channel for receiving reports
    about suspected security incidents. (b) Provide assistance to
    members of its constituency in handling the incidents. (c)
    Disseminate incident-related information to its constituency and
    other involved parties.
 $ computer security object
    (I) The definition or representation of a resource, tool, or
    mechanism used to maintain a condition of security in computerized
    environments. Includes many items referred to in standards that
    are either selected or defined by separate user communities.
    [CSOR] (See: object identifier, Computer Security Objects
    Register.)
 $ Computer Security Objects Register (CSOR)
    (N) A service operated by NIST is establishing a catalog for
    computer security objects to provide stable object definitions
    identified by unique names. The use of this register will enable
    the unambiguous specification of security parameters and
    algorithms to be used in secure data exchanges. (See: object
    identifier.)
    Tutorial: The CSOR follows registration guidelines established by
    the international standards community and ANSI. Those guidelines
    establish minimum responsibilities for registration authorities
    and assign the top branches of an international registration
    hierarchy. Under that international registration hierarchy, the
    CSOR is responsible for the allocation of unique identifiers under
    the branch: {joint-iso-ccitt(2) country(16) us(840)
    organization(1) gov(101) csor(3)}.
 $ computer system
    (I) Synonym for "information system", or a component thereof.
    (Compare: computer platform.)
 $ Computers At Risk
    (O) The 1991 report [NRC91] of the System Security Study
    Committee, sponsored by the U.S. National Academy of Sciences and
    supported by the Defense Advanced Research Projects Agency of the
    U.S. DoD. It made many recommendations for industry and
    governments to improve computer security and trustworthiness. Some
    of the most important recommendations (e.g., establishing an

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    Information Security Foundation chartered by the U.S. Government)
    have not been implemented at all, and others (e.g., codifying
    Generally Accepted System Security Principles similar to
    accounting principles) have been implemented but not widely
    adopted [SP14, SP27].
 $ COMSEC
    (I) See: communication security.
 $ COMSEC account
    (O) /U.S. Government/ "Administrative entity, identified by an
    account number, used to maintain accountability, custody, and
    control of COMSEC material." [C4009] (See: COMSEC custodian.)
 $ COMSEC accounting
    (O) /U.S. Government/ The process of creating, collecting, and
    maintaining data records that describe the status and custody of
    designated items of COMSEC material. (See: accounting legend
    code.)
    Tutorial: Almost any secure information system needs to record a
    security audit trail, but a system that manages COMSEC material
    needs to record additional data about the status and custody of
    COMSEC items.
    -  COMSEC tracking: The process of automatically collecting,
       recording, and managing information that describes the status
       of designated items of COMSEC material at all times during each
       product's lifecycle.
    -  COMSEC controlling: The process of supplementing tracking data
       with custody data, which consists of explicit acknowledgements
       of system entities that they (a) have received specific COMSEC
       items and (b) are responsible for preventing exposure of those
       items.
    For example, a key management system that serves a large customer
    base needs to record tracking data for the same reasons that a
    national parcel delivery system does, i.e., to answer the question
    "Where is that thing now?". If keys are encrypted immediately upon
    generation and handled only in BLACK form between the point of
    generation and the point of use, then tracking may be all that is
    needed. However, in cases where keys are handled at least partly
    in RED form and are potentially subject to exposure, then tracking
    needs to be supplemented by controlling.
    Data that is used purely for tracking need be retained only
    temporarily, until an item's status changes. Data that is used for
    controlling is retained indefinitely to ensure accountability and
    support compromise recovery.

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 $ COMSEC boundary
    (N) "Definable perimeter encompassing all hardware, firmware, and
    software components performing critical COMSEC functions, such as
    key generation and key handling and storage." [C4009] (Compare:
    cryptographic boundary.)
 $ COMSEC custodian
    (O) /U.S. Government/ "Individual designated by proper authority
    to be responsible for the receipt, transfer, accounting,
    safeguarding, and destruction of COMSEC material assigned to a
    COMSEC account." [C4009]
 $ COMSEC material
    (N) /U.S. Government/ Items designed to secure or authenticate
    communications or information in general; these items include (but
    are not limited to) keys; equipment, devices, documents, firmware,
    and software that embodies or describes cryptographic logic; and
    other items that perform COMSEC functions. [C4009] (Compare:
    keying material.)
 $ COMSEC Material Control System (CMCS)
    (O) /U.S. Government/ "Logistics and accounting system through
    which COMSEC material marked 'CRYPTO' is distributed, controlled,
    and safeguarded." [C4009] (See: COMSEC account, COMSEC custodian.)
 $ confidentiality
    See: data confidentiality.
 $ concealment system
    (O) "A method of achieving confidentiality in which sensitive
    information is hidden by embedding it in irrelevant data." [NCS04]
    (Compare: steganography.)
 $ configuration control
    (I) The process of regulating changes to hardware, firmware,
    software, and documentation throughout the development and
    operational life of a system. (See: administrative security,
    harden, trusted distribution.)
    Tutorial: Configuration control helps protect against unauthorized
    or malicious alteration of a system and thus provides assurance of
    system integrity. (See: malicious logic.)
 $ confinement property
    (N) /formal model/ Property of a system whereby a subject has
    write access to an object only if the classification of the object
    dominates the clearance of the subject. (See: *-property, Bell-
    LaPadula model.)

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 $ constraint
    (I) /access control/ A limitation on the function of an identity,
    role, or privilege. (See: rule-based access control.)
    Tutorial: In effect, a constraint is a form of security policy and
    may be either static or dynamic:
    -  "Static constraint": A constraint that must be satisfied at the
       time the policy is defined, and then continues to be satisfied
       until the constraint is removed.
    -  "Dynamic constraint": A constraint that may be defined to apply
       at various times that the identity, role, or other object of
       the constraint is active in the system.
 $ content filter
    (I) /World Wide Web/ Application software used to prevent access
    to certain Web servers, such as by parents who do not want their
    children to access pornography. (See: filter, guard.)
    Tutorial: The filter is usually browser-based, but could be part
    of an intermediate cache server. The two basic content filtering
    techniques are (a) to block a specified list of URLs and (b) to
    block material that contains specified words and phrases.
 $ contingency plan
    (I) A plan for emergency response, backup operations, and post-
    disaster recovery in a system as part of a security program to
    ensure availability of critical system resources and facilitate
    continuity of operations in a crisis. [NCS04] (See: availability.)
 $ control zone
    (O) "The space, expressed in feet of radius, surrounding equipment
    processing sensitive information, that is under sufficient
    physical and technical control to preclude an unauthorized entry
    or compromise." [NCSSG] (Compare: inspectable space, TEMPEST
    zone.)
 $ controlled access protection
    (O) /TCSEC/ The level of evaluation criteria for a C2 computer
    system.
    Tutorial: The major features of the C2 level are individual
    accountability, audit, access control, and object reuse.
 $ controlled cryptographic item (CCI)
    (O) /U.S. Government/ "Secure telecommunications or information
    handling equipment, or associated cryptographic component, that is
    unclassified but governed by a special set of control
    requirements." [C4009] (Compare: EUCI.)

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    Tutorial: This category of equipment was established in 1985 to
    promote broad use of secure equipment for protecting both
    classified and unclassified information in the national interest.
    CCI equipment uses a classified cryptographic logic, but the
    hardware or firmware embodiment of that logic is unclassified.
    Drawings, software implementations, and other descriptions of that
    logic remain classified. [N4001]
 $ controlled interface
    (I) A mechanism that facilitates the adjudication of the different
    security policies of interconnected systems. (See: domain, guard.)
 $ controlled security mode
    (D) /U.S. DoD/ A mode of system operation wherein (a) two or more
    security levels of information are allowed to be handled
    concurrently within the same system when some users having access
    to the system have neither a security clearance nor need-to-know
    for some of the data handled by the system, but (b) separation of
    the users and the classified material on the basis, respectively,
    of clearance and classification level are not dependent only on
    operating system control (like they are in multilevel security
    mode). (See: /system operation/ under "mode", protection level.)
    Deprecated Term: IDOCs SHOULD NOT use this term. It was defined in
    a U.S. Government policy regarding system accreditation and was
    subsumed by "partitioned security mode" in a later policy. Both
    terms were dropped in still later policies.
    Tutorial: Controlled mode was intended to encourage ingenuity in
    meeting data confidentiality requirements in ways less restrictive
    than "dedicated security mode" and "system-high security mode",
    but at a level of risk lower than that generally associated with
    true "multilevel security mode". This was intended to be
    accomplished by implementation of explicit augmenting measures to
    reduce or remove a substantial measure of system software
    vulnerability together with specific limitation of the security
    clearance levels of users having concurrent access to the system.
 $ controlling authority
    (O) /U.S. Government/ "Official responsible for directing the
    operation of a cryptonet and for managing the operational use and
    control of keying material assigned to the cryptonet." [C4009,
    N4006]
 $ cookie
    1. (I) /HTTP/ Data exchanged between an HTTP server and a browser
    (a client of the server) to store state information on the client
    side and retrieve it later for server use.

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    Tutorial: An HTTP server, when sending data to a client, may send
    along a cookie, which the client retains after the HTTP connection
    closes. A server can use this mechanism to maintain persistent
    client-side state information for HTTP-based applications,
    retrieving the state information in later connections. A cookie
    may include a description of the range of URLs for which the state
    is valid. Future requests made by the client in that range will
    also send the current value of the cookie to the server. Cookies
    can be used to generate profiles of web usage habits, and thus may
    infringe on personal privacy.
    2. (I) /IPsec/ Data objects exchanged by ISAKMP to prevent certain
    denial-of-service attacks during the establishment of a security
    association.
    3. (D) /access control/ Synonym for "capability token" or
    "ticket".
    Deprecated Definition: IDOCs SHOULD NOT use this term with
    definition 3; that would duplicate the meaning of better-
    established terms and mix concepts in a potentially misleading
    way.
 $ Coordinated Universal Time (UTC)
    (N) UTC is derived from International Atomic Time (TAI) by adding
    a number of leap seconds. The International Bureau of Weights and
    Measures computes TAI once each month by averaging data from many
    laboratories. (See: GeneralizedTime, UTCTime.)
 $ correction
    (I) /security/ A system change made to eliminate or reduce the
    risk of reoccurrence of a security violation or threat
    consequence. (See: secondary definition under "security".)
 $ correctness
    (I) "The property of a system that is guaranteed as the result of
    formal verification activities." [Huff] (See: correctness proof,
    verification.)
 $ correctness integrity
    (I) The property that the information represented by data is
    accurate and consistent. (Compare: data integrity, source
    integrity.)
    Tutorial: IDOCs SHOULD NOT use this term without providing a
    definition; the term is neither well-known nor precisely defined.
    Data integrity refers to the constancy of data values, and source
    integrity refers to confidence in data values. However,

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    correctness integrity refers to confidence in the underlying
    information that data values represent, and this property is
    closely related to issues of accountability and error handling.
 $ correctness proof
    (I) A mathematical proof of consistency between a specification
    for system security and the implementation of that specification.
    (See: correctness, formal specification.)
 $ corruption
    (I) A type of threat action that undesirably alters system
    operation by adversely modifying system functions or data. (See:
    disruption.)
    Usage: This type of threat action includes the following subtypes:
    -  "Tampering": /corruption/ Deliberately altering a system's
       logic, data, or control information to interrupt or prevent
       correct operation of system functions. (See: misuse, main entry
       for "tampering".)
    -  "Malicious logic": /corruption/ Any hardware, firmware, or
       software (e.g., a computer virus) intentionally introduced into
       a system to modify system functions or data. (See:
       incapacitation, main entry for "malicious logic", masquerade,
       misuse.)
    -  "Human error": /corruption/ Human action or inaction that
       unintentionally results in the alteration of system functions
       or data.
    -  "Hardware or software error": /corruption/ Error that results
       in the alteration of system functions or data.
    -  "Natural disaster": /corruption/ Any "act of God" (e.g., power
       surge caused by lightning) that alters system functions or
       data. [FP031 Section 2]
 $ counter
    1. (N) /noun/ See: counter mode.
    2. (I) /verb/ See: countermeasure.
 $ counter-countermeasure
    (I) An action, device, procedure, or technique used by an attacker
    to offset a defensive countermeasure.
    Tutorial: For every countermeasure devised to protect computers
    and networks, some cracker probably will be able to devise a
    counter-countermeasure. Thus, systems must use "defense in depth".

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 $ counter mode (CTR)
    (N) A block cipher mode that enhances ECB mode by ensuring that
    each encrypted block is different from every other block encrypted
    under the same key. [SP38A] (See: block cipher.)
    Tutorial: This mode operates by first encrypting a generated
    sequence of blocks, called "counters", that are separate from the
    input sequence of plaintext blocks which the mode is intended to
    protect. The resulting sequence of encrypted counters is
    exclusive-ORed with the sequence of plaintext blocks to produce
    the final ciphertext output blocks. The sequence of counters must
    have the property that each counter is different from every other
    counter for all of the plain text that is encrypted under the same
    key.
 $ Counter with Cipher Block Chaining-Message Authentication Code
    (CCM)
    (N) A block cipher mode [SP38C] that provides both data
    confidentiality and data origin authentication, by combining the
    techniques of CTR and a CBC-based message authentication code.
    (See: block cipher.)
 $ countermeasure
    (I) An action, device, procedure, or technique that meets or
    opposes (i.e., counters) a threat, a vulnerability, or an attack
    by eliminating or preventing it, by minimizing the harm it can
    cause, or by discovering and reporting it so that corrective
    action can be taken.
    Tutorial: In an Internet protocol, a countermeasure may take the
    form of a protocol feature, a component function, or a usage
    constraint.
 $ country code
    (I) An identifier that is defined for a nation by ISO. [I3166]
    Tutorial: For each nation, ISO Standard 3166 defines a unique two-
    character alphabetic code, a unique three-character alphabetic
    code, and a three-digit code. Among many uses of these codes, the
    two-character codes are used as top-level domain names.
 $ Courtney's laws
    (N) Principles for managing system security that were stated by
    Robert H. Courtney, Jr.

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    Tutorial: Bill Murray codified Courtney's laws as follows: [Murr]
    -  Courtney's first law: You cannot say anything interesting
       (i.e., significant) about the security of a system except in
       the context of a particular application and environment.
    -  Courtney's second law: Never spend more money eliminating a
       security exposure than tolerating it will cost you. (See:
       acceptable risk, risk analysis.)
       -- First corollary: Perfect security has infinite cost.
       -- Second corollary: There is no such thing as zero risk.
    -  Courtney's third law: There are no technical solutions to
       management problems, but there are management solutions to
       technical problems.
 $ covert action
    (I) An operation that is planned and executed in a way that
    conceals the identity of the operator.
 $ covert channel
    1. (I) An unintended or unauthorized intra-system channel that
    enables two cooperating entities to transfer information in a way
    that violates the system's security policy but does not exceed the
    entities' access authorizations. (See: covert storage channel,
    covert timing channel, out-of-band, tunnel.)
    2. (O) "A communications channel that allows two cooperating
    processes to transfer information in a manner that violates the
    system's security policy." [NCS04]
    Tutorial: The cooperating entities can be either two insiders or
    an insider and an outsider. Of course, an outsider has no access
    authorization at all. A covert channel is a system feature that
    the system architects neither designed nor intended for
    information transfer.
 $ covert storage channel
    (I) A system feature that enables one system entity to signal
    information to another entity by directly or indirectly writing a
    storage location that is later directly or indirectly read by the
    second entity. (See: covert channel.)
 $ covert timing channel
    (I) A system feature that enables one system entity to signal
    information to another by modulating its own use of a system
    resource in such a way as to affect system response time observed
    by the second entity. (See: covert channel.)
 $ CPS
    (I) See: certification practice statement.

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 $ cracker
    (I) Someone who tries to break the security of, and gain
    unauthorized access to, someone else's system, often with
    malicious intent. (See: adversary, intruder, packet monkey, script
    kiddy. Compare: hacker.)
    Usage: Was sometimes spelled "kracker". [NCSSG]
 $ CRAM
    (I) See: Challenge-Response Authentication Mechanism.
 $ CRC
    (I) See: cyclic redundancy check.
 $ credential
    1. (I) /authentication/ "identifier credential": A data object
    that is a portable representation of the association between an
    identifier and a unit of authentication information, and that can
    be presented for use in verifying an identity claimed by an entity
    that attempts to access a system. Example: X.509 public-key
    certificate. (See: anonymous credential.)
    2. (I) /access control/ "authorization credential": A data object
    that is a portable representation of the association between an
    identifier and one or more access authorizations, and that can be
    presented for use in verifying those authorizations for an entity
    that attempts such access. Example: X.509 attribute certificate.
    (See: capability token, ticket.)
    3. (D) /OSIRM/ "Data that is transferred to establish the claimed
    identity of an entity." [I7498-2]
    Deprecated Definition: IDOCs SHOULD NOT use the term with
    definition 3. As explained in the tutorial below, an
    authentication process can involve the transfer of multiple data
    objects, and not all of those are credentials.
    4. (D) /U.S. Government/ "An object that is verified when
    presented to the verifier in an authentication transaction."
    [M0404]
    Deprecated Definition: IDOCs SHOULD NOT use the term with
    definition 4; it mixes concepts in a potentially misleading way.
    For example, in an authentication process, it is the identity that
    is "verified", not the credential; the credential is "validated".
    (See: validate vs. verify.)

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    Tutorial: In general English, "credentials" are evidence or
    testimonials that (a) support a claim of identity or authorization
    and (b) usually are intended to be used more than once (i.e., a
    credential's life is long compared to the time needed for one
    use). Some examples are a policeman's badge, an automobile
    driver's license, and a national passport. An authentication or
    access control process that uses a badge, license, or passport is
    outwardly simple: the holder just shows the thing.
    The problem with adopting this term in Internet security is that
    an automated process for authentication or access control usually
    requires multiple steps using multiple data objects, and it might
    not be immediately obvious which of those objects should get the
    name "credential".
    For example, if the verification step in a user authentication
    process employs public-key technology, then the process involves
    at least three data items: (a) the user's private key, (b) a
    signed value -- signed with that private key and passed to the
    system, perhaps in response to a challenge from the system -- and
    (c) the user's public-key certificate, which is validated by the
    system and provides the public key needed to verify the signature.
    -  Private key: The private key is *not* a credential, because it
       is never transferred or presented. Instead, the private key is
       "authentication information", which is associated with the
       user's identifier for a specified period of time and can be
       used in multiple authentications during that time.
    -  Signed value: The signed value is *not* a credential; the
       signed value is only ephemeral, not long lasting. The OSIRM
       definition could be interpreted to call the signed value a
       credential, but that would conflict with general English.
    -  Certificate: The user's certificate *is* a credential. It can
       be "transferred" or "presented" to any person or process that
       needs it at any time. A public-key certificate may be used as
       an "identity credential", and an attribute certificate may be
       used as an "authorization credential".
 $ critical
    1. (I) /system resource/ A condition of a system resource such
    that denial of access to, or lack of availability of, that
    resource would jeopardize a system user's ability to perform a
    primary function or would result in other serious consequences,
    such as human injury or loss of life. (See: availability,
    precedence. Compare: sensitive.)
    2. (N) /extension/ An indication that an application is not
    permitted to ignore an extension. [X509]

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    Tutorial: Each extension of an X.509 certificate or CRL is flagged
    as either "critical" or "non-critical". In a certificate, if a
    computer program does not recognize an extension's type (i.e.,
    does not implement its semantics), then if the extension is
    critical, the program is required to treat the certificate as
    invalid; but if the extension is non-critical, the program is
    permitted to ignore the extension.
    In a CRL, if a program does not recognize a critical extension
    that is associated with a specific certificate, the program is
    required to assume that the listed certificate has been revoked
    and is no longer valid, and then take whatever action is required
    by local policy.
    When a program does not recognize a critical extension that is
    associated with the CRL as a whole, the program is required to
    assume that all listed certificates have been revoked and are no
    longer valid. However, since failing to process the extension may
    mean that the list has not been completed, the program cannot
    assume that other certificates are valid, and the program needs to
    take whatever action is therefore required by local policy.
 $ critical information infrastructure
    (I) Those systems that are so vital to a nation that their
    incapacity or destruction would have a debilitating effect on
    national security, the economy, or public health and safety.
 $ CRL
    (I) See: certificate revocation list.
 $ CRL distribution point
    (I) See: distribution point.
 $ CRL extension
    (I) See: extension.
 $ cross-certificate
    (I) A public-key certificate issued by a CA in one PKI to a CA in
    another PKI. (See: cross-certification.)
 $ cross-certification
    (I) The act or process by which a CA in one PKI issues a public-
    key certificate to a CA in another PKI. [X509] (See: bridge CA.)
    Tutorial: X.509 says that a CA (say, CA1) may issue a "cross-
    certificate" in which the subject is another CA (say, CA2). X.509
    calls CA2 the "subject CA" and calls CA1 an "intermediate CA", but

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    this Glossary deprecates those terms. (See: intermediate CA,
    subject CA).
    Cross-certification of CA2 by CA1 appears similar to certification
    of a subordinate CA by a superior CA, but cross-certification
    involves a different concept. The "subordinate CA" concept applies
    when both CAs are in the same PKI, i.e., when either (a) CA1 and
    CA2 are under the same root or (b) CA1 is itself a root. The
    "cross-certification" concept applies in other cases:
    First, cross-certification applies when two CAs are in different
    PKIs, i.e., when CA1 and CA2 are under different roots, or perhaps
    are both roots themselves. Issuing the cross-certificate enables
    end entities certified under CA1 in PK1 to construct the
    certification paths needed to validate the certificates of end
    entities certified under CA2 in PKI2. Sometimes, a pair of cross-
    certificates is issued -- by CA1 to CA2, and by CA2 to CA1 -- so
    that an end entity in either PKI can validate certificates issued
    in the other PKI.
    Second, X.509 says that two CAs in some complex, multi-CA PKI can
    cross-certify one another to shorten the certification paths
    constructed by end entities. Whether or not a CA may perform this
    or any other form of cross-certification, and how such
    certificates may be used by end entities, should be addressed by
    the local certificate policy and CPS.
 $ cross-domain solution
    1. (D) Synonym for "guard".
    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    "guard"; this term unnecessarily (and verbosely) duplicates the
    meaning of the long-established "guard".
    2. (O) /U.S. Government/ A process or subsystem that provides a
    capability (which could be either manual or automated) to access
    two or more differing security domains in a system, or to transfer
    information between such domains. (See: domain, guard.)
 $ cryptanalysis
    1. (I) The mathematical science that deals with analysis of a
    cryptographic system to gain knowledge needed to break or
    circumvent the protection that the system is designed to provide.
    (See: cryptology, secondary definition under "intrusion".)
    2. (O) "The analysis of a cryptographic system and/or its inputs
    and outputs to derive confidential variables and/or sensitive data
    including cleartext." [I7498-2]

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    Tutorial: Definition 2 states the traditional goal of
    cryptanalysis, i.e., convert cipher text to plain text (which
    usually is clear text) without knowing the key; but that
    definition applies only to encryption systems. Today, the term is
    used with reference to all kinds of cryptographic algorithms and
    key management, and definition 1 reflects that. In all cases,
    however, a cryptanalyst tries to uncover or reproduce someone
    else's sensitive data, such as clear text, a key, or an algorithm.
    The basic cryptanalytic attacks on encryption systems are
    ciphertext-only, known-plaintext, chosen-plaintext, and chosen-
    ciphertext; and these generalize to the other kinds of
    cryptography.
 $ crypto, CRYPTO
    1. (N) A prefix ("crypto-") that means "cryptographic".
    Usage: IDOCs MAY use this prefix when it is part of a term listed
    in this Glossary. Otherwise, IDOCs SHOULD NOT use this prefix;
    instead, use the unabbreviated adjective, "cryptographic".
    2. (D) In lower case, "crypto" is an abbreviation for the
    adjective "cryptographic", or for the nouns "cryptography" or
    "cryptographic component".
    Deprecated Abbreviation: IDOCs SHOULD NOT use this abbreviation
    because it could easily be misunderstood in some technical sense.
    3. (O) /U.S. Government/ In upper case, "CRYPTO" is a marking or
    designator that identifies "COMSEC keying material used to secure
    or authenticate telecommunications carrying classified or
    sensitive U.S. Government or U.S. Government-derived information."
    [C4009] (See: security label, security marking.)
 $ cryptographic
    (I) An adjective that refers to cryptography.
 $ cryptographic algorithm
    (I) An algorithm that uses the science of cryptography, including
    (a) encryption algorithms, (b) cryptographic hash algorithms, (c)
    digital signature algorithms, and (d) key-agreement algorithms.
 $ cryptographic application programming interface (CAPI)
    (I) The source code formats and procedures through which an
    application program accesses cryptographic services, which are
    defined abstractly compared to their actual implementation.
    Example, see: PKCS #11, [R2628].

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 $ cryptographic association
    (I) A security association that involves the use of cryptography
    to provide security services for data exchanged by the associated
    entities. (See: ISAKMP.)
 $ cryptographic boundary
    (I) See: secondary definition under "cryptographic module".
 $ cryptographic card
    (I) A cryptographic token in the form of a smart card or a PC
    card.
 $ cryptographic component
    (I) A generic term for any system component that involves
    cryptography. (See: cryptographic module.)
 $ cryptographic hash
    (I) See: secondary definition under "hash function".
 $ cryptographic ignition key (CIK)
    1. (N) A physical (usually electronic) token used to store,
    transport, and protect cryptographic keys and activation data.
    (Compare: dongle, fill device.)
    Tutorial: A key-encrypting key could be divided (see: split key)
    between a CIK and a cryptographic module, so that it would be
    necessary to combine the two to regenerate the key, use it to
    decrypt other keys and data contained in the module, and thus
    activate the module.
    2. (O) "Device or electronic key used to unlock the secure mode of
    cryptographic equipment." [C4009] Usage: Abbreviated as "crypto-
    ignition key".
 $ cryptographic key
    (I) See: key. Usage: Usually shortened to just "key".
 $ Cryptographic Message Syntax (CMS)
    (I) An encapsulation syntax (RFC 3852) for digital signatures,
    hashes, and encryption of arbitrary messages.
    Tutorial: CMS derives from PKCS #7. CMS values are specified with
    ASN.1 and use BER encoding. The syntax permits multiple
    encapsulation with nesting, permits arbitrary attributes to be
    signed along with message content, and supports a variety of
    architectures for digital certificate-based key management.

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 $ cryptographic module
    (I) A set of hardware, software, firmware, or some combination
    thereof that implements cryptographic logic or processes,
    including cryptographic algorithms, and is contained within the
    module's "cryptographic boundary", which is an explicitly defined
    contiguous perimeter that establishes the physical bounds of the
    module. [FP140]
 $ cryptographic system
    1. (I) A set of cryptographic algorithms together with the key
    management processes that support use of the algorithms in some
    application context.
    Usage: IDOCs SHOULD use definition 1 because it covers a wider
    range of algorithms than definition 2.
    2. (O) "A collection of transformations from plain text into
    cipher text and vice versa [which would exclude digital signature,
    cryptographic hash, and key-agreement algorithms], the particular
    transformation(s) to be used being selected by keys. The
    transformations are normally defined by a mathematical algorithm."
    [X509]
 $ cryptographic token
    1. (I) A portable, user-controlled, physical device (e.g., smart
    card or PCMCIA card) used to store cryptographic information and
    possibly also perform cryptographic functions. (See: cryptographic
    card, token.)
    Tutorial: A smart token might implement some set of cryptographic
    algorithms and might incorporate related key management functions,
    such as a random number generator. A smart cryptographic token may
    contain a cryptographic module or may not be explicitly designed
    that way.
 $ cryptography
    1. (I) The mathematical science that deals with transforming data
    to render its meaning unintelligible (i.e., to hide its semantic
    content), prevent its undetected alteration, or prevent its
    unauthorized use. If the transformation is reversible,
    cryptography also deals with restoring encrypted data to
    intelligible form. (See: cryptology, steganography.)
    2. (O) "The discipline which embodies principles, means, and
    methods for the transformation of data in order to hide its
    information content, prevent its undetected modification and/or
    prevent its unauthorized use.... Cryptography determines the
    methods used in encipherment and decipherment." [I7498-2]

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    Tutorial: Comprehensive coverage of applied cryptographic
    protocols and algorithms is provided by Schneier [Schn].
    Businesses and governments use cryptography to make data
    incomprehensible to outsiders; to make data incomprehensible to
    both outsiders and insiders, the data is sent to lawyers for a
    rewrite.
 $ Cryptoki
    (N) A CAPI defined in PKCS #11. Pronunciation: "CRYPTO-key".
    Derivation: Abbreviation of "cryptographic token interface".
 $ cryptology
    (I) The science of secret communication, which includes both
    cryptography and cryptanalysis.
    Tutorial: Sometimes the term is used more broadly to denote
    activity that includes both rendering signals secure (see: signal
    security) and extracting information from signals (see: signal
    intelligence) [Kahn].
 $ cryptonet
    (I) A network (i.e., a communicating set) of system entities that
    share a secret cryptographic key for a symmetric algorithm. (See:
    controlling authority.)
    (O) "Stations holding a common key." [C4009]
 $ cryptoperiod
    (I) The time span during which a particular key value is
    authorized to be used in a cryptographic system. (See: key
    management.)
    Usage: This term is long-established in COMPUSEC usage. In the
    context of certificates and public keys, "key lifetime" and
    "validity period" are often used instead.
    Tutorial: A cryptoperiod is usually stated in terms of calendar or
    clock time, but sometimes is stated in terms of the maximum amount
    of data permitted to be processed by a cryptographic algorithm
    using the key. Specifying a cryptoperiod involves a tradeoff
    between the cost of rekeying and the risk of successful
    cryptoanalysis.
 $ cryptosystem
    (I) Contraction of "cryptographic system".
 $ cryptovariable
    (D) Synonym for "key".

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    Deprecated Usage: In contemporary COMSEC usage, the term "key" has
    replaced the term "cryptovariable".
 $ CSIRT
    (I) See: computer security incident response team.
 $ CSOR
    (N) See: Computer Security Objects Register.
 $ CTAK
    (D) See: ciphertext auto-key.
 $ CTR
    (N) See: counter mode.
 $ cut-and-paste attack
    (I) An active attack on the data integrity of cipher text,
    effected by replacing sections of cipher text with other cipher
    text, such that the result appears to decrypt correctly but
    actually decrypts to plain text that is forged to the satisfaction
    of the attacker.
 $ cyclic redundancy check (CRC)
    (I) A type of checksum algorithm that is not a cryptographic hash
    but is used to implement data integrity service where accidental
    changes to data are expected. Sometimes called "cyclic redundancy
    code".
 $ DAC
    (N) See: Data Authentication Code, discretionary access control.
    Deprecated Usage: IDOCs that use this term SHOULD state a
    definition for it because this abbreviation is ambiguous.
 $ daemon
    (I) A computer program that is not invoked explicitly but waits
    until a specified condition occurs, and then runs with no
    associated user (principal), usually for an administrative
    purpose. (See: zombie.)
 $ dangling threat
    (O) A threat to a system for which there is no corresponding
    vulnerability and, therefore, no implied risk.
 $ dangling vulnerability
    (O) A vulnerability of a system for which there is no
    corresponding threat and, therefore, no implied risk.

Shirey Informational [Page 92] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ DASS
    (I) See: Distributed Authentication Security Service.
 $ data
    (I) Information in a specific representation, usually as a
    sequence of symbols that have meaning.
    Usage: Refers to both (a) representations that can be recognized,
    processed, or produced by a computer or other type of machine, and
    (b) representations that can be handled by a human.
 $ Data Authentication Algorithm, data authentication algorithm
    1. (N) /capitalized/ The ANSI standard for a keyed hash function
    that is equivalent to DES cipher block chaining with IV = 0.
    [A9009]
    2. (D) /not capitalized/ Synonym for some kind of "checksum".
    Deprecated Term: IDOCs SHOULD NOT use the uncapitalized form "data
    authentication algorithm" as a synonym for any kind of checksum,
    regardless of whether or not the checksum is based on a hash.
    Instead, use "checksum", "Data Authentication Code", "error
    detection code", "hash", "keyed hash", "Message Authentication
    Code", "protected checksum", or some other specific term,
    depending on what is meant.
    The uncapitalized term can be confused with the Data
    Authentication Code and also mixes concepts in a potentially
    misleading way. The word "authentication" is misleading because
    the checksum may be used to perform a data integrity function
    rather than a data origin authentication function.
 $ Data Authentication Code, data authentication code
    1. (N) /capitalized/ A specific U.S. Government standard [FP113]
    for a checksum that is computed by the Data Authentication
    Algorithm. Usage: a.k.a. Message Authentication Code [A9009].)
    (See: DAC.)
    2. (D) /not capitalized/ Synonym for some kind of "checksum".
    Deprecated Term: IDOCs SHOULD NOT use the uncapitalized form "data
    authentication code" as a synonym for any kind of checksum,
    regardless of whether or not the checksum is based on the Data
    Authentication Algorithm. The uncapitalized term can be confused
    with the Data Authentication Code and also mixes concepts in a
    potentially misleading way (see: authentication code).

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 $ data compromise
    1. (I) A security incident in which information is exposed to
    potential unauthorized access, such that unauthorized disclosure,
    alteration, or use of the information might have occurred.
    (Compare: security compromise, security incident.)
    2. (O) /U.S. DoD/ A "compromise" is a "communication or physical
    transfer of information to an unauthorized recipient." [DoD5]
    3. (O) /U.S. Government/ "Type of [security] incident where
    information is disclosed to unauthorized individuals or a
    violation of the security policy of a system in which unauthorized
    intentional or unintentional disclosure, modification,
    destruction, or loss of an object may have occurred." [C4009]
 $ data confidentiality
    1. (I) The property that data is not disclosed to system entities
    unless they have been authorized to know the data. (See: Bell-
    LaPadula model, classification, data confidentiality service,
    secret. Compare: privacy.)
    2. (D) "The property that information is not made available or
    disclosed to unauthorized individuals, entities, or processes
    [i.e., to any unauthorized system entity]." [I7498-2].
    Deprecated Definition: The phrase "made available" might be
    interpreted to mean that the data could be altered, and that would
    confuse this term with the concept of "data integrity".
 $ data confidentiality service
    (I) A security service that protects data against unauthorized
    disclosure. (See: access control, data confidentiality, datagram
    confidentiality service, flow control, inference control.)
    Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
    "privacy", which is a different concept.
 $ Data Encryption Algorithm (DEA)
    (N) A symmetric block cipher, defined in the U.S. Government's
    DES. DEA uses a 64-bit key, of which 56 bits are independently
    chosen and 8 are parity bits, and maps a 64-bit block into another
    64-bit block. [FP046] (See: AES, symmetric cryptography.)
    Usage: This algorithm is usually referred to as "DES". The
    algorithm has also been adopted in standards outside the
    Government (e.g., [A3092]).

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 $ data encryption key (DEK)
    (I) A cryptographic key that is used to encipher application data.
    (Compare: key-encrypting key.)
 $ Data Encryption Standard (DES)
    (N) A U.S. Government standard [FP046] that specifies the DEA and
    states policy for using the algorithm to protect unclassified,
    sensitive data. (See: AES.)
 $ data integrity
    1. (I) The property that data has not been changed, destroyed, or
    lost in an unauthorized or accidental manner. (See: data integrity
    service. Compare: correctness integrity, source integrity.)
    2. (O) "The property that information has not been modified or
    destroyed in an unauthorized manner." [I7498-2]
    Usage: Deals with (a) constancy of and confidence in data values,
    and not with either (b) information that the values represent
    (see: correctness integrity) or (c) the trustworthiness of the
    source of the values (see: source integrity).
 $ data integrity service
    (I) A security service that protects against unauthorized changes
    to data, including both intentional change or destruction and
    accidental change or loss, by ensuring that changes to data are
    detectable. (See: data integrity, checksum, datagram integrity
    service.)
    Tutorial: A data integrity service can only detect a change and
    report it to an appropriate system entity; changes cannot be
    prevented unless the system is perfect (error-free) and no
    malicious user has access. However, a system that offers data
    integrity service might also attempt to correct and recover from
    changes.
    The ability of this service to detect changes is limited by the
    technology of the mechanisms used to implement the service. For
    example, if the mechanism were a one-bit parity check across each
    entire SDU, then changes to an odd number of bits in an SDU would
    be detected, but changes to an even number of bits would not.
    Relationship between data integrity service and authentication
    services: Although data integrity service is defined separately
    from data origin authentication service and peer entity
    authentication service, it is closely related to them.
    Authentication services depend, by definition, on companion data
    integrity services. Data origin authentication service provides

Shirey Informational [Page 95] RFC 4949 Internet Security Glossary, Version 2 August 2007

    verification that the identity of the original source of a
    received data unit is as claimed; there can be no such
    verification if the data unit has been altered. Peer entity
    authentication service provides verification that the identity of
    a peer entity in a current association is as claimed; there can be
    no such verification if the claimed identity has been altered.
 $ data origin authentication
    (I) "The corroboration that the source of data received is as
    claimed." [I7498-2] (See: authentication.)
 $ data origin authentication service
    (I) A security service that verifies the identity of a system
    entity that is claimed to be the original source of received data.
    (See: authentication, authentication service.)
    Tutorial: This service is provided to any system entity that
    receives or holds the data. Unlike peer entity authentication
    service, this service is independent of any association between
    the originator and the recipient, and the data in question may
    have originated at any time in the past.
    A digital signature mechanism can be used to provide this service,
    because someone who does not know the private key cannot forge the
    correct signature. However, by using the signer's public key,
    anyone can verify the origin of correctly signed data.
    This service is usually bundled with connectionless data integrity
    service. (See: "relationship between data integrity service and
    authentication services" under "data integrity service".
 $ data owner
    (N) The organization that has the final statutory and operational
    authority for specified information.
 $ data privacy
    (D) Synonym for "data confidentiality".
    Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
    in a potentially misleading way. Instead, use either "data
    confidentiality" or "privacy" or both, depending on what is meant.
 $ data recovery
    1. (I) /cryptanalysis/ A process for learning, from some cipher
    text, the plain text that was previously encrypted to produce the
    cipher text. (See: recovery.)

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    2. (I) /system integrity/ The process of restoring information
    following damage or destruction.
 $ data security
    (I) The protection of data from disclosure, alteration,
    destruction, or loss that either is accidental or is intentional
    but unauthorized.
    Tutorial: Both data confidentiality service and data integrity
    service are needed to achieve data security.
 $ datagram
    (I) "A self-contained, independent entity of data [i.e., a packet]
    carrying sufficient information to be routed from the source
    [computer] to the destination computer without reliance on earlier
    exchanges between this source and destination computer and the
    transporting network." [R1983] Example: A PDU of IP.
 $ datagram confidentiality service
    (I) A data confidentiality service that preserves the
    confidentiality of data in a single, independent, packet; i.e.,
    the service applies to datagrams one-at-a-time. Example: ESP.
    (See: data confidentiality.)
    Usage: When a protocol is said to provide data confidentiality
    service, this is usually understood to mean that only the SDU is
    protected in each packet. IDOCs that use the term to mean that the
    entire PDU is protected should include a highlighted definition.
    Tutorial: This basic form of network confidentiality service
    suffices for protecting the data in a stream of packets in both
    connectionless and connection-oriented protocols. Except perhaps
    for traffic flow confidentiality, nothing further is needed to
    protect the confidentiality of data carried by a packet stream.
    The OSIRM distinguishes between connection confidentiality and
    connectionless confidentiality. The IPS need not make that
    distinction, because those services are just instances of the same
    service (i.e., datagram confidentiality) being offered in two
    different protocol contexts. (For data integrity service, however,
    additional effort is needed to protect a stream, and the IPS does
    need to distinguish between "datagram integrity service" and
    "stream integrity service".)
 $ datagram integrity service
    (I) A data integrity service that preserves the integrity of data
    in a single, independent, packet; i.e., the service applies to
    datagrams one-at-a-time. (See: data integrity. Compare: stream
    integrity service.)

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    Tutorial: The ability to provide appropriate data integrity is
    important in many Internet security situations, and so there are
    different kinds of data integrity services suited to different
    applications. This service is the simplest kind; it is suitable
    for connectionless data transfers.
    Datagram integrity service usually is designed only to attempt to
    detect changes to the SDU in each packet, but it might also
    attempt to detect changes to some or all of the PCI in each packet
    (see: selective field integrity). In contrast to this simple,
    one-at-a-time service, some security situations demand a more
    complex service that also attempts to detect deleted, inserted, or
    reordered datagrams within a stream of datagrams (see: stream
    integrity service).
 $ DEA
    (N) See: Data Encryption Algorithm.
 $ deception
    (I) A circumstance or event that may result in an authorized
    entity receiving false data and believing it to be true. (See:
    authentication.)
    Tutorial: This is a type of threat consequence, and it can be
    caused by the following types of threat actions: masquerade,
    falsification, and repudiation.
 $ decipher
    (D) Synonym for "decrypt".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "decrypt". However, see usage note under "encryption".
 $ decipherment
    (D) Synonym for "decryption".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "decryption". However, see the Usage note under "encryption".
 $ declassification
    (I) An authorized process by which information is declassified.
    (Compare: classification.)
 $ declassify
    (I) To officially remove the security level designation of a
    classified information item or information type, such that the
    information is no longer classified (i.e., becomes unclassified).
    (See: classified, classify, security level. Compare: downgrade.)

Shirey Informational [Page 98] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ decode
    1. (I) Convert encoded data back to its original form of
    representation. (Compare: decrypt.)
    2. (D) Synonym for "decrypt".
    Deprecated Definition: Encoding is not usually meant to conceal
    meaning. Therefore, IDOCs SHOULD NOT use this term as a synonym
    for "decrypt", because that would mix concepts in a potentially
    misleading way.
 $ decrypt
    (I) Cryptographically restore cipher text to the plaintext form it
    had before encryption.
 $ decryption
    (I) See: secondary definition under "encryption".
 $ dedicated security mode
    (I) A mode of system operation wherein all users having access to
    the system possess, for all data handled by the system, both (a)
    all necessary authorizations (i.e., security clearance and formal
    access approval) and (b) a need-to-know. (See: /system operation/
    under "mode", formal access approval, need to know, protection
    level, security clearance.)
    Usage: Usually abbreviated as "dedicated mode". This mode was
    defined in U.S. Government policy on system accreditation, but the
    term is also used outside the Government. In this mode, the system
    may handle either (a) a single classification level or category of
    information or (b) a range of levels and categories.
 $ default account
    (I) A system login account (usually accessed with a user
    identifier and password) that has been predefined in a
    manufactured system to permit initial access when the system is
    first put into service. (See: harden.)
    Tutorial: A default account becomes a serious vulnerability if not
    properly administered. Sometimes, the default identifier and
    password are well-known because they are the same in each copy of
    the system. In any case, when a system is put into service, any
    default password should immediately be changed or the default
    account should be disabled.
 $ defense in depth
    (N) "The siting of mutually supporting defense positions designed
    to absorb and progressively weaken attack, prevent initial

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    observations of the whole position by the enemy, and [enable] the
    commander to maneuver the reserve." [JP1]
    Tutorial: In information systems, defense in depth means
    constructing a system's security architecture with layered and
    complementary security mechanisms and countermeasures, so that if
    one security mechanism is defeated, one or more other mechanisms
    (which are "behind" or "beneath" the first mechanism) still
    provide protection.
    This architectural concept is appealing because it aligns with
    traditional warfare doctrine, which applies defense in depth to
    physical, geospatial structures; but applying the concept to
    logical, cyberspace structures of computer networks is more
    difficult. The concept assumes that networks have a spatial or
    topological representation. It also assumes that there can be
    implemented -- from the "outer perimeter" of a network, through
    its various "layers" of components, to its "center" (i.e., to the
    subscriber application systems supported by the network) -- a
    varied series of countermeasures that together provide adequate
    protection. However, it is more difficult to map the topology of
    networks and make certain that no path exists by which an attacker
    could bypass all defensive layers.
 $ Defense Information Infrastructure (DII)
    (O) /U.S. DoD/ The U.S. DoD's shared, interconnected system of
    computers, communications, data, applications, security, people,
    training, and support structures, serving information needs
    worldwide. (See: DISN.) Usage: Has evolved to be called the GIG.
    Tutorial: The DII connects mission support, command and control,
    and intelligence computers and users through voice, data, imagery,
    video, and multimedia services, and provides information
    processing and value-added services to subscribers over the DISN.
    Users' own data and application software are not considered part
    of the DII.
 $ Defense Information Systems Network (DISN)
    (O) /U.S. DoD/ The U.S. DoD's consolidated, worldwide, enterprise
    level telecommunications infrastructure that provides end-to-end
    information transfer for supporting military operations; a part of
    the DII. (Compare: GIG.)
 $ degauss
    1a. (N) Apply a magnetic field to permanently remove data from a
    magnetic storage medium, such as a tape or disk [NCS25]. (Compare:
    erase, purge, sanitize.)

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    1b. (N) Reduce magnetic flux density to zero by applying a
    reversing magnetic field. (See: magnetic remanence.)
 $ degausser
    (N) An electrical device that can degauss magnetic storage media.
 $ DEK
    (I) See: data encryption key.
 $ delay
    (I) /packet/ See: secondary definition under "stream integrity
    service".
 $ deletion
    (I) /packet/ See: secondary definition under "stream integrity
    service".
 $ deliberate exposure
    (I) /threat action/ See: secondary definition under "exposure".
 $ delta CRL
    (I) A partial CRL that only contains entries for certificates that
    have been revoked since the issuance of a prior, base CRL [X509].
    This method can be used to partition CRLs that become too large
    and unwieldy. (Compare: CRL distribution point.)
 $ demilitarized zone (DMZ)
    (D) Synonym for "buffer zone".
    Deprecated Term: IDOCs SHOULD NOT use this term because it mixes
    concepts in a potentially misleading way. (See: Deprecated Usage
    under "Green Book".)
 $ denial of service
    (I) The prevention of authorized access to a system resource or
    the delaying of system operations and functions. (See:
    availability, critical, flooding.)
    Tutorial: A denial-of-service attack can prevent the normal
    conduct of business on the Internet. There are four types of
    solutions to this security problem:
    -  Awareness: Maintaining cognizance of security threats and
       vulnerabilities. (See: CERT.)
    -  Detection: Finding attacks on end systems and subnetworks.
       (See: intrusion detection.)
    -  Prevention: Following defensive practices on network-connected
       systems. (See: [R2827].)

Shirey Informational [Page 101] RFC 4949 Internet Security Glossary, Version 2 August 2007

  1. Response: Reacting effectively when attacks occur. (See: CSIRT,

contingency plan.)

 $ DES
    (N) See: Data Encryption Standard.
 $ designated approving authority (DAA)
    (O) /U.S. Government/ Synonym for "accreditor".
 $ detection
    (I) See: secondary definition under "security".
 $ deterrence
    (I) See: secondary definition under "security".
 $ dictionary attack
    (I) An attack that uses a brute-force technique of successively
    trying all the words in some large, exhaustive list.
    Examples: Attack an authentication service by trying all possible
    passwords. Attack an encryption service by encrypting some known
    plaintext phrase with all possible keys so that the key for any
    given encrypted message containing that phrase may be obtained by
    lookup.
 $ Diffie-Hellman
 $ Diffie-Hellman-Merkle
    (N) A key-agreement algorithm published in 1976 by Whitfield
    Diffie and Martin Hellman [DH76, R2631].
    Usage: The algorithm is most often called "Diffie-Hellman".
    However, in the November 1978 issue of "IEEE Communications
    Magazine", Hellman wrote that the algorithm "is a public key
    distribution system, a concept developed by [Ralph C.] Merkle, and
    hence should be called 'Diffie-Hellman-Merkle' ... to recognize
    Merkle's equal contribution to the invention of public key
    cryptography."
    Tutorial: Diffie-Hellman-Merkle does key establishment, not
    encryption. However, the key that it produces may be used for
    encryption, for further key management operations, or for any
    other cryptography.
    The algorithm is described in [R2631] and [Schn]. In brief, Alice
    and Bob together pick large integers that satisfy certain
    mathematical conditions, and then use the integers to each
    separately compute a public-private key pair. They send each other
    their public key. Each person uses their own private key and the

Shirey Informational [Page 102] RFC 4949 Internet Security Glossary, Version 2 August 2007

    other person's public key to compute a key, k, that, because of
    the mathematics of the algorithm, is the same for each of them.
    Passive wiretapping cannot learn the shared k, because k is not
    transmitted, and neither are the private keys needed to compute k.
    The difficulty of breaking Diffie-Hellman-Merkle is considered to
    be equal to the difficulty of computing discrete logarithms modulo
    a large prime. However, without additional mechanisms to
    authenticate each party to the other, a protocol based on the
    algorithm may be vulnerable to a man-in-the-middle attack.
 $ digest
    See: message digest.
 $ digital certificate
    (I) A certificate document in the form of a digital data object (a
    data object used by a computer) to which is appended a computed
    digital signature value that depends on the data object. (See:
    attribute certificate, public-key certificate.)
    Deprecated Usage: IDOCs SHOULD NOT use this term to refer to a
    signed CRL or CKL. Although the recommended definition can be
    interpreted to include other signed items, the security community
    does not use the term with those meanings.
 $ digital certification
    (D) Synonym for "certification".
    Deprecated Definition: IDOCs SHOULD NOT use this definition unless
    the context is not sufficient to distinguish between digital
    certification and another kind of certification, in which case it
    would be better to use "public-key certification" or another
    phrase that indicates what is being certified.
 $ digital document
    (I) An electronic data object that represents information
    originally written in a non-electronic, non-magnetic medium
    (usually ink on paper) or is an analogue of a document of that
    type.
 $ digital envelope
    (I) A combination of (a) encrypted content data (of any kind)
    intended for a recipient and (b) the content encryption key in an
    encrypted form that has been prepared for the use of the
    recipient.

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    Usage: In IDOCs, the term SHOULD be defined at the point of first
    use because, although the term is defined in PKCS #7 and used in
    S/MIME, it is not widely known.
    Tutorial: Digital enveloping is not simply a synonym for
    implementing data confidentiality with encryption; digital
    enveloping is a hybrid encryption scheme to "seal" a message or
    other data, by encrypting the data and sending both it and a
    protected form of the key to the intended recipient, so that no
    one other than the intended recipient can "open" the message. In
    PKCS #7, it means first encrypting the data using a symmetric
    encryption algorithm and a secret key, and then encrypting the
    secret key using an asymmetric encryption algorithm and the public
    key of the intended recipient. In S/MIME, additional methods are
    defined for encrypting the content encryption key.
 $ Digital ID(service mark)
    (D) Synonym for "digital certificate".
    Deprecated Term: IDOCs SHOULD NOT use this term. It is a service
    mark of a commercial firm, and it unnecessarily duplicates the
    meaning of a better-established term. (See: credential.)
 $ digital key
    (D) Synonym for an input parameter of a cryptographic algorithm or
    other process. (See: key.)
    Deprecated Usage: The adjective "digital" need not be used with
    "key" or "cryptographic key", unless the context is insufficient
    to distinguish the digital key from another kind of key, such as a
    metal key for a door lock.
 $ digital notary
    (I) An electronic functionary analogous to a notary public.
    Provides a trusted timestamp for a digital document, so that
    someone can later prove that the document existed at that point in
    time; verifies the signature(s) on a signed document before
    applying the stamp. (See: notarization.)
 $ digital signature
    1. (I) A value computed with a cryptographic algorithm and
    associated with a data object in such a way that any recipient of
    the data can use the signature to verify the data's origin and
    integrity. (See: data origin authentication service, data
    integrity service, signer. Compare: digitized signature,
    electronic signature.)

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    2. (O) "Data appended to, or a cryptographic transformation of, a
    data unit that allows a recipient of the data unit to prove the
    source and integrity of the data unit and protect against forgery,
    e.g. by the recipient." [I7498-2]
    Tutorial: A digital signature should have these properties:
    -  Be capable of being verified. (See: validate vs. verify.)
    -  Be bound to the signed data object in such a way that if the
       data is changed, then when an attempt is made to verify the
       signature, it will be seen as not authentic. (In some schemes,
       the signature is appended to the signed object as stated by
       definition 2, but in other it, schemes is not.)
    -  Uniquely identify a system entity as being the signer.
    -  Be under the signer's sole control, so that it cannot be
       created by any other entity.
    To achieve these properties, the data object is first input to a
    hash function, and then the hash result is cryptographically
    transformed using a private key of the signer. The final resulting
    value is called the digital signature of the data object. The
    signature value is a protected checksum, because the properties of
    a cryptographic hash ensure that if the data object is changed,
    the digital signature will no longer match it. The digital
    signature is unforgeable because one cannot be certain of
    correctly creating or changing the signature without knowing the
    private key of the supposed signer.
    Some digital signature schemes use an asymmetric encryption
    algorithm (e.g., "RSA") to transform the hash result. Thus, when
    Alice needs to sign a message to send to Bob, she can use her
    private key to encrypt the hash result. Bob receives both the
    message and the digital signature. Bob can use Alice's public key
    to decrypt the signature, and then compare the plaintext result to
    the hash result that he computes by hashing the message himself.
    If the values are equal, Bob accepts the message because he is
    certain that it is from Alice and has arrived unchanged. If the
    values are not equal, Bob rejects the message because either the
    message or the signature was altered in transit.
    Other digital signature schemes (e.g., "DSS") transform the hash
    result with an algorithm (e.g., "DSA", "El Gamal") that cannot be
    directly used to encrypt data. Such a scheme creates a signature
    value from the hash and provides a way to verify the signature
    value, but does not provide a way to recover the hash result from
    the signature value. In some countries, such a scheme may improve
    exportability and avoid other legal constraints on usage. Alice
    sends the signature value to Bob along with both the message and
    its hash result. The algorithm enables Bob to use Alice's public

Shirey Informational [Page 105] RFC 4949 Internet Security Glossary, Version 2 August 2007

    signature key and the signature value to verify the hash result he
    receives. Then, as before, he compares that hash result she sent
    to the one that he computes by hashing the message himself.
 $ Digital Signature Algorithm (DSA)
    (N) An asymmetric cryptographic algorithm for a digital signature
    in the form of a pair of large numbers. The signature is computed
    using rules and parameters such that the identity of the signer
    and the integrity of the signed data can be verified. (See: DSS.)
 $ Digital Signature Standard (DSS)
    (N) The U.S. Government standard [FP186] that specifies the DSA.
 $ digital watermarking
    (I) Computing techniques for inseparably embedding unobtrusive
    marks or labels as bits in digital data -- text, graphics, images,
    video, or audio -- and for detecting or extracting the marks
    later.
    Tutorial: A "digital watermark", i.e., the set of embedded bits,
    is sometimes hidden, usually imperceptible, and always intended to
    be unobtrusive. Depending on the particular technique that is
    used, digital watermarking can assist in proving ownership,
    controlling duplication, tracing distribution, ensuring data
    integrity, and performing other functions to protect intellectual
    property rights. [ACM]
 $ digitized signature
    (D) Denotes various forms of digitized images of handwritten
    signatures. (Compare: digital signature).
    Deprecated Term: IDOCs SHOULD NOT use this term without including
    this definition. This term suggests careless use of "digital
    signature", which is the term standardized by [I7498-2]. (See:
    electronic signature.)
 $ DII
    (O) See: Defense Information Infrastructure.
 $ direct attack
    (I) See: secondary definition under "attack". (Compare: indirect
    attack.)
 $ directory, Directory
    1. (I) /not capitalized/ Refers generically to a database server
    or other system that stores and provides access to values of
    descriptive or operational data items that are associated with the
    components of a system. (Compare: repository.)

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    2. (N) /capitalized/ Refers specifically to the X.500 Directory.
    (See: DN, X.500.)
 $ Directory Access Protocol (DAP)
    (N) An OSI protocol [X519] for communication between a Directory
    User Agent (a type of X.500 client) and a Directory System Agent
    (a type of X.500 server). (See: LDAP.)
 $ disaster plan
    (O) Synonym for "contingency plan".
    Deprecated Term: IDOCs SHOULD NOT use this term; instead, for
    consistency and neutrality of language, IDOCs SHOULD use
    "contingency plan".
 $ disclosure
    See: unauthorized disclosure. Compare: exposure.
 $ discretionary access control
    1a. (I) An access control service that (a) enforces a security
    policy based on the identity of system entities and the
    authorizations associated with the identities and (b) incorporates
    a concept of ownership in which access rights for a system
    resource may be granted and revoked by the entity that owns the
    resource. (See: access control list, DAC, identity-based security
    policy, mandatory access control.)
    Derivation: This service is termed "discretionary" because an
    entity can be granted access rights to a resource such that the
    entity can by its own volition enable other entities to access the
    resource.
    1b. (O) /formal model/ "A means of restricting access to objects
    based on the identity of subjects and/or groups to which they
    belong. The controls are discretionary in the sense that a subject
    with a certain access permission is capable of passing that
    permission (perhaps indirectly) on to any other subject." [DoD1]
 $ DISN
    (O) See: Defense Information Systems Network (DISN).
 $ disruption
    (I) A circumstance or event that interrupts or prevents the
    correct operation of system services and functions. (See:
    availability, critical, system integrity, threat consequence.)

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    Tutorial: Disruption is a type of threat consequence; it can be
    caused by the following types of threat actions: incapacitation,
    corruption, and obstruction.
 $ Distinguished Encoding Rules (DER)
    (N) A subset of the Basic Encoding Rules that always provides only
    one way to encode any data structure defined by ASN.1. [X690].
    Tutorial: For a data structure defined abstractly in ASN.1, BER
    often provides for encoding the structure into an octet string in
    more than one way, so that two separate BER implementations can
    legitimately produce different octet strings for the same ASN.1
    definition. However, some applications require all encodings of a
    structure to be the same, so that encodings can be compared for
    equality. Therefore, DER is used in applications in which unique
    encoding is needed, such as when a digital signature is computed
    on a structure defined by ASN.1.
 $ distinguished name (DN)
    (N) An identifier that uniquely represents an object in the X.500
    Directory Information Tree (DIT) [X501]. (Compare: domain name,
    identity, naming authority.)
    Tutorial: A DN is a set of attribute values that identify the path
    leading from the base of the DIT to the object that is named. An
    X.509 public-key certificate or CRL contains a DN that identifies
    its issuer, and an X.509 attribute certificate contains a DN or
    other form of name that identifies its subject.
 $ distributed attack
    1a. (I) An attack that is implemented with distributed computing.
    (See: zombie.)
    1b. (I) An attack that deploys multiple threat agents.
 $ Distributed Authentication Security Service (DASS)
    (I) An experimental Internet protocol [R1507] that uses
    cryptographic mechanisms to provide strong, mutual authentication
    services in a distributed environment.
 $ distributed computing
    (I) A technique that disperses a single, logically related set of
    tasks among a group of geographically separate yet cooperating
    computers. (See: distributed attack.)

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 $ distribution point
    (I) An X.500 Directory entry or other information source that is
    named in a v3 X.509 public-key certificate extension as a location
    from which to obtain a CRL that may list the certificate.
    Tutorial: A v3 X.509 public-key certificate may have a
    "cRLDistributionPoints" extension that names places to get CRLs on
    which the certificate might be listed. (See: certificate profile.)
    A CRL obtained from a distribution point may (a) cover either all
    reasons for which a certificate might be revoked or only some of
    the reasons, (b) be issued by either the authority that signed the
    certificate or some other authority, and (c) contain revocation
    entries for only a subset of the full set of certificates issued
    by one CA or (d) contain revocation entries for multiple CAs.
 $ DKIM
    (I) See: Domain Keys Identified Mail.
 $ DMZ
    (D) See: demilitarized zone.
 $ DN
    (N) See: distinguished name.
 $ DNS
    (I) See: Domain Name System.
 $ doctrine
    See: security doctrine.
 $ DoD
    (N) Department of Defense.
    Usage: To avoid international misunderstanding, IDOCs SHOULD use
    this abbreviation only with a national qualifier (e.g., U.S. DoD).
 $ DOI
    (I) See: Domain of Interpretation.
 $ domain
    1a. (I) /general security/ An environment or context that (a)
    includes a set of system resources and a set of system entities
    that have the right to access the resources and (b) usually is
    defined by a security policy, security model, or security
    architecture. (See: CA domain, domain of interpretation, security
    perimeter. Compare: COI, enclave.)

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    Tutorial: A "controlled interface" or "guard" is required to
    transfer information between network domains that operate under
    different security policies.
    1b. (O) /security policy/ A set of users, their information
    objects, and a common security policy. [DoD6, SP33]
    1c. (O) /security policy/ A system or collection of systems that
    (a) belongs to a community of interest that implements a
    consistent security policy and (b) is administered by a single
    authority.
    2. (O) /COMPUSEC/ An operating state or mode of a set of computer
    hardware.
    Tutorial: Most computers have at least two hardware operating
    modes [Gass]:
    -  "Privileged" mode: a.k.a. "executive", "master", "system",
       "kernel", or "supervisor" mode. In this mode, software can
       execute all machine instructions and access all storage
       locations.
    -  "Unprivileged" mode: a.k.a. "user", "application", or "problem"
       mode. In this mode, software is restricted to a subset of the
       instructions and a subset of the storage locations.
    3. (O) "A distinct scope within which certain common
    characteristics are exhibited and common rules are observed."
    [CORBA]
    4. (O) /MISSI/ The domain of a MISSI CA is the set of MISSI users
    whose certificates are signed by the CA.
    5. (I) /Internet/ That part of the tree-structured name space of
    the DNS that is at or below the name that specifies the domain. A
    domain is a subdomain of another domain if it is contained within
    that domain. For example, D.C.B.A is a subdomain of C.B.A
    6. (O) /OSI/ An administrative partition of a complex distributed
    OSI system.
 $ Domain Keys Identified Mail (DKIM)
    (I) A protocol, which is being specified by the IETF working group
    of the same name, to provide data integrity and domain-level (see:
    DNS, domain name) data origin authentication for Internet mail
    messages. (Compare: PEM.)
    Tutorial: DKIM employs asymmetric cryptography to create a digital
    signature for an Internet email message's body and selected

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    headers (see RFC 1822), and the signature is then carried in a
    header of the message. A recipient of the message can verify the
    signature and, thereby, authenticate the identity of the
    originating domain and the integrity of the signed content, by
    using a public key belonging to the domain. The key can be
    obtained from the DNS.
 $ domain name
    (I) The style of identifier that is defined for subtrees in the
    Internet DNS -- i.e., a sequence of case-insensitive ASCII labels
    separated by dots (e.g., "bbn.com") -- and also is used in other
    types of Internet identifiers, such as host names (e.g.,
    "rosslyn.bbn.com"), mailbox names (e.g., "rshirey@bbn.com") and
    URLs (e.g., "http://www.rosslyn.bbn.com/foo"). (See: domain.
    Compare: DN.)
    Tutorial: The name space of the DNS is a tree structure in which
    each node and leaf holds records describing a resource. Each node
    has a label. The domain name of a node is the list of labels on
    the path from the node to the root of the tree. The labels in a
    domain name are printed or read left to right, from the most
    specific (lowest, farthest from the root) to the least specific
    (highest, closest to the root), but the root's label is the null
    string. (See: country code.)
 $ Domain Name System (DNS)
    (I) The main Internet operations database, which is distributed
    over a collection of servers and used by client software for
    purposes such as (a) translating a domain name-style host name
    into an IP address (e.g., "rosslyn.bbn.com" translates to
    "192.1.7.10") and (b) locating a host that accepts mail for a
    given mailbox address. (RFC 1034) (See: domain name.)
    Tutorial: The DNS has three major components:
    -  Domain name space and resource records: Specifications for the
       tree-structured domain name space, and data associated with the
       names.
    -  Name servers: Programs that hold information about a subset of
       the tree's structure and data holdings, and also hold pointers
       to other name servers that can provide information from any
       part of the tree.
    -  Resolvers: Programs that extract information from name servers
       in response to client requests; typically, system routines
       directly accessible to user programs.
    Extensions to the DNS [R4033, R4034, R4035] support (a) key
    distribution for public keys needed for the DNS and for other
    protocols, (b) data origin authentication service and data

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    integrity service for resource records, (c) data origin
    authentication service for transactions between resolvers and
    servers, and (d) access control of records.
 $ domain of interpretation (DOI)
    (I) /IPsec/ A DOI for ISAKMP or IKE defines payload formats,
    exchange types, and conventions for naming security-relevant
    information such as security policies or cryptographic algorithms
    and modes. Example: See [R2407].
    Derivation: The DOI concept is based on work by the TSIG's CIPSO
    Working Group.
 $ dominate
    (I) Security level A is said to "dominate" security level B if the
    (hierarchical) classification level of A is greater (higher) than
    or equal to that of B, and A's (nonhierarchical) categories
    include (as a subset) all of B's categories. (See: lattice,
    lattice model.)
 $ dongle
    (I) A portable, physical, usually electronic device that is
    required to be attached to a computer to enable a particular
    software program to run. (See: token.)
    Tutorial: A dongle is essentially a physical key used for copy
    protection of software; that is, the program will not run unless
    the matching dongle is attached. When the software runs, it
    periodically queries the dongle and quits if the dongle does not
    reply with the proper authentication information. Dongles were
    originally constructed as an EPROM (erasable programmable read-
    only memory) to be connected to a serial input-output port of a
    personal computer.
 $ downgrade
    (I) /data security/ Reduce the security level of data (especially
    the classification level) without changing the information content
    of the data. (Compare: downgrade.)
 $ downgrade attack
    (I) A type of man-in-the-middle attack in which the attacker can
    cause two parties, at the time they negotiate a security
    association, to agree on a lower level of protection than the
    highest level that could have been supported by both of them.
    (Compare: downgrade.)

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 $ draft RFC
    (D) A preliminary, temporary version of a document that is
    intended to become an RFC. (Compare: Internet-Draft.)
    Deprecated Term: IDOCs SHOULD NOT use this term. The RFC series is
    archival in nature and consists only of documents in permanent
    form. A document that is intended to become an RFC usually needs
    to be published first as an Internet-Draft (RFC 2026). (See:
    "Draft Standard" under "Internet Standard".)
 $ Draft Standard
    (I) See: secondary definition under "Internet Standard".
 $ DSA
    (N) See: Digital Signature Algorithm.
 $ DSS
    (N) See: Digital Signature Standard.
 $ dual control
    (I) A procedure that uses two or more entities (usually persons)
    operating in concert to protect a system resource, such that no
    single entity acting alone can access that resource. (See: no-lone
    zone, separation of duties, split knowledge.)
 $ dual signature
    (O) /SET/ A single digital signature that protects two separate
    messages by including the hash results for both sets in a single
    encrypted value. [SET2]
    Deprecated Usage: IDOCs SHOULD NOT use this term except when
    qualified as "SET(trademark) dual signature" with this definition.
    Tutorial: Generated by hashing each message separately,
    concatenating the two hash results, and then hashing that value
    and encrypting the result with the signer's private key. Done to
    reduce the number of encryption operations and to enable
    verification of data integrity without complete disclosure of the
    data.
 $ dual-use certificate
    (O) A certificate that is intended for use with both digital
    signature and data encryption services. [SP32]
    Usage: IDOCs that use this term SHOULD state a definition for it
    by identifying the intended uses of the certificate, because there
    are more than just these two uses mentioned in the NIST
    publication. A v3 X.509 public-key certificate may have a "key

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    Usage" extension, which indicates the purposes for which the
    public key may be used. (See: certificate profile.)
 $ duty
    (I) An attribute of a role that obligates an entity playing the
    role to perform one or more tasks, which usually are essential for
    the functioning of the system. [Sand] (Compare authorization,
    privilege. See: role, billet.)
 $ e-cash
    (O) Electronic cash; money that is in the form of data and can be
    used as a payment mechanism on the Internet. (See: IOTP.)
    Usage: IDOCs that use this term SHOULD state a definition for it
    because many different types of electronic cash have been devised
    with a variety of security mechanisms.
 $ EAP
    (I) See: Extensible Authentication Protocol.
 $ EAL
    (O) See: evaluation assurance level.
 $ Easter egg
    (O) "Hidden functionality within an application program, which
    becomes activated when an undocumented, and often convoluted, set
    of commands and keystrokes is entered. Easter eggs are typically
    used to display the credits for the development team and [are]
    intended to be non-threatening" [SP28], but Easter eggs have the
    potential to contain malicious code.
    Deprecated Usage: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
    Usage under "Green Book".)
 $ eavesdropping
    (I) Passive wiretapping done secretly, i.e., without the knowledge
    of the originator or the intended recipients of the communication.
 $ ECB
    (N) See: electronic codebook.
 $ ECDSA
    (N) See: Elliptic Curve Digital Signature Algorithm.

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 $ economy of alternatives
    (I) The principle that a security mechanism should be designed to
    minimize the number of alternative ways of achieving a service.
    (Compare: economy of mechanism.)
 $ economy of mechanism
    (I) The principle that a security mechanism should be designed to
    be as simple as possible, so that (a) the mechanism can be
    correctly implemented and (b) it can be verified that the
    operation of the mechanism enforces the system's security policy.
    (Compare: economy of alternatives, least privilege.)
 $ ECU
    (N) See: end cryptographic unit.
 $ EDI
    (I) See: electronic data interchange.
 $ EDIFACT
    (N) See: secondary definition under "electronic data interchange".
 $ EE
    (D) Abbreviation of "end entity" and other terms.
    Deprecated Abbreviation: IDOCs SHOULD NOT use this abbreviation;
    there could be confusion among "end entity", "end-to-end
    encryption", "escrowed encryption standard", and other terms.
 $ EES
    (O) See: Escrowed Encryption Standard.
 $ effective key length
    (O) "A measure of strength of a cryptographic algorithm,
    regardless of actual key length." [IATF] (See: work factor.)
 $ effectiveness
    (O) /ITSEC/ A property of a TOE representing how well it provides
    security in the context of its actual or proposed operational use.
 $ El Gamal algorithm
    (N) An algorithm for asymmetric cryptography, invented in 1985 by
    Taher El Gamal, that is based on the difficulty of calculating
    discrete logarithms and can be used for both encryption and
    digital signatures. [ElGa]

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 $ electronic codebook (ECB)
    (N) A block cipher mode in which a plaintext block is used
    directly as input to the encryption algorithm and the resultant
    output block is used directly as cipher text [FP081]. (See: block
    cipher, [SP38A].)
 $ electronic commerce
    1. (I) Business conducted through paperless exchanges of
    information, using electronic data interchange, electronic funds
    transfer (EFT), electronic mail, computer bulletin boards,
    facsimile, and other paperless technologies.
    2. (O) /SET/ "The exchange of goods and services for payment
    between the cardholder and merchant when some or all of the
    transaction is performed via electronic communication." [SET2]
 $ electronic data interchange (EDI)
    (I) Computer-to-computer exchange, between trading partners, of
    business data in standardized document formats.
    Tutorial: EDI formats have been standardized primarily by ANSI X12
    and by EDIFACT (EDI for Administration, Commerce, and
    Transportation), which is an international, UN-sponsored standard
    primarily used in Europe and Asia. X12 and EDIFACT are aligning to
    create a single, global EDI standard.
 $ Electronic Key Management System (EKMS)
    (O) "Interoperable collection of systems developed by ... the U.S.
    Government to automate the planning, ordering, generating,
    distributing, storing, filling, using, and destroying of
    electronic keying material and the management of other types of
    COMSEC material." [C4009]
 $ electronic signature
    (D) Synonym for "digital signature" or "digitized signature".
    Deprecated Term: IDOCs SHOULD NOT use this term; there is no
    current consensus on its definition. Instead, use "digital
    signature", if that is what was intended
 $ electronic wallet
    (D) A secure container to hold, in digitized form, some sensitive
    data objects that belong to the owner, such as electronic money,
    authentication material, and various types of personal
    information. (See: IOTP.)
    Deprecated Term: IDOCs SHOULD NOT use this term. There is no
    current consensus on its definition; and some uses and definitions

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    may be proprietary. Meanings range from virtual wallets
    implemented by data structures to physical wallets implemented by
    cryptographic tokens. (See: Deprecated Usage under "Green Book".)
 $ elliptic curve cryptography (ECC)
    (I) A type of asymmetric cryptography based on mathematics of
    groups that are defined by the points on a curve, where the curve
    is defined by a quadratic equation in a finite field. [Schn]
    Tutorial: ECC is based on mathematics different than that
    originally used to define the Diffie-Hellman-Merkle algorithm and
    the DSA, but ECC can be used to define an algorithm for key
    agreement that is an analog of Diffie-Hellman-Merkle [A9063] and
    an algorithm for digital signature that is an analog of DSA
    [A9062]. The mathematical problem upon which ECC is based is
    believed to be more difficult than the problem upon which Diffie-
    Hellman-Merkle is based and, therefore, that keys for ECC can be
    shorter for a comparable level of security. (See: ECDSA.)
 $ Elliptic Curve Digital Signature Algorithm (ECDSA)
    (N) A standard [A9062] that is the analog, in elliptic curve
    cryptography, of the Digital Signature Algorithm.
 $ emanation
    (I) A signal (e.g., electromagnetic or acoustic) that is emitted
    by a system (e.g., through radiation or conductance) as a
    consequence (i.e., byproduct) of the system's operation, and that
    may contain information. (See: emanations security.)
 $ emanations analysis
    (I) /threat action/ See: secondary definition under
    "interception".
 $ emanations security (EMSEC)
    (I) Physical security measures to protect against data compromise
    that could occur because of emanations that might be received and
    read by an unauthorized party. (See: emanation, TEMPEST.)
    Usage: Refers either to preventing or limiting emanations from a
    system and to preventing or limiting the ability of unauthorized
    parties to receive the emissions.
 $ embedded cryptography
    (N) "Cryptography engineered into an equipment or system whose
    basic function is not cryptographic." [C4009]
 $ emergency plan
    (D) Synonym for "contingency plan".

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    Deprecated Term: IDOCs SHOULD NOT use this term. Instead, for
    neutrality and consistency of language, use "contingency plan".
 $ emergency response
    (O) An urgent response to a fire, flood, civil commotion, natural
    disaster, bomb threat, or other serious situation, with the intent
    of protecting lives, limiting damage to property, and minimizing
    disruption of system operations. [FP087] (See: availability, CERT,
    emergency plan.)
 $ EMSEC
    (I) See: emanations security.
 $ EMV
    (N) Abbreviation of "Europay, MasterCard, Visa". Refers to a
    specification for smart cards that are used as payment cards, and
    for related terminals and applications. [EMV1, EMV2, EMV3]
 $ Encapsulating Security Payload (ESP)
    (I) An Internet protocol [R2406, R4303] designed to provide data
    confidentiality service and other security services for IP
    datagrams. (See: IPsec. Compare: AH.)
    Tutorial: ESP may be used alone, or in combination with AH, or in
    a nested fashion with tunneling. Security services can be provided
    between a pair of communicating hosts, between a pair of
    communicating security gateways, or between a host and a gateway.
    The ESP header is encapsulated by the IP header, and the ESP
    header encapsulates either the upper-layer protocol header
    (transport mode) or an IP header (tunnel mode). ESP can provide
    data confidentiality service, data origin authentication service,
    connectionless data integrity service, an anti-replay service, and
    limited traffic-flow confidentiality. The set of services depends
    on the placement of the implementation and on options selected
    when the security association is established.
 $ encipher
    (D) Synonym for "encrypt".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "encrypt". However, see Usage note under "encryption".
 $ encipherment
    (D) Synonym for "encryption".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "encryption". However, see Usage note under "encryption".

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 $ enclave
    1. (I) A set of system resources that operate in the same security
    domain and that share the protection of a single, common,
    continuous security perimeter. (Compare: domain.)
    2. (D) /U.S. Government/ "Collection of computing environments
    connected by one or more internal networks under the control of a
    single authority and security policy, including personnel and
    physical security." [C4009]
    Deprecated Definition: IDOCs SHOULD NOT use this term with
    definition 2 because the definition applies to what is usually
    called a "security domain". That is, a security domain is a set of
    one or more security enclaves.
 $ encode
    1. (I) Use a system of symbols to represent information, which
    might originally have some other representation. Example: Morse
    code. (See: ASCII, BER.) (See: code, decode.)
    2. (D) Synonym for "encrypt".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "encrypt"; encoding is not always meant to conceal meaning.
 $ encrypt
    (I) Cryptographically transform data to produce cipher text. (See:
    encryption. Compare: seal.)
 $ encryption
    1. (I) Cryptographic transformation of data (called "plain text")
    into a different form (called "cipher text") that conceals the
    data's original meaning and prevents the original form from being
    used. The corresponding reverse process is "decryption", a
    transformation that restores encrypted data to its original form.
    (See: cryptography.)
    2. (O) "The cryptographic transformation of data to produce
    ciphertext." [I7498-2]
    Usage: For this concept, IDOCs SHOULD use the verb "to encrypt"
    (and related variations: encryption, decrypt, and decryption).
    However, because of cultural biases involving human burial, some
    international documents (particularly ISO and CCITT standards)
    avoid "to encrypt" and instead use the verb "to encipher" (and
    related variations: encipherment, decipher, decipherment).

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    Tutorial: Usually, the plaintext input to an encryption operation
    is clear text. But in some cases, the plain text may be cipher
    text that was output from another encryption operation. (See:
    superencryption.)
    Encryption and decryption involve a mathematical algorithm for
    transforming data. Besides the data to be transformed, the
    algorithm has one or more inputs that are control parameters: (a)
    a key that varies the transformation and, in some cases, (b) an IV
    that establishes the starting state of the algorithm.
 $ encryption certificate
    (I) A public-key certificate that contains a public key that is
    intended to be used for encrypting data, rather than for verifying
    digital signatures or performing other cryptographic functions.
    Tutorial: A v3 X.509 public-key certificate may have a "keyUsage"
    extension that indicates the purpose for which the certified
    public key is intended. (See: certificate profile.)
 $ end cryptographic unit (ECU)
    1. (N) Final destination device into which a key is loaded for
    operational use.
    2. (N) A device that (a) performs cryptographic functions, (b)
    typically is part of a larger system for which the device provides
    security services, and (c), from the viewpoint of a supporting
    security infrastructure such as a key management system, is the
    lowest level of identifiable component with which a management
    transaction can be conducted
 $ end entity
    1. (I) A system entity that is the subject of a public-key
    certificate and that is using, or is permitted and able to use,
    the matching private key only for purposes other than signing a
    digital certificate; i.e., an entity that is not a CA.
    2. (O) "A certificate subject [that] uses its public [sic] key for
    purposes other than signing certificates." [X509]
    Deprecated Definition: IDOCs SHOULD NOT use definition 2, which is
    misleading and incomplete. First, that definition should have said
    "private key" rather than "public key" because certificates are
    not usefully signed with a public key. Second, the X.509
    definition is ambiguous regarding whether an end entity may or may
    not use the private key to sign a certificate, i.e., whether the
    subject may be a CA. The intent of X.509's authors was that an end
    entity certificate is not valid for use in verifying a signature

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    on an X.509 certificate or X.509 CRL. Thus, it would have been
    better for the X.509 definition to have said "only for purposes
    other than signing certificates".
    Usage: Despite the problems in the X.509 definition, the term
    itself is useful in describing applications of asymmetric
    cryptography. The way the term is used in X.509 implies that it
    was meant to be defined, as we have done here, relative to roles
    that an entity (which is associated with an OSI end system) is
    playing or is permitted to play in applications of asymmetric
    cryptography other than the PKI that supports applications.
    Tutorial: Whether a subject can play both CA and non-CA roles,
    with either the same or different certificates, is a matter of
    policy. (See: CPS.) A v3 X.509 public-key certificate may have a
    "basicConstraints" extension containing a "cA" value that
    specifically "indicates whether or not the public key may be used
    to verify certificate signatures". (See: certificate profile.)
 $ end system
    (N) /OSIRM/ A computer that implements all seven layers of the
    OSIRM and may attach to a subnetwork. Usage: In the IPS context,
    an end system is called a "host".
 $ end-to-end encryption
    (I) Continuous protection of data that flows between two points in
    a network, effected by encrypting data when it leaves its source,
    keeping it encrypted while it passes through any intermediate
    computers (such as routers), and decrypting it only when it
    arrives at the intended final destination. (See: wiretapping.
    Compare: link encryption.)
    Examples: A few are BLACKER, CANEWARE, IPLI, IPsec, PLI, SDNS,
    SILS, SSH, SSL, TLS.
    Tutorial: When two points are separated by multiple communication
    links that are connected by one or more intermediate relays, end-
    to-end encryption enables the source and destination systems to
    protect their communications without depending on the intermediate
    systems to provide the protection.
 $ end user
    1. (I) /information system/ A system entity, usually a human
    individual, that makes use of system resources, primarily for
    application purposes as opposed to system management purposes.
    2. (D) /PKI/ Synonym for "end entity".

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    Deprecated Definition: IDOCs SHOULD NOT use "end user" as a
    synonym for "end entity", because that would mix concepts in a
    potentially misleading way.
 $ endorsed-for-unclassified cryptographic item (EUCI)
    (O) /U.S. Government/ "Unclassified cryptographic equipment that
    embodies a U.S. Government classified cryptographic logic and is
    endorsed by NSA for the protection of national security
    information." [C4009] (Compare: CCI, type 2 product.)
 $ entity
    See: system entity.
 $ entrapment
    (I) "The deliberate planting of apparent flaws in a system for the
    purpose of detecting attempted penetrations or confusing an
    intruder about which flaws to exploit." [FP039] (See: honey pot.)
 $ entropy
    1. (I) An information-theoretic measure (usually stated as a
    number of bits) of the amount of uncertainty that an attacker
    faces to determine the value of a secret. [SP63] (See: strength.)
    Example: If a password is said to contain at least 20 bits of
    entropy, that means that it must be as hard to find the password
    as to guess a 20-bit random number.
    2. (I) An information-theoretic measure (usually stated as a
    number of bits) of the amount of information in a message; i.e.,
    the minimum number of bits needed to encode all possible meanings
    of that message. [Schn] (See: uncertainty.)
 $ ephemeral
    (I) /adjective/ Refers to a cryptographic key or other
    cryptographic parameter or data object that is short-lived,
    temporary, or used one time. (See: session key. Compare: static.)
 $ erase
    1. (I) Delete stored data. (See: sanitize, zeroize.)
    2. (O) /U.S. Government/ Delete magnetically stored data in such a
    way that the data cannot be recovered by ordinary means, but might
    be recoverable by laboratory methods. [C4009] (Compare: /U.S.
    Government/ purge.)
 $ error detection code
    (I) A checksum designed to detect, but not correct, accidental
    (i.e., unintentional) changes in data.

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 $ Escrowed Encryption Standard (EES)
    (N) A U.S. Government standard [FP185] that specifies how to use a
    symmetric encryption algorithm (SKIPJACK) and create a Law
    Enforcement Access Field (LEAF) for implementing part of a key
    escrow system that enables decryption of telecommunications when
    interception is lawfully authorized.
    Tutorial: Both SKIPJACK and the LEAF are intended for use in
    equipment used to encrypt and decrypt sensitive, unclassified,
    telecommunications data.
 $ ESP
    (I) See: Encapsulating Security Payload.
 $ Estelle
    (N) A language (ISO 9074-1989) for formal specification of
    computer network protocols.
 $ ETSI
    (N) See: European Telecommunication Standards Institute.
 $ EUCI
    (O) See: endorsed-for-unclassified cryptographic item.
 $ European Telecommunication Standards Institute (ETSI)
    (N) An independent, non-profit organization, based in France, that
    is officially recognized by the European Commission and
    responsible for standardization of information and communication
    technologies within Europe.
    Tutorial: ETSI maintains the standards for a number of security
    algorithms, including encryption algorithms for mobile telephone
    systems in Europe.
 $ evaluated system
    (I) A system that has been evaluated against security criteria
    (for example, against the TCSEC or against a profile based on the
    Common Criteria).
 $ evaluation
    (I) Assessment of an information system against defined security
    criteria (for example, against the TCSEC or against a profile
    based on the Common Criteria). (Compare: certification.)
 $ evaluation assurance level (EAL)
    (N) A predefined package of assurance components that represents a
    point on the Common Criteria's scale for rating confidence in the
    security of information technology products and systems.

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    Tutorial: The Common Criteria defines a scale of seven,
    hierarchically ordered EALs for rating a TOE. From highest to
    lowest, they are as follows:
    -  EAL7. Formally verified design and tested.
    -  EAL6. Semiformally verified design and tested.
    -  EAL5. Semiformally designed and tested.
    -  EAL4. Methodically designed, tested, and reviewed.
    -  EAL3. Methodically tested and checked.
    -  EAL2. Structurally tested.
    -  EAL1. Functionally tested.
    An EAL is a consistent, baseline set of requirements. The increase
    in assurance from EAL to EAL is accomplished by substituting
    higher assurance components (i.e., criteria of increasing rigor,
    scope, or depth) from seven assurance classes: (a) configuration
    management, (b) delivery and operation, (c) development, (d)
    guidance documents, (e) lifecycle support, (f) tests, and (g)
    vulnerability assessment.
    The EALs were developed with the goal of preserving concepts of
    assurance that were adopted from earlier criteria, so that results
    of previous evaluations would remain relevant. For example, EALs
    levels 2-7 are generally equivalent to the assurance portions of
    the TCSEC C2-A1 scale. However, this equivalency should be used
    with caution. The levels do not derive assurance in the same
    manner, and exact mappings do not exist.
 $ expire
    (I) /credential/ Cease to be valid (i.e., change from being valid
    to being invalid) because its assigned lifetime has been exceeded.
    (See: certificate expiration.)
 $ exposure
    (I) A type of threat action whereby sensitive data is directly
    released to an unauthorized entity. (See: unauthorized
    disclosure.)
    Usage: This type of threat action includes the following subtypes:
    -  "Deliberate Exposure": Intentional release of sensitive data to
       an unauthorized entity.
    -  "Scavenging": Searching through data residue in a system to
       gain unauthorized knowledge of sensitive data.
    -  "Human error": /exposure/ Human action or inaction that
       unintentionally results in an entity gaining unauthorized
       knowledge of sensitive data. (Compare: corruption,
       incapacitation.)
    -  "Hardware or software error": /exposure/ System failure that
       unintentionally results in an entity gaining unauthorized

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       knowledge of sensitive data. (Compare: corruption,
       incapacitation.)
 $ Extended Security Option
    (I) See: secondary definition under "IPSO".
 $ Extensible Authentication Protocol (EAP)
    (I) An extension framework for PPP that supports multiple,
    optional authentication mechanisms, including cleartext passwords,
    challenge-response, and arbitrary dialog sequences. [R3748]
    (Compare: GSS-API, SASL.)
    Tutorial: EAP typically runs directly over IPS data link protocols
    or OSIRM Layer 2 protocols, i.e., without requiring IP.
    Originally, EAP was developed for use in PPP, by a host or router
    that connects to a network server via switched circuits or dial-up
    lines. Today, EAP's domain of applicability includes other areas
    of network access control; it is used in wired and wireless LANs
    with IEEE 802.1X, and in IPsec with IKEv2. EAP is conceptually
    related to other authentication mechanism frameworks, such as SASL
    and GSS-API.
 $ Extensible Markup Language (XML)
    (N) A version of Standard Generalized Markup Language (ISO 8879)
    that separately represents a document's content and its structure.
    XML was designed by W3C for use on the World Wide Web.
 $ extension
    (I) /protocol/ A data item or a mechanism that is defined in a
    protocol to extend the protocol's basic or original functionality.
    Tutorial: Many protocols have extension mechanisms, and the use of
    these extension is usually optional. IP and X.509 are two examples
    of protocols that have optional extensions. In IP version 4,
    extensions are called "options", and some of the options have
    security purposes (see: IPSO).
    In X.509, certificate and CRL formats can be extended to provide
    methods for associating additional attributes with subjects and
    public keys and for managing a certification hierarchy:
    -  A "certificate extension": X.509 defines standard extensions
       that may be included in v3 certificates to provide additional
       key and security policy information, subject and issuer
       attributes, and certification path constraints.
    -  A "CRL extension": X.509 defines extensions that may be
       included in v2 CRLs to provide additional issuer key and name
       information, revocation reasons and constraints, and
       information about distribution points and delta CRLs.

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  1. A "private extension": Additional extensions, each named by an

OID, can be locally defined as needed by applications or

       communities. (See: Authority Information Access extension, SET
       private extensions.)
 $ external controls
    (I) /COMPUSEC/ Refers to administrative security, personnel
    security, and physical security. (Compare: internal controls.)
 $ extranet
    (I) A computer network that an organization uses for application
    data traffic between the organization and its business partners.
    (Compare: intranet.)
    Tutorial: An extranet can be implemented securely, either on the
    Internet or using Internet technology, by constructing the
    extranet as a VPN.
 $ extraction resistance
    (O) Ability of cryptographic equipment to resist efforts to
    extract keying material directly from the equipment (as opposed to
    gaining knowledge of keying material by cryptanalysis). [C4009]
 $ extrusion detection
    (I) Monitoring for unauthorized transfers of sensitive information
    and other communications that originate inside a system's security
    perimeter and are directed toward the outside; i.e., roughly the
    opposite of "intrusion detection".
 $ fail-safe
    1. (I) Synonym for "fail-secure".
    2. (I) A mode of termination of system functions that prevents
    damage to specified system resources and system entities (i.e.,
    specified data, property, and life) when a failure occurs or is
    detected in the system (but the failure still might cause a
    security compromise). (See: failure control.)
    Tutorial: Definitions 1 and 2 are opposing design alternatives.
    Therefore, IDOCs SHOULD NOT use this term without providing a
    definition for it. If definition 1 is intended, IDOCs can avoid
    ambiguity by using "fail-secure" instead.
 $ fail-secure
    (I) A mode of termination of system functions that prevents loss
    of secure state when a failure occurs or is detected in the system
    (but the failure still might cause damage to some system resource
    or system entity). (See: failure control. Compare: fail-safe.)

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 $ fail-soft
    (I) Selective termination of affected, non-essential system
    functions when a failure occurs or is detected in the system.
    (See: failure control.)
 $ failure control
    (I) A methodology used to provide fail-safe, fail-secure or fail-
    soft termination and recovery of system functions. [FP039]
 $ fairness
    (I) A property of an access protocol for a system resource whereby
    the resource is made equitably or impartially available to all
    eligible users. (RFC 3753)
    Tutorial: Fairness can be used to defend against some types of
    denial-of-service attacks on a system connected to a network.
    However, this technique assumes that the system can properly
    receive and process inputs from the network. Therefore, the
    technique can mitigate flooding but is ineffective against
    jamming.
 $ falsification
    (I) A type of threat action whereby false data deceives an
    authorized entity. (See: active wiretapping, deception.)
    Usage: This type of threat action includes the following subtypes:
    -  "Substitution": Altering or replacing valid data with false
       data that serves to deceive an authorized entity.
    -  "Insertion": Introducing false data that serves to deceive an
       authorized entity.
 $ fault tree
    (I) A branching, hierarchical data structure that is used to
    represent events and to determine the various combinations of
    component failures and human acts that could result in a specified
    undesirable system event. (See: attack tree, flaw hypothesis
    methodology.)
    Tutorial: "Fault-tree analysis" is a technique in which an
    undesired state of a system is specified and the system is studied
    in the context of its environment and operation to find all
    credible ways in which the event could occur. The specified fault
    event is represented as the root of the tree. The remainder of the
    tree represents AND or OR combinations of subevents, and
    sequential combinations of subevents, that could cause the root
    event to occur. The main purpose of a fault-tree analysis is to
    calculate the probability of the root event, using statistics or
    other analytical methods and incorporating actual or predicted

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    quantitative reliability and maintainability data. When the root
    event is a security violation, and some of the subevents are
    deliberate acts intended to achieve the root event, then the fault
    tree is an attack tree.
 $ FEAL
    (O) A family of symmetric block ciphers that was developed in
    Japan; uses a 64-bit block, keys of either 64 or 128 bits, and a
    variable number of rounds; and has been successfully attacked by
    cryptanalysts. [Schn]
 $ Federal Information Processing Standards (FIPS)
    (N) The Federal Information Processing Standards Publication (FIPS
    PUB) series issued by NIST under the provisions of Section 111(d)
    of the Federal Property and Administrative Services Act of 1949 as
    amended by the Computer Security Act of 1987 (Public Law 100-235)
    as technical guidelines for U.S. Government procurements of
    information processing system equipment and services. (See:
    "[FPxxx]" items in Section 7, Informative References.)
 $ Federal Public-key Infrastructure (FPKI)
    (O) A PKI being planned to establish facilities, specifications,
    and policies needed by the U.S. Government to use public-key
    certificates in systems involving unclassified but sensitive
    applications and interactions between Federal agencies as well as
    with entities of state and local governments, the business
    community, and the public. [FPKI]
 $ Federal Standard 1027
    (N) An U.S. Government document defining emanation, anti-tamper,
    security fault analysis, and manual key management criteria for
    DES encryption devices, primary for OSIRM Layer 2. Was renamed
    "FIPS PUB 140" when responsibility for protecting unclassified,
    sensitive information was transferred from NSA to NIST, and has
    since been superseded by newer versions of that standard [FP140].
 $ File Transfer Protocol (FTP)
    (I) A TCP-based, Application-Layer, Internet Standard protocol
    (RFC 959) for moving data files from one computer to another.
 $ fill device
    (N) /COMSEC/ A device used to transfer or store keying material in
    electronic form or to insert keying material into cryptographic
    equipment.
 $ filter
    1. (I) /noun/ Synonym for "guard". (Compare: content filter,
    filtering router.)

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    2. (I) /verb/ To process a flow of data and selectively block
    passage or permit passage of individual data items according to a
    security policy.
 $ filtering router
    (I) An internetwork router that selectively prevents the passage
    of data packets according to a security policy. (See: guard.)
    Tutorial: A router usually has two or more physical connections to
    networks or other systems; and when the router receives a packet
    on one of those connections, it forwards the packet on a second
    connection. A filtering router does the same; but it first
    decides, according to some security policy, whether the packet
    should be forwarded at all. The policy is implemented by rules
    (packet filters) loaded into the router. The rules mostly involve
    values of data packet control fields (especially IP source and
    destination addresses and TCP port numbers) [R2179]. A filtering
    router may be used alone as a simple firewall or be used as a
    component of a more complex firewall.
 $ financial institution
    (N) "An establishment responsible for facilitating customer-
    initiated transactions or transmission of funds for the extension
    of credit or the custody, loan, exchange, or issuance of money."
    [SET2]
 $ fingerprint
    1. (I) A pattern of curves formed by the ridges on a fingertip.
    (See: biometric authentication. Compare: thumbprint.)
    2. (D) /PGP/ A hash result ("key fingerprint") used to
    authenticate a public key or other data. [PGP]
    Deprecated Definition: IDOCs SHOULD NOT use this term with
    definition 2, and SHOULD NOT use this term as a synonym for "hash
    result" of *any* kind. Either use would mix concepts in a
    potentially misleading way.
 $ FIPS
    (N) See: Federal Information Processing Standards.
 $ FIPS PUB 140
    (N) The U.S. Government standard [FP140] for security requirements
    to be met by a cryptographic module when the module is used to
    protect unclassified information in computer and communication
    systems. (See: Common Criteria, FIPS, Federal Standard 1027.)

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    Tutorial: The standard specifies four increasing levels (from
    "Level 1" to "Level 4") of requirements to cover a wide range of
    potential applications and environments. The requirements address
    basic design and documentation, module interfaces, authorized
    roles and services, physical security, software security,
    operating system security, key management, cryptographic
    algorithms, electromagnetic interference and electromagnetic
    compatibility (EMI/EMC), and self-testing. NIST and the Canadian
    Communication Security Establishment jointly certify modules.
 $ FIREFLY
    (O) /U.S. Government/ "Key management protocol based on public-key
    cryptography." [C4009]
 $ firewall
    1. (I) An internetwork gateway that restricts data communication
    traffic to and from one of the connected networks (the one said to
    be "inside" the firewall) and thus protects that network's system
    resources against threats from the other network (the one that is
    said to be "outside" the firewall). (See: guard, security
    gateway.)
    2. (O) A device or system that controls the flow of traffic
    between networks using differing security postures. [SP41]
    Tutorial: A firewall typically protects a smaller, secure network
    (such as a corporate LAN, or even just one host) from a larger
    network (such as the Internet). The firewall is installed at the
    point where the networks connect, and the firewall applies policy
    rules to control traffic that flows in and out of the protected
    network.
    A firewall is not always a single computer. For example, a
    firewall may consist of a pair of filtering routers and one or
    more proxy servers running on one or more bastion hosts, all
    connected to a small, dedicated LAN (see: buffer zone) between the
    two routers. The external router blocks attacks that use IP to
    break security (IP address spoofing, source routing, packet
    fragments), while proxy servers block attacks that would exploit a
    vulnerability in a higher-layer protocol or service. The internal
    router blocks traffic from leaving the protected network except
    through the proxy servers. The difficult part is defining criteria
    by which packets are denied passage through the firewall, because
    a firewall not only needs to keep unauthorized traffic (i.e.,
    intruders) out, but usually also needs to let authorized traffic
    pass both in and out.

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 $ firmware
    (I) Computer programs and data stored in hardware -- typically in
    read-only memory (ROM) or programmable read-only memory (PROM) --
    such that the programs and data cannot be dynamically written or
    modified during execution of the programs. (See: hardware,
    software.)
 $ FIRST
    (N) See: Forum of Incident Response and Security Teams.
 $ flaw
    1. (I) An error in the design, implementation, or operation of an
    information system. A flaw may result in a vulnerability.
    (Compare: vulnerability.)
    2. (D) "An error of commission, omission, or oversight in a system
    that allows protection mechanisms to be bypassed." [NCSSG]
    (Compare: vulnerability. See: brain-damaged.)
    Deprecated Definition: IDOCs SHOULD NOT use this term with
    definition 2; not every flaw is a vulnerability.
 $ flaw hypothesis methodology
    (I) An evaluation or attack technique in which specifications and
    documentation for a system are analyzed to hypothesize flaws in
    the system. The list of hypothetical flaws is prioritized on the
    basis of the estimated probability that a flaw exists and,
    assuming it does, on the ease of exploiting it and the extent of
    control or compromise it would provide. The prioritized list is
    used to direct a penetration test or attack against the system.
    [NCS04] (See: fault tree, flaw.)
 $ flooding
    1. (I) An attack that attempts to cause a failure in a system by
    providing more input than the system can process properly. (See:
    denial of service, fairness. Compare: jamming.)
    Tutorial: Flooding uses "overload" as a type of "obstruction"
    intended to cause "disruption".
    2. (I) The process of delivering data or control messages to every
    node of a network. (RFC 3753)
 $ flow analysis
    (I) An analysis performed on a nonprocedural, formal, system
    specification that locates potential flows of information between
    system variables. By assigning security levels to the variables,
    the analysis can find some types of covert channels. [Huff]

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 $ flow control
    1. (I) /data security/ A procedure or technique to ensure that
    information transfers within a system are not made from one
    security level to another security level, and especially not from
    a higher level to a lower level. [Denns] (See: covert channel,
    confinement property, information flow policy, simple security
    property.)
    2. (O) /data security/ "A concept requiring that information
    transfers within a system be controlled so that information in
    certain types of objects cannot, via any channel within the
    system, flow to certain other types of objects." [NCSSG]
 $ For Official Use Only (FOUO)
    (O) /U.S. DoD/ A U.S. Government designation for information that
    has not been given a security classification pursuant to the
    criteria of an Executive Order dealing with national security, but
    which may be withheld from the public because disclosure would
    cause a foreseeable harm to an interest protected by one of the
    exemptions stated in the Freedom of Information Act (Section 552
    of title 5, United States Code). (See: security label, security
    marking. Compare: classified.)
 $ formal
    (I) Expressed in a restricted syntax language with defined
    semantics based on well-established mathematical concepts. [CCIB]
    (Compare: informal, semiformal.)
 $ formal access approval
    (O) /U.S. Government/ Documented approval by a data owner to allow
    access to a particular category of information in a system. (See:
    category.)
 $ Formal Development Methodology
    (O) See: Ina Jo.
 $ formal model
    (I) A security model that is formal. Example: Bell-LaPadula model.
    [Land] (See: formal, security model.)
 $ formal proof
    (I) "A complete and convincing mathematical argument, presenting
    the full logical justification for each step in the proof, for the
    truth of a theorem or set of theorems." [NCSSG]
 $ formal specification
    (I) A precise description of the (intended) behavior of a system,
    usually written in a mathematical language, sometimes for the

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    purpose of supporting formal verification through a correctness
    proof. [Huff] (See: Affirm, Gypsy, HDM, Ina Jo.) (See: formal.)
    Tutorial: A formal specification can be written at any level of
    detail but is usually a top-level specification.
 $ formal top-level specification
    (I) "A top-level specification that is written in a formal
    mathematical language to allow theorems showing the correspondence
    of the system specification to its formal requirements to be
    hypothesized and formally proven." [NCS04] (See: formal
    specification.)
 $ formulary
    (I) A technique for enabling a decision to grant or deny access to
    be made dynamically at the time the access is attempted, rather
    than earlier when an access control list or ticket is created.
 $ FORTEZZA(trademark)
    (O) A registered trademark of NSA, used for a family of
    interoperable security products that implement a NIST/NSA-approved
    suite of cryptographic algorithms for digital signature, hash,
    encryption, and key exchange. The products include a PC card
    (which contains a CAPSTONE chip), and compatible serial port
    modems, server boards, and software implementations.
 $ Forum of Incident Response and Security Teams (FIRST)
    (N) An international consortium of CSIRTs (e.g., CIAC) that work
    together to handle computer security incidents and promote
    preventive activities. (See: CSIRT, security incident.)
    Tutorial: FIRST was founded in 1990 and, as of July 2004, had more
    than 100 members spanning the globe. Its mission includes:
    -  Provide members with technical information, tools, methods,
       assistance, and guidance.
    -  Coordinate proactive liaison activities and analytical support.
    -  Encourage development of quality products and services.
    -  Improve national and international information security for
       governments, private industry, academia, and the individual.
    -  Enhance the image and status of the CSIRT community.
 $ forward secrecy
    (I) See: perfect forward secrecy.
 $ FOUO
    (O) See: For Official Use Only.

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 $ FPKI
    (O) See: Federal Public-Key Infrastructure.
 $ fraggle attack
    (D) /slang/ A synonym for "smurf attack".
    Deprecated Term: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term.
    Derivation: The Fraggles are a fictional race of small humanoids
    (represented as hand puppets in a children's television series,
    "Fraggle Rock") that live underground.
 $ frequency hopping
    (N) Repeated switching of frequencies during radio transmission
    according to a specified algorithm. [C4009] (See: spread
    spectrum.)
    Tutorial: Frequency hopping is a TRANSEC technique to minimize the
    potential for unauthorized interception or jamming.
 $ fresh
    (I) Recently generated; not replayed from some earlier interaction
    of the protocol.
    Usage: Describes data contained in a PDU that is received and
    processed for the first time. (See: liveness, nonce, replay
    attack.)
 $ FTP
    (I) See: File Transfer Protocol.
 $ gateway
    (I) An intermediate system (interface, relay) that attaches to two
    (or more) computer networks that have similar functions but
    dissimilar implementations and that enables either one-way or two-
    way communication between the networks. (See: bridge, firewall,
    guard, internetwork, proxy server, router, and subnetwork.)
    Tutorial: The networks may differ in any of several aspects,
    including protocols and security mechanisms. When two computer
    networks differ in the protocol by which they offer service to
    hosts, a gateway may translate one protocol into the other or
    otherwise facilitate interoperation of hosts (see: Internet
    Protocol). In theory, gateways between computer networks are
    conceivable at any OSIRM layer. In practice, they usually operate

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    at OSIRM Layer 2 (see: bridge), 3 (see: router), or 7 (see: proxy
    server).
 $ GCA
    (O) See: geopolitical certificate authority.
 $ GDOI
    (O) See: Group Domain of Interpretation.
 $ GeldKarte
    (O) A smartcard-based, electronic money system that is maintained
    by the German banking industry, incorporates cryptography, and can
    be used to make payments via the Internet. (See: IOTP.)
 $ GeneralizedTime
    (N) The ASN.1 data type "GeneralizedTime" (ISO 8601) contains a
    calendar date (YYYYMMDD) and a time of day, which is either (a)
    the local time, (b) the Coordinated Universal Time, or (c) both
    the local time and an offset that enables Coordinated Universal
    Time to be calculated. (See: Coordinated Universal Time. Compare:
    UTCTime.)
 $ Generic Security Service Application Program Interface (GSS-API)
    (I) An Internet Standard protocol [R2743] that specifies calling
    conventions by which an application (typically another
    communication protocol) can obtain authentication, integrity, and
    confidentiality security services independently of the underlying
    security mechanisms and technologies, thus enabling the
    application source code to be ported to different environments.
    (Compare: EAP, SASL.)
    Tutorial: "A GSS-API caller accepts tokens provided to it by its
    local GSS-API implementation and transfers the tokens to a peer on
    a remote system; that peer passes the received tokens to its local
    GSS-API implementation for processing. The security services
    available through GSS-API in this fashion are implementable (and
    have been implemented) over a range of underlying mechanisms based
    on [symmetric] and [asymmetric cryptography]." [R2743]
 $ geopolitical certificate authority (GCA)
    (O) /SET/ In a SET certification hierarchy, an optional level that
    is certified by a BCA and that may certify cardholder CAs,
    merchant CAs, and payment gateway CAs. Using GCAs enables a brand
    to distribute responsibility for managing certificates to
    geographic or political regions, so that brand policies can vary
    between regions as needed.

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 $ GIG
    (O) See: Global Information Grid.
 $ Global Information Grid (GIG)
    (O) /U.S. DoD/ The GIG is "a globally interconnected, end-to-end
    set of information capabilities, associated processes and
    personnel for collecting, processing, storing, disseminating, and
    managing information on demand to war fighters, policy makers, and
    support personnel." [IATF] Usage: Formerly referred to as the DII.
 $ good engineering practice(s)
    (N) A term used to specify or characterize design, implementation,
    installation, or operating practices for an information system,
    when a more explicit specification is not possible. Generally
    understood to refer to the state of the engineering art for
    commercial systems that have problems and solutions equivalent to
    the system in question.
 $ granularity
    1. (N) /access control/ Relative fineness to which an access
    control mechanism can be adjusted.
    2. (N) /data security/ "The size of the smallest protectable unit
    of information" in a trusted system. [Huff]
 $ Green Book
    (D) /slang/ Synonym for "Defense Password Management Guideline"
    [CSC2].
    Deprecated Term: Except as an explanatory appositive, IDOCs SHOULD
    NOT use this term, regardless of the associated definition.
    Instead, use the full proper name of the document or, in
    subsequent references, a conventional abbreviation. (See: Rainbow
    Series.)
    Deprecated Usage: To improve international comprehensibility of
    Internet Standards and the Internet Standards Process, IDOCs
    SHOULD NOT use "cute" synonyms. No matter how clearly understood
    or popular a nickname may be in one community, it is likely to
    cause confusion or offense in others. For example, several other
    information system standards also are called "the Green Book"; the
    following are some examples:
    -  Each volume of 1992 ITU-T (known at that time as CCITT)
       standards.
    -  "PostScript Language Program Design", Adobe Systems, Addison-
       Wesley, 1988.
    -  IEEE 1003.1 POSIX Operating Systems Interface.

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  1. "Smalltalk-80: Bits of History, Words of Advice", Glenn

Krasner, Addison-Wesley, 1983.

  1. "X/Open Compatibility Guide".
  2. A particular CD-ROM format developed by Phillips.
 $ Group Domain of Interpretation (GDOI)
    (I) An ISAKMP/IKE domain of interpretation for group key
    management; i.e., a phase 2 protocol in ISAKMP. [R3547] (See:
    secure multicast.)
    Tutorial: In this group key management model that extends the
    ISAKMP standard, the protocol is run between a group member and a
    "group controller/key server", which establishes security
    associations [R4301] among authorized group members. The GDOI
    protocol is itself protected by an ISAKMP phase 1 association.
    For example, multicast applications may use ESP to protect their
    data traffic. GDOI carries the needed security association
    parameters for ESP. In this way, GDOI supports multicast ESP with
    group authentication of ESP packets using a shared, group key.
 $ group identity
    (I) See: secondary definition under "identity".
 $ group security association
    (I) "A bundling of [security associations] (SAs) that together
    define how a group communicates securely. The [group SA] may
    include a registration protocol SA, a rekey protocol SA, and one
    or more data security protocol SAs." [R3740]
 $ GSS-API
    (I) See: Generic Security Service Application Program Interface.
 $ guard
    (I) A computer system that (a) acts as gateway between two
    information systems operating under different security policies
    and (b) is trusted to mediate information data transfers between
    the two. (See: controlled interface, cross-domain solution,
    domain, filter. Compare: firewall.)
    Usage: Frequently understood to mean that one system is operating
    at a higher security level than the other, and that the gateway's
    purpose is to prevent unauthorized disclosure of data from the
    higher system to the lower. However, the purpose might also be to
    protect the data integrity, availability, or general system
    integrity of one system from threats posed by connecting to the
    other system. The mediation may be entirely automated or may
    involve "reliable human review".

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 $ guest login
    (I) See: anonymous login.
 $ GULS
    (I) Generic Upper Layer Security service element (ISO 11586), a
    five-part standard for the exchange of security information and
    security-transformation functions that protect confidentiality and
    integrity of application data.
 $ Gypsy verification environment
    (O) A methodology, language, and integrated set of software tools
    developed at the University of Texas for specifying, coding, and
    verifying software to produce correct and reliable programs.
    [Cheh]
 $ H field
    (D) See: Deprecated Usage under "Handling Restrictions field".
 $ hack
    1a. (I) /verb/ To work on something, especially to program a
    computer. (See: hacker.)
    1b. (I) /verb/ To do some kind of mischief, especially to play a
    prank on, or penetrate, a system. (See: hacker, cracker.)
    2. (I) /noun/ An item of completed work, or a solution for a
    problem, that is non-generalizable, i.e., is very specific to the
    application area or problem being solved.
    Tutorial: Often, the application area or problem involves computer
    programming or other use of a computer. Characterizing something
    as a hack can be a compliment, such as when the solution is
    minimal and elegant; or it can be derogatory, such as when the
    solution fixes the problem but leaves the system in an
    unmaintainable state.
    See [Raym] for several other meanings of this term and also
    definitions of several derivative terms.
 $ hacker
    1. (I) Someone with a strong interest in computers, who enjoys
    learning about them, programming them, and experimenting and
    otherwise working with them. (See: hack. Compare: adversary,
    cracker, intruder.)
    Usage: This first definition is the original meaning of the term
    (circa 1960); it then had a neutral or positive connotation of
    "someone who figures things out and makes something cool happen".

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    2. (O) "An individual who spends an inordinate amount of time
    working on computer systems for other than professional purposes."
    [NCSSG]
    3. (D) Synonym for "cracker".
    Deprecated Usage: Today, the term is frequently (mis)used
    (especially by journalists) with definition 3.
 $ handle
    1. (I) /verb/ Perform processing operations on data, such as
    receive and transmit, collect and disseminate, create and delete,
    store and retrieve, read and write, and compare. (See: access.)
    2. (I) /noun/ An online pseudonym, particularly one used by a
    cracker; derived from citizens' band radio culture.
 $ handling restriction
    (I) A type of access control other than (a) the rule-based
    protections of mandatory access control and (b) the identity-based
    protections of discretionary access control; usually involves
    administrative security.
 $ Handling Restrictions field
    (I) A 16-bit field that specifies a control and release marking in
    the security option (option type 130) of IP's datagram header
    format. The valid field values are alphanumeric digraphs assigned
    by the U.S. Government, as specified in RFC 791.
    Deprecated Abbreviation: IDOCs SHOULD NOT use the abbreviation "H
    field" because it is potentially ambiguous. Instead, use "Handling
    Restrictions field".
 $ handshake
    (I) Protocol dialogue between two systems for identifying and
    authenticating themselves to each other, or for synchronizing
    their operations with each other.
 $ Handshake Protocol
    (I) /TLS/ The TLS Handshake Protocol consists of three parts
    (i.e., subprotocols) that enable peer entities to agree upon
    security parameters for the record layer, authenticate themselves
    to each other, instantiate negotiated security parameters, and
    report error conditions to each other. [R4346]

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 $ harden
    (I) To protect a system by configuring it to operate in a way that
    eliminates or mitigates known vulnerabilities. Example: [RSCG].
    (See: default account.)
 $ hardware
    (I) The material physical components of an information system.
    (See: firmware, software.)
 $ hardware error
    (I) /threat action/ See: secondary definitions under "corruption",
    "exposure", and "incapacitation".
 $ hardware token
    See: token.
 $ hash code
    (D) Synonym for "hash result" or "hash function".
    Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
    in a potentially misleading way. A hash result is not a "code",
    and a hash function does not "encode" in any sense defined by this
    glossary. (See: hash value, message digest.)
 $ hash function
    1. (I) A function H that maps an arbitrary, variable-length bit
    string, s, into a fixed-length string, h = H(s) (called the "hash
    result"). For most computing applications, it is desirable that
    given a string s with H(s) = h, any change to s that creates a
    different string s' will result in an unpredictable hash result
    H(s') that is, with high probability, not equal to H(s).
    2. (O) "A (mathematical) function which maps values from a large
    (possibly very large) domain into a smaller range. A 'good' hash
    function is such that the results of applying the function to a
    (large) set of values in the domain will be evenly distributed
    (and apparently at random) over the range." [X509]
    Tutorial: A hash function operates on variable-length input (e.g.,
    a message or a file) and outputs a fixed-length output, which
    typically is much shorter than most input values. If the algorithm
    is "good" as described in the "O" definition, then the hash
    function may be a candidate for use in a security mechanism to
    detect accidental changes in data, but not necessarily for a
    mechanism to detect changes made by active wiretapping. (See:
    Tutorial under "checksum".)

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    Security mechanisms require a "cryptographic hash function" (e.g.,
    MD2, MD4, MD5, SHA-1, Snefru), i.e., a good hash function that
    also has the one-way property and one of the two collision-free
    properties:
    -  "One-way property": Given H and a hash result h = H(s), it is
       hard (i.e., computationally infeasible, "impossible") to find
       s. (Of course, given H and an input s, it must be relatively
       easy to compute the hash result H(s).)
    -  "Weakly collision-free property": Given H and an input s, it is
       hard (i.e., computationally infeasible, "impossible") to find a
       different input, s', such that H(s) = H(s').
    -  "Strongly collision-free property": Given H, it is hard to find
       any pair of inputs s and s' such that H(s) = H(s').
    If H produces a hash result N bits long, then to find an s' where
    H(s') = H(s) for a specific given s, the amount of computation
    required is O(2**n); i.e., it is necessary to try on the order of
    2 to the power n values of s' before finding a collision. However,
    to simply find any pair of values s and s' that collide, the
    amount of computation required is only O(2**(n/2)); i.e., after
    computing H(s) for 2 to the power n/2 randomly chosen values of s,
    the probability is greater than 1/2 that two of those values have
    the same hash result. (See: birthday attack.)
 $ hash result
    1. (I) The output of a hash function. (See: hash code, hash value.
    Compare: hash value.)
    2. (O) "The output produced by a hash function upon processing a
    message" (where "message" is broadly defined as "a digital
    representation of data"). [DSG]
    Usage: IDOCs SHOULD avoid the unusual usage of "message" that is
    seen in the "O" definition.
 $ hash value
    (D) Synonym for "hash result".
    Deprecated Term: IDOCs SHOULD NOT use this term for the output of
    a hash function; the term could easily be confused with "hashed
    value", which means the input to a hash function. (See: hash code,
    hash result, message digest.)
 $ HDM
    (O) See: Hierarchical Development Methodology.

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 $ Hierarchical Development Methodology (HDM)
    (O) A methodology, language, and integrated set of software tools
    developed at SRI International for specifying, coding, and
    verifying software to produce correct and reliable programs.
    [Cheh]
 $ hierarchical PKI
    (I) A PKI architecture based on a certification hierarchy.
    (Compare: mesh PKI, trust-file PKI.)
 $ hierarchy management
    (I) The process of generating configuration data and issuing
    public-key certificates to build and operate a certification
    hierarchy. (See: certificate management.)
 $ hierarchy of trust
    (D) Synonym for "certification hierarchy".
    Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
    in a potentially misleading way. (See: certification hierarchy,
    trust, web of trust.)
 $ high-assurance guard
    (O) "An oxymoron," said Lt. Gen. William H. Campbell, former U.S.
    Army chief information officer, speaking at an Armed Forces
    Communications and Electronics Association conference.
    Usage: IDOCs that use this term SHOULD state a definition for it
    because the term mixes concepts and could easily be misunderstood.
 $ hijack attack
    (I) A form of active wiretapping in which the attacker seizes
    control of a previously established communication association.
    (See: man-in-the-middle attack, pagejacking, piggyback attack.)
 $ HIPAA
    (N) Health Information Portability and Accountability Act of 1996,
    a U.S. law (Public Law 104-191) that is intended to protect the
    privacy of patients' medical records and other health information
    in all forms, and mandates security for that information,
    including for its electronic storage and transmission.
 $ HMAC
    (I) A keyed hash [R2104] that can be based on any iterated
    cryptographic hash (e.g., MD5 or SHA-1), so that the cryptographic
    strength of HMAC depends on the properties of the selected
    cryptographic hash. (See: [R2202, R2403, R2404].)

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    Derivation: Hash-based MAC. (Compare: CMAC.)
    Tutorial: Assume that H is a generic cryptographic hash in which a
    function is iterated on data blocks of length B bytes. L is the
    length of the of hash result of H. K is a secret key of length L
    <= K <= B. The values IPAD and OPAD are fixed strings used as
    inner and outer padding and defined as follows: IPAD = the byte
    0x36 repeated B times, and OPAD = the byte 0x5C repeated B times.
    HMAC is computed by H(K XOR OPAD, H(K XOR IPAD, inputdata)).
    HMAC has the following goals:
    -  To use available cryptographic hash functions without
       modification, particularly functions that perform well in
       software and for which software is freely and widely available.
    -  To preserve the original performance of the selected hash
       without significant degradation.
    -  To use and handle keys in a simple way.
    -  To have a well-understood cryptographic analysis of the
       strength of the mechanism based on reasonable assumptions about
       the underlying hash function.
    -  To enable easy replacement of the hash function in case a
       faster or stronger hash is found or required.
 $ honey pot
    (N) A system (e.g., a web server) or system resource (e.g., a file
    on a server) that is designed to be attractive to potential
    crackers and intruders, like honey is attractive to bears. (See:
    entrapment.)
    Usage: It is likely that other cultures use different metaphors
    for this concept. Therefore, to avoid international
    misunderstanding, an IDOC SHOULD NOT use this term without
    providing a definition for it. (See: Deprecated Usage under "Green
    Book".)
 $ host
    1. (I) /general/ A computer that is attached to a communication
    subnetwork or internetwork and can use services provided by the
    network to exchange data with other attached systems. (See: end
    system. Compare: server.)
    2. (I) /IPS/ A networked computer that does not forward IP packets
    that are not addressed to the computer itself. (Compare: router.)
    Derivation: As viewed by its users, a host "entertains" them,
    providing Application-Layer services or access to other computers
    attached to the network. However, even though some traditional
    peripheral service devices, such as printers, can now be

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    independently connected to networks, they are not usually called
    hosts.
 $ HTML
    (I) See: Hypertext Markup Language.
 $ HTTP
    (I) See: Hypertext Transfer Protocol.
 $ https
    (I) When used in the first part of a URL (the part that precedes
    the colon and specifies an access scheme or protocol), this term
    specifies the use of HTTP enhanced by a security mechanism, which
    is usually SSL. (Compare: S-HTTP.)
 $ human error
    (I) /threat action/ See: secondary definitions under "corruption",
    "exposure", and "incapacitation".
 $ hybrid encryption
    (I) An application of cryptography that combines two or more
    encryption algorithms, particularly a combination of symmetric and
    asymmetric encryption. Examples: digital envelope, MSP, PEM, PGP.
    (Compare: superencryption.)
    Tutorial: Asymmetric algorithms require more computation than
    equivalently strong symmetric ones. Thus, asymmetric encryption is
    not normally used for data confidentiality except to distribute a
    symmetric key in a hybrid encryption scheme, where the symmetric
    key is usually very short (in terms of bits) compared to the data
    file it protects. (See: bulk key.)
 $ hyperlink
    (I) In hypertext or hypermedia, an information object (such as a
    word, a phrase, or an image, which usually is highlighted by color
    or underscoring) that points (i.e., indicates how to connect) to
    related information that is located elsewhere and can be retrieved
    by activating the link (e.g., by selecting the object with a mouse
    pointer and then clicking).
 $ hypermedia
    (I) A generalization of hypertext; any media that contain
    hyperlinks that point to material in the same or another data
    object.

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 $ hypertext
    (I) A computer document, or part of a document, that contains
    hyperlinks to other documents; i.e., text that contains active
    pointers to other text. Usually written in HTML and accessed using
    a web browser. (See: hypermedia.)
 $ Hypertext Markup Language (HTML)
    (I) A platform-independent system of syntax and semantics (RFC
    1866) for adding characters to data files (particularly text
    files) to represent the data's structure and to point to related
    data, thus creating hypertext for use in the World Wide Web and
    other applications. (Compare: XML.)
 $ Hypertext Transfer Protocol (HTTP)
    (I) A TCP-based, Application-Layer, client-server, Internet
    protocol (RFC 2616) that is used to carry data requests and
    responses in the World Wide Web. (See: hypertext.)
 $ IAB
    (I) See: Internet Architecture Board.
 $ IANA
    (I) See: Internet Assigned Numbers Authority.
 $ IATF
    (O) See: Information Assurance Technical Framework.
 $ ICANN
    (I) See: Internet Corporation for Assigned Names and Numbers.
 $ ICMP
    (I) See: Internet Control Message Protocol.
 $ ICMP flood
    (I) A denial-of-service attack that sends a host more ICMP echo
    request ("ping") packets than the protocol implementation can
    handle. (See: flooding, smurf.)
 $ ICRL
    (N) See: indirect certificate revocation list.
 $ IDEA
    (N) See: International Data Encryption Algorithm.
 $ identification
    (I) An act or process that presents an identifier to a system so
    that the system can recognize a system entity and distinguish it
    from other entities. (See: authentication.)

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 $ identification information
    (D) Synonym for "identifier"; synonym for "authentication
    information". (See: authentication, identifying information.)
    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    either of those terms; this term (a) is not as precise as they are
    and (b) mixes concepts in a potentially misleading way. Instead,
    use "identifier" or "authentication information", depending on
    what is meant.
 $ Identification Protocol
    (I) A client-server Internet protocol [R1413] for learning the
    identity of a user of a particular TCP connection.
    Tutorial: Given a TCP port number pair, the server returns a
    character string that identifies the owner of that connection on
    the server's system. The protocol does not provide an
    authentication service and is not intended for authorization or
    access control. At best, it provides additional auditing
    information with respect to TCP.
 $ identifier
    (I) A data object -- often, a printable, non-blank character
    string -- that definitively represents a specific identity of a
    system entity, distinguishing that identity from all others.
    (Compare: identity.)
    Tutorial: Identifiers for system entities must be assigned very
    carefully, because authenticated identities are the basis for
    other security services, such as access control service.
 $ identifier credential
    1. (I) See: /authentication/ under "credential".
    2. (D) Synonym for "signature certificate".
    Usage: IDOCs that use this term SHOULD state a definition for it
    because the term is used in many ways and could easily be
    misunderstood.
 $ identifying information
    (D) Synonym for "identifier"; synonym for "authentication
    information". (See: authentication, identification information.)
    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    either of those terms; this term (a) is not as precise as they are
    and (b) mixes concepts in a potentially misleading way. Instead,

Shirey Informational [Page 146] RFC 4949 Internet Security Glossary, Version 2 August 2007

    use "identifier" or "authentication information", depending on
    what is meant.
 $ identity
    (I) The collective aspect of a set of attribute values (i.e., a
    set of characteristics) by which a system user or other system
    entity is recognizable or known. (See: authenticate, registration.
    Compare: identifier.)
    Usage: An IDOC MAY apply this term to either a single entity or a
    set of entities. If an IDOC involves both meanings, the IDOC
    SHOULD use the following terms and definitions to avoid ambiguity:
    -  "Singular identity": An identity that is registered for an
       entity that is one person or one process.
    -  "Shared identity": An identity that is registered for an entity
       that is a set of singular entities (1) in which each member is
       authorized to assume the identity individually and (2) for
       which the registering system maintains a record of the singular
       entities that comprise the set. In this case, we would expect
       each member entity to be registered with a singular identity
       before becoming associated with the shared identity.
    -  "Group identity": An identity that is registered for an entity
       (1) that is a set of entities (2) for which the registering
       system does not maintain a record of singular entities that
       comprise the set.
    Tutorial: When security services are based on identities, two
    properties are desirable for the set of attributes used to define
    identities:
    -  The set should be sufficient to distinguish each entity from
       all other entities, i.e., to represent each entity uniquely.
    -  The set should be sufficient to distinguish each identity from
       any other identities of the same entity.
    The second property is needed if a system permits an entity to
    register two or more concurrent identities. Having two or more
    identities for the same entity implies that the entity has two
    separate justifications for registration. In that case, the set of
    attributes used for identities must be sufficient to represent
    multiple identities for a single entity.
    Having two or more identities registered for the same entity is
    different from concurrently associating two different identifiers
    with the same identity, and also is different from a single
    identity concurrently accessing the system in two different roles.
    (See: principal, role-based access control.)

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    When an identity of a user is being registered in a system, the
    system may require presentation of evidence that proves the
    identity's authenticity (i.e., that the user has the right to
    claim or use the identity) and its eligibility (i.e., that the
    identity is qualified to be registered and needs to be
    registered).
    The following diagram illustrates how this term relates to some
    other terms in a PKI system: authentication information,
    identifier, identifier credential, registration, registered user,
    subscriber, and user.
    Relationships:  === one-to-one, ==> one-to-many, <=> many-to-many.
                +- - - - - - - - - - - - - - - - - - - - - - - - - - +
                |                      PKI System                    |
    + - - - - + | +------------------+   +-------------------------+ |
    |  User,  | | |Subscriber, i.e., |   | Identity of Subscriber  | |
    |i.e., one| | | Registered User, |   |    is system-unique     | |
    | of the  | | | is system-unique |   | +---------------------+ | |
    |following| | | +--------------+ |   | |     Subscriber      | | |
    |         | | | | User's core  | |   | |     Identity's      | | |
    | +-----+ |===| | Registration | |==>| |  Registration data  | | |
    | |human| | | | | data, i.e.,  | |   | |+-------------------+| | |
    | |being| | | | | an entity's  | |   | ||  same core data   || | |
    | +-----+ | | | |distinguishing|========|for all Identities || | |
    |   or    | | | |  attribute   | |   | || of the same User  || | |
    | +-----+ | | | |   values     | | +===|+-------------------+| | |
    | |auto-| | | | +--------------+ | | | +---------------------+ | |
    | |mated| | | +------------------+ | +------------|------------+ |
    | |pro- | | |         |    +=======+              |              |
    | |cess | | | +-------v----|----------------------|------------+ |
    | +-----+ | | | +----------v---+     +------------v----------+ | |
    |   or    | | | |Authentication|<===>|Identifier of Identity | | |
    |+-------+| | | | Information  |     |    is system-unique   | | |
    || a set || | | +--------------+     +-----------------------+ | |
    ||  of   || | | Identifier Credential that associates unit of  | |
    || either|| | | Authentication Information with the Identifier | |
    |+-------+| | +------------------------------------------------+ |
    + - - - - + + - - - - - - - - - - - - - - - - - - - - - - - - - -+
 $ identity-based security policy
    (I) "A security policy based on the identities and/or attributes
    of users, a group of users, or entities acting on behalf of the
    users and the resources/objects being accessed." [I7498-2] (See:
    rule-based security policy.)

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 $ identity proofing
    (I) A process that vets and verifies the information that is used
    to establish the identity of a system entity. (See: registration.)
 $ IDOC
    (I) An abbreviation used in this Glossary to refer to a document
    or other item of written material that is generated in the
    Internet Standards Process (RFC 2026), i.e., an RFC, an Internet-
    Draft, or some other item of discourse.
    Deprecated Usage: This abbreviation SHOULD NOT be used in an IDOC
    unless it is first defined in the IDOC because the abbreviation
    was invented for this Glossary and is not widely known.
 $ IDS
    (I) See: intrusion detection system.
 $ IEEE
    (N) See: Institute of Electrical and Electronics Engineers, Inc.
 $ IEEE 802.10
    (N) An IEEE committee developing security standards for LANs.
    (See: SILS.)
 $ IEEE P1363
    (N) An IEEE working group, Standard for Public-Key Cryptography,
    engaged in developing a comprehensive reference standard for
    asymmetric cryptography. Covers discrete logarithm (e.g., DSA),
    elliptic curve, and integer factorization (e.g., RSA); and covers
    key agreement, digital signature, and encryption.
 $ IESG
    (I) See: Internet Engineering Steering Group.
 $ IETF
    (I) See: Internet Engineering Task Force.
 $ IKE
    (I) See: IPsec Key Exchange.
 $ IMAP4
    (I) See: Internet Message Access Protocol, version 4.
 $ IMAP4 AUTHENTICATE
    (I) An IMAP4 command (better described as a transaction type, or
    subprotocol) by which an IMAP4 client optionally proposes a
    mechanism to an IMAP4 server to authenticate the client to the
    server and provide other security services. (See: POP3.)

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    Tutorial: If the server accepts the proposal, the command is
    followed by performing a challenge-response authentication
    protocol and, optionally, negotiating a protection mechanism for
    subsequent POP3 interactions. The security mechanisms that are
    used by IMAP4 AUTHENTICATE -- including Kerberos, GSS-API, and
    S/Key -- are described in [R1731].
 $ impossible
    (O) Cannot be done in any reasonable amount of time. (See: break,
    brute force, strength, work factor.)
 $ in the clear
    (I) Not encrypted. (See: clear text.)
 $ Ina Jo
    (O) A methodology, language, and integrated set of software tools
    developed at the System Development Corporation for specifying,
    coding, and verifying software to produce correct and reliable
    programs. Usage: a.k.a. the Formal Development Methodology. [Cheh]
 $ incapacitation
    (I) A type of threat action that prevents or interrupts system
    operation by disabling a system component. (See: disruption.)
    Usage: This type of threat action includes the following subtypes:
    -  "Malicious logic": In context of incapacitation, any hardware,
       firmware, or software (e.g., logic bomb) intentionally
       introduced into a system to destroy system functions or
       resources. (See: corruption, main entry for "malicious logic",
       masquerade, misuse.)
    -  "Physical destruction": Deliberate destruction of a system
       component to interrupt or prevent system operation.
    -  "Human error": /incapacitation/ Action or inaction that
       unintentionally disables a system component. (See: corruption,
       exposure.)
    -  "Hardware or software error": /incapacitation/ Error that
       unintentionally causes failure of a system component and leads
       to disruption of system operation. (See: corruption, exposure.)
    -  "Natural disaster": /incapacitation/ Any "act of God" (e.g.,
       fire, flood, earthquake, lightning, or wind) that disables a
       system component. [FP031 Section 2]
 $ incident
    See: security incident.
 $ INCITS
    (N) See: "International Committee for Information Technology
    Standardization" under "ANSI".

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 $ indicator
    (N) An action -- either specific, generalized, or theoretical --
    that an adversary might be expected to take in preparation for an
    attack. [C4009] (See: "attack sensing, warning, and response".
    Compare: message indicator.)
 $ indirect attack
    (I) See: secondary definition under "attack". Compare: direct
    attack.
 $ indirect certificate revocation list (ICRL)
    (N) In X.509, a CRL that may contain certificate revocation
    notifications for certificates issued by CAs other than the issuer
    (i.e., signer) of the ICRL.
 $ indistinguishability
    (I) An attribute of an encryption algorithm that is a
    formalization of the notion that the encryption of some string is
    indistinguishable from the encryption of an equal-length string of
    nonsense. (Compare: semantic security.)
 $ inference
    1. (I) A type of threat action that reasons from characteristics
    or byproducts of communication and thereby indirectly accesses
    sensitive data, but not necessarily the data contained in the
    communication. (See: traffic analysis, signal analysis.)
    2. (I) A type of threat action that indirectly gains unauthorized
    access to sensitive information in a database management system by
    correlating query responses with information that is already
    known.
 $ inference control
    (I) Protection of data confidentiality against inference attack.
    (See: traffic-flow confidentiality.)
    Tutorial: A database management system containing N records about
    individuals may be required to provide statistical summaries about
    subsets of the population, while not revealing sensitive
    information about a single individual. An attacker may try to
    obtain sensitive information about an individual by isolating a
    desired record at the intersection of a set of overlapping
    queries. A system can attempt to prevent this by restricting the
    size and overlap of query sets, distorting responses by rounding
    or otherwise perturbing database values, and limiting queries to
    random samples. However, these techniques may be impractical to
    implement or use, and no technique is totally effective. For
    example, restricting the minimum size of a query set -- that is,

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    not responding to queries for which there are fewer than K or more
    than N-K records that satisfy the query -- usually cannot prevent
    unauthorized disclosure. An attacker can pad small query sets with
    extra records, and then remove the effect of the extra records.
    The formula for identifying the extra records is called the
    "tracker". [Denns]
 $ INFOCON
    (O) See: information operations condition
 $ informal
    (N) Expressed in natural language. [CCIB] (Compare: formal,
    semiformal.)
 $ information
    1. (I) Facts and ideas, which can be represented (encoded) as
    various forms of data.
    2. (I) Knowledge -- e.g., data, instructions -- in any medium or
    form that can be communicated between system entities.
    Tutorial: Internet security could be defined simply as protecting
    information in the Internet. However, the perceived need to use
    different protective measures for different types of information
    (e.g., authentication information, classified information,
    collateral information, national security information, personal
    information, protocol control information, sensitive compartmented
    information, sensitive information) has led to the diversity of
    terminology listed in this Glossary.
 $ information assurance
    (N) /U.S. Government/ "Measures that protect and defend
    information and information systems by ensuring their availability
    integrity, authentication, confidentiality, and non-repudiation.
    These measures include providing for restoration of information
    systems by incorporating protection, detection, and reaction
    capabilities." [C4009]
 $ Information Assurance Technical Framework (IATF)
    (O) A publicly available document [IATF], developed through a
    collaborative effort by organizations in the U.S. Government and
    industry, and issued by NSA. Intended for security managers and
    system security engineers as a tutorial and reference document
    about security problems in information systems and networks, to
    improve awareness of tradeoffs among available technology
    solutions and of desired characteristics of security approaches
    for particular problems. (See: ISO 17799, [SP14].)

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 $ information domain
    (O) See: secondary definition under "domain".
 $ information domain security policy
    (O) See: secondary definition under "domain".
 $ information flow policy
    (N) /formal model/ A triple consisting of a set of security levels
    (or their equivalent security labels), a binary operator that maps
    each pair of security levels into a security level, and a binary
    relation on the set that selects a set of pairs of levels such
    that information is permitted to flow from an object of the first
    level to an object of the second level. (See: flow control,
    lattice model.)
 $ information operations condition (INFOCON)
    (O) /U.S. DoD/ A comprehensive defense posture and response based
    on the status of information systems, military operations, and
    intelligence assessments of adversary capabilities and intent.
    (See: threat)
    Derivation: From DEFCON, i.e., defense condition.
    Tutorial: The U.S. DoD defines five INFOCON levels: NORMAL (normal
    activity), ALPHA (increased risk of attack), BRAVO (specific risk
    of attack), CHARLIE (limited attack), and DELTA (general attack).
 $ information security (INFOSEC)
    (N) Measures that implement and assure security services in
    information systems, including in computer systems (see: COMPUSEC)
    and in communication systems (see: COMSEC).
 $ information system
    (I) An organized assembly of computing and communication resources
    and procedures -- i.e., equipment and services, together with
    their supporting infrastructure, facilities, and personnel -- that
    create, collect, record, process, store, transport, retrieve,
    display, disseminate, control, or dispose of information to
    accomplish a specified set of functions. (See: system entity,
    system resource. Compare: computer platform.)
 $ Information Technology Security Evaluation Criteria (ITSEC)
    (N) A Standard [ITSEC] jointly developed by France, Germany, the
    Netherlands, and the United Kingdom for use in the European Union;
    accommodates a wider range of security assurance and functionality
    combinations than the TCSEC. Superseded by the Common Criteria.

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 $ INFOSEC
    (I) See: information security.
 $ ingress filtering
    (I) A method [R2827] for countering attacks that use packets with
    false IP source addresses, by blocking such packets at the
    boundary between connected networks.
    Tutorial: Suppose network A of an internet service provider (ISP)
    includes a filtering router that is connected to customer network
    B, and an attacker in B at IP source address "foo" attempts to
    send packets with false source address "bar" into A. The false
    address may be either fixed or randomly changing, and it may
    either be unreachable or be a forged address that legitimately
    exists within either B or some other network C. In ingress
    filtering, the ISP's router blocks all inbound packet that arrive
    from B with a source address that is not within the range of
    legitimately advertised addresses for B. This method does not
    prevent all attacks that can originate from B, but the actual
    source of such attacks can be more easily traced because the
    originating network is known.
 $ initialization value (IV)
    (I) /cryptography/ An input parameter that sets the starting state
    of a cryptographic algorithm or mode. (Compare: activation data.)
    Tutorial: An IV can be used to synchronize one cryptographic
    process with another; e.g., CBC, CFB, and OFB use IVs. An IV also
    can be used to introduce cryptographic variance (see: salt)
    besides that provided by a key.
 $ initialization vector
    (D) /cryptography/ Synonym for "initialization value".
    Deprecated Term: To avoid international misunderstanding, IDOCs
    SHOULD NOT use this term in the context of cryptography because
    most dictionary definitions of "vector" includes a concept of
    direction or magnitude, which are irrelevant to cryptographic use.
 $ insertion
    1. (I) /packet/ See: secondary definition under "stream integrity
    service".
    2. (I) /threat action/ See: secondary definition under
    "falsification".
 $ inside attack
    (I) See: secondary definition under "attack". Compare: insider.

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 $ insider
    1. (I) A user (usually a person) that accesses a system from a
    position that is inside the system's security perimeter. (Compare:
    authorized user, outsider, unauthorized user.)
    Tutorial: An insider has been assigned a role that has more
    privileges to access system resources than do some other types of
    users, or can access those resources without being constrained by
    some access controls that are applied to outside users. For
    example, a salesclerk is an insider who has access to the cash
    register, but a store customer is an outsider.
    The actions performed by an insider in accessing the system may be
    either authorized or unauthorized; i.e., an insider may act either
    as an authorized user or as an unauthorized user.
    2. (O) A person with authorized physical access to the system.
    Example: In this sense, an office janitor is an insider, but a
    burglar or casual visitor is not. [NRC98]
    3. (O) A person with an organizational status that causes the
    system or members of the organization to view access requests as
    being authorized. Example: In this sense, a purchasing agent is an
    insider but a vendor is not. [NRC98]
 $ inspectable space
    (O) /EMSEC/ "Three-dimensional space surrounding equipment that
    process classified and/or sensitive information within which
    TEMPEST exploitation is not considered practical or where legal
    authority to identify and/or remove a potential TEMPEST
    exploitation exists." [C4009] (Compare: control zone, TEMPEST
    zone.)
 $ Institute of Electrical and Electronics Engineers, Inc. (IEEE)
    (N) The IEEE is a not-for-profit association of approximately
    300,000 individual members in 150 countries. The IEEE produces
    nearly one third of the world's published literature in electrical
    engineering, computers, and control technology; holds hundreds of
    major, annual conferences; and maintains more than 800 active
    standards, with many more under development. (See: SILS.)
 $ integrity
    See: data integrity, datagram integrity service, correctness
    integrity, source integrity, stream integrity service, system
    integrity.

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 $ integrity check
    (D) A computation that is part of a mechanism to provide data
    integrity service or data origin authentication service. (Compare:
    checksum.)
    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    "cryptographic hash" or "protected checksum". This term
    unnecessarily duplicates the meaning of other, well-established
    terms; this term only mentions integrity, even though the intended
    service may be data origin authentication; and not every checksum
    is cryptographically protected.
 $ integrity label
    (I) A security label that tells the degree of confidence that may
    be placed in the data, and may also tell what countermeasures are
    required to be applied to protect the data from alteration and
    destruction. (See: integrity. Compare: classification label.)
 $ intelligent threat
    (I) A circumstance in which an adversary has the technical and
    operational ability to detect and exploit a vulnerability and also
    has the demonstrated, presumed, or inferred intent to do so. (See:
    threat.)
 $ interception
    (I) A type of threat action whereby an unauthorized entity
    directly accesses sensitive data while the data is traveling
    between authorized sources and destinations. (See: unauthorized
    disclosure.)
    Usage: This type of threat action includes the following subtypes:
    -  "Theft": Gaining access to sensitive data by stealing a
       shipment of a physical medium, such as a magnetic tape or disk,
       that holds the data.
    -  "Wiretapping (passive)": Monitoring and recording data that is
       flowing between two points in a communication system. (See:
       wiretapping.)
    -  "Emanations analysis": Gaining direct knowledge of communicated
       data by monitoring and resolving a signal that is emitted by a
       system and that contains the data but was not intended to
       communicate the data. (See: emanation.)
 $ interference
    (I) /threat action/ See: secondary definition under "obstruction".
 $ intermediate CA
    (D) The CA that issues a cross-certificate to another CA. [X509]
    (See: cross-certification.)

Shirey Informational [Page 156] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Deprecated Term: IDOCs SHOULD NOT use this term because it is not
    widely known and mixes concepts in a potentially misleading way.
    For example, suppose that end entity 1 ("EE1) is in one PKI
    ("PKI1"), end entity 2 ("EE2) is in another PKI ("PKI2"), and the
    root in PKI1 ("CA1") cross-certifies the root CA in PKI2 ("CA2").
    Then, if EE1 constructs the certification path CA1-to-CA2-to-EE2
    to validate a certificate of EE2, conventional English usage would
    describe CA2 as being in the "intermediate" position in that path,
    not CA1.
 $ internal controls
    (I) /COMPUSEC/ Functions, features, and technical characteristics
    of computer hardware and software, especially of operating
    systems. Includes mechanisms to regulate the operation of a
    computer system with regard to access control, flow control, and
    inference control. (Compare: external controls.)
 $ International Data Encryption Algorithm (IDEA)
    (N) A patented, symmetric block cipher that uses a 128-bit key and
    operates on 64-bit blocks. [Schn] (See: symmetric cryptography.)
 $ International Standard
    (N) See: secondary definition under "ISO".
 $ International Traffic in Arms Regulations (ITAR)
    (O) Rules issued by the U.S. State Department, by authority of the
    Arms Export Control Act (22 U.S.C. 2778), to control export and
    import of defense articles and defense services, including
    information security systems, such as cryptographic systems, and
    TEMPEST suppression technology. (See: type 1 product, Wassenaar
    Arrangement.)
 $ internet, Internet
    1. (I) /not capitalized/ Abbreviation of "internetwork".
    2. (I) /capitalized/ The Internet is the single, interconnected,
    worldwide system of commercial, governmental, educational, and
    other computer networks that share (a) the protocol suite
    specified by the IAB (RFC 2026) and (b) the name and address
    spaces managed by the ICANN. (See: Internet Layer, Internet
    Protocol Suite.)
    Usage: Use with definite article ("the") when using as a noun. For
    example, say "My LAN is small, but the Internet is large." Don't
    say "My LAN is small, but Internet is large."

Shirey Informational [Page 157] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ Internet Architecture Board (IAB)
    (I) A technical advisory group of the ISOC, chartered by the ISOC
    Trustees to provide oversight of Internet architecture and
    protocols and, in the context of Internet Standards, a body to
    which decisions of the IESG may be appealed. Responsible for
    approving appointments to the IESG from among nominees submitted
    by the IETF nominating committee. (RFC 2026)
 $ Internet Assigned Numbers Authority (IANA)
    (I) From the early days of the Internet, the IANA was chartered by
    the ISOC and the U.S. Government's Federal Network Council to be
    the central coordination, allocation, and registration body for
    parameters for Internet protocols. Superseded by ICANN.
 $ Internet Control Message Protocol (ICMP)
    (I) An Internet Standard protocol (RFC 792) that is used to report
    error conditions during IP datagram processing and to exchange
    other information concerning the state of the IP network.
 $ Internet Corporation for Assigned Names and Numbers (ICANN)
    (I) The non-profit, private corporation that has assumed
    responsibility for the IP address space allocation, protocol
    parameter assignment, DNS management, and root server system
    management functions formerly performed under U.S. Government
    contract by IANA and other entities.
    Tutorial: The IPS, as defined by the IETF and the IESG, contains
    numerous parameters, such as Internet addresses, domain names,
    autonomous system numbers, protocol numbers, port numbers,
    management information base OIDs, including private enterprise
    numbers, and many others. The Internet community requires that the
    values used in these parameter fields be assigned uniquely. ICANN
    makes those assignments as requested and maintains a registry of
    the current values.
    ICANN was formed in October 1998, by a coalition of the Internet's
    business, technical, and academic communities. The U.S. Government
    designated ICANN to serve as the global consensus entity with
    responsibility for coordinating four key functions for the
    Internet: allocation of IP address space, assignment of protocol
    parameters, management of the DNS, and management of the DNS root
    server system.
 $ Internet-Draft
    (I) A working document of the IETF, its areas, and its working
    groups. (RFC 2026) (Compare: RFC.)

Shirey Informational [Page 158] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Usage: The term is customarily hyphenated when used either as a
    adjective or a noun, even though the latter is not standard
    English punctuation.
    Tutorial: An Internet-Draft is not an archival document like an
    RFC is. Instead, an Internet-Draft is a preliminary or working
    document that is valid for a maximum of six months and may be
    updated, replaced, or made obsolete by other documents at any
    time. It is inappropriate to use an Internet-Draft as reference
    material or to cite it other than as a "work in progress".
    Although most of the Internet-Drafts are produced by the IETF, any
    interested organization may request to have its working documents
    published as Internet-Drafts.
 $ Internet Engineering Steering Group (IESG)
    (I) The part of the ISOC responsible for technical management of
    IETF activities and administration of the Internet Standards
    Process according to procedures approved by the ISOC Trustees.
    Directly responsible for actions along the "standards track",
    including final approval of specifications as Internet Standards.
    Composed of IETF Area Directors and the IETF chairperson, who also
    chairs the IESG. (RFC 2026)
 $ Internet Engineering Task Force (IETF)
    (I) A self-organized group of people who make contributions to the
    development of Internet technology. The principal body engaged in
    developing Internet Standards, although not itself a part of the
    ISOC. Composed of Working Groups, which are arranged into Areas
    (such as the Security Area), each coordinated by one or more Area
    Directors. Nominations to the IAB and the IESG are made by a
    committee selected at random from regular IETF meeting attendees
    who have volunteered. (RFCs 2026, 3935) [R2323]
 $ Internet Key Exchange (IKE)
    (I) An Internet, IPsec, key-establishment protocol [R4306] for
    putting in place authenticated keying material (a) for use with
    ISAKMP and (b) for other security associations, such as in AH and
    ESP.
    Tutorial: IKE is based on three earlier protocol designs: ISAKMP,
    OAKLEY, and SKEME.
 $ Internet Layer
    (I) See: Internet Protocol Suite.
 $ Internet Message Access Protocol, version 4 (IMAP4)
    (I) An Internet protocol (RFC 2060) by which a client workstation
    can dynamically access a mailbox on a server host to manipulate

Shirey Informational [Page 159] RFC 4949 Internet Security Glossary, Version 2 August 2007

    and retrieve mail messages that the server has received and is
    holding for the client. (See: POP3.)
    Tutorial: IMAP4 has mechanisms for optionally authenticating a
    client to a server and providing other security services. (See:
    IMAP4 AUTHENTICATE.)
 $ Internet Open Trading Protocol (IOTP)
    (I) An Internet protocol [R2801] proposed as a general framework
    for Internet commerce, able to encapsulate transactions of various
    proprietary payment systems (e.g., GeldKarte, Mondex, SET, Visa
    Cash). Provides optional security services by incorporating
    various Internet security mechanisms (e.g., MD5) and protocols
    (e.g., TLS).
 $ Internet Policy Registration Authority (IPRA)
    (I) An X.509-compliant CA that is the top CA of the Internet
    certification hierarchy operated under the auspices of the ISOC
    [R1422]. (See: /PEM/ under "certification hierarchy".)
 $ Internet Private Line Interface (IPLI)
    (O) A successor to the PLI, updated to use TCP/IP and newer
    military-grade COMSEC equipment (TSEC/KG-84). The IPLI was a
    portable, modular system that was developed for use in tactical,
    packet-radio networks. (See: end-to-end encryption.)
 $ Internet Protocol (IP)
    (I) An Internet Standard, Internet-Layer protocol that moves
    datagrams (discrete sets of bits) from one computer to another
    across an internetwork but does not provide reliable delivery,
    flow control, sequencing, or other end-to-end services that TCP
    provides. IP version 4 (IPv4) is specified in RFC 791, and IP
    version 6 (IPv6) is specified in RFC 2460. (See: IP address,
    TCP/IP.)
    Tutorial: If IP were used in an OSIRM stack, IP would be placed at
    the top of Layer 3, above other Layer 3 protocols in the stack.
    In any IPS stack, IP is always present in the Internet Layer and
    is always placed at the top of that layer, on top of any other
    protocols that are used in that layer. In some sense, IP is the
    only protocol specified for the IPS Internet Layer; other
    protocols used there, such as AH and ESP, are just IP variations.
 $ Internet Protocol security
    See: IP Security Protocol.

Shirey Informational [Page 160] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ Internet Protocol Security Option (IPSO)
    (I) Refers to one of three types of IP security options, which are
    fields that may be added to an IP datagram for carrying security
    information about the datagram. (Compare: IPsec.)
    Deprecated Usage: IDOCs SHOULD NOT use this term without a
    modifier to indicate which of the following three types is meant:
    -  "DoD Basic Security Option" (IP option type 130): Defined for
       use on U.S. DoD common-use data networks. Identifies the DoD
       classification level at which the datagram is to be protected
       and the protection authorities whose rules apply to the
       datagram. (A "protection authority" is a National Access
       Program (e.g., GENSER, SIOP-ESI, SCI, NSA, Department of
       Energy) or Special Access Program that specifies protection
       rules for transmission and processing of the information
       contained in the datagram.) [R1108]
    -  "DoD Extended Security Option" (IP option type 133): Permits
       additional security labeling information, beyond that present
       in the Basic Security Option, to be supplied in the datagram to
       meet the needs of registered authorities. [R1108]
    -  "Common IP Security Option" (CIPSO) (IP option type 134):
       Designed by TSIG to carry hierarchic and non-hierarchic
       security labels. (Formerly called "Commercial IP Security
       Option"; a version 2.3 draft was published 9 March 1993 as an
       Internet-Draft but did not advance to RFC form.) [CIPSO]
 $ Internet Protocol Suite (IPS)
    (I) The set of network communication protocols that are specified
    by the IETF, and approved as Internet Standards by the IESG,
    within the oversight of the IAB. (See: OSIRM Security
    Architecture. Compare: OSIRM.)
    Usage: This set of protocols is popularly known as "TCP/IP"
    because TCP and IP are its most basic and important components.
    For clarity, this Glossary refers to IPS protocol layers by name
    and capitalizes those names, and refers to OSIRM protocol layers
    by number.
    Tutorial: The IPS does have architectural principles [R1958], but
    there is no Internet Standard that defines a layered IPS reference
    model like the OSIRM. Still, Internet community literature has
    referred (inconsistently) to IPS layers since early in the
    Internet's development [Padl].

Shirey Informational [Page 161] RFC 4949 Internet Security Glossary, Version 2 August 2007

    This Glossary treats the IPS as having five protocol layers --
    Application, Transport, Internet, Network Interface, and Network
    Hardware (or Network Substrate) -- which are illustrated in the
    following diagram:
    OSIRM Layers       Examples          IPS Layers     Examples
    ------------------ ---------------  --------------- --------------
    Message Format:    P2   [X420]      Message Format: ARPA (RFC 822)
    +----------------+                  +-------------+
    |7.Application   | P1   [X419]      | Application | SMTP (RFC 821)
    +----------------+ -  -  -  -  -  - |             |
    |6.Presentation  |      [I8823]     |             |
    +----------------+ -  -  -  -  -  - |             |
    |5.Session       |      [I8327]     +-------------+
    +----------------+ -  -  -  -  -  - |  Transport  | TCP  (RFC 793)
    |4.Transport     | TP4  [I8073]     |             |
    +----------------+ -  -  -  -  -  - +-------------+
    |3.Network       | CLNP [I8473]     |  Internet   | IP   (RFC 791)
    |                |                  +-------------+
    |                |                  |   Network   | IP over IEEE
    +----------------+ -  -  -  -  -  - |  Interface  | 802 (RFC 1042)
    |2.Data Link     |                  +-------------+
    |                | LLC  [I8802-2]   -   Network   - The IPS does
    |                | MAC  [I8802-3]   -  Hardware   - not include
    +----------------+                  - (or Network - standards for
    |1.Physical      | Baseband         -  Substrate) - this layer.
    +----------------+ Signaling [Stal] + - - - - - - +
    The diagram approximates how the five IPS layers align with the
    seven OSIRM layers, and it offers examples of protocol stacks that
    provide roughly equivalent electronic mail service over a private
    LAN that uses baseband signaling.
  1. IPS Application Layer: The user runs an application program.

The program selects the data transport service it needs –

       either a sequence of data messages or a continuous stream of
       data -- and hands application data to the Transport Layer for
       delivery.
  1. IPS Transport Layer: This layer divides application data into

packets, adds a destination address to each, and communicates

       them end-to-end -- from one application program to another --
       optionally regulating the flow and ensuring reliable (error-
       free and sequenced) delivery.
  1. IPS Internet Layer: This layer carries transport packets in IP

datagrams. It moves each datagram independently, from its

       source computer to its addressed destination computer, routing

Shirey Informational [Page 162] RFC 4949 Internet Security Glossary, Version 2 August 2007

       the datagram through a sequence of networks and relays and
       selecting appropriate network interfaces en route.
  1. IPS Network Interface Layer: This layer accepts datagrams for

transmission over a specific network. This layer specifies

       interface conventions for carrying IP over OSIRM Layer 3
       protocols and over Media Access Control sublayer protocols of
       OSIRM Layer 2. An example is IP over IEEE 802 (RFD 1042).
  1. IPS Network Hardware Layer: This layer consists of specific,

physical communication media. However, the IPS does not specify

       its own peer-to-peer protocols in this layer. Instead, the
       layering conventions specified by the Network Interface Layer
       use Layer 2 and Layer 3 protocols that are specified by bodies
       other than the IETF. That is, the IPS addresses *inter*-network
       functions and does not address *intra*-network functions.
    The two models are most dissimilar in the upper layers, where the
    IPS model does not include Session and Presentation layers.
    However, this omission causes fewer functional differences between
    the models than might be imagined, and the differences have
    relatively few security implications:
  1. Formal separation of OSIRM Layers 5, 6, and 7 is not needed in

implementations; the functions of these layers sometimes are

       mixed in a single software unit, even in protocols in the OSI
       suite.
  1. Some OSIRM Layer 5 services – for example, connection

termination – are built into TCP, and the remaining Layer 5

       and 6 functions are built into IPS Application-Layer protocols
       where needed.
  1. The OSIRM does not place any security services in Layer 5 (see:

OSIRM Security Architecture).

  1. The lack of an explicit Presentation Layer in the IPS sometimes

makes it simpler to implement security in IPS applications. For

       example, a primary function of Layer 6 is to convert data
       between internal and external forms, using a transfer syntax to
       unambiguously encode data for transmission. If an OSIRM
       application encrypts data to protect against disclosure during
       transmission, the transfer encoding must be done before the
       encryption. If an application does encryption, as is done in
       OSI message handling and directory service protocols, then
       Layer 6 functions must be replicated in Layer 7. [X400, X500].

Shirey Informational [Page 163] RFC 4949 Internet Security Glossary, Version 2 August 2007

    The two models are most alike at the top of OSIRM Layer 3, where
    the OSI Connectionless Network Layer Protocol (CLNP) and the IPS
    IP are quite similar. Connection-oriented security services
    offered in OSIRM Layer 3 are inapplicable in the IPS, because the
    IPS Internet Layer lacks the explicit, connection-oriented service
    offered in the OSIRM.
 $ Internet Security Association and Key Management Protocol (ISAKMP)
    (I) An Internet IPsec protocol [R2408] to negotiate, establish,
    modify, and delete security associations, and to exchange key
    generation and authentication data, independent of the details of
    any specific key generation technique, key establishment protocol,
    encryption algorithm, or authentication mechanism.
    Tutorial: ISAKMP supports negotiation of security associations for
    protocols at all IPS layers. By centralizing management of
    security associations, ISAKMP reduces duplicated functionality
    within each protocol. ISAKMP can also reduce connection setup
    time, by negotiating a whole stack of services at once. Strong
    authentication is required on ISAKMP exchanges, and a digital
    signature algorithm based on asymmetric cryptography is used
    within ISAKMP's authentication component.
    ISAKMP negotiations are conducted in two "phases":
    -  "Phase 1 negotiation". A phase 1 negotiation establishes a
       security association to be used by ISAKMP to protect its own
       protocol operations.
    -  "Phase 2 negotiation". A phase 2 negotiation (which is
       protected by a security association that was established by a
       phase 1 negotiation) establishes a security association to be
       used to protect the operations of a protocol other than ISAKMP,
       such as ESP.
 $ Internet Society (ISOC)
    (I) A professional society concerned with Internet development
    (including technical Internet Standards); with how the Internet is
    and can be used; and with social, political, and technical issues
    that result. The ISOC Board of Trustees approves appointments to
    the IAB from among nominees submitted by the IETF nominating
    committee. (RFC 2026)
 $ Internet Standard
    (I) A specification, approved by the IESG and published as an RFC,
    that is stable and well-understood, is technically competent, has
    multiple, independent, and interoperable implementations with
    substantial operational experience, enjoys significant public
    support, and is recognizably useful in some or all parts of the
    Internet. (RFC 2026) (Compare: RFC.)

Shirey Informational [Page 164] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Tutorial: The "Internet Standards Process" is an activity of the
    ISOC and is organized and managed by the IAB and the IESG. The
    process is concerned with all protocols, procedures, and
    conventions used in or by the Internet, whether or not they are
    part of the IPS. The "Internet Standards Track" has three levels
    of increasing maturity: Proposed Standard, Draft Standard, and
    Standard. (Compare: ISO, W3C.)
 $ internetwork
    (I) A system of interconnected networks; a network of networks.
    Usually shortened to "internet". (See: internet, Internet.)
    Tutorial: An internet can be built using OSIRM Layer 3 gateways to
    implement connections between a set of similar subnetworks. With
    dissimilar subnetworks, i.e., subnetworks that differ in the Layer
    3 protocol service they offer, an internet can be built by
    implementing a uniform internetwork protocol (e.g., IP) that
    operates at the top of Layer 3 and hides the underlying
    subnetworks' heterogeneity from hosts that use communication
    services provided by the internet. (See: router.)
 $ intranet
    (I) A computer network, especially one based on Internet
    technology, that an organization uses for its own internal (and
    usually private) purposes and that is closed to outsiders. (See:
    extranet, VPN.)
 $ intruder
    (I) An entity that gains or attempts to gain access to a system or
    system resource without having authorization to do so. (See:
    intrusion. Compare: adversary, cracker, hacker.)
 $ intrusion
    1. (I) A security event, or a combination of multiple security
    events, that constitutes a security incident in which an intruder
    gains, or attempts to gain, access to a system or system resource
    without having authorization to do so. (See: IDS.)
    2. (I) A type of threat action whereby an unauthorized entity
    gains access to sensitive data by circumventing a system's
    security protections. (See: unauthorized disclosure.)
    Usage: This type of threat action includes the following subtypes:
    -  "Trespass": Gaining physical access to sensitive data by
       circumventing a system's protections.
    -  "Penetration": Gaining logical access to sensitive data by
       circumventing a system's protections.

Shirey Informational [Page 165] RFC 4949 Internet Security Glossary, Version 2 August 2007

  1. "Reverse engineering": Acquiring sensitive data by

disassembling and analyzing the design of a system component.

  1. "Cryptanalysis": Transforming encrypted data into plain text

without having prior knowledge of encryption parameters or

       processes. (See: main entry for "cryptanalysis".)
 $ intrusion detection
    (I) Sensing and analyzing system events for the purpose of
    noticing (i.e., becoming aware of) attempts to access system
    resources in an unauthorized manner. (See: anomaly detection, IDS,
    misuse detection. Compare: extrusion detection.) [IDSAN, IDSSC,
    IDSSE, IDSSY]
    Usage: This includes the following subtypes:
    -  "Active detection": Real-time or near-real-time analysis of
       system event data to detect current intrusions, which result in
       an immediate protective response.
    -  "Passive detection": Off-line analysis of audit data to detect
       past intrusions, which are reported to the system security
       officer for corrective action. (Compare: security audit.)
 $ intrusion detection system (IDS)
    1. (N) A process or subsystem, implemented in software or
    hardware, that automates the tasks of (a) monitoring events that
    occur in a computer network and (b) analyzing them for signs of
    security problems. [SP31] (See: intrusion detection.)
    2. (N) A security alarm system to detect unauthorized entry.
    [DC6/9].
    Tutorial: Active intrusion detection processes can be either host-
    based or network-based:
    -  "Host-based": Intrusion detection components -- traffic sensors
       and analyzers -- run directly on the hosts that they are
       intended to protect.
    -  "Network-based": Sensors are placed on subnetwork components,
       and analysis components run either on subnetwork components or
       hosts.
 $ invalidity date
    (N) An X.509 CRL entry extension that "indicates the date at which
    it is known or suspected that the [revoked certificate's private
    key] was compromised or that the certificate should otherwise be
    considered invalid." [X509].
    Tutorial: This date may be earlier than the revocation date in the
    CRL entry, and may even be earlier than the date of issue of
    earlier CRLs. However, the invalidity date is not, by itself,

Shirey Informational [Page 166] RFC 4949 Internet Security Glossary, Version 2 August 2007

    sufficient for purposes of non-repudiation service. For example,
    to fraudulently repudiate a validly generated signature, a private
    key holder may falsely claim that the key was compromised at some
    time in the past.
 $ IOTP
    (I) See: Internet Open Trading Protocol.
 $ IP
    (I) See: Internet Protocol.
 $ IP address
    (I) A computer's internetwork address that is assigned for use by
    IP and other protocols.
    Tutorial: An IP version 4 address (RFC 791) has four 8-bit parts
    and is written as a series of four decimal numbers separated by
    periods. Example: The address of the host named "rosslyn.bbn.com"
    is 192.1.7.10.
    An IP version 6 address (RFC 2373) has eight 16-bit parts and is
    written as eight hexadecimal numbers separated by colons.
    Examples: 1080:0:0:0:8:800:200C:417A and
    FEDC:BA98:7654:3210:FEDC:BA98:7654:3210.
 $ IP Security Option
    (I) See: Internet Protocol Security Option.
 $ IP Security Protocol (IPsec)
    1a. (I) The name of the IETF working group that is specifying an
    architecture [R2401, R4301] and set of protocols to provide
    security services for IP traffic. (See: AH, ESP, IKE, SAD, SPD.
    Compare: IPSO.)
    1b. (I) A collective name for the IP security architecture [R4301]
    and associated set of protocols (primarily AH, ESP, and IKE).
    Usage: In IDOCs that use the abbreviation "IPsec", the letters
    "IP" SHOULD be in uppercase, and the letters "sec" SHOULD NOT.
    Tutorial: The security services provided by IPsec include access
    control service, connectionless data integrity service, data
    origin authentication service, protection against replays
    (detection of the arrival of duplicate datagrams, within a
    constrained window), data confidentiality service, and limited
    traffic-flow confidentiality. IPsec specifies (a) security
    protocols (AH and ESP), (b) security associations (what they are,
    how they work, how they are managed, and associated processing),

Shirey Informational [Page 167] RFC 4949 Internet Security Glossary, Version 2 August 2007

    (c) key management (IKE), and (d) algorithms for authentication
    and encryption. Implementation of IPsec is optional for IP version
    4, but mandatory for IP version 6. (See: transport mode, tunnel
    mode.)
 $ IPLI
    (I) See: Internet Private Line Interface.
 $ IPRA
    (I) See: Internet Policy Registration Authority.
 $ IPS
    (I) See: Internet Protocol Suite.
 $ IPsec
    (I) See: IP Security Protocol.
 $ IPSO
    (I) See: Internet Protocol Security Option.
 $ ISAKMP
    (I) See: Internet Security Association and Key Management
    Protocol.
 $ ISO
    (I) International Organization for Standardization, a voluntary,
    non-treaty, non-governmental organization, established in 1947,
    with voting members that are designated standards bodies of
    participating nations and non-voting observer organizations.
    (Compare: ANSI, IETF, ITU-T, W3C.)
    Tutorial: Legally, ISO is a Swiss, non-profit, private
    organization. ISO and the IEC (the International Electrotechnical
    Commission) form the specialized system for worldwide
    standardization. National bodies that are members of ISO or IEC
    participate in developing international standards through ISO and
    IEC technical committees that deal with particular fields of
    activity. Other international governmental and non-governmental
    organizations, in liaison with ISO and IEC, also take part. (ANSI
    is the U.S. voting member of ISO. ISO is a class D member of ITU-
    T.)
    The ISO standards development process has four levels of
    increasing maturity: Working Draft (WD), Committee Draft (CD),
    Draft International Standard (DIS), and International Standard
    (IS). (Compare: "Internet Standards Track" under "Internet
    Standard".) In information technology, ISO and IEC have a joint
    technical committee, ISO/IEC JTC 1. DISs adopted by JTC 1 are

Shirey Informational [Page 168] RFC 4949 Internet Security Glossary, Version 2 August 2007

    circulated to national bodies for voting, and publication as an IS
    requires approval by at least 75% of the national bodies casting a
    vote.
 $ ISO 17799
    (N) An International Standard that is a code of practice, derived
    from Part 1 of British Standard 7799, for managing the security of
    information systems in an organization. This standard does not
    provide definitive or specific material on any security topic. It
    provides general guidance on a wide variety of topics, but
    typically does not go into depth. (See: IATF, [SP14].)
 $ ISOC
    (I) See: Internet Society.
 $ issue
    (I) /PKI/ Generate and sign a digital certificate (or a CRL) and,
    usually, distribute it and make it available to potential
    certificate users (or CRL users). (See: certificate creation.)
    Usage: The term "issuing" is usually understood to refer not only
    to creating a digital certificate (or a CRL) but also to making it
    available to potential users, such as by storing it in a
    repository or other directory or otherwise publishing it. However,
    the ABA [DSG] explicitly limits this term to the creation process
    and excludes any related publishing or distribution process.
 $ issuer
    1. (I) /certificate, CRL/ The CA that signs a digital certificate
    or CRL.
    Tutorial: An X.509 certificate always includes the issuer's name.
    The name may include a common name value.
    2. (O) /payment card, SET/ "The financial institution or its agent
    that issues the unique primary account number to the cardholder
    for the payment card brand." [SET2]
    Tutorial: The institution that establishes the account for a
    cardholder and issues the payment card also guarantees payment for
    authorized transactions that use the card in accordance with card
    brand regulations and local legislation. [SET1]
 $ ITAR
    (O) See: International Traffic in Arms Regulations.
 $ ITSEC
    (N) See: Information Technology System Evaluation Criteria.

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 $ ITU-T
    (N) International Telecommunications Union, Telecommunication
    Standardization Sector (formerly "CCITT"), a United Nations treaty
    organization that is composed mainly of postal, telephone, and
    telegraph authorities of the member countries and that publishes
    standards called "Recommendations". (See: X.400, X.500.)
    Tutorial: The Department of State represents the United States.
    ITU-T works on many kinds of communication systems. ITU-T
    cooperates with ISO on communication protocol standards, and many
    Recommendations in that area are also published as an ISO standard
    with an ISO name and number.
 $ IV
    (I) See: initialization value.
 $ jamming
    (N) An attack that attempts to interfere with the reception of
    broadcast communications. (See: anti-jam, denial of service.
    Compare: flooding.)
    Tutorial: Jamming uses "interference" as a type of "obstruction"
    intended to cause "disruption". Jamming a broadcast signal is
    typically done by broadcasting a second signal that receivers
    cannot separate from the first one. Jamming is mainly thought of
    in the context of wireless communication, but also can be done in
    some wired technologies, such as LANs that use contention
    techniques to share a broadcast medium.
 $ KAK
    (D) See: key-auto-key. (Compare: KEK.)
 $ KDC
    (I) See: Key Distribution Center.
 $ KEA
    (N) See: Key Exchange Algorithm.
 $ KEK
    (I) See: key-encrypting key. (Compare: KAK.)
 $ Kerberos
    (I) A system developed at the Massachusetts Institute of
    Technology that depends on passwords and symmetric cryptography
    (DES) to implement ticket-based, peer entity authentication
    service and access control service distributed in a client-server
    network environment. [R4120, Stei] (See: realm.)

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    Tutorial: Kerberos was originally developed by Project Athena and
    is named for the mythical three-headed dog that guards Hades. The
    system architecture includes authentication servers and ticket-
    granting servers that function as an ACC and a KDC.
    RFC 4556 describes extensions to the Kerberos specification that
    modify the initial authentication exchange between a client and
    the KDC. The extensions employ public-key cryptography to enable
    the client and KDC to mutually authenticate and establish shared,
    symmetric keys that are used to complete the exchange. (See:
    PKINIT.)
 $ kernel
    (I) A small, trusted part of a system that provides services on
    which the other parts of the system depend. (See: security
    kernel.)
 $ Kernelized Secure Operating System (KSOS)
    (O) An MLS computer operating system, designed to be a provably
    secure replacement for UNIX Version 6, and consisting of a
    security kernel, non-kernel security-related utility programs, and
    optional UNIX application development and support environments.
    [Perr]
    Tutorial: KSOS-6 was the implementation on a SCOMP. KSOS-11 was
    the implementation by Ford Aerospace and Communications
    Corporation on the DEC PDP-11/45 and PDP-11/70 computers.
 $ key
    1a. (I) /cryptography/ An input parameter used to vary a
    transformation function performed by a cryptographic algorithm.
    (See: private key, public key, storage key, symmetric key, traffic
    key. Compare: initialization value.)
    1b. (O) /cryptography/ Used in singular form as a collective noun
    referring to keys or keying material. Example: A fill device can
    be used transfer key between two cryptographic devices.
    2. (I) /anti-jam/ An input parameter used to vary a process that
    determines patterns for an anti-jam measure. (See: frequency
    hopping, spread spectrum.)
    Tutorial: A key is usually specified as a sequence of bits or
    other symbols. If a key value needs to be kept secret, the
    sequence of symbols that comprise it should be random, or at least
    pseudorandom, because that makes the key harder for an adversary
    to guess. (See: brute-force attack, cryptanalysis, strength.)

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 $ key agreement (algorithm or protocol)
    1. (I) A key establishment method (especially one involving
    asymmetric cryptography) by which two or more entities, without
    prior arrangement except a public exchange of data (such as public
    keys), each can generate the same key value. That is, the method
    does not send a secret from one entity to the other; instead, both
    entities, without prior arrangement except a public exchange of
    data, can compute the same secret value, but that value cannot be
    computed by other, unauthorized entities. (See: Diffie-Hellman-
    Merkle, key establishment, KEA, MQV. Compare: key transport.)
    2. (O) "A method for negotiating a key value on line without
    transferring the key, even in an encrypted form, e.g., the Diffie-
    Hellman technique." [X509] (See: Diffie-Hellman-Merkle.)
    3. (O) "The procedure whereby two different parties generate
    shared symmetric keys such that any of the shared symmetric keys
    is a function of the information contributed by all legitimate
    participants, so that no party [alone] can predetermine the value
    of the key." [A9042]
    Example: A message originator and the intended recipient can each
    use their own private key and the other's public key with the
    Diffie-Hellman-Merkle algorithm to first compute a shared secret
    value and, from that value, derive a session key to encrypt the
    message.
 $ key authentication
    (N) "The assurance of the legitimate participants in a key
    agreement [i.e., in a key-agreement protocol] that no non-
    legitimate party possesses the shared symmetric key." [A9042]
 $ key-auto-key (KAK)
    (D) "Cryptographic logic [i.e., a mode of operation] using
    previous key to produce key." [C4009, A1523] (See: CTAK,
    /cryptographic operation/ under "mode".)
    Deprecated Term: IDOCs SHOULD NOT use this term; it is neither
    well-known nor precisely defined. Instead, use terms associated
    with modes that are defined in standards, such as CBC, CFB, and
    OFB.
 $ key center
    (I) A centralized, key-distribution process (used in symmetric
    cryptography), usually a separate computer system, that uses
    master keys (i.e., KEKs) to encrypt and distribute session keys
    needed by a community of users.

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    Tutorial: An ANSI standard [A9017] defines two types of key
    center: "key distribution center" and "key translation center".
 $ key confirmation
    (N) "The assurance [provided to] the legitimate participants in a
    key establishment protocol that the [parties that are intended to
    share] the symmetric key actually possess the shared symmetric
    key." [A9042]
 $ key distribution
    (I) A process that delivers a cryptographic key from the location
    where it is generated to the locations where it is used in a
    cryptographic algorithm. (See: key establishment, key management.)
 $ key distribution center (KDC)
    1. (I) A type of key center (used in symmetric cryptography) that
    implements a key-distribution protocol to provide keys (usually,
    session keys) to two (or more) entities that wish to communicate
    securely. (Compare: key translation center.)
    2. (N) "COMSEC facility generating and distributing key in
    electrical form." [C4009]
    Tutorial: A KDC distributes keys to Alice and Bob, who (a) wish to
    communicate with each other but do not currently share keys, (b)
    each share a KEK with the KDC, and (c) may not be able to generate
    or acquire keys by themselves. Alice requests the keys from the
    KDC. The KDC generates or acquires the keys and makes two
    identical sets. The KDC encrypts one set in the KEK it shares with
    Alice, and sends that encrypted set to Alice. The KDC encrypts the
    second set in the KEK it shares with Bob, and either (a) sends
    that encrypted set to Alice for her to forward to Bob or (b) sends
    it directly to Bob (although the latter option is not supported in
    the ANSI standard [A9017]).
 $ key encapsulation
    (N) A key recovery technique for storing knowledge of a
    cryptographic key by encrypting it with another key and ensuring
    that only certain third parties called "recovery agents" can
    perform the decryption operation to retrieve the stored key. Key
    encapsulation typically permits direct retrieval of a secret key
    used to provide data confidentiality. (Compare: key escrow.)
 $ key-encrypting key (KEK)
    (I) A cryptographic key that (a) is used to encrypt other keys
    (either DEKs or other TEKs) for transmission or storage but (b)
    (usually) is not used to encrypt application data. Usage:
    Sometimes called "key-encryption key".

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 $ key escrow
    (N) A key recovery technique for storing knowledge of a
    cryptographic key or parts thereof in the custody of one or more
    third parties called "escrow agents", so that the key can be
    recovered and used in specified circumstances. (Compare: key
    encapsulation.)
    Tutorial: Key escrow is typically implemented with split knowledge
    techniques. For example, the Escrowed Encryption Standard [FP185]
    entrusts two components of a device-unique split key to separate
    escrow agents. The agents provide the components only to someone
    legally authorized to conduct electronic surveillance of
    telecommunications encrypted by that specific device. The
    components are used to reconstruct the device-unique key, and it
    is used to obtain the session key needed to decrypt
    communications.
 $ key establishment (algorithm or protocol)
    1. (I) A procedure that combines the key-generation and key-
    distribution steps needed to set up or install a secure
    communication association.
    2. (I) A procedure that results in keying material being shared
    among two or more system entities. [A9042, SP56]
    Tutorial: The two basic techniques for key establishment are "key
    agreement" and "key transport".
 $ Key Exchange Algorithm (KEA)
    (N) A key-agreement method [SKIP, R2773] that is based on the
    Diffie-Hellman-Merkle algorithm and uses 1024-bit asymmetric keys.
    (See: CAPSTONE, CLIPPER, FORTEZZA, SKIPJACK.)
    Tutorial: KEA was developed by NSA and formerly classified at the
    U.S. DoD "Secret" level. On 23 June 1998, the NSA announced that
    KEA had been declassified.
 $ key generation
    (I) A process that creates the sequence of symbols that comprise a
    cryptographic key. (See: key management.)
 $ key generator
    1. (I) An algorithm that uses mathematical rules to
    deterministically produce a pseudorandom sequence of cryptographic
    key values.
    2. (I) An encryption device that incorporates a key-generation
    mechanism and applies the key to plain text to produce cipher text

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    (e.g., by exclusive OR-ing (a) a bit-string representation of the
    key with (b) a bit-string representation of the plaintext).
 $ key length
    (I) The number of symbols (usually stated as a number of bits)
    needed to be able to represent any of the possible values of a
    cryptographic key. (See: key space.)
 $ key lifetime
    1. (D) Synonym for "cryptoperiod".
    Deprecated Definition: IDOCs SHOULD NOT use this term with
    definition 1 because a key's cryptoperiod may be only a part of
    the key's lifetime. A key could be generated at some time prior to
    when its cryptoperiod begins and might not be destroyed (i.e.,
    zeroized) until some time after its cryptoperiod ends.
    2. (O) /MISSI/ An attribute of a MISSI key pair that specifies a
    time span that bounds the validity period of any MISSI X.509
    public-key certificate that contains the public component of the
    pair. (See: cryptoperiod.)
 $ key loader
    (N) Synonym for "fill device".
 $ key loading and initialization facility (KLIF)
    (N) A place where ECU hardware is activated after being
    fabricated. (Compare: CLEF.)
    Tutorial: Before going to its KLIF, an ECU is not ready to be
    fielded, usually because it is not yet able to receive DEKs. The
    KLIF employs trusted processes to complete the ECU by installing
    needed data such as KEKs, seed values, and, in some cases,
    cryptographic software. After KLIF processing, the ECU is ready
    for deployment.
 $ key management
    1a. (I) The process of handling keying material during its life
    cycle in a cryptographic system; and the supervision and control
    of that process. (See: key distribution, key escrow, keying
    material, public-key infrastructure.)
    Usage: Usually understood to include ordering, generating,
    storing, archiving, escrowing, distributing, loading, destroying,
    auditing, and accounting for the material.
    1b. (O) /NIST/ "The activities involving the handling of
    cryptographic keys and other related security parameters (e.g.,

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    IVs, counters) during the entire life cycle of the keys, including
    their generation, storage, distribution, entry and use, deletion
    or destruction, and archiving." [FP140, SP57]
    2. (O) /OSIRM/ "The generation, storage, distribution, deletion,
    archiving and application of keys in accordance with a security
    policy." [I7498-2]
 $ Key Management Protocol (KMP)
    (N) A protocol to establish a shared symmetric key between a pair
    (or a group) of users. (One version of KMP was developed by SDNS,
    and another by SILS.) Superseded by ISAKMP and IKE.
 $ key material
    (D) Synonym for "keying material".
    Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
    "keying material".
 $ key pair
    (I) A set of mathematically related keys -- a public key and a
    private key -- that are used for asymmetric cryptography and are
    generated in a way that makes it computationally infeasible to
    derive the private key from knowledge of the public key. (See:
    Diffie-Hellman-Merkle, RSA.)
    Tutorial: A key pair's owner discloses the public key to other
    system entities so they can use the key to (a) encrypt data, (b)
    verify a digital signature, or (c) generate a key with a key-
    agreement algorithm. The matching private key is kept secret by
    the owner, who uses it to (a') decrypt data, (b') generate a
    digital signature, or (c') generate a key with a key-agreement
    algorithm.
 $ key recovery
    1. (I) /cryptanalysis/ A process for learning the value of a
    cryptographic key that was previously used to perform some
    cryptographic operation. (See: cryptanalysis, recovery.)
    2. (I) /backup/ Techniques that provide an intentional, alternate
    means to access the key used for data confidentiality service in
    an encrypted association. [DoD4] (Compare: recovery.)
    Tutorial: It is assumed that the cryptographic system includes a
    primary means of obtaining the key through a key-establishment
    algorithm or protocol. For the secondary means, there are two
    classes of key recovery techniques: key encapsulation and key
    escrow.

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 $ key space
    (I) The range of possible values of a cryptographic key; or the
    number of distinct transformations supported by a particular
    cryptographic algorithm. (See: key length.)
 $ key translation center
    (I) A type of key center that implements a key-distribution
    protocol (based on symmetric cryptography) to convey keys between
    two (or more) parties who wish to communicate securely. (Compare:
    key distribution center.)
    Tutorial: A key translation center transfers keys for future
    communication between Bob and Alice, who (a) wish to communicate
    with each other but do not currently share keys, (b) each share a
    KEK with the center, and (c) have the ability to generate or
    acquire keys by themselves. Alice generates or acquires a set of
    keys for communication with Bob. Alice encrypts the set in the KEK
    she shares with the center and sends the encrypted set to the
    center. The center decrypts the set, reencrypts the set in the KEK
    it shares with Bob, and either (a) sends that reencrypted set to
    Alice for her to forward to Bob or (b) sends it directly to Bob
    (although direct distribution is not supported in the ANSI
    standard [A9017]).
 $ key transport (algorithm or protocol)
    1. (I) A key establishment method by which a secret key is
    generated by a system entity in a communication association and
    securely sent to another entity in the association. (Compare: key
    agreement.)
    Tutorial: Either (a) one entity generates a secret key and
    securely sends it to the other entity, or (b) each entity
    generates a secret value and securely sends it to the other
    entity, where the two values are combined to form a secret key.
    For example, a message originator can generate a random session
    key and then use the RSA algorithm to encrypt that key with the
    public key of the intended recipient.
    2. (O) "The procedure to send a symmetric key from one party to
    other parties. As a result, all legitimate participants share a
    common symmetric key in such a way that the symmetric key is
    determined entirely by one party." [A9042]
 $ key update
    1. (I) Derive a new key from an existing key. (Compare: rekey.)
    2. (O) Irreversible cryptographic process that modifies a key to
    produce a new key. [C4009]

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 $ key validation
    1. (I) "The procedure for the receiver of a public key to check
    that the key conforms to the arithmetic requirements for such a
    key in order to thwart certain types of attacks." [A9042] (See:
    weak key)
    2. (D) Synonym for "certificate validation".
    Deprecated Usage: IDOCs SHOULD NOT use the term as a synonym for
    "certificate validation"; that would unnecessarily duplicate the
    meaning of the latter term and mix concepts in a potentially
    misleading way. In validating an X.509 public-key certificate, the
    public key contained in the certificate is normally treated as an
    opaque data object.
 $ keyed hash
    (I) A cryptographic hash (e.g., [R1828]) in which the mapping to a
    hash result is varied by a second input parameter that is a
    cryptographic key. (See: checksum.)
    Tutorial: If the input data object is changed, a new,
    corresponding hash result cannot be correctly computed without
    knowledge of the secret key. Thus, the secret key protects the
    hash result so it can be used as a checksum even when there is a
    threat of an active attack on the data. There are two basic types
    of keyed hash:
    -  A function based on a keyed encryption algorithm. Example: Data
       Authentication Code.
    -  A function based on a keyless hash that is enhanced by
       combining (e.g., by concatenating) the input data object
       parameter with a key parameter before mapping to the hash
       result. Example: HMAC.
 $ keying material
    1. (I) Data that is needed to establish and maintain a
    cryptographic security association, such as keys, key pairs, and
    IVs.
    2. (O) "Key, code, or authentication information in physical or
    magnetic form." [C4009] (Compare: COMSEC material.)
 $ keying material identifier (KMID)
    1. (I) An identifier assigned to an item of keying material.
    2. (O) /MISSI/ A 64-bit identifier that is assigned to a key pair
    when the public key is bound in a MISSI X.509 public-key
    certificate.

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 $ Khafre
    (N) A patented, symmetric block cipher designed by Ralph C. Merkle
    as a plug-in replacement for DES. [Schn]
    Tutorial: Khafre was designed for efficient encryption of small
    amounts of data. However, because Khafre does not precompute
    tables used for encryption, it is slower than Khufu for large
    amounts of data.
 $ Khufu
    (N) A patented, symmetric block cipher designed by Ralph C. Merkle
    as a plug-in replacement for DES. [Schn]
    Tutorial: Khufu was designed for fast encryption of large amounts
    of data. However, because Khufu precomputes tables used in
    encryption, it is less efficient than Khafre for small amounts of
    data.
 $ KLIF
    (N) See: key loading and initialization facility.
 $ KMID
    (I) See: keying material identifier.
 $ known-plaintext attack
    (I) A cryptanalysis technique in which the analyst tries to
    determine the key from knowledge of some plaintext-ciphertext
    pairs (although the analyst may also have other clues, such as
    knowing the cryptographic algorithm).
 $ kracker
    (O) Old spelling for "cracker".
 $ KSOS, KSOS-6, KSOS-11
    (O) See: Kernelized Secure Operating System.
 $ L2F
    (N) See: Layer 2 Forwarding Protocol.
 $ L2TP
    (N) See: Layer 2 Tunneling Protocol.
 $ label
    See: time stamp, security label.

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 $ laboratory attack
    (O) "Use of sophisticated signal recovery equipment in a
    laboratory environment to recover information from data storage
    media." [C4009]
 $ LAN
    (I) Abbreviation for "local area network" [R1983]. (See: [FP191].)
 $ land attack
    (I) A denial-of-service attack that sends an IP packet that (a)
    has the same address in both the Source Address and Destination
    Address fields and (b) contains a TCP SYN packet that has the same
    port number in both the Source Port and Destination Port fields.
    Derivation: This single-packet attack was named for "land", the
    program originally published by the cracker who invented this
    exploit. Perhaps that name was chosen because the inventor thought
    of multi-packet (i.e., flooding) attacks as arriving by sea.
 $ Language of Temporal Ordering Specification (LOTOS)
    (N) A language (ISO 8807-1990) for formal specification of
    computer network protocols; describes the order in which events
    occur.
 $ lattice
    (I) A finite set together with a partial ordering on its elements
    such that for every pair of elements there is a least upper bound
    and a greatest lower bound.
    Example: A lattice is formed by a finite set S of security levels
    -- i.e., a set S of all ordered pairs (x,c), where x is one of a
    finite set X of hierarchically ordered classification levels X(1),
    non-hierarchical categories C(1), ..., C(M) -- together with the
    "dominate" relation. Security level (x,c) is said to "dominate"
    (x',c') if and only if (a) x is greater (higher) than or equal to
    x' and (b) c includes at least all of the elements of c'. (See:
    dominate, lattice model.)
    Tutorial: Lattices are used in some branches of cryptography, both
    as a basis for hard computational problems upon which
    cryptographic algorithms can be defined, and also as a basis for
    attacks on cryptographic algorithms.
 $ lattice model
    1. (I) A description of the semantic structure formed by a finite
    set of security levels, such as those used in military
    organizations. (See: dominate, lattice, security model.)

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    2. (I) /formal model/ A model for flow control in a system, based
    on the lattice that is formed by the finite security levels in a
    system and their partial ordering. [Denn]
 $ Law Enforcement Access Field (LEAF)
    (N) A data item that is automatically embedded in data encrypted
    by devices (e.g., CLIPPER chip) that implement the Escrowed
    Encryption Standard.
 $ Layer 1, 2, 3, 4, 5, 6, 7
    (N) See: OSIRM.
 $ Layer 2 Forwarding Protocol (L2F)
    (N) An Internet protocol (originally developed by Cisco
    Corporation) that uses tunneling of PPP over IP to create a
    virtual extension of a dial-up link across a network, initiated by
    the dial-up server and transparent to the dial-up user. (See:
    L2TP.)
 $ Layer 2 Tunneling Protocol (L2TP)
    (N) An Internet client-server protocol that combines aspects of
    PPTP and L2F and supports tunneling of PPP over an IP network or
    over frame relay or other switched network. (See: VPN.)
    Tutorial: PPP can in turn encapsulate any OSIRM Layer 3 protocol.
    Thus, L2TP does not specify security services; it depends on
    protocols layered above and below it to provide any needed
    security.
 $ LDAP
    (I) See: Lightweight Directory Access Protocol.
 $ least common mechanism
    (I) The principle that a security architecture should minimize
    reliance on mechanisms that are shared by many users.
    Tutorial: Shared mechanisms may include cross-talk paths that
    permit a breach of data security, and it is difficult to make a
    single mechanism operate in a correct and trusted manner to the
    satisfaction of a wide range of users.
 $ least privilege
    (I) The principle that a security architecture should be designed
    so that each system entity is granted the minimum system resources
    and authorizations that the entity needs to do its work. (Compare:
    economy of mechanism, least trust.)

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    Tutorial: This principle tends to limit damage that can be caused
    by an accident, error, or unauthorized act. This principle also
    tends to reduce complexity and promote modularity, which can make
    certification easier and more effective. This principle is similar
    to the principle of protocol layering, wherein each layer provides
    specific, limited communication services, and the functions in one
    layer are independent of those in other layers.
 $ least trust
    (I) The principle that a security architecture should be designed
    in a way that minimizes (a) the number of components that require
    trust and (b) the extent to which each component is trusted.
    (Compare: least privilege, trust level.)
 $ legacy system
    (I) A system that is in operation but will not be improved or
    expanded while a new system is being developed to supersede it.
 $ legal non-repudiation
    (I) See: secondary definition under "non-repudiation".
 $ leap of faith
    1. (I) /general security/ Operating a system as though it began
    operation in a secure state, even though it cannot be proven that
    such a state was established (i.e., even though a security
    compromise might have occurred at or before the time when
    operation began).
    2. (I) /COMSEC/ The initial part, i.e., the first communication
    step, or steps, of a protocol that is vulnerable to attack
    (especially a man-in-the-middle attack) during that part but, if
    that part is completed without being attacked, is subsequently not
    vulnerable in later steps (i.e., results in a secure communication
    association for which no man-in-the-middle attack is possible).
    Usage: This term is listed in English dictionaries, but their
    definitions are broad and can be interpreted in many ways in
    Internet contexts. Similarly, the definition stated here can be
    interpreted in several ways. Therefore, IDOCs that use this term
    (especially IDOCs that are protocol specifications) SHOULD state a
    more specific definition for it.
    Tutorial: In a protocol, a leap of faith typically consists of
    accepting a claim of peer identity, data origin, or data integrity
    without authenticating that claim. When a protocol includes such a
    step, the protocol might also be designed so that if a man-in-
    the-middle attack succeeds during the vulnerable first part, then
    the attacker must remain in the middle for all subsequent

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    exchanges or else one of the legitimate parties will be able to
    detect the attack.
 $ level of concern
    (N) /U.S. DoD/ A rating assigned to an information system that
    indicates the extent to which protective measures, techniques, and
    procedures must be applied. (See: critical, sensitive, level of
    robustness.)
 $ level of robustness
    (N) /U.S. DoD/ A characterization of (a) the strength of a
    security function, mechanism, service, or solution and (b) the
    assurance (or confidence) that it is implemented and functioning.
    [Cons, IATF] (See: level of concern.)
 $ Liberty Alliance
    (O) An international consortium of more than 150 commercial,
    nonprofit, and governmental organizations that was created in 2001
    to address technical, business, and policy problems of identity
    and identity-based Web services and develop a standard for
    federated network identity that supports current and emerging
    network devices.
 $ Lightweight Directory Access Protocol (LDAP)
    (I) An Internet client-server protocol (RFC 3377) that supports
    basic use of the X.500 Directory (or other directory servers)
    without incurring the resource requirements of the full Directory
    Access Protocol (DAP).
    Tutorial: Designed for simple management and browser applications
    that provide simple read/write interactive directory service.
    Supports both simple authentication and strong authentication of
    the client to the directory server.
 $ link
    1a. (I) A communication facility or physical medium that can
    sustain data communications between multiple network nodes, in the
    protocol layer immediately below IP. (RFC 3753)
    1b. (I) /subnetwork/ A communication channel connecting subnetwork
    relays (especially one between two packet switches) that is
    implemented at OSIRM Layer 2. (See: link encryption.)
    Tutorial: The relay computers assume that links are logically
    passive. If a computer at one end of a link sends a sequence of
    bits, the sequence simply arrives at the other end after a finite
    time, although some bits may have been changed either accidentally
    (errors) or by active wiretapping.

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    2. (I) /World Wide Web/ See: hyperlink.
 $ link encryption
    (I) Stepwise (link-by-link) protection of data that flows between
    two points in a network, provided by encrypting data separately on
    each network link, i.e., by encrypting data when it leaves a host
    or subnetwork relay and decrypting when it arrives at the next
    host or relay. Each link may use a different key or even a
    different algorithm. [R1455] (Compare: end-to-end encryption.)
 $ liveness
    (I) A property of a communication association or a feature of a
    communication protocol that provides assurance to the recipient of
    data that the data is being freshly transmitted by its originator,
    i.e., that the data is not being replayed, by either the
    originator or a third party, from a previous transmission. (See:
    fresh, nonce, replay attack.)
 $ logic bomb
    (I) Malicious logic that activates when specified conditions are
    met. Usually intended to cause denial of service or otherwise
    damage system resources. (See: Trojan horse, virus, worm.)
 $ login
    1a. (I) An act by which a system entity establishes a session in
    which the entity can use system resources. (See: principal,
    session.)
    1b. (I) An act by which a system user has its identity
    authenticated by the system. (See: principal, session.)
    Usage: Usually understood to be accomplished by providing an
    identifier and matching authentication information (e.g., a
    password) to a security mechanism that authenticates the user's
    identity; but sometimes refers to establishing a connection with a
    server when no authentication or specific authorization is
    involved.
    Derivation: Refers to "log" file, a security audit trail that
    records (a) security events, such as the beginning of a session,
    and (b) the names of the system entities that initiate events.
 $ long title
    (O) /U.S. Government/ "Descriptive title of [an item of COMSEC
    material]." [C4009] (Compare: short title.)

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 $ low probability of detection
    (I) Result of TRANSEC measures used to hide or disguise a
    communication.
 $ low probability of intercept
    (I) Result of TRANSEC measures used to prevent interception of a
    communication.
 $ LOTOS
    (N) See: Language of Temporal Ordering Specification.
 $ MAC
    (N) See: mandatory access control, Message Authentication Code.
    Deprecated Usage: IDOCs that use this term SHOULD state a
    definition for it because this abbreviation is ambiguous.
 $ magnetic remanence
    (N) Magnetic representation of residual information remaining on a
    magnetic medium after the medium has been cleared. [NCS25] (See:
    clear, degauss, purge.)
 $ main mode
    (I) See: /IKE/ under "mode".
 $ maintenance hook
    (N) "Special instructions (trapdoors) in software allowing easy
    maintenance and additional feature development. Since maintenance
    hooks frequently allow entry into the code without the usual
    checks, they are a serious security risk if they are not removed
    prior to live implementation." [C4009] (See: back door.)
 $ malicious logic
    (I) Hardware, firmware, or software that is intentionally included
    or inserted in a system for a harmful purpose. (See: logic bomb,
    Trojan horse, spyware, virus, worm. Compare: secondary definitions
    under "corruption", "incapacitation", "masquerade", and "misuse".)
 $ malware
    (D) A contraction of "malicious software". (See: malicious logic.)
    Deprecated Term: IDOCs SHOULD NOT use this term; it is not listed
    in most dictionaries and could confuse international readers.
 $ MAN
    (I) metropolitan area network.

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 $ man-in-the-middle attack
    (I) A form of active wiretapping attack in which the attacker
    intercepts and selectively modifies communicated data to
    masquerade as one or more of the entities involved in a
    communication association. (See: hijack attack, piggyback attack.)
    Tutorial: For example, suppose Alice and Bob try to establish a
    session key by using the Diffie-Hellman-Merkle algorithm without
    data origin authentication service. A "man in the middle" could
    (a) block direct communication between Alice and Bob and then (b)
    masquerade as Alice sending data to Bob, (c) masquerade as Bob
    sending data to Alice, (d) establish separate session keys with
    each of them, and (e) function as a clandestine proxy server
    between them to capture or modify sensitive information that Alice
    and Bob think they are sending only to each other.
 $ manager
    (I) A person who controls the service configuration of a system or
    the functional privileges of operators and other users. (See:
    administrative security. Compare: operator, SSO, user.)
 $ mandatory access control
    1. (I) An access control service that enforces a security policy
    based on comparing (a) security labels, which indicate how
    sensitive or critical system resources are, with (b) security
    clearances, which indicate that system entities are eligible to
    access certain resources. (See: discretionary access control, MAC,
    rule-based security policy.)
    Derivation: This kind of access control is called "mandatory"
    because an entity that has clearance to access a resource is not
    permitted, just by its own volition, to enable another entity to
    access that resource.
    2. (O) "A means of restricting access to objects based on the
    sensitivity (as represented by a label) of the information
    contained in the objects and the formal authorization (i.e.,
    clearance) of subjects to access information of such sensitivity."
    [DoD1]
 $ manipulation detection code
    (D) Synonym for "checksum".
    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    "checksum"; the word "manipulation" implies protection against
    active attacks, which an ordinary checksum might not provide.
    Instead, if such protection is intended, use "protected checksum"
    or some particular type thereof, depending on which is meant. If

Shirey Informational [Page 186] RFC 4949 Internet Security Glossary, Version 2 August 2007

    such protection is not intended, use "error detection code" or
    some specific type of checksum that is not protected.
 $ marking
    See: time stamp, security marking.
 $ MARS
    (O) A symmetric, 128-bit block cipher with variable key length
    (128 to 448 bits), developed by IBM as a candidate for the AES.
 $ Martian
    (D) /slang/ A packet that arrives unexpectedly at the wrong
    address or on the wrong network because of incorrect routing or
    because it has a non-registered or ill-formed IP address. [R1208]
    Deprecated Term: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
    Usage under "Green Book".)
 $ masquerade
    (I) A type of threat action whereby an unauthorized entity gains
    access to a system or performs a malicious act by illegitimately
    posing as an authorized entity. (See: deception.)
    Usage: This type of threat action includes the following subtypes:
    -  "Spoof": Attempt by an unauthorized entity to gain access to a
       system by posing as an authorized user.
    -  "Malicious logic": In context of masquerade, any hardware,
       firmware, or software (e.g., Trojan horse) that appears to
       perform a useful or desirable function, but actually gains
       unauthorized access to system resources or tricks a user into
       executing other malicious logic. (See: corruption,
       incapacitation, main entry for "malicious logic", misuse.)
 $ MCA
    (O) See: merchant certification authority.
 $ MD2
    (N) A cryptographic hash [R1319] that produces a 128-bit hash
    result, was designed by Ron Rivest, and is similar to MD4 and MD5
    but slower.
    Derivation: Apparently, an abbreviation of "message digest", but
    that term is deprecated by this Glossary.

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 $ MD4
    (N) A cryptographic hash [R1320] that produces a 128-bit hash
    result and was designed by Ron Rivest. (See: Derivation under
    "MD2", SHA-1.)
 $ MD5
    (N) A cryptographic hash [R1321] that produces a 128-bit hash
    result and was designed by Ron Rivest to be an improved version of
    MD4. (See: Derivation under "MD2".)
 $ merchant
    (O) /SET/ "A seller of goods, services, and/or other information
    who accepts payment for these items electronically." [SET2] A
    merchant may also provide electronic selling services and/or
    electronic delivery of items for sale. With SET, the merchant can
    offer its cardholders secure electronic interactions, but a
    merchant that accepts payment cards is required to have a
    relationship with an acquirer. [SET1, SET2]
 $ merchant certificate
    (O) /SET/ A public-key certificate issued to a merchant. Sometimes
    used to refer to a pair of such certificates where one is for
    digital signature use and the other is for encryption.
 $ merchant certification authority (MCA)
    (O) /SET/ A CA that issues digital certificates to merchants and
    is operated on behalf of a payment card brand, an acquirer, or
    another party according to brand rules. Acquirers verify and
    approve requests for merchant certificates prior to issuance by
    the MCA. An MCA does not issue a CRL, but does distribute CRLs
    issued by root CAs, brand CAs, geopolitical CAs, and payment
    gateway CAs. [SET2]
 $ mesh PKI
    (I) A non-hierarchical PKI architecture in which there are several
    trusted CAs rather than a single root. Each certificate user bases
    path validations on the public key of one of the trusted CAs,
    usually the one that issued that user's own public-key
    certificate. Rather than having superior-to-subordinate
    relationships between CAs, the relationships are peer-to-peer, and
    CAs issue cross-certificates to each other. (Compare: hierarchical
    PKI, trust-file PKI.)
 $ Message Authentication Code (MAC), message authentication code
    1. (N) /capitalized/ A specific ANSI standard for a checksum that
    is computed with a keyed hash that is based on DES. [A9009] Usage:
    a.k.a. Data Authentication Code, which is a U.S. Government
    standard. [FP113] (See: MAC.)

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    2. (D) /not capitalized/ Synonym for "error detection code".
    Deprecated Term: IDOCs SHOULD NOT use the uncapitalized form
    "message authentication code". Instead, use "checksum", "error
    detection code", "hash", "keyed hash", "Message Authentication
    Code", or "protected checksum", depending on what is meant. (See:
    authentication code.)
    The uncapitalized form mixes concepts in a potentially misleading
    way. The word "message" is misleading because it implies that the
    mechanism is particularly suitable for or limited to electronic
    mail (see: Message Handling Systems). The word "authentication" is
    misleading because the mechanism primarily serves a data integrity
    function rather than an authentication function. The word "code"
    is misleading because it implies that either encoding or
    encryption is involved or that the term refers to computer
    software.
 $ message digest
    (D) Synonym for "hash result". (See: cryptographic hash.)
    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    "hash result"; this term unnecessarily duplicates the meaning of
    the other, more general term and mixes concepts in a potentially
    misleading way. The word "message" is misleading because it
    implies that the mechanism is particularly suitable for or limited
    to electronic mail (see: Message Handling Systems).
 $ message handling system
    (D) Synonym for the Internet electronic mail system.
    Deprecated Term: IDOCs SHOULD NOT use this term, because it could
    be confused with Message Handling System. Instead, use "Internet
    electronic mail" or some other, more specific term.
 $ Message Handling System
    (O) An ITU-T system concept that encompasses the notion of
    electronic mail but defines more comprehensive OSI systems and
    services that enable users to exchange messages on a store-and-
    forward basis. (The ISO equivalent is "Message Oriented Text
    Interchange System".) (See: X.400.)
 $ message indicator
    1. (D) /cryptographic function/ Synonym for "initialization
    value". (Compare: indicator.)
    2. (D) "Sequence of bits transmitted over a communications system
    for synchronizing cryptographic equipment." [C4009]

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    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    "initialization value"; the term mixes concepts in a potentially
    misleading way. The word "message" is misleading because it
    suggests that the mechanism is specific to electronic mail. (See:
    Message Handling System.)
 $ message integrity check
 $ message integrity code (MIC)
    (D) Synonyms for some form of "checksum".
    Deprecated Term: IDOCs SHOULD NOT use these terms for any form of
    checksum. Instead, use "checksum", "error detection code", "hash",
    "keyed hash", "Message Authentication Code", or "protected
    checksum", depending on what is meant.
    These two terms mix concepts in potentially misleading ways. The
    word "message" is misleading because it suggests that the
    mechanism is particularly suitable for or limited to electronic
    mail. The word "integrity" is misleading because the checksum may
    be used to perform a data origin authentication function rather
    than an integrity function. The word "code" is misleading because
    it suggests either that encoding or encryption is involved or that
    the term refers to computer software.
 $ Message Security Protocol (MSP)
    (N) A secure message handling protocol [SDNS7] for use with X.400
    and Internet mail protocols. Developed by NSA's SDNS program and
    used in the U.S. DoD's Defense Message System.
 $ meta-data
    (I) Descriptive information about a data object; i.e., data about
    data, or data labels that describe other data. (See: security
    label. Compare: metadata)
    Tutorial: Meta-data can serve various management purposes:
    -  System management: File name, type, size, creation date.
    -  Application management: Document title, version, author.
    -  Usage management: Data categories, keywords, classifications.
    Meta-data can be associated with a data object in two basic ways:
    -  Explicitly: Be part of the data object (e.g., a header field of
       a data file or packet) or be linked to the object.
    -  Implicitly: Be associated with the data object because of some
       other, explicit attribute of the object.
 $ metadata, Metadata(trademark), METADATA(trademark)
    (D) Proprietary variants of "meta-data". (See: SPAM(trademark).)

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    Deprecated Usage: IDOCs SHOULD NOT use these unhypenated forms;
    IDOCs SHOULD use only the uncapitalized, hyphenated "meta-data".
    The terms "Metadata" and "METADATA" are claimed as registered
    trademarks (numbers 1,409,260 and 2,185,504) owned by The Metadata
    Company, originally known as Metadata Information Partners, a
    company founded by Jack Myers. The status of "metadata" is
    unclear.
 $ MHS
    (N) See: message handling system.
 $ MIC
    (D) See: message integrity code.
 $ MIME
    (I) See: Multipurpose Internet Mail Extensions.
 $ MIME Object Security Services (MOSS)
    (I) An Internet protocol [R1848] that applies end-to-end
    encryption and digital signature to MIME message content, using
    symmetric cryptography for encryption and asymmetric cryptography
    for key distribution and signature. MOSS is based on features and
    specifications of PEM. (See: S/MIME.)
 $ Minimum Interoperability Specification for PKI Components (MISPC)
    (N) A technical description to provide a basis for interoperation
    between PKI components from different vendors; consists primarily
    of a profile of certificate and CRL extensions and a set of
    transactions for PKI operation. [SP15]
 $ misappropriation
    (I) A type of threat action whereby an entity assumes unauthorized
    logical or physical control of a system resource. (See:
    usurpation.)
    Usage: This type of threat action includes the following subtypes:
    -  Theft of data: Unauthorized acquisition and use of data
       contained in a system.
    -  Theft of service: Unauthorized use of a system service.
    -  Theft of functionality: Unauthorized acquisition of actual
       hardware, firmware, or software of a system component.
 $ MISPC
    (N) See: Minimum Interoperability Specification for PKI
    Components.

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 $ MISSI
    (O) Multilevel Information System Security Initiative, an NSA
    program to encourage development of interoperable, modular
    products for constructing secure network information systems in
    support of a wide variety of U.S. Government missions. (See: MSP,
    SP3, SP4.)
 $ MISSI user
    (O) /MISSI/ A system entity that is the subject of one or more
    MISSI X.509 public-key certificates issued under a MISSI
    certification hierarchy. (See: personality.)
    Tutorial: MISSI users include both end users and the authorities
    that issue certificates. A MISSI user is usually a person but may
    be a machine or other automated process. Machines that are
    required to operate nonstop may be issued their own certificates
    to avoid downtime needed to exchange the FORTEZZA cards of machine
    operators at shift changes.
 $ mission
    (I) A statement of a (relatively long-term) duty or (relatively
    short-term) task that is assigned to an organization or system,
    indicates the purpose and objectives of the duty or task, and may
    indicate the actions to be taken to achieve it.
 $ mission critical
    (I) A condition of a system service or other system resource such
    that denial of access to, or lack of availability of, the resource
    would jeopardize a system user's ability to perform a primary
    mission function or would result in other serious consequences.
    (See: Critical. Compare: mission essential.)
 $ mission essential
    (O) /U.S. DoD/ Refers to materiel that is authorized and available
    to combat, combat support, combat service support, and combat
    readiness training forces to accomplish their assigned missions.
    [JP1] (Compare: mission critical.)
 $ misuse
    1. (I) The intentional use (by authorized users) of system
    resources for other than authorized purposes. Example: An
    authorized system administrator creates an unauthorized account
    for a friend. (See: misuse detection.)
    2. (I) A type of threat action that causes a system component to
    perform a function or service that is detrimental to system
    security. (See: usurpation.)

Shirey Informational [Page 192] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Usage: This type of threat action includes the following subtypes:
    -  "Tampering": /misuse/ Deliberately altering a system's logic,
       data, or control information to cause the system to perform
       unauthorized functions or services. (See: corruption, main
       entry for "tampering".)
    -  "Malicious logic": /misuse/ Any hardware, firmware, or software
       intentionally introduced into a system to perform or control
       execution of an unauthorized function or service. (See:
       corruption, incapacitation, main entry for "malicious logic",
       masquerade.)
    -  "Violation of authorizations": Action by an entity that exceeds
       the entity's system privileges by executing an unauthorized
       function. (See: authorization.)
 $ misuse detection
    (I) An intrusion detection method that is based on rules that
    specify system events, sequences of events, or observable
    properties of a system that are believed to be symptomatic of
    security incidents. (See: IDS, misuse. Compare: anomaly
    detection.)
 $ MLS
    (I) See: multilevel secure
 $ mobile code
    1a. (I) Software that originates from a remote server, is
    transmitted across a network, and is loaded onto and executed on a
    local client system without explicit initiation by the client's
    user and, in some cases, without that user's knowledge. (Compare:
    active content.)
    Tutorial: One form of mobile code is active content in a file that
    is transferred across a network.
    1b. (O) /U.S. DoD/ "Software modules obtained from remote systems,
    transferred across a network, and then downloaded and executed on
    local systems without explicit installation or execution by the
    recipient." [JP1]
    2a. (O) /U.S. DoD/ Technology that enables the creation of
    executable information that can be delivered to an information
    system and directly executed on any hardware/software architecture
    that has an appropriate host execution environment.
    2b. (O) "Programs (e.g., script, macro, or other portable
    instruction) that can be shipped unchanged to a heterogeneous
    collection of platforms and executed with identical semantics"
    [SP28]. (See: active content.)

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    Tutorial: Mobile code might be malicious. Using techniques such as
    "code signing" and a "sandbox" can reduce the risks of receiving
    and executing mobile code.
 $ mode
 $ mode of operation
    1. (I) /cryptographic operation/ A technique for enhancing the
    effect of a cryptographic algorithm or adapting the algorithm for
    an application, such as applying a block cipher to a sequence of
    data blocks or a data stream. (See: CBC, CCM, CMAC, CFB, CTR, ECB,
    OFB.)
    2. (I) /system operation/ A type of security policy that states
    the range of classification levels of information that a system is
    permitted to handle and the range of clearances and authorizations
    of users who are permitted to access the system. (See:
    compartmented security mode, controlled security mode, dedicated
    security mode, multilevel security mode, partitioned security
    mode, system-high security mode. Compare: protection level.)
    3. (I) /IKE/ IKE refers to its various types of ISAKMP-scripted
    exchanges of messages as "modes". Among these are the following:
    -  "Main mode": One of IKE's two phase 1 modes. (See: ISAKMP.)
    -  "Quick mode": IKE's only phase 2 mode. (See: ISAKMP.)
 $ model
    See: formal model, security model.
 $ modulus
    (I) The defining constant in modular arithmetic, and usually a
    part of the public key in asymmetric cryptography that is based on
    modular arithmetic. (See: Diffie-Hellman-Merkle, RSA.)
 $ Mondex
    (O) A smartcard-based electronic money system that incorporates
    cryptography and can be used to make payments via the Internet.
    (See: IOTP.)
 $ Morris Worm
    (I) A worm program that flooded the ARPANET in November 1988,
    causing problems for thousands of hosts. [R1135] (See: community
    risk, worm)
 $ MOSS
    (I) See: MIME Object Security Services.

Shirey Informational [Page 194] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ MQV
    (N) A key-agreement protocol [Mene] that was proposed by A.J.
    Menezes, M. Qu, and S.A. Vanstone in 1995 and is based on the
    Diffie-Hellman-Merkle algorithm.
 $ MSP
    (N) See: Message Security Protocol.
 $ multicast security
    See: secure multicast
 $ Multics
    (N) MULTiplexed Information and Computing Service, an MLS computer
    timesharing system designed and implemented during 1965-69 by a
    consortium including Massachusetts Institute of Technology,
    General Electric, and Bell Laboratories, and later offered
    commercially by Honeywell.
    Tutorial: Multics was one of the first large, general-purpose,
    operating systems to include security as a primary goal from the
    inception of the design and development and was rated in TCSEC
    Class B2. Its many innovative hardware and software security
    mechanisms (e.g., protection ring) were adopted by later systems.
 $ multilevel secure (MLS)
    (I) Describes an information system that is trusted to contain,
    and maintain separation between, resources (particularly stored
    data) of different security levels. (Examples: BLACKER, CANEWARE,
    KSOS, Multics, SCOMP.)
    Usage: Usually understood to mean that the system permits
    concurrent access by users who differ in their access
    authorizations, while denying users access to resources for which
    they lack authorization.
 $ multilevel security mode
    1. (N) A mode of system operation wherein (a) two or more security
    levels of information are allowed to be to be handled concurrently
    within the same system when some users having access to the system
    have neither a security clearance nor need-to-know for some of the
    data handled by the system and (b) separation of the users and the
    classified material on the basis, respectively, of clearance and
    classification level are dependent on operating system control.
    (See: /system operation/ under "mode", need to know, protection
    level, security clearance. Compare: controlled mode.)

Shirey Informational [Page 195] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Usage: Usually abbreviated as "multilevel mode". This term was
    defined in U.S. Government policy regarding system accreditation,
    but the term is also used outside the Government.
    2. (O) A mode of system operation in which all three of the
    following statements are true: (a) Some authorized users do not
    have a security clearance for all the information handled in the
    system. (b) All authorized users have the proper security
    clearance and appropriate specific access approval for the
    information to which they have access. (c) All authorized users
    have a need-to-know only for information to which they have
    access. [C4009] (See: formal access approval, protection level.)
 $ Multipurpose Internet Mail Extensions (MIME)
    (I) An Internet protocol (RFC 2045) that enhances the basic format
    of Internet electronic mail messages (RFC 822) (a) to enable
    character sets other than U.S. ASCII to be used for textual
    headers and content and (b) to carry non-textual and multi-part
    content. (See: S/MIME.)
 $ mutual suspicion
    (I) The state that exists between two interacting system entities
    in which neither entity can trust the other to function correctly
    with regard to some security requirement.
 $ name
    (I) Synonym for "identifier".
 $ naming authority
    (O) /U.S. DoD/ An organizational entity responsible for assigning
    DNs and for assuring that each DN is meaningful and unique within
    its domain. [DoD9]
 $ National Computer Security Center (NCSC)
    (O) A U.S. DoD organization, housed in NSA, that has
    responsibility for encouraging widespread availability of trusted
    systems throughout the U.S. Federal Government. It has established
    criteria for, and performed evaluations of, computer and network
    systems that have a TCB. (See: Rainbow Series, TCSEC.)
 $ National Information Assurance Partnership (NIAP)
    (N) A joint initiative of NIST and NSA to enhance the quality of
    commercial products for information security and increase consumer
    confidence in those products through objective evaluation and
    testing methods.

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    Tutorial: NIAP is registered, through the U.S. DoD, as a National
    Performance Review Reinvention Laboratory. NIAP functions include
    the following:
    -  Developing tests, test methods, and other tools that developers
       and testing laboratories may use to improve and evaluate
       security products.
    -  Collaborating with industry and others on research and testing
       programs.
    -  Using the Common Criteria to develop protection profiles and
       associated test sets for security products and systems.
    -  Cooperating with the NIST National Voluntary Laboratory
       Accreditation Program to develop a program to accredit private-
       sector laboratories for the testing of information security
       products using the Common Criteria.
    -  Working to establish a formal, international mutual recognition
       scheme for a Common Criteria-based evaluation.
 $ National Institute of Standards and Technology (NIST)
    (N) A U.S. Department of Commerce organization that promotes U.S.
    economic growth by working with industry to develop and apply
    technology, measurements, and standards. Has primary U.S.
    Government responsibility for INFOSEC standards for sensitive
    unclassified information. (See: ANSI, DES, DSA, DSS, FIPS, NIAP,
    NSA.)
 $ National Reliability and Interoperability Council (NRIC)
    (N) An advisory committee chartered by the U.S. Federal
    Communications Commission (FCC), with participation by network
    service providers and vendors, to provide recommendations to the
    FCC for assuring reliability, interoperability, robustness, and
    security of wireless, wireline, satellite, cable, and public data
    communication networks.
 $ national security
    (O) /U.S. Government/ The national defense or foreign relations of
    the United States of America.
 $ National Security Agency (NSA)
    (N) A U.S. DoD organization that has primary U.S. Government
    responsibility for INFOSEC standards for classified information
    and for sensitive unclassified information handled by national
    security systems. (See: FORTEZZA, KEA, MISSI, national security
    system, NIAP, NIST, SKIPJACK.)
 $ national security information
    (O) /U.S. Government/ Information that has been determined,
    pursuant to Executive Order 12958 or any predecessor order, to
    require protection against unauthorized disclosure. [C4009]

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 $ national security system
    (O) /U.S. Government/ Any Government-operated information system
    for which the function, operation, or use (a) involves
    intelligence activities; (b) involves cryptologic activities
    related to national security; (c) involves command and control of
    military forces; (d) involves equipment that is an integral part
    of a weapon or weapon system; or (e) is critical to the direct
    fulfillment of military or intelligence missions and does not
    include a system that is to be used for routine administrative and
    business applications (including payroll, finance, logistics, and
    personnel management applications). [Title 40 U.S.C. Section 1552,
    Information Technology Management Reform Act of 1996.] (See: type
    2 product.)
 $ natural disaster
    (I) /threat action/ See: secondary definitions under "corruption"
    and "incapacitation".
 $ NCSC
    (O) See: National Computer Security Center.
 $ need to know, need-to-know
    (I) The necessity for access to, knowledge of, or possession of
    specific information required to carry out official duties.
    Usage: The compound "need-to-know" is commonly used as either an
    adjective or a noun.
    Tutorial: The need-to-know criterion is used in security
    procedures that require a custodian of sensitive information,
    prior to disclosing the information to someone else, to establish
    that the intended recipient has proper authorization to access the
    information.
 $ network
    (I) An information system comprised of a collection of
    interconnected nodes. (See: computer network.)
 $ Network Hardware Layer
    (I) See: Internet Protocol Suite.
 $ Network Interface Layer
    (I) See: Internet Protocol Suite.
 $ Network Layer Security Protocol (NLSP).
    (N) An OSI protocol (IS0 11577) for end-to-end encryption services
    at the top of OSIRM Layer 3. NLSP is derived from SP3 but is more
    complex. (Compare: IPsec.)

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 $ Network Substrate Layer
    (I) Synonym for "Network Hardware Layer".
 $ network weaving
    (I) A penetration technique in which an intruder avoids detection
    and traceback by using multiple, linked, communication networks to
    access and attack a system. [C4009]
 $ NIAP
    (N) See: National Information Assurance Partnership.
 $ nibble
    (D) Half of a byte (i.e., usually, 4 bits).
    Deprecated Term: To avoid international misunderstanding, IDOCs
    SHOULD NOT use this term; instead, state the size of the block
    explicitly (e.g., "4-bit block"). (See: Deprecated Usage under
    "Green Book".)
 $ NIPRNET
    (O) The U.S. DoD's common-use Non-Classified Internet Protocol
    Router Network; the part of the Internet that is wholly controlled
    by the U.S. DoD and is used for official DoD business.
 $ NIST
    (N) See: National Institute of Standards and Technology.
 $ NLSP
    (N) See: Network Layer Security Protocol
 $ no-lone zone
    (I) A room or other space or area to which no person may have
    unaccompanied access and that, when occupied, is required to be
    occupied by two or more appropriately authorized persons. [C4009]
    (See: dual control.)
 $ no-PIN ORA (NORA)
    (O) /MISSI/ An organizational RA that operates in a mode in which
    the ORA performs no card management functions and, therefore, does
    not require knowledge of either the SSO PIN or user PIN for an end
    user's FORTEZZA PC card.
 $ node
    (I) A collection of related subsystems located on one or more
    computer platforms at a single site. (See: site.)

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 $ nonce
    (I) A random or non-repeating value that is included in data
    exchanged by a protocol, usually for the purpose of guaranteeing
    liveness and thus detecting and protecting against replay attacks.
    (See: fresh.)
 $ non-critical
    See: critical.
 $ non-repudiation service
    1. (I) A security service that provide protection against false
    denial of involvement in an association (especially a
    communication association that transfers data). (See: repudiation,
    time stamp.)
    Tutorial: Two separate types of denial are possible -- an entity
    can deny that it sent a data object, or it can deny that it
    received a data object -- and, therefore, two separate types of
    non-repudiation service are possible. (See: non-repudiation with
    proof of origin, non-repudiation with proof of receipt.)
    2. (D) "Assurance [that] the sender of data is provided with proof
    of delivery and the recipient is provided with proof of the
    sender's identity, so neither can later deny having processed the
    data." [C4009]
    Deprecated Definition: IDOCs SHOULD NOT use definition 2 because
    it bundles two security services -- non-repudiation with proof of
    origin, and non-repudiation with proof of receipt -- that can be
    provided independently of each other.
    Usage: IDOCs SHOULD distinguish between the technical aspects and
    the legal aspects of a non-repudiation service:
    -  "Technical non-repudiation": Refers to the assurance a relying
       party has that if a public key is used to validate a digital
       signature, then that signature had to have been made by the
       corresponding private signature key. [SP32]
    -  "Legal non-repudiation": Refers to how well possession or
       control of the private signature key can be established. [SP32]
    Tutorial: Non-repudiation service does not prevent an entity from
    repudiating a communication. Instead, the service provides
    evidence that can be stored and later presented to a third party
    to resolve disputes that arise if and when a communication is
    repudiated by one of the entities involved.

Shirey Informational [Page 200] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Ford describes the six phases of a complete non-repudiation
    service and uses "critical action" to refer to the act of
    communication that is the subject of the service [For94, For97]:
  1. ——- ——– ——– ——– ——– . ——–

Phase 1: Phase 2: Phase 3: Phase 4: Phase 5: . Phase 6:

    Request    Generate   Transfer   Verify     Retain     . Resolve
    Service    Evidence   Evidence   Evidence   Evidence   . Dispute
    --------   --------   --------   --------   --------   . --------
    Service    Critical   Evidence   Evidence   Archive    . Evidence
    Request => Action  => Stored  => Is      => Evidence   . Is
    Is Made    Occurs     For Later  Tested     In Case    . Verified
               and        Use |          ^      Critical   .    ^
               Evidence       v          |      Action Is  .    |
               Is         +-------------------+ Repudiated .    |
               Generated  |Verifiable Evidence|------> ... . ----+
                          +-------------------+
    Phase / Explanation
    -------------------
    1. Request service: Before the critical action, the service
       requester asks, either implicitly or explicitly, to have
       evidence of the action be generated.
    2. Generate evidence: When the critical action occurs, evidence is
       generated by a process involving the potential repudiator and
       possibly also a trusted third party.
    3. Transfer evidence: The evidence is transferred to the requester
       or stored by a third party, for later use (if needed).
    4. Verify evidence: The entity that holds the evidence tests it to
       be sure that it will suffice if a dispute arises.
    5. Retain evidence: The evidence is retained for possible future
       retrieval and use.
    6. Resolve dispute: In this phase, which occurs only if the
       critical action is repudiated, the evidence is retrieved from
       storage, presented, and verified to resolve the dispute.
 $ non-repudiation with proof of origin
    (I) A security service that provides the recipient of data with
    evidence that proves the origin of the data, and thus protects the
    recipient against an attempt by the originator to falsely deny
    sending the data. (See: non-repudiation service.)
    Tutorial: This service is a strong version of data origin
    authentication service. This service can not only verify the
    identity of a system entity that is the original source of
    received data; it can also provide proof of that identity to a
    third party.

Shirey Informational [Page 201] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ non-repudiation with proof of receipt
    (I) A security service that provides the originator of data with
    evidence that proves the data was received as addressed, and thus
    protects the originator against an attempt by the recipient to
    falsely deny receiving the data. (See: non-repudiation service.)
 $ non-volatile media
    (I) Storage media that, once written into, provide stable storage
    of information without an external power supply. (Compare:
    permanent storage, volatile media.)
 $ NORA
    (O) See: no-PIN ORA.
 $ notarization
    (I) Registration of data under the authority or in the care of a
    trusted third party, thus making it possible to provide subsequent
    assurance of the accuracy of characteristics claimed for the data,
    such as content, origin, time of existence, and delivery.
    [I7498-2] (See: digital notary.)
 $ NRIC
    (N) See: Network Reliability and Interoperability Council.
 $ NSA
    (N) See: National Security Agency
 $ null
    (N) /encryption/ "Dummy letter, letter symbol, or code group
    inserted into an encrypted message to delay or prevent its
    decryption or to complete encrypted groups for transmission or
    transmission security purposes." [C4009]
 $ NULL encryption algorithm
    (I) An algorithm [R2410] that is specified as doing nothing to
    transform plaintext data; i.e., a no-op. It originated because ESP
    always specifies the use of an encryption algorithm for
    confidentiality. The NULL encryption algorithm is a convenient way
    to represent the option of not applying encryption in ESP (or in
    any other context where a no-op is needed). (Compare: null.)
 $ OAKLEY
    (I) A key establishment protocol (proposed for IPsec but
    superseded by IKE) based on the Diffie-Hellman-Merkle algorithm
    and designed to be a compatible component of ISAKMP. [R2412]
    Tutorial: OAKLEY establishes a shared key with an assigned
    identifier and associated authenticated identities for parties;

Shirey Informational [Page 202] RFC 4949 Internet Security Glossary, Version 2 August 2007

    i.e., OAKLEY provides authentication service to ensure the
    entities of each other's identity, even if the Diffie-Hellman-
    Merkle exchange is threatened by active wiretapping. Also, it
    provides public-key forward secrecy for the shared key and
    supports key updates, incorporation of keys distributed by out-of-
    band mechanisms, and user-defined abstract group structures for
    use with Diffie-Hellman-Merkle.
 $ object
    (I) /formal model/ Trusted-system modeling usage: A system
    component that contains or receives information. (See: Bell-
    LaPadula model, object reuse, trusted system.)
 $ object identifier (OID)
    1. (N) An official, globally unique name for a thing, written as a
    sequence of integers (which are formed and assigned as defined in
    the ASN.1 standard) and used to reference the thing in abstract
    specifications and during negotiation of security services in a
    protocol.
    2. (O) "A value (distinguishable from all other such values)
    [that] is associated with an object." [X680]
    Tutorial: Objects named by OIDs are leaves of the object
    identifier tree (which is similar to but different from the X.500
    Directory Information Tree). Each arc (i.e., each branch of the
    tree) is labeled with a non-negative integer. An OID is the
    sequence of integers on the path leading from the root of the tree
    to a named object.
    The OID tree has three arcs immediately below the root: {0} for
    use by ITU-T, {1} for use by ISO, and {2} for use by both jointly.
    Below ITU-T are four arcs, where {0 0} is for ITU-T
    recommendations. Below {0 0} are 26 arcs, one for each series of
    recommendations starting with the letters A to Z, and below these
    are arcs for each recommendation. Thus, the OID for ITU-T
    Recommendation X.509 is {0 0 24 509}. Below ISO are four arcs,
    where {1 0 }is for ISO standards, and below these are arcs for
    each ISO standard. Thus, the OID for ISO/IEC 9594-8 (the ISO
    number for X.509) is {1 0 9594 8}.
    ANSI registers organization names below the branch {joint-iso-
    ccitt(2) country(16) US(840) organization(1) gov(101) csor(3)}.
    The NIST CSOR records PKI objects below the branch {joint-iso-itu-
    t(2) country(16) us(840) organization (1) gov(101) csor(3)}. The
    U.S. DoD registers INFOSEC objects below the branch {joint-iso-
    itu-t(2) country(16) us(840) organization(1) gov(101) dod(2)
    infosec(1)}.

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    The IETF's Public-Key Infrastructure (pkix) Working Group
    registers PKI objects below the branch {iso(1) identified-
    organization(3) dod(6) internet(1) security(5) mechanisms(5)
    pkix(7)}. [R3280]
 $ object reuse
    (N) /COMPUSEC/ Reassignment and reuse of an area of a storage
    medium (e.g., random-access memory, floppy disk, magnetic tape)
    that once contained sensitive data objects. Before being
    reassigned for use by a new subject, the area needs to be erased
    or, in some cases, purged. [NCS04] (See: object.)
 $ obstruction
    (I) A type of threat action that interrupts delivery of system
    services by hindering system operations. (See: disruption.)
    Tutorial: This type of threat action includes the following
    subtypes:
    -  "Interference": Disruption of system operations by blocking
       communication of user data or control information. (See:
       jamming.)
    -  "Overload": Hindrance of system operation by placing excess
       burden on the performance capabilities of a system component.
       (See: flooding.)
 $ OCSP
    (I) See: Online Certificate Status Protocol.
 $ octet
    (I) A data unit of eight bits. (Compare: byte.)
    Usage: This term is used in networking (especially in OSI
    standards) in preference to "byte", because some systems use
    "byte" for data storage units of a size other than eight bits.
 $ OFB
    (N) See: output feedback.
 $ off-line attack
    (I) See: secondary definition under "attack".
 $ ohnosecond
    (D) That minuscule fraction of time in which you realize that your
    private key has been compromised.
    Deprecated Usage: IDOCs SHOULD NOT use this term; it is a joke for
    English speakers. (See: Deprecated Usage under "Green Book".)

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 $ OID
    (N) See: object identifier.
 $ Online Certificate Status Protocol (OCSP)
    (I) An Internet protocol [R2560] used by a client to obtain from a
    server the validity status and other information about a digital
    certificate. (Mentioned in [X509] but not specified there.)
    Tutorial: In some applications, such as those involving high-value
    commercial transactions, it may be necessary either (a) to obtain
    certificate revocation status that is timelier than is possible
    with CRLs or (b) to obtain other kinds of status information. OCSP
    may be used to determine the current revocation status of a
    digital certificate, in lieu of or as a supplement to checking
    against a periodic CRL. An OCSP client issues a status request to
    an OCSP server and suspends acceptance of the certificate in
    question until the server provides a response.
 $ one-time pad
    1. (N) A manual encryption system in the form of a paper pad for
    one-time use.
    2. (I) An encryption algorithm in which the key is a random
    sequence of symbols and each symbol is used for encryption only
    one time -- i.e., used to encrypt only one plaintext symbol and
    thus produce only one ciphertext symbol -- and a copy of the key
    is used similarly for decryption.
    Tutorial: To ensure one-time use, the copy of the key used for
    encryption is destroyed after use, as is the copy used for
    decryption. This is the only encryption algorithm that is truly
    unbreakable, even given unlimited resources for cryptanalysis
    [Schn], but key management costs and synchronization problems make
    it impractical except in special situations.
 $ one-time password, One-Time Password (OTP)
    1. (I) /not capitalized/ A "one-time password" is a simple
    authentication technique in which each password is used only once
    as authentication information that verifies an identity. This
    technique counters the threat of a replay attack that uses
    passwords captured by wiretapping.
    2. (I) /capitalized/ "One-Time Password" is an Internet protocol
    [R2289] that is based on S/KEY and uses a cryptographic hash
    function to generate one-time passwords for use as authentication
    information in system login and in other processes that need
    protection against replay attacks.

Shirey Informational [Page 205] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ one-way encryption
    (I) Irreversible transformation of plain text to cipher text, such
    that the plain text cannot be recovered from the cipher text by
    other than exhaustive procedures even if the cryptographic key is
    known. (See: brute force, encryption.)
 $ one-way function
    (I) "A (mathematical) function, f, [that] is easy to compute, but
    which for a general value y in the range, it is computationally
    difficult to find a value x in the domain such that f(x) = y.
    There may be a few values of y for which finding x is not
    computationally difficult." [X509]
    Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
    "cryptographic hash".
 $ onion routing
    (I) A system that can be used to provide both (a) data
    confidentiality and (b) traffic-flow confidentiality for network
    packets, and also provide (c) anonymity for the source of the
    packets.
    Tutorial: The source, instead of sending a packet directly to the
    intended destination, sends it to an "onion routing proxy" that
    builds an anonymous connection through several other "onion
    routers" to the destination. The proxy defines a route through the
    "onion routing network" by encapsulating the original payload in a
    layered data packet called an "onion", in which each layer defines
    the next hop in the route and each layer is also encrypted. Along
    the route, each onion router that receives the onion peels off one
    layer; decrypts that layer and reads from it the address of the
    next onion router on the route; pads the remaining onion to some
    constant size; and sends the padded onion to that next router.
 $ open security environment
    (O) /U.S. DoD/ A system environment that meets at least one of the
    following two conditions: (a) Application developers (including
    maintainers) do not have sufficient clearance or authorization to
    provide an acceptable presumption that they have not introduced
    malicious logic. (b) Configuration control does not provide
    sufficient assurance that applications and the equipment are
    protected against the introduction of malicious logic prior to and
    during the operation of system applications. [NCS04] (See: "first
    law" under "Courtney's laws". Compare: closed security
    environment.)

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 $ open storage
    (N) /U.S. Government/ "Storage of classified information within an
    accredited facility, but not in General Services Administration
    approved secure containers, while the facility is unoccupied by
    authorized personnel." [C4009]
 $ Open Systems Interconnection (OSI) Reference Model (OSIRM)
    (N) A joint ISO/ITU-T standard [I7498-1] for a seven-layer,
    architectural communication framework for interconnection of
    computers in networks. (See: OSIRM Security Architecture. Compare:
    Internet Protocol Suite.)
    Tutorial: OSIRM-based standards include communication protocols
    that are mostly incompatible with the IPS, but also include
    security models, such as X.509, that are used in the Internet.
    The OSIRM layers, from highest to lowest, are (7) Application, (6)
    Presentation, (5) Session, (4) Transport, (3) Network, (2) Data
    Link, and (1) Physical.
    Usage: This Glossary refers to OSIRM layers by number to avoid
    confusing them with IPS layers, which are referred to by name.
    Some unknown person described how the OSIRM layers correspond to
    the seven deadly sins:
    7. Wrath: Application is always angry with the mess it sees below
       itself. (Hey! Who is it to be pointing fingers?)
    6. Sloth: Presentation is too lazy to do anything productive by
       itself.
    5. Lust: Session is always craving and demanding what truly
       belongs to Application's functionality.
    4. Avarice: Transport wants all of the end-to-end functionality.
       (Of course, it deserves it, but life isn't fair.)
    3. Gluttony: (Connection-Oriented) Network is overweight and
       overbearing after trying too often to eat Transport's lunch.
    2. Envy: Poor Data Link is always starved for attention. (With
       Asynchronous Transfer Mode, maybe now it is feeling less
       neglected.)
    1. Pride: Physical has managed to avoid much of the controversy,
       and nearly all of the embarrassment, suffered by the others.
    John G. Fletcher described how the OSIRM layers correspond to Snow
    White's dwarf friends:
    7. Doc: Application acts as if it is in charge, but sometimes
       muddles its syntax.

Shirey Informational [Page 207] RFC 4949 Internet Security Glossary, Version 2 August 2007

    6. Sleepy: Presentation is indolent, being guilty of the sin of
       Sloth.
    5. Dopey: Session is confused because its charter is not very
       clear.
    4. Grumpy: Transport is irritated because Network has encroached
       on Transport's turf.
    3. Happy: Network smiles for the same reason that Transport is
       irritated.
    2. Sneezy: Data Link makes loud noises in the hope of attracting
       attention.
    1. Bashful: Physical quietly does its work, unnoticed by the
       others.
 $ operational integrity
    (I) Synonym for "system integrity"; this synonym emphasizes the
    actual performance of system functions rather than just the
    ability to perform them.
 $ operational security
    1. (I) System capabilities, or performance of system functions,
    that are needed either (a) to securely manage a system or (b) to
    manage security features of a system. (Compare: operations
    security (OPSEC).)
    Usage: IDOCs that use this term SHOULD state a definition because
    (a) the definition provided here is general and vague and (b) the
    term could easily be confused with "operations security", which is
    a different concept.
    Tutorial: For example, in the context of an Internet service
    provider, the term could refer to capabilities to manage network
    devices in the event of attacks, simplify troubleshooting, keep
    track of events that affect system integrity, help analyze sources
    of attacks, and provide administrators with control over network
    addresses and protocols to help mitigate the most common attacks
    and exploits. [R3871]
    2. (D) Synonym for "administrative security".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "administrative security". Any type of security may affect
    system operations; therefore, the term may be misleading. Instead,
    use "administrative security", "communication security", "computer
    security", "emanations security", "personnel security", "physical
    security", or whatever specific type is meant. (See: security
    architecture. Compare: operational integrity, OPSEC.)

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 $ operations security (OPSEC)
    (I) A process to identify, control, and protect evidence of the
    planning and execution of sensitive activities and operations, and
    thereby prevent potential adversaries from gaining knowledge of
    capabilities and intentions. (See: communications cover. Compare:
    operational security.)
 $ operator
    (I) A person who has been authorized to direct selected functions
    of a system. (Compare: manager, user.)
    Usage: IDOCs that use this term SHOULD state a definition for it
    because a system operator may or may not be treated as a "user".
 $ OPSEC
    1. (I) Abbreviation for "operations security".
    2. (D) Abbreviation for "operational security".
    Deprecated Usage: IDOCs SHOULD NOT use this abbreviation for
    "operational security" (as defined in this Glossary), because its
    use for "operations security" has been well established for many
    years, particular in the military community.
 $ ORA
    See: organizational registration authority.
 $ Orange Book
    (D) /slang/ Synonym for "Trusted Computer System Evaluation
    Criteria" [CSC1, DoD1].
    Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
    "Trusted Computer System Evaluation Criteria" [CSC1, DoD1].
    Instead, use the full, proper name of the document or, in
    subsequent references, the abbreviation "TCSEC". (See: Deprecated
    Usage under "Green Book".)
 $ organizational certificate
    1. (I) An X.509 public-key certificate in which the "subject"
    field contains the name of an institution or set (e.g., a
    business, government, school, labor union, club, ethnic group,
    nationality, system, or group of individuals playing the same
    role), rather than the name of an individual person or device.
    (Compare: persona certificate, role certificate.)
    Tutorial: Such a certificate might be issued for one of the
    following purposes:

Shirey Informational [Page 209] RFC 4949 Internet Security Glossary, Version 2 August 2007

  1. To enable an individual to prove membership in the

organization.

  1. To enable an individual to represent the organization, i.e., to

act in its name and with its powers or permissions.

    2. (O) /MISSI/ A type of MISSI X.509 public-key certificate that
    is issued to support organizational message handling for the U.S.
    DoD's Defense Message System.
 $ organizational registration authority (ORA)
    1. (I) /PKI/ An RA for an organization.
    2. (O) /MISSI/ An end entity that (a) assists a PCA, CA, or SCA to
    register other end entities, by gathering, verifying, and entering
    data and forwarding it to the signing authority and (b) may also
    assist with card management functions. An ORA is a local
    administrative authority, and the term refers both to the role and
    to the person who plays that role. An ORA does not sign
    certificates, CRLs, or CKLs. (See: no-PIN ORA, SSO-PIN ORA, user-
    PIN ORA.)
 $ origin authentication
    (D) Synonym for "data origin authentication". (See:
    authentication, data origin authentication.)
    Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
    careless use of the internationally standardized term "data origin
    authentication" and also could be confused with "peer entity
    authentication."
 $ origin authenticity
    (D) Synonym for "data origin authentication". (See: authenticity,
    data origin authentication.)
    Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
    careless use of the internationally standardized term "data origin
    authentication" and mixes concepts in a potentially misleading
    way.
 $ OSI, OSIRM
    (N) See: Open Systems Interconnection Reference Model.
 $ OSIRM Security Architecture
    (N) The part of the OSIRM [I7498-2] that specifies the security
    services and security mechanisms that can be applied to protect
    communications between two systems. (See: security architecture.)

Shirey Informational [Page 210] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Tutorial: This part of the OSIRM includes an allocation of
    security services to protocol layers. The following table shows
    which security services (see definitions in this Glossary) are
    permitted by the OSIRM in each of its layers. (Also, an
    application process that operates above the Application Layer may
    itself provide security services.) Similarly, the table suggests
    which services are suitable for each IPS layer. However,
    explaining and justifying these allocations is beyond the scope of
    this Glossary.
    Legend for Table Entries:
       O = Yes, [I7498-2] permits the service in this OSIRM layer.
       I = Yes, the service can be incorporated in this IPS layer.
       * = This layer subsumed by Application Layer in IPS.
    IPS Protocol Layers    +-----------------------------------------+
                           |Network| Net |In-| Trans |  Application  |
                           |  H/W  |Inter|ter| -port |               |
                           |       |-face|net|       |               |
    OSIRM Protocol Layers  +-----------------------------------------+
                           |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
    Confidentiality        +-----------------------------------------+
    -  Datagram            | O I | O I | O I | O I |     | O * | O I |
    -  Selective Field     |     |     |   I |     |     | O * | O I |
    -  Traffic Flow        | O   |     | O   |     |     |     | O   |
       -- Full             |   I |     |     |     |     |     |     |
       -- Partial          |     |   I |   I |     |     |     |   I |
    Integrity              +-----------------------------------------+
    -  Datagram            |   I |   I | O I | O I |     |     | O I |
    -  Selective Field     |     |     |   I |     |     |     | O I |
    -  Stream              |     |     | O I | O I |     |     | O I |
    Authentication         +-----------------------------------------+
    -  Peer Entity         |     |   I | O I | O I |     |     | O I |
    -  Data Origin         |     |   I | O I | O I |     |     | O I |
    Access Control         +-----------------------------------------+
    -  type as appropriate |     |   I | O I | O I |     |     | O I |
    Non-Repudiation        +-----------------------------------------+
    -  of Origin           |     |     |     |     |     |     | O I |
    -  of Receipt          |     |     |     |     |     |     | O I |
                           +-----------------------------------------+
 $ OTAR
    (N) See: over-the-air rekeying.
 $ OTP
    (I) See: One-Time Password.

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 $ out-of-band
    (I) /adjective, adverb/ Information transfer using a channel or
    method that is outside (i.e., separate from or different from) the
    main channel or normal method.
    Tutorial: Out-of-band mechanisms are often used to distribute
    shared secrets (e.g., a symmetric key) or other sensitive
    information items (e.g., a root key) that are needed to initialize
    or otherwise enable the operation of cryptography or other
    security mechanisms. Example: Using postal mail to distribute
    printed or magnetic media containing symmetric cryptographic keys
    for use in Internet encryption devices. (See: key distribution.)
 $ output feedback (OFB)
    (N) A block cipher mode that modifies ECB mode to operate on
    plaintext segments of variable length less than or equal to the
    block length. [FP081] (See: block cipher, [SP38A].)
    Tutorial: This mode operates by directly using the algorithm's
    previously generated output block as the algorithm's next input
    block (i.e., by "feeding back" the output block) and combining
    (exclusive OR-ing) the output block with the next plaintext
    segment (of block length or less) to form the next ciphertext
    segment.
 $ outside attack
    (I) See: secondary definition under "attack". Compare: outsider.)
 $ outsider
    (I) A user (usually a person) that accesses a system from a
    position that is outside the system's security perimeter.
    (Compare: authorized user, insider, unauthorized user.)
    Tutorial: The actions performed by an outsider in accessing the
    system may be either authorized or unauthorized; i.e., an outsider
    may act either as an authorized user or as an unauthorized user.
 $ over-the-air rekeying (OTAR)
    (N) Changing a key in a remote cryptographic device by sending a
    new key directly to the device via a channel that the device is
    protecting. [C4009]
 $ overload
    (I) /threat action/ See: secondary definition under "obstruction".
 $ P1363
    (N) See: IEEE P1363.

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 $ PAA
    (O) See: policy approving authority.
 $ package
    (N) /Common Criteria/ A reusable set of either functional or
    assurance components, combined in a single unit to satisfy a set
    of identified security objectives. (Compare: protection profile.)
    Example: The seven EALs defined in Part 3 of the Common Criteria
    are predefined assurance packages.
    Tutorial: A package is a combination of security requirement
    components and is intended to be reusable in the construction of
    either more complex packages or protection profiles and security
    targets. A package expresses a set of either functional or
    assurance requirements that meet some particular need, expressed
    as a set of security objectives.
 $ packet
    (I) A block of data that is carried from a source to a destination
    through a communication channel or, more generally, across a
    network. (Compare: datagram, PDU.)
 $ packet filter
    (I) See: secondary definition under "filtering router".
 $ packet monkey
    (D) /slang/ Someone who floods a system with packets, creating a
    denial-of-service condition for the system's users. (See:
    cracker.)
    Deprecated Term: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
    Usage under "Green Book".)
 $ pagejacking
    (D) /slang/ A contraction of "Web page hijacking". A masquerade
    attack in which the attacker copies (steals) a home page or other
    material from the target server, rehosts the page on a server the
    attacker controls, and causes the rehosted page to be indexed by
    the major Web search services, thereby diverting browsers from the
    target server to the attacker's server.
    Deprecated Term: IDOCs SHOULD NOT use this contraction. The term
    is not listed in most dictionaries and could confuse international
    readers. (See: Deprecated Usage under "Green Book".)

Shirey Informational [Page 213] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ PAN
    (O) See: primary account number.
 $ PAP
    (I) See: Password Authentication Protocol.
 $ parity bit
    (I) A checksum that is computed on a block of bits by computing
    the binary sum of the individual bits in the block and then
    discarding all but the low-order bit of the sum. (See: checksum.)
 $ partitioned security mode
    (N) A mode of system operation wherein all users having access to
    the system have the necessary security clearances for all data
    handled by the system, but some users might not have either formal
    access approval or need-to-know for all the data. (See: /system
    operation/ under "mode", formal access approval, need to know,
    protection level, security clearance.)
    Usage: Usually abbreviated as "partitioned mode". This term was
    defined in U.S. Government policy on system accreditation.
 $ PASS
    (N) See: personnel authentication system string.
 $ passive attack
    (I) See: secondary definition under "attack".
 $ passive user
    (I) See: secondary definition under "system user".
 $ passive wiretapping
    (I) A wiretapping attack that attempts only to observe a
    communication flow and gain knowledge of the data it contains, but
    does not alter or otherwise affect that flow. (See: wiretapping.
    Compare: passive attack, active wiretapping.)
 $ password
    1a. (I) A secret data value, usually a character string, that is
    presented to a system by a user to authenticate the user's
    identity. (See: authentication information, challenge-response,
    PIN, simple authentication.)
    1b. (O) "A character string used to authenticate an identity."
    [CSC2]

Shirey Informational [Page 214] RFC 4949 Internet Security Glossary, Version 2 August 2007

    1c. (O) "A string of characters (letters, numbers, and other
    symbols) used to authenticate an identity or to verify access
    authorization." [FP140]
    1d. (O) "A secret that a claimant memorizes and uses to
    authenticate his or her identity. Passwords are typically
    character strings." [SP63]
    Tutorial: A password is usually paired with a user identifier that
    is explicit in the authentication process, although in some cases
    the identifier may be implicit. A password is usually verified by
    matching it to a stored value held by the access control system
    for that identifier.
    Using a password as authentication information is based on
    assuming that the password is known only by the system entity for
    which the identity is being authenticated. Therefore, in a network
    environment where wiretapping is possible, simple authentication
    that relies on transmission of static (i.e., repetitively used)
    passwords in cleartext form is inadequate. (See: one-time
    password, strong authentication.)
 $ Password Authentication Protocol (PAP)
    (I) A simple authentication mechanism in PPP. In PAP, a user
    identifier and password are transmitted in cleartext form. [R1334]
    (See: CHAP.)
 $ password sniffing
    (D) /slang/ Passive wiretapping to gain knowledge of passwords.
    (See: Deprecated Usage under "sniffing".)
 $ path discovery
    (I) For a digital certificate, the process of finding a set of
    public-key certificates that comprise a certification path from a
    trusted key to that specific certificate.
 $ path validation
    (I) The process of validating (a) all of the digital certificates
    in a certification path and (b) the required relationships between
    those certificates, thus validating the contents of the last
    certificate on the path. (See: certificate validation.)
    Tutorial: To promote interoperable PKI applications in the
    Internet, RFC 3280 specifies a detailed algorithm for validation
    of a certification path.

Shirey Informational [Page 215] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ payment card
    (N) /SET/ Collectively refers "to credit cards, debit cards,
    charge cards, and bank cards issued by a financial institution and
    which reflects a relationship between the cardholder and the
    financial institution." [SET2]
 $ payment gateway
    (O) /SET/ A system operated by an acquirer, or a third party
    designated by an acquirer, to provide electronic commerce services
    to the merchants in support of the acquirer, and which interfaces
    to the acquirer to support the authorization, capture, and
    processing of merchant payment messages, including payment
    instructions from cardholders. [SET1, SET2]
 $ payment gateway certification authority (SET PCA)
    (O) /SET/ A CA that issues digital certificates to payment
    gateways and is operated on behalf of a payment card brand, an
    acquirer, or another party according to brand rules. A SET PCA
    issues a CRL for compromised payment gateway certificates. [SET2]
    (See: PCA.)
 $ PC card
    (N) A type of credit card-sized, plug-in peripheral device that
    was originally developed to provide memory expansion for portable
    computers, but is also used for other kinds of functional
    expansion. (See: FORTEZZA, PCMCIA.)
    Tutorial: The international PC Card Standard defines a non-
    proprietary form factor in three sizes -- Types I, II, and III --
    each of which have a 68-pin interface between the card and the
    socket into which it plugs. All three types have the same length
    and width, roughly the size of a credit card, but differ in their
    thickness from 3.3 to 10.5 mm. Examples include storage modules,
    modems, device interface adapters, and cryptographic modules.
 $ PCA
    (D) Abbreviation of various kinds of "certification authority".
    (See: Internet policy certification authority, (MISSI) policy
    creation authority, (SET) payment gateway certification
    authority.)
    Deprecated Usage: An IDOC that uses this abbreviation SHOULD
    define it at the point of first use.
 $ PCI
    (N) See: "protocol control information" under "protocol data
    unit".

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 $ PCMCIA
    (N) Personal Computer Memory Card International Association, a
    group of manufacturers, developers, and vendors, founded in 1989
    to standardize plug-in peripheral memory cards for personal
    computers and now extended to deal with any technology that works
    in the PC Card form factor. (See: PC card.)
 $ PDS
    (N) See: protective distribution system.
 $ PDU
    (N) See: protocol data unit.
 $ peer entity authentication
    (I) "The corroboration that a peer entity in an association is the
    one claimed." [I7498-2] (See: authentication.)
 $ peer entity authentication service
    (I) A security service that verifies an identity claimed by or for
    a system entity in an association. (See: authentication,
    authentication service.)
    Tutorial: This service is used at the establishment of, or at
    times during, an association to confirm the identity of one entity
    to another, thus protecting against a masquerade by the first
    entity. However, unlike data origin authentication service, this
    service requires an association to exist between the two entities,
    and the corroboration provided by the service is valid only at the
    current time that the service is provided. (See: "relationship
    between data integrity service and authentication services" under
    "data integrity service").
 $ PEM
    (I) See: Privacy Enhanced Mail.
 $ penetrate
    1a. (I) Circumvent a system's security protections. (See: attack,
    break, violation.)
    1b. (I) Successfully and repeatedly gain unauthorized access to a
    protected system resource. [Huff]
 $ penetration
    (I) /threat action/ See: secondary definition under "intrusion".

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 $ penetration test
    (I) A system test, often part of system certification, in which
    evaluators attempt to circumvent the security features of a
    system. [NCS04, SP42] (See: tiger team.)
    Tutorial: Penetration testing evaluates the relative vulnerability
    of a system to attacks and identifies methods of gaining access to
    a system by using tools and techniques that are available to
    adversaries. Testing may be performed under various constraints
    and conditions, including a specified level of knowledge of the
    system design and implementation. For a TCSEC evaluation, testers
    are assumed to have all system design and implementation
    documentation, including source code, manuals, and circuit
    diagrams, and to work under no greater constraints than those
    applied to ordinary users.
 $ perfect forward secrecy
    (I) For a key agreement protocol, the property that compromises
    long-term keying material does not compromise session keys that
    were previously derived from the long-term material. (Compare:
    public-key forward secrecy.)
    Usage: Some existing RFCs use this term but either do not define
    it or do not define it precisely. While preparing this Glossary,
    we found this to be a muddled area. Experts did not agree. For all
    practical purposes, the literature defines "perfect forward
    secrecy" by stating the Diffie-Hellman-Merkle algorithm. The term
    "public-key forward secrecy" (suggested by Hilarie Orman) and the
    definition stated for it in this Glossary were crafted to be
    compatible with current Internet documents, yet be narrow and
    leave room for improved terminology.
    Challenge to the Internet security community: We need a taxonomy
    of terms and definitions to cover the basic properties discussed
    here for the full range of cryptographic algorithms and protocols
    used in Internet Standards:
    Involvement of session keys vs. long-term keys: Experts disagree
    about the basic ideas involved:
    -  One concept of "forward secrecy" is that, given observations of
       the operation of a key establishment protocol up to time t, and
       given some of the session keys derived from those protocol
       runs, you cannot derive unknown past session keys or future
       session keys.
    -  A related property is that, given observations of the protocol
       and knowledge of the derived session keys, you cannot derive
       one or more of the long-term private keys.

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  1. The "I" definition presented above involves a third concept of

"forward secrecy" that refers to the effect of the compromise

       of long-term keys.
    -  All three concepts involve the idea that a compromise of "this"
       encryption key is not supposed to compromise the "next" one.
       There also is the idea that compromise of a single key will
       compromise only the data protected by the single key. In
       Internet literature, the focus has been on protection against
       decryption of back traffic in the event of a compromise of
       secret key material held by one or both parties to a
       communication.
    Forward vs. backward: Experts are unhappy with the word "forward",
    because compromise of "this" encryption key also is not supposed
    to compromise the "previous" one, which is "backward" rather than
    forward. In S/KEY, if the key used at time t is compromised, then
    all keys used prior to that are compromised. If the "long-term"
    key (i.e., the base of the hashing scheme) is compromised, then
    all keys past and future are compromised; thus, you could say that
    S/KEY has neither forward nor backward secrecy.
    Asymmetric cryptography vs. symmetric: Experts disagree about
    forward secrecy in the context of symmetric cryptographic systems.
    In the absence of asymmetric cryptography, compromise of any long-
    term key seems to compromise any session key derived from the
    long-term key. For example, Kerberos isn't forward secret, because
    compromising a client's password (thus compromising the key shared
    by the client and the authentication server) compromises future
    session keys shared by the client and the ticket-granting server.
    Ordinary forward secrecy vs. "perfect" forward secret: Experts
    disagree about the difference between these two. Some say there is
    no difference, and some say that the initial naming was
    unfortunate and suggest dropping the word "perfect". Some suggest
    using "forward secrecy" for the case where one long-term private
    key is compromised, and adding "perfect" for when both private
    keys (or, when the protocol is multi-party, all private keys) are
    compromised.
    Acknowledgements: Bill Burr, Burt Kaliski, Steve Kent, Paul Van
    Oorschot, Jonathan Trostle, Michael Wiener, and, especially,
    Hilarie Orman contributed ideas to this discussion.
 $ perimeter
    See: security perimeter.

Shirey Informational [Page 219] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ periods processing
    (I) A mode of system operation in which information of different
    sensitivities is processed at distinctly different times by the
    same system, with the system being properly purged or sanitized
    between periods. (See: color change.)
    Tutorial: The security mode of operation and maximum
    classification of data handled by the system is established for an
    interval of time and then is changed for the following interval of
    time. A period extends from the secure initialization of the
    system to the completion of any purging of sensitive data handled
    by the system during the period.
 $ permanent storage
    (I) Non-volatile media that, once written into, can never be
    completely erased.
 $ permission
    1a. (I) Synonym for "authorization". (Compare: privilege.)
    1b. (N) An authorization or set of authorizations to perform
    security-relevant functions in the context of role-based access
    control. [ANSI]
    Tutorial: A permission is a positively stated authorization for
    access that (a) can be associated with one or more roles and (b)
    enables a user in a role to access a specified set of system
    resources by causing a specific set of system actions to be
    performed on the resources.
 $ persona certificate
    (I) An X.509 certificate issued to a system entity that wishes to
    use a persona to conceal its true identity when using PEM or other
    Internet services that depend on PKI support. (See: anonymity.)
    [R1422]
    Tutorial: PEM designers intended that (a) a CA issuing persona
    certificates would explicitly not be vouching for the identity of
    the system entity to whom the certificate is issued, (b) such
    certificates would be issued only by CAs subordinate to a policy
    CA having a policy stating that purpose (i.e., that would warn
    relying parties that the "subject" field DN represented only a
    persona and not a true, vetted user identity), and (c) the CA
    would not need to maintain records binding the true identity of
    the subject to the certificate.

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    However, the PEM designers also intended that a CA issuing persona
    certificates would establish procedures (d) to enable "the holder
    of a PERSONA certificate to request that his certificate be
    revoked" and (e) to ensure that it did not issue the same subject
    DN to multiple users. The latter condition implies that a persona
    certificate is not an organizational certificate unless the
    organization has just one member or representative.
 $ personal identification number (PIN)
    1a. (I) A character string used as a password to gain access to a
    system resource. (See: authentication information.)
    Example: A cryptographic token typically requires its user to
    enter a PIN in order to access information stored in the token and
    invoke the token's cryptographic functions.
    1b. (O) An alphanumeric code or password used to authenticate an
    identity.
    Tutorial: Despite the words "identification" and "number", a PIN
    seldom serves as a user identifier, and a PIN's characters are not
    necessarily all numeric. Retail banking applications use 4-digit
    numeric user PINs, but the FORTEZZA PC card uses 12-character
    alphanumeric SSO PINs. (See: SSO PIN, user PIN.)
    A better name for this concept would have been "personnel
    authentication system string" (PASS), in which case, an
    alphanumeric character string for this purpose would have been
    called, obviously, a "PASSword".
 $ personal information
    (I) Information about a particular person, especially information
    of an intimate or critical nature, that could cause harm or pain
    to that person if disclosed to unauthorized parties. Examples:
    medical record, arrest record, credit report, academic transcript,
    training report, job application, credit card number, Social
    Security number. (See: privacy.)
 $ personality
    1. (I) Synonym for "principal".
    2. (O) /MISSI/ A set of MISSI X.509 public-key certificates that
    have the same subject DN, together with their associated private
    keys and usage specifications, that is stored on a FORTEZZA PC
    card to support a role played by the card's user.
    Tutorial: When a card's user selects a personality to use in a
    FORTEZZA-aware application, the data determines behavior traits

Shirey Informational [Page 221] RFC 4949 Internet Security Glossary, Version 2 August 2007

    (the personality) of the application. A card's user may have
    multiple personalities on the card. Each has a "personality
    label", a user-friendly character string that applications can
    display to the user for selecting or changing the personality to
    be used. For example, a military user's card might contain three
    personalities: GENERAL HALFTRACK, COMMANDER FORT SWAMPY, and NEW
    YEAR'S EVE PARTY CHAIRMAN. Each personality includes one or more
    certificates of different types (such as DSA versus RSA), for
    different purposes (such as digital signature versus encryption),
    or with different authorizations.
 $ personnel authentication system string (PASS)
    (N) See: Tutorial under "personal identification number".
 $ personnel security
    (I) Procedures to ensure that persons who access a system have
    proper clearance, authorization, and need-to-know as required by
    the system's security policy. (See: security architecture.)
 $ PGP(trademark)
    (O) See: Pretty Good Privacy(trademark).
 $ phase 1 negotiation
 $ phase 2 negotiation
    (I) /ISAKMP/ See: secondary definition under "Internet Security
    Association and Key Management Protocol".
 $ phishing
    (D) /slang/ A technique for attempting to acquire sensitive data,
    such as bank account numbers, through a fraudulent solicitation in
    email or on a Web site, in which the perpetrator masquerades as a
    legitimate business or reputable person. (See: social
    engineering.)
    Derivation: Possibly from "phony fishing"; the solicitation
    usually involves some kind of lure or bait to hook unwary
    recipients. (Compare: phreaking.)
    Deprecated Term: IDOCs SHOULD NOT use this term; it is not listed
    in most dictionaries and could confuse international readers.
    (See: Deprecated Usage under "Green Book".)
 $ Photuris
    (I) A UDP-based, key establishment protocol for session keys,
    designed for use with the IPsec protocols AH and ESP. Superseded
    by IKE.

Shirey Informational [Page 222] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ phreaking
    (D) A contraction of "telephone breaking". An attack on or
    penetration of a telephone system or, by extension, any other
    communication or information system. [Raym]
    Deprecated Term: IDOCs SHOULD NOT use this contraction; it is not
    listed in most dictionaries and could confuse international
    readers. (See: Deprecated Usage under "Green Book".)
 $ physical destruction
    (I) /threat action/ See: secondary definition under
    "incapacitation".
 $ physical security
    (I) Tangible means of preventing unauthorized physical access to a
    system. Examples: Fences, walls, and other barriers; locks, safes,
    and vaults; dogs and armed guards; sensors and alarm bells.
    [FP031, R1455] (See: security architecture.)
 $ piggyback attack
    (I) A form of active wiretapping in which the attacker gains
    access to a system via intervals of inactivity in another user's
    legitimate communication connection. Sometimes called a "between-
    the-lines" attack. (See: hijack attack, man-in-the-middle attack.)
    Deprecated Usage: IDOCs that use this term SHOULD state a
    definition for it because the term could confuse international
    readers.
 $ PIN
    (I) See: personal identification number.
 $ ping of death
    (D) A denial-of-service attack that sends an improperly large ICMP
    echo request packet (a "ping") with the intent of causing the
    destination system to fail. (See: ping sweep, teardrop.)
    Deprecated Term: IDOCs SHOULD NOT use this term; instead, use
    "ping packet overflow attack" or some other term that is specific
    with regard to the attack mechanism.
    Tutorial: This attack seeks to exploit an implementation
    vulnerability. The IP specification requires hosts to be prepared
    to accept datagrams of up to 576 octets, but also permits IP
    datagrams to be up to 65,535 octets long. If an IP implementation
    does not properly handle very long IP packets, the ping packet may
    overflow the input buffer and cause a fatal system error.

Shirey Informational [Page 223] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ ping sweep
    (I) An attack that sends ICMP echo requests ("pings") to a range
    of IP addresses, with the goal of finding hosts that can be probed
    for vulnerabilities. (See: ping of death. Compare: port scan.)
 $ PKCS
    (N) See: Public-Key Cryptography Standards.
 $ PKCS #5
    (N) A standard [PKC05] (see: RFC 2898) from the PKCS series;
    defines a method for encrypting an octet string with a secret key
    derived from a password.
    Tutorial: Although the method can be used for arbitrary octet
    strings, its intended primary application in public-key
    cryptography is for encrypting private keys when transferring them
    from one computer system to another, as described in PKCS #8.
 $ PKCS #7
    (N) A standard [PKC07] (see: RFC 2315) from the PKCS series;
    defines a syntax for data that may have cryptography applied to
    it, such as for digital signatures and digital envelopes. (See:
    CMS.)
 $ PKCS #10
    (N) A standard [PKC10] (see: RFC 2986) from the PKCS series;
    defines a syntax for certification requests. (See: certification
    request.)
    Tutorial: A PKCS #10 request contains a DN and a public key, and
    may contain other attributes, and is signed by the entity making
    the request. The request is sent to a CA, who converts it to an
    X.509 public-key certificate (or some other form), and returns it,
    possibly in PKCS #7 format.
 $ PKCS #11
    (N) A standard [PKC11] from the PKCS series; defines CAPI called
    "Cryptoki" for devices that hold cryptographic information and
    perform cryptographic functions.
 $ PKI
    (I) See: public-key infrastructure.
 $ PKINIT
    (I) Abbreviation for "Public Key Cryptography for Initial
    Authentication in Kerberos" (RFC 4556). (See: Tutorial under
    "Kerberos".)

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 $ PKIX
    1a. (I) A contraction of "Public-Key Infrastructure (X.509)", the
    name of the IETF working group that is specifying an architecture
    [R3280] and set of protocols [R4210] to provide X.509-based PKI
    services for the Internet.
    1b. (I) A collective name for that Internet PKI architecture and
    associated set of protocols.
    Tutorial: The goal of PKIX is to facilitate the use of X.509
    public-key certificates in multiple Internet applications and to
    promote interoperability between different implementations that
    use those certificates. The resulting PKI is intended to provide a
    framework that supports a range of trust and hierarchy
    environments and a range of usage environments. PKIX specifies (a)
    profiles of the v3 X.509 public-key certificate standards and the
    v2 X.509 CRL standards for the Internet, (b) operational protocols
    used by relying parties to obtain information such as certificates
    or certificate status, (c) management protocols used by system
    entities to exchange information needed for proper management of
    the PKI, and (d) information about certificate policies and CPSs,
    covering the areas of PKI security not directly addressed in the
    rest of PKIX.
 $ plain text
    1. (I) /noun/ Data that is input to an encryption process. (See:
    plaintext. Compare: cipher text, clear text.)
    2. (D) /noun/ Synonym for "clear text".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "clear text". Sometimes plain text that is input to an
    encryption operation is clear text, but other times plain text is
    cipher text that was output from a previous encryption operation.
    (See: superencryption.)
 $ plaintext
    1. (O) /noun/ Synonym for "plain text".
    2. (I) /adjective/ Referring to plain text. Usage: Commonly used
    instead of "plain-text". (Compare: ciphertext, cleartext.)
    3. (D) /noun/ Synonym for "cleartext".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "cleartext". Cleartext data is, by definition, not encrypted;
    but plaintext data that is input to an encryption operation may be

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    cleartext data or may be ciphertext data that was output from a
    previous encryption operation. (See: superencryption.)
 $ PLI
    (I) See: Private Line Interface.
 $ PMA
    (N) See: policy management authority.
 $ Point-to-Point Protocol (PPP)
    (I) An Internet Standard protocol (RFC 1661) for encapsulation and
    full-duplex transportation of protocol data packets in OSIRM Layer
    3 over an OSIRM Layer 2 link between two peers, and for
    multiplexing different Layer 3 protocols over the same link.
    Includes optional negotiation to select and use a peer entity
    authentication protocol to authenticate the peers to each other
    before they exchange Layer 3 data. (See: CHAP, EAP, PAP.)
 $ Point-to-Point Tunneling Protocol (PPTP)
    (I) An Internet client-server protocol (RFC 2637) (originally
    developed by Ascend and Microsoft) that enables a dial-up user to
    create a virtual extension of the dial-up link across a network by
    tunneling PPP over IP. (See: L2TP.)
    Tutorial: PPP can encapsulate any IPS Network Interface Layer
    protocol or OSIRM Layer 3 protocol. Therefore, PPTP does not
    specify security services; it depends on protocols above and below
    it to provide any needed security. PPTP makes it possible to
    divorce the location of the initial dial-up server (i.e., the PPTP
    Access Concentrator, the client, which runs on a special-purpose
    host) from the location at which the dial-up protocol (PPP)
    connection is terminated and access to the network is provided
    (i.e., at the PPTP Network Server, which runs on a general-purpose
    host).
 $ policy
    1a. (I) A plan or course of action that is stated for a system or
    organization and is intended to affect and direct the decisions
    and deeds of that entity's components or members. (See: security
    policy.)
    1b. (O) A definite goal, course, or method of action to guide and
    determine present and future decisions, that is implemented or
    executed within a particular context, such as within a business
    unit. [R3198]
    Deprecated Abbreviation: IDOCs SHOULD NOT use "policy" as an
    abbreviation of either "security policy" or "certificate policy".

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    Instead, to avoid misunderstanding, use a fully qualified term, at
    least at the point of first usage.
    Tutorial: The introduction of new technology to replace
    traditional systems can result in new systems being deployed
    without adequate policy definition and before the implications of
    the new technology are fully understand. In some cases, it can be
    difficult to establish policies for new technology before the
    technology has been operationally tested and evaluated. Thus,
    policy changes tend to lag behind technological changes, such that
    either old policies impede the technical innovation, or the new
    technology is deployed without adequate policies to govern its
    use.
    When new technology changes the ways that things are done, new
    "procedures" must be defined to establish operational guidelines
    for using the technology and achieving satisfactory results, and
    new "practices" must be established for managing new systems and
    monitoring results. Practices and procedures are more directly
    coupled to actual systems and business operations than are
    polices, which tend to be more abstract.
    -  "Practices" define how a system is to be managed and what
       controls are in place to monitor the system and detect abnormal
       behavior or quality problems. Practices are established to
       ensure that a system is managed in compliance with stated
       policies. System audits are primarily concerned with whether or
       not practices are being followed. Auditors evaluate the
       controls to make sure they conform to accepted industry
       standards, and then confirm that controls are in place and that
       control measurements are being gathered. Audit trails are
       examples of control measurements that are recorded as part of
       system operations.
    -  "Procedures" define how a system is operated, and relate
       closely to issues of what technology is used, who the operators
       are, and how the system is deployed physically. Procedures
       define both normal and abnormal operating circumstances.
    -  For every control defined by a practice statement, there should
       be corresponding procedures to implement the control and
       provide ongoing measurement of the control parameters.
       Conversely, procedures require management practices to insure
       consistent and correct operational behavior.
 $ policy approval authority
    (D) /PKI/ Synonym for "policy management authority". [PAG]
    Deprecated Term: IDOCs SHOULD NOT use this term as synonym for
    "policy management authority". The term suggests a limited,
    passive role that is not typical of PMAs.

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 $ policy approving authority (PAA)
    (O) /MISSI/ The top-level signing authority of a MISSI
    certification hierarchy. The term refers both to that
    authoritative office or role and to the person who plays that
    role. (See: policy management authority, root registry.)
    Tutorial: A MISSI PAA (a) registers MISSI PCAs and signs their
    X.509 public-key certificates, (b) issues CRLs but does not issue
    a CKL, and (c) may issue cross-certificates to other PAAs.
 $ policy authority
    (D) /PKI/ Synonym for "policy management authority". [PAG]
    Deprecated Term: IDOCs SHOULD NOT use this term as synonym for
    "policy management authority". The term is unnecessarily vague and
    thus may be confused with other PKI entities, such as CAs and RAs,
    that enforce of apply various aspects of PKI policy.
 $ policy certification authority (Internet PCA)
    (I) An X.509-compliant CA at the second level of the Internet
    certification hierarchy, under the IPRA. Each PCA operates under
    its published security policy (see: certificate policy, CPS) and
    within constraints established by the IPRA for all PCAs. [R1422].
    (See: policy creation authority.)
 $ policy creation authority (MISSI PCA)
    (O) /MISSI/ The second level of a MISSI certification hierarchy;
    the administrative root of a security policy domain of MISSI users
    and other, subsidiary authorities. The term refers both to that
    authoritative office or role and to the person who fills that
    office. (See: policy certification authority.)
    Tutorial: A MISSI PCA's certificate is issued by a PAA. The PCA
    registers the CAs in its domain, defines their configurations, and
    issues their X.509 public-key certificates. (The PCA may also
    issue certificates for SCAs, ORAs, and other end entities, but a
    PCA does not usually do this.) The PCA periodically issues CRLs
    and CKLs for its domain.
 $ policy management authority (PMA)
    (I) /PKI/ A person, role, or organization within a PKI that is
    responsible for (a) creating or approving the content of the
    certificate policies and CPSs that are used in the PKI; (b)
    ensuring the administration of those policies; and (c) approving
    any cross-certification or interoperability agreements with CAs
    external to the PKI and any related policy mappings. The PMA may
    also be the accreditor for the PKI as a whole or for some of its

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    components or applications. [DoD9, PAG] (See: policy approving
    authority.)
    Example: In the U.S. Department of Defense, an organization called
    the Policy Management Authority is responsible for DoD PKI [DoD9].
 $ policy mapping
    (I) "Recognizing that, when a CA in one domain certifies a CA in
    another domain, a particular certificate policy in the second
    domain may be considered by the authority of the first domain to
    be equivalent (but not necessarily identical in all respects) to a
    particular certificate policy in the first domain." [X509]
 $ policy rule
    (I) A building block of a security policy; it (a) defines a set of
    system conditions and (b) specifies a set of system actions that
    are to be performed if those conditions occur. [R3198]
 $ POP3
    (I) See: Post Office Protocol, version 3.
 $ POP3 APOP
    (I) A POP3 command (better described as a transaction type, or
    subprotocol) by which a POP3 client optionally uses a keyed hash
    (based on MD5) to authenticate itself to a POP3 server and,
    depending on the server implementation, to protect against replay
    attacks. (See: CRAM, POP3 AUTH, IMAP4 AUTHENTICATE.)
    Tutorial: The server includes a unique time stamp in its greeting
    to the client. The subsequent APOP command sent by the client to
    the server contains the client's name and the hash result of
    applying MD5 to a string formed from both the time stamp and a
    shared secret value that is known only to the client and the
    server. APOP was designed to provide an alternative to using
    POP3's USER and PASS (i.e., password) command pair, in which the
    client sends a cleartext password to the server.
 $ POP3 AUTH
    (I) A POP3 command [R1734] (better described as a transaction
    type, or subprotocol) by which a POP3 client optionally proposes a
    mechanism to a POP3 server to authenticate the client to the
    server and provide other security services. (See: POP3 APOP, IMAP4
    AUTHENTICATE.)
    Tutorial: If the server accepts the proposal, the command is
    followed by performing a challenge-response authentication
    protocol and, optionally, negotiating a protection mechanism for

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    subsequent POP3 interactions. The security mechanisms used by POP3
    AUTH are those used by IMAP4.
 $ port scan
    (I) A technique that sends client requests to a range of service
    port addresses on a host. (See: probe. Compare: ping sweep.)
    Tutorial: A port scan can be used for pre-attack surveillance,
    with the goal of finding an active port and subsequently
    exploiting a known vulnerability of that port's service. A port
    scan can also be used as a flooding attack.
 $ positive authorization
    (I) The principle that a security architecture should be designed
    so that access to system resources is permitted only when
    explicitly granted; i.e., in the absence of an explicit
    authorization that grants access, the default action shall be to
    refuse access. (See: authorization, access.)
 $ POSIX
    (N) Portable Operating System Interface for Computer Environments,
    a standard [FP151, I9945] (originally IEEE Standard P1003.1) that
    defines an operating system interface and environment to support
    application portability at the source code level. It is intended
    to be used by both application developers and system implementers.
    Tutorial: P1003.1 supports security functionality like that on
    most UNIX systems, including discretionary access control and
    privileges. IEEE Draft Standard P1003.6 specifies additional
    functionality not provided in the base standard, including (a)
    discretionary access control, (b) audit trail mechanisms, (c)
    privilege mechanisms, (d) mandatory access control, and (e)
    information label mechanisms.
 $ Post Office Protocol, version 3 (POP3)
    (I) An Internet Standard protocol (RFC 1939) by which a client
    workstation can dynamically access a mailbox on a server host to
    retrieve mail messages that the server has received and is holding
    for the client. (See: IMAP4.)
    Tutorial: POP3 has mechanisms for optionally authenticating a
    client to a server and providing other security services. (See:
    POP3 APOP, POP3 AUTH.)
 $ PPP
    (I) See: Point-to-Point Protocol.

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 $ PPTP
    (I) See: Point-to-Point Tunneling Protocol.
 $ preauthorization
    (N) /PKI/ A CAW feature that enables certification requests to be
    automatically validated against data provided in advance to the CA
    by an authorizing entity.
 $ precedence
    1. (I) /information system/ A ranking assigned to events or data
    objects that determines the relative order in which they are
    processed.
    2. (N) /communication system/ A designation assigned to a
    communication (i.e., packet, message, data stream, connection,
    etc.) by the originator to state the importance or urgency of that
    communication versus other communications, and thus indicate to
    the transmission system the relative order of handling, and
    indicate to the receiver the order in which the communication is
    to be noted. [F1037] (See: availability, critical, preemption.)
    Example: The "Precedence" subfield of the "Type of Service" field
    of the IPv4 header supports the following designations (in
    descending order of importance): 111 Network Control, 110
    Internetwork Control, 101 CRITIC/ECP (Critical Intelligence
    Communication/Emergency Command Precedence), 100 Flash Override,
    011 Flash, 010 Immediate, 001 Priority, and 000 Routine. These
    designations were adopted from U.S. DoD systems that existed
    before ARPANET.
 $ preemption
    (N) The seizure, usually automatic, of system resources that are
    being used to serve a lower-precedence communication, in order to
    serve immediately a higher-precedence communication. [F1037]
 $ Pretty Good Privacy(trademark) (PGP(trademark))
    (O) Trademarks of Network Associates, Inc., referring to a
    computer program (and related protocols) that uses cryptography to
    provide data security for electronic mail and other applications
    on the Internet. (Compare: DKIM, MOSS, MSP, PEM, S/MIME.)
    Tutorial: PGP encrypts messages with a symmetric algorithm
    (originally, IDEA in CFB mode), distributes the symmetric keys by
    encrypting them with an asymmetric algorithm (originally, RSA),
    and creates digital signatures on messages with a cryptographic
    hash and an asymmetric encryption algorithm (originally, MD5 and
    RSA). To establish ownership of public keys, PGP depends on the
    "web of trust".

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 $ prevention
    (I) See: secondary definition under "security".
 $ primary account number (PAN)
    (O) /SET/ "The assigned number that identifies the card issuer and
    cardholder. This account number is composed of an issuer
    identification number, an individual account number
    identification, and an accompanying check digit as defined by ISO
    7812-1985." [SET2, I7812] (See: bank identification number.)
    Tutorial: The PAN is embossed, encoded, or both on a magnetic-
    strip-based credit card. The PAN identifies the issuer to which a
    transaction is to be routed and the account to which it is to be
    applied unless specific instructions indicate otherwise. The
    authority that assigns the BIN part of the PAN is the American
    Bankers Association.
 $ principal
    (I) A specific identity claimed by a user when accessing a system.
    Usage: Usually understood to be an identity that is registered in
    and authenticated by the system; equivalent to the notion of login
    account identifier. Each principal is normally assigned to a
    single user, but a single user may be assigned (or attempt to use)
    more than one principal. Each principal can spawn one or more
    subjects, but each subject is associated with only one principal.
    (Compare: role, subject, user.)
    (I) /Kerberos/ A uniquely identified (i.e., uniquely named) client
    or server instance that participates in a network communication.
 $ priority
    (I) /information system/ Precedence for processing an event or
    data object, determined by security importance or other factors.
    (See: precedence.)
 $ privacy
    1. (I) The right of an entity (normally a person), acting in its
    own behalf, to determine the degree to which it will interact with
    its environment, including the degree to which the entity is
    willing to share its personal information with others. (See:
    HIPAA, personal information, Privacy Act of 1974. Compare:
    anonymity, data confidentiality.) [FP041]
    2. (O) "The right of individuals to control or influence what
    information related to them may be collected and stored and by
    whom and to whom that information may be disclosed." [I7498-2]

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    3. (D) Synonym for "data confidentiality".
    Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
    for "data confidentiality" or "data confidentiality service",
    which are different concepts. Privacy is a reason for security
    rather than a kind of security. For example, a system that stores
    personal data needs to protect the data to prevent harm,
    embarrassment, inconvenience, or unfairness to any person about
    whom data is maintained, and to protect the person's privacy. For
    that reason, the system may need to provide data confidentiality
    service.
    Tutorial: The term "privacy" is used for various separate but
    related concepts, including bodily privacy, territorial privacy,
    personal information privacy, and communication privacy. IDOCs are
    expected to address only communication privacy, which in this
    Glossary is defined primarily by "data confidentiality" and
    secondarily by "data integrity".
    IDOCs are not expected to address information privacy, but this
    Glossary provides definition 1 for that concept because personal
    information privacy is often confused with communication privacy.
    IDOCs are not expected to address bodily privacy or territorial
    privacy, and this Glossary does not define those concepts because
    they are not easily confused with communication privacy.
 $ Privacy Act of 1974
    (O) A U.S. Federal law (Section 552a of Title 5, United States
    Code) that seeks to balance the U.S. Government's need to maintain
    data about individuals with the rights of individuals to be
    protected against unwarranted invasions of their privacy stemming
    from federal agencies' collection, maintenance, use, and
    disclosure of personal data. (See: privacy.)
    Tutorial: In 1974, the U.S. Congress was concerned with the
    potential for abuses that could arise from the Government's
    increasing use of computers to store and retrieve personal data.
    Therefore, the Act has four basic policy objectives:
    -  To restrict disclosure of personally identifiable records
       maintained by Federal agencies.
    -  To grant individuals increased rights of access to Federal
       agency records maintained on themselves.
    -  To grant individuals the right to seek amendment of agency
       records maintained on themselves upon a showing that the
       records are not accurate, relevant, timely, or complete.
    -  To establish a code of "fair information practices" that
       requires agencies to comply with statutory norms for
       collection, maintenance, and dissemination of records.

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 $ Privacy Enhanced Mail (PEM)
    (I) An Internet protocol to provide data confidentiality, data
    integrity, and data origin authentication for electronic mail.
    [R1421, R1422]. (Compare: DKIM, MOSS, MSP, PGP, S/MIME.)
    Tutorial: PEM encrypts messages with a symmetric algorithm
    (originally, DES in CBC mode), provides distribution for the
    symmetric keys by encrypting them with an asymmetric algorithm
    (originally, RSA), and signs messages with an asymmetric
    encryption algorithm over a cryptographic hash (originally, RSA
    over either MD2 or MD5). To establish ownership of public keys,
    PEM uses a certification hierarchy, with X.509 public-key
    certificates and X.509 CRLs that are signed with an asymmetric
    encryption algorithm over a cryptographic hash (originally, RSA
    over MD2).
    PEM is designed to be compatible with a wide range of key
    management methods, but is limited to specifying security services
    only for text messages and, like MOSS, has not been widely
    implemented in the Internet.
 $ private component
    (I) Synonym for "private key".
    Deprecated Usage: In most cases, IDOCs SHOULD NOT use this term;
    instead, to avoid confusing readers, use "private key". However,
    the term MAY be used when discussing a key pair; e.g., "A key pair
    has a public component and a private component."
 $ private extension
    (I) See: secondary definition under "extension".
 $ private key
    1. (I) The secret component of a pair of cryptographic keys used
    for asymmetric cryptography. (See: key pair, public key, secret
    key.)
    2. (O) In a public key cryptosystem, "that key of a user's key
    pair which is known only by that user." [X509]
 $ Private Line Interface (PLI)
    (I) The first end-to-end packet encryption system for a computer
    network, developed by BBN starting in 1975 for the U.S. DoD,
    incorporating U.S. Government-furnished, military-grade COMSEC
    equipment (TSEC/KG-34). [B1822] (Compare: IPLI.)

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 $ privilege
    1a. (I) /access control/ A synonym for "authorization". (See
    authorization. Compare: permission.)
    1b. (I) /computer platform/ An authorization to perform a
    security-relevant function in the context of a computer's
    operating system.
 $ privilege management infrastructure
    (O) "The infrastructure able to support the management of
    privileges in support of a comprehensive authorization service and
    in relationship with a" PKI; i.e., processes concerned with
    attribute certificates. [X509]
    Deprecated Usage: IDOCs SHOULD NOT use this term with this
    definition. This definition is vague, and there is no consensus on
    a more specific one.
 $ privileged process
    (I) A computer process that is authorized (and, therefore,
    trusted) to perform some security-relevant functions that ordinary
    processes are not. (See: privilege, trusted process.)
 $ privileged user
    (I) An user that has access to system control, monitoring, or
    administration functions. (See: privilege, /UNIX/ under "root",
    superuser, user.)
    Tutorial: Privileged users include the following types:
    -  Users with near or complete control of a system, who are
       authorized to set up and administer user accounts, identifiers,
       and authentication information, or are authorized to assign or
       change other users' access to system resources.
    -  Users that are authorized to change control parameters (e.g.,
       network addresses, routing tables, processing priorities) on
       routers, multiplexers, and other important equipment.
    -  Users that are authorized to monitor or perform troubleshooting
       for a system's security functions, typically using special
       tools and features that are not available to ordinary users.
 $ probe
    (I) /verb/ A technique that attempts to access a system to learn
    something about the system. (See: port scan.)
    Tutorial: The purpose of a probe may be offensive, e.g., an
    attempt to gather information for circumventing the system's
    protections; or the purpose may be defensive, e.g., to verify that
    the system is working properly.

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 $ procedural security
    (D) Synonym for "administrative security".
    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    "administrative security". The term may be misleading because any
    type of security may involve procedures, and procedures may be
    either external to the system or internal. Instead, use
    "administrative security", "communication security", "computer
    security", "emanations security", "personnel security", "physical
    security", or whatever specific type is meant. (See: security
    architecture.)
 $ profile
    See: certificate profile, protection profile.
 $ proof-of-possession protocol
    (I) A protocol whereby a system entity proves to another that it
    possesses and controls a cryptographic key or other secret
    information. (See: zero-knowledge proof.)
 $ proprietary
    (I) Refers to information (or other property) that is owned by an
    individual or organization and for which the use is restricted by
    that entity.
 $ protected checksum
    (I) A checksum that is computed for a data object by means that
    protect against active attacks that would attempt to change the
    checksum to make it match changes made to the data object. (See:
    digital signature, keyed hash, Tutorial under "checksum".)
 $ protective packaging
    (N) "Packaging techniques for COMSEC material that discourage
    penetration, reveal a penetration has occurred or was attempted,
    or inhibit viewing or copying of keying material prior to the time
    it is exposed for use." [C4009] (See: tamper-evident, tamper-
    resistant. Compare: QUADRANT.)
 $ protection authority
    (I) See: secondary definition under "Internet Protocol Security
    Option".
 $ protection level
    (N) /U.S. Government/ An indication of the trust that is needed in
    a system's technical ability to enforce security policy for
    confidentiality. (Compare: /system operation/ under "mode of
    operation".)

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    Tutorial: An organization's security policy could define
    protection levels that are based on comparing (a) the sensitivity
    of information handled by a system to (b) the authorizations of
    users that receive information from the system without manual
    intervention and reliable human review. For each level, the policy
    could specify security features and assurances that must be
    included in any system that was intended to operate at that level.
    Example: Given some set of data objects that are classified at one
    or more hierarchical levels and in one or more non-hierarchical
    categories, the following table defines five protection levels for
    systems that would handle that data. Beginning with PL1 and
    evolving to PL5, each successive level would require stronger
    features and assurances to handle the dataset. (See: clearance,
    formal access approval, and need-to-know.)
           Lowest Clearance      Formal Access       Need-To-Know
            Among All Users    Approval of Users      of Users
         +-------------------+-------------------+-------------------+
    PL5  | Some user has no  | [Does not matter.]| [Does not matter.]|
    High | clearance at all. |                   |                   |
         +-------------------+-------------------+-------------------+
    PL4  | All are cleared   | [Does not matter.]| [Does not matter.]|
         | for some data.    |                   |                   |
         +-------------------+-------------------+-------------------+
    PL3  | All are cleared   | Some not approved | [Does not matter.]|
         | for all data.     | for all data.     |                   |
         +-------------------+-------------------+-------------------+
    PL2  | All are cleared   | All are approved  | Some don't need to|
         | for all data.     | for all data.     | to know all data. |
         +-------------------+-------------------+-------------------+
    PL1  | All are cleared   | All are approved  | All have a need   |
    Low  | for all data.     | for all data.     | to know all data. |
         +-------------------+-------------------+-------------------+
 Each of these protection levels can be viewed as being equivalent to
 one or more modes of system operation defined in this Glossary:
 -  PL5 is equivalent to multilevel security mode.
 -  PL4 is equivalent to either multilevel or compartmented
    security mode, depending on the details of users' clearances.
 -  PL3 is equivalent to partitioned security mode.
 -  PL2 is equivalent to system-high security mode.
 -  PL1 is equivalent to dedicated security mode.
 $ protection profile
    (N) /Common Criteria/ An implementation-independent set of
    security requirements for a category of targets of evaluation that

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    meet specific consumer needs. [CCIB] Example: [IDSAN]. (See:
    target of evaluation. Compare: certificate profile, package.)
    Tutorial: A protection profile (PP) is the kind of document used
    by consumers to specify functional requirements they want in a
    product, and a security target (ST) is the kind of document used
    by vendors to make functional claims about a product.
    A PP is intended to be a reusable statement of product security
    needs, which are known to be useful and effective, for a set of
    information technology security products that could be built. A PP
    contains a set of security requirements, preferably taken from the
    catalogs in Parts 2 and 3 of the Common Criteria, and should
    include an EAL. A PP could be developed by user communities,
    product developers, or any other parties interested in defining a
    common set of requirements.
 $ protection ring
    (I) One of a hierarchy of privileged operation modes of a system
    that gives certain access rights to processes authorized to
    operate in that mode. (See: Multics.)
 $ protective distribution system (PDS)
    (N) A wireline or fiber-optic communication system used to
    transmit cleartext classified information through an area of
    lesser classification or control. [N7003]
 $ protocol
    1a. (I) A set of rules (i.e., formats and procedures) to implement
    and control some type of association (e.g., communication) between
    systems. Example: Internet Protocol.
    1b. (I) A series of ordered computing and communication steps that
    are performed by two or more system entities to achieve a joint
    objective. [A9042]
 $ protocol control information (PCI)
    (N) See: secondary definition under "protocol data unit".
 $ protocol data unit (PDU)
    (N) A data packet that is defined for peer-to-peer transfers in a
    protocol layer.
    Tutorial: A PDU consists of two disjoint subsets of data: the SDU
    and the PCI. (Although these terms -- PDU, SDU, and PCI --
    originated in the OSIRM, they are also useful and permissible in
    an IPS context.)

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  1. The "service data unit" (SDU) in a packet is data that the

protocol transfers between peer protocol entities on behalf of

       the users of that layer's services. For Layers 1 through 6, the
       layer's users are peer protocol entities at a higher layer; for
       Layer 7, the users are application entities outside the scope
       of the OSIRM.
    -  The "protocol control information" (PCI) in a packet is data
       that peer protocol entities exchange between themselves to
       control their joint operation of the layer.
 $ protocol suite
    (I) A complementary collection of communication protocols used in
    a computer network. (See: IPS, OSI.)
 $ proxy
    1. (I) A computer process that acts on behalf of a user or client.
    2. (I) A computer process -- often used as, or as part of, a
    firewall -- that relays application transactions or a protocol
    between client and server computer systems, by appearing to the
    client to be the server and appearing to the server to be the
    client. (See: SOCKS.)
    Tutorial: In a firewall, a proxy server usually runs on a bastion
    host, which may support proxies for several applications and
    protocols (e.g., FTP, HTTP, and TELNET). Instead of a client in
    the protected enclave connecting directly to an external server,
    the internal client connects to the proxy server, which in turn
    connects to the external server. The proxy server waits for a
    request from inside the firewall, forwards the request to the
    server outside the firewall, gets the response, then sends the
    response back to the client. The proxy may be transparent to the
    clients, or they may need to connect first to the proxy server,
    and then use that association to also initiate a connection to the
    real server.
    Proxies are generally preferred over SOCKS for their ability to
    perform caching, high-level logging, and access control. A proxy
    can provide security service beyond that which is normally part of
    the relayed protocol, such as access control based on peer entity
    authentication of clients, or peer entity authentication of
    servers when clients do not have that ability. A proxy at OSIRM
    Layer 7 can also provide finer-grained security service than can a
    filtering router at Layer 3. For example, an FTP proxy could
    permit transfers out of, but not into, a protected network.

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 $ proxy certificate
    (I) An X.509 public-key certificate derived from an end-entity
    certificate, or from another proxy certificate, for the purpose of
    establishing proxies and delegating authorizations in the context
    of a PKI-based authentication system. [R3820]
    Tutorial: A proxy certificate has the following properties:
    -  It contains a critical extension that (a) identifies it as a
       proxy certificate and (b) may contain a certification path
       length constraint and policy constraints.
    -  It contains the public component of a key pair that is distinct
       from that associated with any other certificate.
    -  It is signed by the private component of a key pair that is
       associated with an end-entity certificate or another proxy
       certificate.
    -  Its associated private key can be used to sign only other proxy
       certificates (not end-entity certificates).
    -  Its "subject" DN is derived from its "issuer" DN and is unique.
    -  Its "issuer" DN is the "subject" DN of an end-entity
       certificate or another proxy certificate.
 $ pseudorandom
    (I) A sequence of values that appears to be random (i.e.,
    unpredictable) but is actually generated by a deterministic
    algorithm. (See: compression, random, random number generator.)
 $ pseudorandom number generator
    (I) See: secondary definition under "random number generator".
 $ public component
    (I) Synonym for "public key".
    Deprecated Usage: In most cases, IDOCs SHOULD NOT use this term;
    to avoid confusing readers, use "private key" instead. However,
    the term MAY be used when discussing a key pair; e.g., "A key pair
    has a public component and a private component."
 $ public key
    1. (I) The publicly disclosable component of a pair of
    cryptographic keys used for asymmetric cryptography. (See: key
    pair. Compare: private key.)
    2. (O) In a public key cryptosystem, "that key of a user's key
    pair which is publicly known." [X509]

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 $ public-key certificate
    1. (I) A digital certificate that binds a system entity's
    identifier to a public key value, and possibly to additional,
    secondary data items; i.e., a digitally signed data structure that
    attests to the ownership of a public key. (See: X.509 public-key
    certificate.)
    2. (O) "The public key of a user, together with some other
    information, rendered unforgeable by encipherment with the private
    key of the certification authority which issued it." [X509]
    Tutorial: The digital signature on a public-key certificate is
    unforgeable. Thus, the certificate can be published, such as by
    posting it in a directory, without the directory having to protect
    the certificate's data integrity.
 $ public-key cryptography
    (I) Synonym for "asymmetric cryptography".
 $ Public-Key Cryptography Standards (PKCS)
    (N) A series of specifications published by RSA Laboratories for
    data structures and algorithms used in basic applications of
    asymmetric cryptography. [PKCS] (See: PKCS #5 through PKCS #11.)
    Tutorial: The PKCS were begun in 1991 in cooperation with industry
    and academia, originally including Apple, Digital, Lotus,
    Microsoft, Northern Telecom, Sun, and MIT. Today, the
    specifications are widely used, but they are not sanctioned by an
    official standards organization, such as ANSI, ITU-T, or IETF. RSA
    Laboratories retains sole decision-making authority over the PKCS.
 $ public-key forward secrecy (PFS)
    (I) For a key-agreement protocol based on asymmetric cryptography,
    the property that ensures that a session key derived from a set of
    long-term public and private keys will not be compromised if one
    of the private keys is compromised in the future. (See: Usage note
    and other discussion under "perfect forward secrecy".)
 $ public-key Kerberos
    (I) See: Tutorial under "Kerberos", PKINIT.
 $ public-key infrastructure (PKI)
    1. (I) A system of CAs (and, optionally, RAs and other supporting
    servers and agents) that perform some set of certificate
    management, archive management, key management, and token
    management functions for a community of users in an application of
    asymmetric cryptography. (See: hierarchical PKI, mesh PKI,
    security management infrastructure, trust-file PKI.)

Shirey Informational [Page 241] RFC 4949 Internet Security Glossary, Version 2 August 2007

    2. (I) /PKIX/ The set of hardware, software, people, policies, and
    procedures needed to create, manage, store, distribute, and revoke
    digital certificates based on asymmetric cryptography.
    Tutorial: The core PKI functions are (a) to register users and
    issue their public-key certificates, (b) to revoke certificates
    when required, and (c) to archive data needed to validate
    certificates at a much later time. Key pairs for data
    confidentiality may be generated (and perhaps escrowed) by CAs or
    RAs, but requiring a PKI client to generate its own digital
    signature key pair helps maintain system integrity of the
    cryptographic system, because then only the client ever possesses
    the private key it uses. Also, an authority may be established to
    approve or coordinate CPSs, which are security policies under
    which components of a PKI operate.
    A number of other servers and agents may support the core PKI, and
    PKI clients may obtain services from them, such as certificate
    validation services. The full range of such services is not yet
    fully understood and is evolving, but supporting roles may include
    archive agent, certified delivery agent, confirmation agent,
    digital notary, directory, key escrow agent, key generation agent,
    naming agent who ensures that issuers and subjects have unique
    identifiers within the PKI, repository, ticket-granting agent,
    time-stamp agent, and validation agent.
 $ purge
    1. (I) Synonym for "erase".
    2. (O) /U.S. Government/ Use degaussing or other methods to render
    magnetically stored data unusable and irrecoverable by any means,
    including laboratory methods. [C4009] (Compare: /U.S. Government/
    erase.)
 $ QUADRANT
    (O) /U.S. Government/ Short name for technology and methods that
    protect cryptographic equipment by making the equipment tamper-
    resistant. [C4009] (Compare: protective packaging, TEMPEST.)
    Tutorial: Equipment cannot be made completely tamper-proof, but it
    can be made tamper-resistant or tamper-evident.
 $ qualified certificate
    (I) A public-key certificate that has the primary purpose of
    identifying a person with a high level of assurance, where the
    certificate meets some qualification requirements defined by an
    applicable legal framework, such as the European Directive on
    Electronic Signature. [R3739]

Shirey Informational [Page 242] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ quick mode
    (I) See: /IKE/ under "mode".
 $ RA
    (I) See: registration authority.
 $ RA domains
    (I) A feature of a CAW that allows a CA to divide the
    responsibility for certificate requests among multiple RAs.
    Tutorial: This ability might be used to restrict access to private
    authorization data that is provided with a certificate request,
    and to distribute the responsibility to review and approve
    certificate requests in high-volume environments. RA domains might
    segregate certificate requests according to an attribute of the
    certificate's subject, such as an organizational unit.
 $ RADIUS
    (I) See: Remote Authentication Dial-In User Service.
 $ Rainbow Series
    (O) /COMPUSEC/ A set of more than 30 technical and policy
    documents with colored covers, issued by the NCSC, that discuss in
    detail the TCSEC and provide guidance for meeting and applying the
    criteria. (See: Green Book, Orange Book, Red Book, Yellow Book.)
 $ random
    (I) In essence, "random" means "unpredictable". [SP22, Knut,
    R4086] (See: cryptographic key, pseudorandom.)
    -  "Random sequence": A sequence in which each successive value is
       obtained merely by chance and does not depend on the preceding
       values of the sequence. In a random sequence of bits, each bit
       is unpredictable; i.e., (a) the probability of each bit being a
       "0" or "1" is 1/2, and (b) the value of each bit is independent
       of any other bit in the sequence.
    -  "Random value": An individual value that is unpredictable;
       i.e., each value in the total population of possibilities has
       equal probability of being selected.
 $ random number generator
    (I) A process that is invoked to generate a random sequence of
    values (usually a sequence of bits) or an individual random value.
    Tutorial: There are two basic types of generators. [SP22]
    -  "(True) random number generator": It uses one or more non-
       deterministic bit sources (e.g., electrical circuit noise,
       timing of human processes such as key strokes or mouse
       movements, semiconductor quantum effects, and other physical

Shirey Informational [Page 243] RFC 4949 Internet Security Glossary, Version 2 August 2007

       phenomena) and a processing function that formats the bits, and
       it outputs a sequence of values that is unpredictable and
       uniformly distributed.
    -  "Pseudorandom number generator": It uses a deterministic
       computational process (usually implemented by software) that
       has one or more inputs called "seeds", and it outputs a
       sequence of values that appears to be random according to
       specified statistical tests.
 $ RBAC
    (N) See: role-based access control, rule-based access control.
    Deprecated Usage: IDOCs that use this term SHOULD state a
    definition for it because the abbreviation is ambiguous.
 $ RC2, RC4, RC6
    (N) See: Rivest Cipher #2, #4, #6.
 $ read
    (I) /security model/ A system operation that causes a flow of
    information from an object to a subject. (See: access mode.
    Compare: write.)
 $ realm
    (I) /Kerberos/ A domain consisting of a set of Kerberized clients,
    Kerberized application servers, and one or more Kerberos
    authentication servers and ticket-granting servers that support
    the clients and applications, all operating under the same
    security policy. (See: domain.)
 $ recovery
    1. (I) /cryptography/ The process of learning or obtaining
    cryptographic data or plain text through cryptanalysis. (See: key
    recovery, data recovery.)
    2a. (I) /system integrity/ The process of restoring a secure state
    in a system after there has been an accidental failure or a
    successful attack. (See: secondary definition under "security",
    system integrity.)
    2b. (I) /system integrity/ The process of restoring an information
    system's assets and operation following damage or destruction.
    (See: contingency plan.)
 $ RED
    1. (N) Designation for data that consists only of clear text, and
    for information system equipment items and facilities that handle

Shirey Informational [Page 244] RFC 4949 Internet Security Glossary, Version 2 August 2007

    clear text. Example: "RED key". (See: BCR, color change, RED/BLACK
    separation. Compare: BLACK.)
    Derivation: From the practice of marking equipment with colors to
    prevent operational errors.
    2. (O) /U.S. Government/ Designation applied to information
    systems, and to associated areas, circuits, components, and
    equipment, "in which unencrypted national security information is
    being processed." [C4009]
 $ RED/BLACK separation
    (N) An architectural concept for cryptographic systems that
    strictly separates the parts of a system that handle plain text
    (i.e., RED information) from the parts that handle cipher text
    (i.e., BLACK information). (See: BLACK, RED.)
 $ Red Book
    (D) /slang/ Synonym for "Trusted Network Interpretation of the
    Trusted Computer System Evaluation Criteria" [NCS05].
    Deprecated Term: IDOCs SHOULD NOT use this term. Instead, use the
    full proper name of the document or, in subsequent references, a
    more conventional abbreviation, e.g., TNI-TCSEC. (See: TCSEC,
    Rainbow Series, Deprecated Usage under "Green Book".)
 $ RED key
    (N) A cleartext key, which is usable in its present form (i.e., it
    does not need to be decrypted before being used). (See: RED.
    Compare: BLACK key.)
 $ reference monitor
    (I) "An access control concept that refers to an abstract machine
    that mediates all accesses to objects by subjects." [NCS04] (See:
    security kernel.)
    Tutorial: This concept was described in the Anderson report. A
    reference monitor should be (a) complete (i.e., it mediates every
    access), (b) isolated (i.e., it cannot be modified by other system
    entities), and (c) verifiable (i.e., small enough to be subjected
    to analysis and tests to ensure that it is correct).
 $ reflection attack
    (I) An attack in which a valid data transmission is replayed to
    the originator by an attacker who intercepts the original
    transmission. (Compare: indirect attack, replay attack.)

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 $ reflector attack
    (D) Synonym for "indirect attack".
    Deprecated Term: IDOCs SHOULD NOT use this term; it could be
    confused with "reflection attack", which is a different concept.
 $ registered user
    (I) A system entity that is authorized to receive a system's
    products and services or otherwise access system resources. (See:
    registration, user.)
 $ registration
    1. (I) /information system/ A system process that (a) initializes
    an identity (of a system entity) in the system, (b) establishes an
    identifier for that identity, (c) may associate authentication
    information with that identifier, and (d) may issue an identifier
    credential (depending on the type of authentication mechanism
    being used). (See: authentication information, credential,
    identifier, identity, identity proofing.)
    2. (I) /PKI/ An administrative act or process whereby an entity's
    name and other attributes are established for the first time at a
    CA, prior to the CA issuing a digital certificate that has the
    entity's name as the subject. (See: registration authority.)
    Tutorial: Registration may be accomplished either directly, by the
    CA, or indirectly, by a separate RA. An entity is presented to the
    CA or RA, and the authority either records the name(s) claimed for
    the entity or assigns the entity's name(s). The authority also
    determines and records other attributes of the entity that are to
    be bound in a certificate (such as a public key or authorizations)
    or maintained in the authority's database (such as street address
    and telephone number). The authority is responsible, possibly
    assisted by an RA, for verifying the entity's identity and vetting
    the other attributes, in accordance with the CA's CPS.
    Among the registration issues that a CPS may address are the
    following [R3647]:
    -  How a claimed identity and other attributes are verified.
    -  How organization affiliation or representation is verified.
    -  What forms of names are permitted, such as X.500 DN, domain
       name, or IP address.
    -  Whether names are required to be meaningful or unique, and
       within what domain.
    -  How naming disputes are resolved, including the role of
       trademarks.
    -  Whether certificates are issued to entities that are not
       persons.

Shirey Informational [Page 246] RFC 4949 Internet Security Glossary, Version 2 August 2007

  1. Whether a person is required to appear before the CA or RA, or

can instead be represented by an agent.

  1. Whether and how an entity proves possession of the private key

matching a public key.

 $ registration authority (RA)
    1. (I) An optional PKI entity (separate from the CAs) that does
    not sign either digital certificates or CRLs but has
    responsibility for recording or verifying some or all of the
    information (particularly the identities of subjects) needed by a
    CA to issue certificates and CRLs and to perform other certificate
    management functions. (See: ORA, registration.)
    2. (I) /PKIX/ An optional PKI component, separate from the CA(s).
    The functions that the RA performs will vary from case to case but
    may include identity authentication and name assignment, key
    generation and archiving of key pairs, token distribution, and
    revocation reporting. [R4210]
    Tutorial: Sometimes, a CA may perform all certificate management
    functions for all end users for which the CA signs certificates.
    Other times, such as in a large or geographically dispersed
    community, it may be necessary or desirable to offload secondary
    CA functions and delegate them to an assistant, while the CA
    retains the primary functions (signing certificates and CRLs). The
    tasks that are delegated to an RA by a CA may include personal
    authentication, name assignment, token distribution, revocation
    reporting, key generation, and archiving.
    An RA is an optional PKI entity, separate from the CA, that is
    assigned secondary functions. The duties assigned to RAs vary from
    case to case but may include the following:
    -  Verifying a subject's identity, i.e., performing personal
       authentication functions.
    -  Assigning a name to a subject. (See: distinguished name.)
    -  Verifying that a subject is entitled to have the attributes
       requested for a certificate.
    -  Verifying that a subject possesses the private key that matches
       the public key requested for a certificate.
    -  Performing functions beyond mere registration, such as
       generating key pairs, distributing tokens, handling revocation
       reports, and archiving data. (Such functions may be assigned to
       a PKI component that is separate from both the CA and the RA.)
    3. (O) /SET/ "An independent third-party organization that
    processes payment card applications for multiple payment card
    brands and forwards applications to the appropriate financial
    institutions." [SET2]

Shirey Informational [Page 247] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ regrade
    (I) Deliberately change the security level (especially the
    hierarchical classification level) of information in an authorized
    manner. (See: downgrade, upgrade.)
 $ rekey
    (I) Change the value of a cryptographic key that is being used in
    an application of a cryptographic system. (See: certificate
    rekey.)
    Tutorial: Rekey is required at the end of a cryptoperiod or key
    lifetime.
 $ reliability
    (I) The ability of a system to perform a required function under
    stated conditions for a specified period of time. (Compare:
    availability, survivability.)
 $ reliable human review
    (I) Any manual, automated, or hybrid process or procedure that
    ensures that a human examines a digital object, such as text or an
    image, to determine whether the object may be permitted, according
    to some security policy, to be transferred across a controlled
    interface. (See: guard.)
 $ relying party
    (I) Synonym for "certificate user".
    Usage: Used in a legal context to mean a recipient of a
    certificate who acts in reliance on that certificate. (See: ABA
    Guidelines.)
 $ remanence
    (I) Residual information that can be recovered from a storage
    medium after clearing. (See: clear, magnetic remanence, purge.)
 $ Remote Authentication Dial-In User Service (RADIUS)
    (I) An Internet protocol [R2865] for carrying dial-in users'
    authentication information and configuration information between a
    shared, centralized authentication server (the RADIUS server) and
    a network access server (the RADIUS client) that needs to
    authenticate the users of its network access ports. (See: TACACS.)
    User presents authentication and possibly other information to the
    RADIUS client (e.g., health information regarding the user
    device).

Shirey Informational [Page 248] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Tutorial: A user presents authentication information and possibly
    other information to the RADIUS client, and the client passes that
    information to the RADIUS server. The server authenticates the
    client using a shared secret value and checks the presented
    information, and then returns to the client all authorization and
    configuration information needed by the client to serve the user.
 $ renew
    See: certificate renewal.
 $ reordering
    (I) /packet/ See: secondary definition under "stream integrity
    service".
 $ replay attack
    (I) An attack in which a valid data transmission is maliciously or
    fraudulently repeated, either by the originator or by a third
    party who intercepts the data and retransmits it, possibly as part
    of a masquerade attack. (See: active wiretapping, fresh, liveness,
    nonce. Compare: indirect attack, reflection attack.)
 $ repository
    1. (I) A system for storing and distributing digital certificates
    and related information (including CRLs, CPSs, and certificate
    policies) to certificate users. (Compare: archive, directory.)
    2. (O) "A trustworthy system for storing and retrieving
    certificates or other information relevant to certificates." [DSG]
    Tutorial: A certificate is published to those who might need it by
    putting it in a repository. The repository usually is a publicly
    accessible, on-line server. In the FPKI, for example, the expected
    repository is a directory that uses LDAP, but also may be an X.500
    Directory that uses DAP, or an HTTP server, or an FTP server that
    permits anonymous login.
 $ repudiation
    1. (I) Denial by a system entity that was involved in an
    association (especially a communication association that transfers
    data) of having participated in the relationship. (See:
    accountability, non-repudiation service.)
    2. (I) A type of threat action whereby an entity deceives another
    by falsely denying responsibility for an act. (See: deception.)

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    Usage: This type of threat action includes the following subtypes:
    -  False denial of origin: Action whereby an originator denies
       responsibility for sending data.
    -  False denial of receipt: Action whereby a recipient denies
       receiving and possessing data.
    3. (O) /OSIRM/ "Denial by one of the entities involved in a
    communication of having participated in all or part of the
    communication." [I7498-2]
 $ Request for Comment (RFC)
    1. (I) One of the documents in the archival series that is the
    official channel for IDOCs and other publications of the Internet
    Engineering Steering Group, the Internet Architecture Board, and
    the Internet community in general. (RFC 2026, 2223) (See: Internet
    Standard.)
    2. (D) A popularly misused synonym for a document on the Internet
    Standards Track, i.e., an Internet Standard, Draft Standard, or
    Proposed Standard. (See: Internet Standard.)
    Deprecated Definition: IDOCs SHOULD NOT use this term with
    definition 2 because many other types of documents also are
    published as RFCs.
 $ residual risk
    (I) The portion of an original risk or set of risks that remains
    after countermeasures have been applied. (Compare: acceptable
    risk, risk analysis.)
 $ restore
    See: card restore.
 $ reverse engineering
    (I) /threat action/ See: secondary definition under "intrusion".
 $ revocation
    See: certificate revocation.
 $ revocation date
    (N) /X.509/ In a CRL entry, a date-time field that states when the
    certificate revocation occurred, i.e., when the CA declared the
    digital certificate to be invalid. (See: invalidity date.)
    Tutorial: The revocation date may not resolve some disputes
    because, in the worst case, all signatures made during the
    validity period of the certificate may have to be considered
    invalid. However, it may be desirable to treat a digital signature

Shirey Informational [Page 250] RFC 4949 Internet Security Glossary, Version 2 August 2007

    as valid even though the private key used to sign was compromised
    after the signing. If more is known about when the compromise
    actually occurred, a second date-time, an "invalidity date", can
    be included in an extension of the CRL entry.
 $ revocation list
    See: certificate revocation list.
 $ revoke
    (I) See: certificate revocation.
 $ RFC
    (I) See: Request for Comment.
 $ Rijndael
    (N) A symmetric, block cipher that was designed by Joan Daemen and
    Vincent Rijmen as a candidate for the AES, and that won that
    competition. [Daem] (See: Advanced Encryption Standard.)
 $ risk
    1. (I) An expectation of loss expressed as the probability that a
    particular threat will exploit a particular vulnerability with a
    particular harmful result. (See: residual risk.)
    2. (O) /SET/ "The possibility of loss because of one or more
    threats to information (not to be confused with financial or
    business risk)." [SET2]
    Tutorial: There are four basic ways to deal with a risk [SP30]:
    -  "Risk avoidance": Eliminate the risk by either countering the
       threat or removing the vulnerability. (Compare: "avoidance"
       under "security".)
    -  "Risk transference": Shift the risk to another system or
       entity; e.g., buy insurance to compensate for potential loss.
    -  "Risk limitation": Limit the risk by implementing controls that
       minimize resulting loss.
    -  "Risk assumption": Accept the potential for loss and continue
       operating the system.
 $ risk analysis
    (I) An assessment process that systematically (a) identifies
    valuable system resources and threats to those resources, (b)
    quantifies loss exposures (i.e., loss potential) based on
    estimated frequencies and costs of occurrence, and (c)
    (optionally) recommends how to allocate available resources to
    countermeasures so as to minimize total exposure. (See: risk
    management, business-case analysis. Compare: threat analysis.)

Shirey Informational [Page 251] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Tutorial: Usually, it is financially and technically infeasible to
    avoid or transfer all risks (see: "first corollary" of "second
    law" under "Courtney's laws"), and some residual risks will
    remain, even after all available countermeasures have been
    deployed (see: "second corollary" of "second law" under
    "Courtney's laws"). Thus, a risk analysis typically lists risks in
    order of cost and criticality, thereby determining where
    countermeasures should be applied first. [FP031, R2196]
    In some contexts, it is infeasible or inadvisable to attempt a
    complete or quantitative risk analysis because needed data, time,
    and expertise are not available. Instead, basic answers to
    questions about threats and risks may be already built into
    institutional security policies. For example, U.S. DoD policies
    for data confidentiality "do not explicitly itemize the range of
    expected threats" but instead "reflect an operational approach ...
    by stating the particular management controls that must be used to
    achieve [confidentiality] ... Thus, they avoid listing threats,
    which would represent a severe risk in itself, and avoid the risk
    of poor security design implicit in taking a fresh approach to
    each new problem". [NRC91]
 $ risk assumption
    (I) See: secondary definition under "risk".
 $ risk avoidance
    (I) See: secondary definition under "risk".
 $ risk limitation
    (I) See: secondary definition under "risk".
 $ risk management
    1. (I) The process of identifying, measuring, and controlling
    (i.e., mitigating) risks in information systems so as to reduce
    the risks to a level commensurate with the value of the assets
    protected. (See: risk analysis.)
    2. (I) The process of controlling uncertain events that may affect
    information system resources.
    3. (O) "The total process of identifying, controlling, and
    mitigating information system-related risks. It includes risk
    assessment; cost-benefit analysis; and the selection,
    implementation, test, and security evaluation of safeguards. This
    overall system security review considers both effectiveness and
    efficiency, including impact on the mission and constraints due to
    policy, regulations, and laws." [SP30]

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 $ risk transference
    (I) See: secondary definition under "risk".
 $ Rivest Cipher #2 (RC2)
    (N) A proprietary, variable-key-length block cipher invented by
    Ron Rivest for RSA Data Security, Inc.
 $ Rivest Cipher #4 (RC4)
    (N) A proprietary, variable-key-length stream cipher invented by
    Ron Rivest for RSA Data Security, Inc.
 $ Rivest Cipher #6 (RC6)
    (N) A symmetric, block cipher with 128-bit or longer key length,
    developed by Ron Rivest for RSA Data Security, Inc. as a candidate
    for the AES.
 $ Rivest-Shamir-Adleman (RSA)
    (N) An algorithm for asymmetric cryptography, invented in 1977 by
    Ron Rivest, Adi Shamir, and Leonard Adleman [RSA78].
    Tutorial: RSA uses exponentiation modulo the product of two large
    prime numbers. The difficulty of breaking RSA is believed to be
    equivalent to the difficulty of factoring integers that are the
    product of two large prime numbers of approximately equal size.
    To create an RSA key pair, randomly choose two large prime
    numbers, p and q, and compute the modulus, n = pq. Randomly choose
    a number e, the public exponent, that is less than n and
    relatively prime to (p-1)(q-1). Choose another number d, the
    private exponent, such that ed-1 evenly divides (p-1)(q-1). The
    public key is the set of numbers (n,e), and the private key is the
    set (n,d).
    It is assumed to be difficult to compute the private key (n,d)
    from the public key (n,e). However, if n can be factored into p
    and q, then the private key d can be computed easily. Thus, RSA
    security depends on the assumption that it is computationally
    difficult to factor a number that is the product of two large
    prime numbers. (Of course, p and q are treated as part of the
    private key, or else are destroyed after computing n.)
    For encryption of a message, m, to be sent to Bob, Alice uses
    Bob's public key (n,e) to compute m**e (mod n) = c. She sends c to
    Bob. Bob computes c**d (mod n) = m. Only Bob knows d, so only Bob
    can compute c**d (mod n) to recover m.
    To provide data origin authentication of a message, m, to be sent
    to Bob, Alice computes m**d (mod n) = s, where (d,n) is Alice's

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    private key. She sends m and s to Bob. To recover the message that
    only Alice could have sent, Bob computes s**e (mod n) = m, where
    (e,n) is Alice's public key.
    To ensure data integrity in addition to data origin authentication
    requires extra computation steps in which Alice and Bob use a
    cryptographic hash function h (see: digital signature). Alice
    computes the hash value h(m) = v, and then encrypts v with her
    private key to get s. She sends m and s. Bob receives m' and s',
    either of which might have been changed from the m and s that
    Alice sent. To test this, he decrypts s' with Alice's public key
    to get v'. He then computes h(m') = v". If v' equals v", Bob is
    assured that m' is the same m that Alice sent.
 $ robustness
    (N) See: level of robustness.
 $ role
    1. (I) A job function or employment position to which people or
    other system entities may be assigned in a system. (See: role-
    based access control. Compare: duty, billet, principal, user.)
    2. (O) /Common Criteria/ A pre-defined set of rules establishing
    the allowed interactions between a user and the TOE.
 $ role-based access control
    (I) A form of identity-based access control wherein the system
    entities that are identified and controlled are functional
    positions in an organization or process. [Sand] (See:
    authorization, constraint, identity, principal, role.)
    Tutorial: Administrators assign permissions to roles as needed to
    perform functions in the system. Administrators separately assign
    user identities to roles. When a user accesses the system in an
    identity (for which the user has been registered) and initiates a
    session using a role (to which the user has been assigned), then
    the permissions that have been assigned to the role are available
    to be exercised by the user.
    The following diagram shows that role-based access control
    involves five different relationships: (a) administrators assign
    identities to roles, (b) administrators assign permissions to
    roles, (c) administrators assign roles to roles, (d) users select
    identities in sessions, and (e) users select roles in sessions.
    Security policies may define constraints on these assignments and
    selections.

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       (c) Permission Inheritance Assignments (i.e., Role Hierarchy)
                             [Constraints]
                                +=====+
                                |     |
                 (a) Identity   v     v  (b) Permission
    +----------+  Assignments  +-------+  Assignments  +----------+
    |Identities|<=============>| Roles |<=============>|Permissions|
    +----------+ [Constraints] +-------+ [Constraints] +----------+
         |   |                   ^   ^
         |   |   +-----------+   |   |       +---------------------+
         |   |   | +-------+ |   |   |       |       Legend        |
         |   +====>|Session|=====+   |       |                     |
         |       | +-------+ |       |       |     One-to-One      |
         |       |    ...   |       |       | =================== |
         |       | +-------+ |       |       |                     |
         +========>|Session|=========+       |     One-to-Many     |
    (d) Identity | +-------+ |  (e) Role     | ==================> |
     Selections  |           | Selections    |                     |
    [Constraints]|  Access   |[Constraints]  |    Many-to-Many     |
                 | Sessions  |               | <=================> |
                 +-----------+               +---------------------+
 $ role certificate
    (I) An organizational certificate that is issued to a system
    entity that is a member of the set of users that have identities
    that are assigned to the same role. (See: role-based access
    control.)
 $ root, root CA
    1. (I) /PKI/ A CA that is directly trusted by an end entity. (See:
    trust anchor, trusted CA.)
    2. (I) /hierarchical PKI/ The CA that is the highest level (most
    trusted) CA in a certification hierarchy; i.e., the authority upon
    whose public key all certificate users base their validation of
    certificates, CRLs, certification paths, and other constructs.
    (See: top CA.)
    Tutorial: The root CA in a certification hierarchy issues public-
    key certificates to one or more additional CAs that form the
    second-highest level. Each of these CAs may issue certificates to
    more CAs at the third-highest level, and so on. To initialize
    operation of a hierarchical PKI, the root's initial public key is
    securely distributed to all certificate users in a way that does
    not depend on the PKI's certification relationships, i.e., by an
    out-of-band procedure. The root's public key may be distributed
    simply as a numerical value, but typically is distributed in a
    self-signed certificate in which the root is the subject. The

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    root's certificate is signed by the root itself because there is
    no higher authority in a certification hierarchy. The root's
    certificate is then the first certificate in every certification
    path.
    3. (I) /DNS/ The base of the tree structure that defines the name
    space for the Internet DNS. (See: domain name.)
    4. (O) /MISSI/ A name previously used for a MISSI policy creation
    authority, which is not a root as defined above for general usage,
    but is a CA at the second level of the MISSI hierarchy,
    immediately subordinate to a MISSI policy approving authority.
    5. (O) /UNIX/ A user account (a.k.a. "superuser") that has all
    privileges (including all security-related privileges) and thus
    can manage the system and its other user accounts.
 $ root certificate
    1. (I) /PKI/ A certificate for which the subject is a root. (See:
    trust anchor certificate, trusted certificate.)
    2. (I) /hierarchical PKI/ The self-signed public-key certificate
    at the top of a certification hierarchy.
 $ root key
    (I) /PKI/ A public key for which the matching private key is held
    by a root. (See: trust anchor key, trusted key.)
 $ root registry
    (O) /MISSI/ A name previously used for a MISSI PAA.
 $ ROT13
    (I) See: secondary definition under "Caesar cipher".
 $ router
    1a. (I) /IP/ A networked computer that forwards IP packets that
    are not addressed to the computer itself. (Compare: host.)
    1b. (I) /IPS/ A gateway that operates in the IPS Internet Layer to
    connect two or more subnetworks.
    1c. (N) /OSIRM/ A computer that is a gateway between two networks
    at OSIRM Layer 3 and that relays and directs data packets through
    that internetwork. (Compare: bridge, proxy.)
 $ RSA
    (N) See: Rivest-Shamir-Adleman.

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 $ rule
    See: policy rule.
 $ rule-based security policy
    (I) "A security policy based on global rules [i.e., policy rules]
    imposed for all users. These rules usually rely on comparison of
    the sensitivity of the resource being accessed and the possession
    of corresponding attributes of users, a group of users, or
    entities acting on behalf of users." [I7498-2] (Compare: identity-
    based security policy, policy rule, RBAC.)
 $ rules of behavior
    (I) A body of security policy that has been established and
    implemented concerning the responsibilities and expected behavior
    of entities that have access to a system. (Compare: [R1281].)
    Tutorial: For persons employed by a corporation or government, the
    rules might cover such matters as working at home, remote access,
    use of the Internet, use of copyrighted works, use of system
    resources for unofficial purpose, assignment and limitation of
    system privileges, and individual accountability.
 $ S field
    (D) See: Security Level field.
 $ S-BGP
    (I) See: Secure BGP.
 $ S-HTTP
    (I) See: Secure Hypertext Transfer Protocol.
 $ S/Key
    (I) A security mechanism that uses a cryptographic hash function
    to generate a sequence of 64-bit, one-time passwords for remote
    user login. [R1760]
    Tutorial: The client generates a one-time password by applying the
    MD4 cryptographic hash function multiple times to the user's
    secret key. For each successive authentication of the user, the
    number of hash applications is reduced by one. (Thus, an intruder
    using wiretapping cannot compute a valid password from knowledge
    of one previously used.) The server verifies a password by hashing
    the currently presented password (or initialization value) one
    time and comparing the hash result with the previously presented
    password.
 $ S/MIME
    (I) See: Secure/MIME.

Shirey Informational [Page 257] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ SAD
    (I) See: Security Association Database.
 $ safety
    (I) The property of a system being free from risk of causing harm
    (especially physical harm) to its system entities. (Compare:
    security.)
 $ SAID
    (I) See: security association identifier.
 $ salami swindle
    (D) /slang/ "Slicing off a small amount from each transaction.
    This kind of theft was made worthwhile by automation. Given a high
    transaction flow, even rounding down to the nearest cent and
    putting the 'extra' in a bogus account can be very profitable."
    [NCSSG]
    Deprecated Term: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
    Usage under "Green Book".)
 $ salt
    (I) A data value used to vary the results of a computation in a
    security mechanism, so that an exposed computational result from
    one instance of applying the mechanism cannot be reused by an
    attacker in another instance. (Compare: initialization value.)
    Example: A password-based access control mechanism might protect
    against capture or accidental disclosure of its password file by
    applying a one-way encryption algorithm to passwords before
    storing them in the file. To increase the difficulty of off-line,
    dictionary attacks that match encrypted values of potential
    passwords against a copy of the password file, the mechanism can
    concatenate each password with its own random salt value before
    applying the one-way function.
 $ SAML
    (N) See: Security Assertion Markup Language (SAML).
 $ sandbox
    (I) A restricted, controlled execution environment that prevents
    potentially malicious software, such as mobile code, from
    accessing any system resources except those for which the software
    is authorized.

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 $ sanitize
    1. (I) Delete sensitive data from a file, device, or system. (See:
    erase, zeroize.)
    2. (I) Modify data so as to be able either (a) to completely
    declassify it or (b) to downgrade it to a lower security level.
 $ SAP
    (O) See: special access program.
 $ SASL
    (I) See: Simple Authentication and Security Layer.
 $ SCA
    (I) See: subordinate certification authority.
 $ scavenging
    (I) /threat action/ See: secondary definition under "exposure".
 $ SCI
    (O) See: sensitive compartmented information.
 $ SCIF
    (O) See: sensitive compartmented information facility.
 $ SCOMP
    (N) Secure COMmunications Processor; an enhanced, MLS version of
    the Honeywell Level 6 minicomputer. It was the first system to be
    rated in TCSEC Class A1. (See: KSOS.)
 $ screen room
    (D) /slang/ Synonym for "shielded enclosure" in the context of
    electromagnetic emanations. (See: EMSEC, TEMPEST.)
    Deprecated Term: To avoid international misunderstanding, IDOCs
    SHOULD NOT use this term.
 $ screening router
    (I) Synonym for "filtering router".
 $ script kiddy
    (D) /slang/ A cracker who is able to use existing attack
    techniques (i.e., to read scripts) and execute existing attack
    software, but is unable to invent new exploits or manufacture the
    tools to perform them; pejoratively, an immature or novice
    cracker.

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    Deprecated Term: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
    Usage under "Green Book".)
 $ SDE
    (N) See: Secure Data Exchange.
 $ SDNS
    (O) See: Secure Data Network System.
 $ SDU
    (N) See: "service data unit" under "protocol data unit".
 $ seal
    1. (I) To use asymmetric cryptography to encrypt plain text with a
    public key in such a way that only the holder of the matching
    private key can learn what was the plain text. [Chau] (Compare:
    shroud, wrap.)
    Deprecated Usage: An IDOC SHOULD NOT use this term with definition
    1 unless the IDOC includes the definition, because the definition
    is not widely known and the concept can be expressed by using
    other, standard terms. Instead, use "salt and encrypt" or other
    terminology that is specific with regard to the mechanism being
    used.
    Tutorial: The definition does *not* say "only the holder of the
    matching private key can decrypt the ciphertext to learn what was
    the plaintext"; sealing is stronger than that. If Alice simply
    encrypts a plaintext P with a public key K to produce ciphertext C
    = K(P), then if Bob guesses that P = X, Bob could verify the guess
    by checking whether K(P) = K(X). To "seal" P and block Bob's
    guessing attack, Alice could attach a long string R of random bits
    to P before encrypting to produce C = K(P,R); if Bob guesses that
    P = X, Bob can only test the guess by also guessing R. (See:
    salt.)
    2. (D) To use cryptography to provide data integrity service for a
    data object. (See: sign.)
    Deprecated Definition: IDOCs SHOULD NOT use this term with
    definition 2. Instead, use a term that is more specific with
    regard to the mechanism used to provide the data integrity
    service; e.g., use "sign" when the mechanism is digital signature.

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 $ secret
    1a. (I) /adjective/ The condition of information being protected
    from being known by any system entities except those that are
    intended to know it. (See: data confidentiality.)
    1b. (I) /noun/ An item of information that is protected thusly.
    Usage: This term applies to symmetric keys, private keys, and
    passwords.
 $ secret key
    (D) A key that is kept secret or needs to be kept secret.
    Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
    in a potentially misleading way. In the context of asymmetric
    cryptography, IDOCs SHOULD use "private key". In the context of
    symmetric cryptography, the adjective "secret" is unnecessary
    because all keys must be kept secret.
 $ secret-key cryptography
    (D) Synonym for "symmetric cryptography".
    Deprecated Term: IDOCs SHOULD NOT use this term; it could be
    confused with "asymmetric cryptography", in which the private key
    is kept secret.
    Derivation: Symmetric cryptography is sometimes called "secret-key
    cryptography" because entities that share the key, such as the
    originator and the recipient of a message, need to keep the key
    secret from other entities.
 $ Secure BGP (S-BGP)
    (I) A project of BBN Technologies, sponsored by the U.S. DoD's
    Defense Advanced Research Projects Agency, to design and
    demonstrate an architecture to secure the Border Gateway Protocol
    (RFC 1771) and to promote deployment of that architecture in the
    Internet.
    Tutorial: S-BGP incorporates three security mechanisms:
    -  A PKI supports authentication of ownership of IP address
       blocks, autonomous system (AS) numbers, an AS's identity, and a
       BGP router's identity and its authorization to represent an AS.
       This PKI parallels and takes advantage of the Internet's
       existing IP address and AS number assignment system.
    -  A new, optional, BGP transitive path attribute carries digital
       signatures (in "attestations") covering the routing information
       in a BGP UPDATE. These signatures along with certificates from
       the S-BGP PKI enable the receiver of a BGP routing UPDATE to

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       validate the attribute and gain trust in the address prefixes
       and path information that it contains.
    -  IPsec provides data and partial sequence integrity, and enables
       BGP routers to authenticate each other for exchanges of BGP
       control traffic.
 $ Secure Data Exchange (SDE)
    (N) A LAN security protocol defined by the IEEE 802.10 standard.
 $ Secure Data Network System (SDNS)
    (O) An NSA program that developed security protocols for
    electronic mail (see: MSP), OSIRM Layer 3 (see: SP3), OSIRM Layer
    4 (see: SP4), and key establishment (see: KMP).
 $ secure distribution
    (I) See: trusted distribution.
 $ Secure Hash Algorithm (SHA)
    (N) A cryptographic hash function (specified in SHS) that produces
    an output (see: "hash result") -- of selectable length of either
    160, 224, 256, 384, or 512 bits -- for input data of any length <
    2**64 bits.
 $ Secure Hash Standard (SHS)
    (N) The U.S. Government standard [FP180] that specifies SHA.
 $ Secure Hypertext Transfer Protocol (S-HTTP)
    (I) An Internet protocol [R2660] for providing client-server
    security services for HTTP communications. (Compare: https.)
    Tutorial: S-HTTP was originally specified by CommerceNet, a
    coalition of businesses interested in developing the Internet for
    commercial uses. Several message formats may be incorporated into
    S-HTTP clients and servers, particularly CMS and MOSS. S-HTTP
    supports choice of security policies, key management mechanisms,
    and cryptographic algorithms through option negotiation between
    parties for each transaction. S-HTTP supports modes of operation
    for both asymmetric and symmetric cryptography. S-HTTP attempts to
    avoid presuming a particular trust model, but it attempts to
    facilitate multiply rooted, hierarchical trust and anticipates
    that principals may have many public-key certificates.
 $ Secure/MIME (S/MIME)
    (I) Secure/Multipurpose Internet Mail Extensions, an Internet
    protocol [R3851] to provide encryption and digital signatures for
    Internet mail messages.

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 $ secure multicast
    (I) Refers generally to providing security services for multicast
    groups of various types (e.g., 1-to-N and M-to-N) and to classes
    of protocols used to protect multicast packets.
    Tutorial: Multicast applications include video broadcast and
    multicast file transfer, and many of these applications require
    network security services. The Multicast Security Reference
    Framework [R3740] covers three functional areas:
    -  Multicast data handling: Security-related treatment of
       multicast data by the sender and the receiver.
    -  Group key management: Secure distribution and refreshment of
       keying material. (See: Group Domain of Interpretation.)
    -  Multicast security policy: Policy translation and
       interpretation across the multiple administrative domains that
       typically are spanned by a multicast application.
 $ Secure Shell(trademark) (SSH(trademark))
    (N) Refers to a protocol for secure remote login and other secure
    network services.
    Usage: On the Web site of SSH Communication Security Corporation,
    at http://www.ssh.com/legal_notice.html, it says, "SSH [and] the
    SSH logo ... are either trademarks or registered trademarks of
    SSH." This Glossary seeks to make readers aware of this trademark
    claim but takes no position on its validity.
    Tutorial: SSH has three main parts:
    -  Transport layer protocol: Provides server authentication,
       confidentiality, and integrity; and can optionally provide
       compression. This layer typically runs over a TCP connection,
       but might also run on top of any other reliable data stream.
    -  User authentication protocol: Authenticates the client-side
       user to the server. It runs over the transport layer protocol.
    -  Connection protocol: Multiplexes the encrypted tunnel into
       several logical channels. It runs over the user authentication
       protocol.
 $ Secure Sockets Layer (SSL)
    (N) An Internet protocol (originally developed by Netscape
    Communications, Inc.) that uses connection-oriented end-to-end
    encryption to provide data confidentiality service and data
    integrity service for traffic between a client (often a web
    browser) and a server, and that can optionally provide peer entity
    authentication between the client and the server. (See: Transport
    Layer Security.)

Shirey Informational [Page 263] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Tutorial: SSL has two layers; SSL's lower layer, the SSL Record
    Protocol, is layered on top of an IPS Transport-Layer protocol and
    encapsulates protocols that run in the upper layer. The upper-
    layer protocols are the three SSL management protocols -- SSL
    Handshake Protocol, SSL Change Cipher Spec Protocol, or SSL Alert
    Protocol -- and some Application-Layer protocol (e.g., HTTP).
    The SSL management protocols provide asymmetric cryptography for
    server authentication (verifying the server's identity to the
    client) and optional client authentication (verifying the client's
    identity to the server), and also enable them, before the
    application protocol transmits or receives data, to negotiate a
    symmetric encryption algorithm and secret session key (to use for
    data confidentiality service) and a keyed hash (to use for data
    integrity service).
    SSL is independent of the application it encapsulates, and any
    application can layer on top of SSL transparently. However, many
    Internet applications might be better served by IPsec.
 $ secure state
    1a. (I) A system condition in which the system is in conformance
    with the applicable security policy. (Compare: clean system,
    transaction.)
    1b. (I) /formal model/ A system condition in which no subject can
    access any object in an unauthorized manner. (See: secondary
    definition under "Bell-LaPadula model".)
 $ security
    1a. (I) A system condition that results from the establishment and
    maintenance of measures to protect the system.
    1b. (I) A system condition in which system resources are free from
    unauthorized access and from unauthorized or accidental change,
    destruction, or loss. (Compare: safety.)
    2. (I) Measures taken to protect a system.
    Tutorial: Parker [Park] suggests that providing a condition of
    system security may involve the following six basic functions,
    which overlap to some extent:
    -  "Deterrence": Reducing an intelligent threat by discouraging
       action, such as by fear or doubt. (See: attack, threat action.)
    -  "Avoidance": Reducing a risk by either reducing the value of
       the potential loss or reducing the probability that the loss
       will occur. (See: risk analysis. Compare: "risk avoidance"
       under "risk".)

Shirey Informational [Page 264] RFC 4949 Internet Security Glossary, Version 2 August 2007

  1. "Prevention": Impeding or thwarting a potential security

violation by deploying a countermeasure.

  1. "Detection": Determining that a security violation is

impending, is in progress, or has recently occurred, and thus

       make it possible to reduce the potential loss. (See: intrusion
       detection.)
    -  "Recovery": Restoring a normal state of system operation by
       compensating for a security violation, possibly by eliminating
       or repairing its effects. (See: contingency plan, main entry
       for "recovery".)
    -  "Correction": Changing a security architecture to eliminate or
       reduce the risk of reoccurrence of a security violation or
       threat consequence, such as by eliminating a vulnerability.
 $ security architecture
    (I) A plan and set of principles that describe (a) the security
    services that a system is required to provide to meet the needs of
    its users, (b) the system components required to implement the
    services, and (c) the performance levels required in the
    components to deal with the threat environment (e.g., [R2179]).
    (See: defense in depth, IATF, OSIRM Security Architecture,
    security controls, Tutorial under "security policy".)
    Tutorial: A security architecture is the result of applying the
    system engineering process. A complete system security
    architecture includes administrative security, communication
    security, computer security, emanations security, personnel
    security, and physical security. A complete security architecture
    needs to deal with both intentional, intelligent threats and
    accidental threats.
 $ Security Assertion Markup Language (SAML)
    (N) A protocol consisting of XML-based request and response
    message formats for exchanging security information, expressed in
    the form of assertions about subjects, between on-line business
    partners. [SAML]
 $ security association
    1. (I) A relationship established between two or more entities to
    enable them to protect data they exchange. (See: association,
    ISAKMP, SAD. Compare: session.)
    Tutorial: The relationship is represented by a set of data that is
    shared between the entities and is agreed upon and considered a
    contract between them. The data describes how the associated
    entities jointly use security services. The relationship is used
    to negotiate characteristics of security mechanisms, but the

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    relationship is usually understood to exclude the mechanisms
    themselves.
    2. (I) /IPsec/ A simplex (uni-directional) logical connection
    created for security purposes and implemented with either AH or
    ESP (but not both). The security services offered by a security
    association depend on the protocol (AH or ESP), the IPsec mode
    (transport or tunnel), the endpoints, and the election of optional
    services within the protocol. A security association is identified
    by a triple consisting of (a) a destination IP address, (b) a
    protocol (AH or ESP) identifier, and (c) a Security Parameter
    Index.
    3. (O) "A set of policy and cryptographic keys that provide
    security services to network traffic that matches that policy".
    [R3740] (See: cryptographic association, group security
    association.)
    4. (O) "The totality of communications and security mechanisms and
    functions (e.g., communications protocols, security protocols,
    security mechanisms and functions) that securely binds together
    two security contexts in different end systems or relay systems
    supporting the same information domain." [DoD6]
 $ Security Association Database (SAD)
    (I) /IPsec/ In an IPsec implementation that operates in a network
    node, a database that contains parameters to describe the status
    and operation of each of the active security associations that the
    node has established with other nodes. Separate inbound and
    outbound SADs are needed because of the directionality of IPsec
    security associations. [R4301] (Compare: SPD.)
 $ security association identifier (SAID)
    (I) A data field in a security protocol (such as NLSP or SDE),
    used to identify the security association to which a PDU is bound.
    The SAID value is usually used to select a key for decryption or
    authentication at the destination. (See: Security Parameter
    Index.)
 $ security assurance
    1. (I) An attribute of an information system that provides grounds
    for having confidence that the system operates such that the
    system's security policy is enforced. (Compare: trust.)
    2. (I) A procedure that ensures a system is developed and operated
    as intended by the system's security policy.

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    3. (D) "The degree of confidence one has that the security
    controls operate correctly and protect the system as intended."
    [SP12]
    Deprecated Definition: IDOCs SHOULD NOT use definition 3; it is a
    definition for "assurance level" rather than for "assurance".
    4. (D) /U.S. Government, identity authentication/ The (a) "degree
    of confidence in the vetting process used to establish the
    identity of the individual to whom the [identity] credential was
    issued" and the (b) "degree of confidence that the individual who
    uses the credential is the individual to whom the credential was
    issued". [M0404]
    Deprecated Definition: IDOCs SHOULD NOT use definition 4; it mixes
    concepts in a potentially misleading way. Part "a" is a definition
    for "assurance level" (rather than "security assurance") of an
    identity registration process; and part "b" is a definition for
    "assurance level" (rather than "security assurance") of an
    identity authentication process. Also, the processes of
    registration and authentication should be defined and designed
    separately to ensure clarity in certification.
 $ security audit
    (I) An independent review and examination of a system's records
    and activities to determine the adequacy of system controls,
    ensure compliance with established security policy and procedures,
    detect breaches in security services, and recommend any changes
    that are indicated for countermeasures. [I7498-2, NCS01] (Compare:
    accounting, intrusion detection.)
    Tutorial: The basic audit objective is to establish accountability
    for system entities that initiate or participate in security-
    relevant events and actions. Thus, means are needed to generate
    and record a security audit trail and to review and analyze the
    audit trail to discover and investigate security violations.
 $ security audit trail
    (I) A chronological record of system activities that is sufficient
    to enable the reconstruction and examination of the sequence of
    environments and activities surrounding or leading to an
    operation, procedure, or event in a security-relevant transaction
    from inception to final results. [NCS04] (See: security audit.)
 $ security by obscurity
    (O) Attempting to maintain or increase security of a system by
    keeping secret the design or construction of a security mechanism.

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    Tutorial: This approach has long been discredited in cryptography,
    where the phrase refers to trying to keep an algorithm secret,
    rather than just concealing the keys [Schn]. One must assume that
    mass-produced or widely fielded cryptographic devices eventually
    will be lost or stolen and, therefore, that the algorithms will be
    reverse engineered and become known to the adversary. Thus, one
    should rely on only those algorithms and protocols that are strong
    enough to have been published widely, and have been peer reviewed
    for long enough that their flaws have been found and removed. For
    example, NIST used a long, public process to select AES to replace
    DES.
    In computer and network security, the principle of "no security by
    obscurity" also applies to security mechanisms other than
    cryptography. For example, if the design and implementation of a
    protocol for access control are strong, then reading the
    protocol's source code should not enable you to find a way to
    evade the protection and penetrate the system.
 $ security class
    (D) Synonym for "security level".
    Deprecated Term: IDOCs SHOULD NOT use this term. Instead, use
    "security level", which is more widely established and understood.
 $ security clearance
    (I) A determination that a person is eligible, under the standards
    of a specific security policy, for authorization to access
    sensitive information or other system resources. (See: clearance
    level.)
 $ security compromise
    (I) A security violation in which a system resource is exposed, or
    is potentially exposed, to unauthorized access. (Compare: data
    compromise, exposure, violation.)
 $ security controls
    (N) The management, operational, and technical controls
    (safeguards or countermeasures) prescribed for an information
    system which, taken together, satisfy the specified security
    requirements and adequately protect the confidentiality,
    integrity, and availability of the system and its information.
    [FP199] (See: security architecture.)
 $ security doctrine
    (I) A specified set of procedures or practices that direct or
    provide guidance for how to comply with security policy. (Compare:
    security mechanism, security policy.)

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    Tutorial: Security policy and security doctrine are closely
    related. However, policy deals mainly with strategy, and doctrine
    deals with tactics.
    Security doctrine is often understood to refer mainly to
    administrative security, personnel security, and physical
    security. For example, security mechanisms and devices that
    implement them are normally designed to operate in a limited range
    of environmental and administrative conditions, and these
    conditions must be met to complement and ensure the technical
    protection afforded by the hardware, firmware, and software in the
    devices. Security doctrine specifies how to achieve those
    conditions. (See: "first law" under "Courtney's laws".)
 $ security domain
    (I) See: domain.
 $ security environment
    (I) The set of external entities, procedures, and conditions that
    affect secure development, operation, and maintenance of a system.
    (See: "first law" under "Courtney's laws".)
 $ security event
    (I) An occurrence in a system that is relevant to the security of
    the system. (See: security incident.)
    Tutorial: The term covers both events that are security incidents
    and those that are not. In a CA workstation, for example, a list
    of security events might include the following:
    -  Logging an operator into or out of the system.
    -  Performing a cryptographic operation, e.g., signing a digital
       certificate or CRL.
    -  Performing a cryptographic card operation: creation, insertion,
       removal, or backup.
    -  Performing a digital certificate lifecycle operation: rekey,
       renewal, revocation, or update.
    -  Posting a digital certificate to an X.500 Directory.
    -  Receiving a key compromise notification.
    -  Receiving an improper certification request.
    -  Detecting an alarm condition reported by a cryptographic
       module.
    -  Failing a built-in hardware self-test or a software system
       integrity check.
 $ security fault analysis
    (I) A security analysis, usually performed on hardware at the
    level of gate logic, gate-by-gate, to determine the security
    properties of a device when a hardware fault is encountered.

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 $ security function
    (I) A function in a system that is relevant to the security of the
    system; i.e., a system function that must operate correctly to
    ensure adherence to the system's security policy.
 $ security gateway
    1. (I) An internetwork gateway that separates trusted (or
    relatively more trusted) hosts on one side from untrusted (or less
    trusted) hosts on the other side. (See: firewall and guard.)
    2. (O) /IPsec/ "An intermediate system that implements IPsec
    protocols." [R4301]
    Tutorial: IPsec's AH or ESP can be implemented on a gateway
    between a protected network and an unprotected network, to provide
    security services to the protected network's hosts when they
    communicate across the unprotected network to other hosts and
    gateways.
 $ security incident
    1. (I) A security event that involves a security violation. (See:
    CERT, security event, security intrusion, security violation.)
    Tutorial: In other words, a security event in which the system's
    security policy is disobeyed or otherwise breached.
    2. (D) "Any adverse event [that] compromises some aspect of
    computer or network security." [R2350]
    Deprecated Definition: IDOCs SHOULD NOT use definition 2 because
    (a) a security incident may occur without actually being harmful
    (i.e., adverse) and because (b) this Glossary defines "compromise"
    more narrowly in relation to unauthorized access.
    3. (D) "A violation or imminent threat of violation of computer
    security policies, acceptable use policies, or standard computer
    security practices." [SP61]
    Deprecated Definition: IDOCs SHOULD NOT use definition 3 because
    it mixes concepts in way that does not agree with common usage; a
    security incident is commonly thought of as involving a
    realization of a threat (see: threat action), not just a threat.
 $ security intrusion
    (I) A security event, or a combination of multiple security
    events, that constitutes a security incident in which an intruder
    gains, or attempts to gain, access to a system or system resource
    without having authorization to do so.

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 $ security kernel
    (I) "The hardware, firmware, and software elements of a trusted
    computing base that implement the reference monitor concept. It
    must mediate all accesses, be protected from modification, and be
    verifiable as correct." [NCS04] (See: kernel, TCB.)
    Tutorial: A security kernel is an implementation of a reference
    monitor for a given hardware base. [Huff]
 $ security label
    (I) An item of meta-data that designates the value of one or more
    security-relevant attributes (e.g., security level) of a system
    resource. (See: [R1457]. Compare: security marking.)
    Deprecated usage: To avoid confusion, IDOCs SHOULD NOT use
    "security label" for "security marking", or vice versa, even
    though that is commonly done (including in some national and
    international standards that should know better).
    Tutorial: Humans and automated security mechanisms use a security
    label of a system resource to determine, according to applicable
    security policy, how to control access to the resource (and they
    affix appropriate, matching security markings to physical
    instances of the resource). Security labels are most often used to
    support data confidentiality policy, and sometimes used to support
    data integrity policy.
    As explained in [R1457], the form that is taken by security labels
    of a protocol's packets varies depending on the OSIRM layer in
    which the protocol operates. Like meta-data generally, a security
    label of a data packet may be either explicit (e.g., IPSO) or
    implicit (e.g., Alice treats all messages received from Bob as
    being labeled "Not For Public Release"). In a connectionless
    protocol, every packet might have an explicit label; but in a
    connection-oriented protocol, all packets might have the same
    implicit label that is determined at the time the connection is
    established.
    Both classified and unclassified system resources may require a
    security label. (See: FOUO.)
 $ security level
    (I) The combination of a hierarchical classification level and a
    set of non-hierarchical category designations that represents how
    sensitive a specified type or item of information is. (See:
    dominate, lattice model. Compare: classification level.)

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    Usage: IDOCs that use this term SHOULD state a definition for it.
    The term is usually understood to involve sensitivity to
    disclosure, but it also is used in many other ways and could
    easily be misunderstood.
 $ Security Level field
    (I) A 16-bit field that specifies a security level value in the
    security option (option type 130) of version 4 IP's datagram
    header format.
    Deprecated Abbreviation: IDOCs SHOULD NOT use the abbreviation "S
    field", which is potentially ambiguous.
 $ security management infrastructure (SMI)
    (I) System components and activities that support security policy
    by monitoring and controlling security services and mechanisms,
    distributing security information, and reporting security events.
    Tutorial: The associated functions are as follows [I7498-4]:
    -  Controlling (granting or restricting) access to system
       resources: This includes verifying authorizations and
       identities, controlling access to sensitive security data, and
       modifying access priorities and procedures in the event of
       attacks.
    -  Retrieving (gathering) and archiving (storing) security
       information: This includes logging security events and
       analyzing the log, monitoring and profiling usage, and
       reporting security violations.
    -  Managing and controlling the encryption process: This includes
       performing the functions of key management and reporting on key
       management problems. (See: PKI.)
 $ security marking
    (I) A physical marking that is bound to an instance of a system
    resource and that represents a security label of the resource,
    i.e., that names or designates the value of one or more security-
    relevant attributes of the resource. (Compare: security label.)
    Tutorial: A security label may be represented by various
    equivalent markings depending on the physical form taken by the
    labeled resource. For example, a document could have a marking
    composed of a bit pattern [FP188] when the document is stored
    electronically as a file in a computer, and also a marking of
    printed alphabetic characters when the document is in paper form.

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 $ security mechanism
    (I) A method or process (or a device incorporating it) that can be
    used in a system to implement a security service that is provided
    by or within the system. (See: Tutorial under "security policy".
    Compare: security doctrine.)
    Usage: Usually understood to refer primarily to components of
    communication security, computer security, and emanation security.
    Examples: Authentication exchange, checksum, digital signature,
    encryption, and traffic padding.
 $ security model
    (I) A schematic description of a set of entities and relationships
    by which a specified set of security services are provided by or
    within a system. Example: Bell-LaPadula model, OSIRM. (See:
    Tutorial under "security policy".)
 $ security parameters index (SPI)
    1. (I) /IPsec/ A 32-bit identifier used to distinguish among
    security associations that terminate at the same destination (IP
    address) and use the same security protocol (AH or ESP). Carried
    in AH and ESP to enable the receiving system to determine under
    which security association to process a received packet.
    2. (I) /mobile IP/ A 32-bit index identifying a security
    association from among the collection of associations that are
    available between a pair of nodes, for application to mobile IP
    protocol messages that the nodes exchange.
 $ security perimeter
    (I) A physical or logical boundary that is defined for a domain or
    enclave and within which a particular security policy or security
    architecture applies. (See: insider, outsider.)
 $ security policy
    1. (I) A definite goal, course, or method of action to guide and
    determine present and future decisions concerning security in a
    system. [NCS03, R3198] (Compare: certificate policy.)
    2a. (I) A set of policy rules (or principles) that direct how a
    system (or an organization) provides security services to protect
    sensitive and critical system resources. (See: identity-based
    security policy, policy rule, rule-based security policy, rules of
    behavior. Compare: security architecture, security doctrine,
    security mechanism, security model, [R1281].)

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    2b. (O) A set of rules to administer, manage, and control access
    to network resources. [R3060, R3198]
    2c. (O) /X.509/ A set of rules laid down by an authority to govern
    the use and provision of security services and facilities.
    2d. (O) /Common Criteria/ A set of rules that regulate how assets
    are managed, protected, and distributed within a TOE.
    Tutorial: Ravi Sandhu suggests that security policy is one of four
    layers of the security engineering process (as shown in the
    following diagram). Each layer provides a different view of
    security, ranging from what services are needed to how services
    are implemented.
       What Security Services
       Should Be Provided?        +- - - - - - - - - - - - -+
       ^  +- - - - - - - - - - - -| Mission Functions View  |
       |  | Security Policy       |- - - - - - - - - - - - -+
       |  +- - - - - - - - - - - -| Domain Practices View   |
       |  | Security Model        |- - - - - - - - - - - - -+
       |  +- - - - - - - - - - - -| Enclave Services View   |
       |  | Security Architecture |- - - - - - - - - - - - -+
       |  +- - - - - - - - - - - -| Agent Mechanisms View   |
       |  | Security Mechanism    |- - - - - - - - - - - - -+
       v  +- - - - - - - - - - - -| Platform Devices View   |
       How Are Security           +- - - - - - - - - - - - -+
       Services Implemented?
    We suggest that each of Sandhu's four layers is a mapping between
    two points of view that differ in their degree of abstraction,
    according to the perspectives of various participants in system
    design, development, and operation activities, as follows:.
    -  Mission functions view: The perspective of a user of system
       resources. States time-phased protection needs for resources
       and identifies sensitive and critical resources -- networks,
       hosts, applications, and databases. Independent of rules and
       practices used to achieve protection.
    -  Domain practices view: The perspective of an enterprise manager
       who sets protection standards for resources. States rules and
       practices for protection. Identifies domain members; i.e.,
       entities (users/providers) and resources (including data
       objects). Independent of system topology. Not required to be
       hierarchical.
    -  Enclave services view: The perspective of a system designer who
       allocates security functions to major components. Assigns
       security services to system topology structures and their

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       contents. Independent of security mechanisms. Hierarchical
       across all domains.
    -  Agent mechanisms view: The perspective of a system engineer who
       specifies security mechanisms to implement security services.
       Specifies mechanisms to be used by protocol, database, and
       application engines. Independent of type and manufacture of
       platforms and other physical devices.
    -  Platform devices view: The perspective of an as-built
       description of the system in operation. Specifies exactly how
       to build or assemble the system, and also specifies procedures
       for operating the system.
 $ Security Policy Database (SPD)
    (I) /IPsec/ In an IPsec implementation operating in a network
    node, a database that contains parameters that specify policies
    set by a user or administrator to determine what IPsec services,
    if any, are to be provided to IP datagrams sent or received by the
    node, and in what fashion they are provided. For each datagram,
    the SPD specifies one of three choices: discard the datagram,
    apply IPsec services (e.g., AH or ESP), or bypass IPsec. Separate
    inbound and outbound SPDs are needed because of the directionality
    of IPsec security associations. [R4301] (Compare: SAD.)
 $ Security Protocol 3 (SP3)
    (O) A protocol [SDNS3] developed by SDNS to provide connectionless
    data security at the top of OSIRM Layer 3. (Compare: IPsec, NLSP.)
 $ Security Protocol 4 (SP4)
    (O) A protocol [SDNS4] developed by SDNS to provide either
    connectionless or end-to-end connection-oriented data security at
    the bottom of OSIRM Layer 4. (See: TLSP.)
 $ security-relevant event
    (D) Synonym for "security event".
    Deprecated Term: IDOCs SHOULD NOT use this term; it is wordy.
 $ security-sensitive function
    (D) Synonym for "security function".
    Deprecated Term: IDOCs SHOULD NOT use this term; it is wordy.
 $ security service
    1. (I) A processing or communication service that is provided by a
    system to give a specific kind of protection to system resources.
    (See: access control service, audit service, availability service,
    data confidentiality service, data integrity service, data origin

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    authentication service, non-repudiation service, peer entity
    authentication service, system integrity service.)
    Tutorial: Security services implement security policies, and are
    implemented by security mechanisms.
    2. (O) "A service, provided by a layer of communicating open
    systems, [that] ensures adequate security of the systems or the
    data transfers." [I7498-2]
 $ security situation
    (I) /ISAKMP/ The set of all security-relevant information (e.g.,
    network addresses, security classifications, manner of operation
    such as normal or emergency) that is needed to decide the security
    services that are required to protect the association that is
    being negotiated.
 $ security target
    (N) /Common Criteria/ A set of security requirements and
    specifications to be used as the basis for evaluation of an
    identified TOE.
    Tutorial: A security target (ST) is a statement of security claims
    for a particular information technology security product or
    system, and is the basis for agreement among all parties as to
    what security the product or system offers. An ST parallels the
    structure of a protection profile, but has additional elements
    that include product-specific detailed information. An ST contains
    a summary specification, which defines the specific measures taken
    in the product or system to meet the security requirements.
 $ security token
    (I) See: token.
 $ security violation
    (I) An act or event that disobeys or otherwise breaches security
    policy. (See: compromise, penetration, security incident.)
 $ seed
    (I) A value that is an input to a pseudorandom number generator.
 $ selective-field confidentiality
    (I) A data confidentiality service that preserves confidentiality
    for one or more parts (i.e., fields) of each packet. (See:
    selective-field integrity.)
    Tutorial: Data confidentiality service usually is applied to
    entire SDUs, but some situations might require protection of only

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    part of each packet. For example, when Alice uses a debit card at
    an automated teller machine (ATM), perhaps only her PIN is
    enciphered for confidentiality when her transaction request is
    transmitted from the ATM to her bank's computer.
    In any given operational situation, there could be many different
    reasons for using selective field confidentiality. In the ATM
    example, there are at least four possibilities: The service may
    provide a fail-safe mode of operation, ensuring that the bank can
    still process transactions (although with some risk) even when the
    encryption system fails. It may make messages easier to work with
    when doing system fault isolation. It may avoid problems with laws
    that prevent shipping enciphered data across international
    borders. It may improve efficiency by reducing processing load at
    a central computer site.
 $ selective-field integrity
    (I) A data integrity service that preserves integrity for one or
    more parts (i.e., fields) of each packet. (See: selective-field
    confidentiality.)
    Tutorial: Data integrity service may be implemented in a protocol
    to protect the SDU part of packets, the PCI part, or both.
    -  SDU protection: When service is provided for SDUs, it usually
       is applied to entire SDUs, but it might be applied only to
       parts of SDUs in some situations. For example, an IPS
       Application-Layer protocol might need protection of only part
       of each packet, and this might enable faster processing.
    -  PCI protection: To prevent active wiretapping, it might be
       desirable to apply data integrity service to the entire PCI,
       but some PCI fields in some protocols need to be mutable in
       transit. For example, the "Time to Live" field in IPv4 is
       changed each time a packet passes through a router in the
       Internet Layer. Thus, the value that the field will have when
       the packet arrives at its destination is not predictable by the
       sender and cannot be included in a checksum computed by the
       sender. (See: Authentication Header.)
 $ self-signed certificate
    (I) A public-key certificate for which the public key bound by the
    certificate and the private key used to sign the certificate are
    components of the same key pair, which belongs to the signer.
    (Compare: root certificate.)
    Tutorial: In a self-signed X.509 public-key certificate, the
    issuer's DN is the same as the subject's DN.

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 $ semantic security
    (I) An attribute of an encryption algorithm that is a
    formalization of the notion that the algorithm not only hides the
    plain text but also reveals no partial information about the plain
    text; i.e., whatever is computable about the plain text when given
    the cipher text, is also computable without the cipher text.
    (Compare: indistinguishability.)
 $ semiformal
    (I) Expressed in a restricted syntax language with defined
    semantics. [CCIB] (Compare: formal, informal.)
 $ sensitive
    (I) A condition of a system resource such that the loss of some
    specified property of that resource, such as confidentiality or
    integrity, would adversely affect the interests or business of its
    owner or user. (See: sensitive information. Compare: critical.)
 $ sensitive compartmented information (SCI)
    (O) /U.S. Government/ Classified information concerning or derived
    from intelligence sources, methods, or analytical processes, which
    is required to be handled within formal control systems
    established by the Director of Central Intelligence. [C4009] (See:
    compartment, SAP, SCIF. Compare: collateral information.)
 $ sensitive compartmented information facility (SCIF)
    (O) /U.S. Government/ "An accredited area, room, group of rooms,
    building, or installation where SCI may be stored, used,
    discussed, and/or processed." [C4009] (See: SCI. Compare: shielded
    enclosure.)
 $ sensitive information
    1. (I) Information for which (a) disclosure, (b) alteration, or
    (c) destruction or loss could adversely affect the interests or
    business of its owner or user. (See: data confidentiality, data
    integrity, sensitive. Compare: classified, critical.)
    2. (O) /U.S. Government/ Information for which (a) loss, (b)
    misuse, (c) unauthorized access, or (d) unauthorized modification
    could adversely affect the national interest or the conduct of
    federal programs, or the privacy to which individuals are entitled
    under the Privacy Act of 1974, but that has not been specifically
    authorized under criteria established by an Executive Order or an
    Act of Congress to be kept classified in the interest of national
    defense or foreign policy.
    Tutorial: Systems that are not U.S. national security systems, but
    contain sensitive U.S. Federal Government information, must be

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    protected according to the Computer Security Act of 1987 (Public
    Law 100-235). (See: national security.)
 $ sensitivity label
    (D) Synonym for "classification label".
    Deprecated term: IDOCs SHOULD NOT use this term because the
    definition of "sensitive" involves not only data confidentiality,
    but also data integrity.
 $ sensitivity level
    (D) Synonym for "classification level".
    Deprecated term: IDOCs SHOULD NOT use this term because the
    definition of "sensitive" involves not only data confidentiality,
    but also data integrity.
 $ separation of duties
    (I) The practice of dividing the steps in a system process among
    different individual entities (i.e., different users or different
    roles) so as to prevent a single entity acting alone from being
    able to subvert the process. Usage: a.k.a. "separation of
    privilege". (See: administrative security, dual control.)
 $ serial number
    See: certificate serial number.
 $ Serpent
    (O) A symmetric, 128-bit block cipher designed by Ross Anderson,
    Eli Biham, and Lars Knudsen as a candidate for the AES.
 $ server
    (I) A system entity that provides a service in response to
    requests from other system entities called clients.
 $ service data unit (SDU)
    (N) See: secondary definition under "protocol data unit".
 $ session
    1a. (I) /computer usage/ A continuous period of time, usually
    initiated by a login, during which a user accesses a computer
    system.
    1b. (I) /computer activity/ The set of transactions or other
    computer activities that are performed by or for a user during a
    period of computer usage.

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    2. (I) /access control/ A temporary mapping of a principal to one
    or more roles. (See: role-based access control.)
    Tutorial: A user establishes a session as a principal and
    activates some subset of roles to which the principal has been
    assigned. The authorizations available to the principal in the
    session are the union of the permissions of all the roles
    activated in the session. Each session is associated with a single
    principal and, therefore, with a single user. A principal may have
    multiple, concurrent sessions and may activate a different set of
    roles in each session.
    3. (I) /computer network/ A persistent but (normally) temporary
    association between a user agent (typically a client) and a second
    process (typically a server). The association may persist across
    multiple exchanges of data, including multiple connections.
    (Compare: security association.)
 $ session key
    (I) In the context of symmetric encryption, a key that is
    temporary or is used for a relatively short period of time. (See:
    ephemeral, KDC, session. Compare: master key.)
    Tutorial: A session key is used for a defined period of
    communication between two system entities or components, such as
    for the duration of a single connection or transaction set; or the
    key is used in an application that protects relatively large
    amounts of data and, therefore, needs to be rekeyed frequently.
 $ SET(trademark)
    (O) See: SET Secure Electronic Transaction(trademark).
 $ SET private extension
    (O) One of the private extensions defined by SET for X.509
    certificates. Carries information about hashed root key,
    certificate type, merchant data, cardholder certificate
    requirements, encryption support for tunneling, or message support
    for payment instructions.
 $ SET qualifier
    (O) A certificate policy qualifier that provides information about
    the location and content of a SET certificate policy.
    Tutorial: Besides the policies and qualifiers inherited from its
    own certificate, each CA in the SET certification hierarchy may
    add one qualifying statement to the root policy when the CA issues
    a certificate. The additional qualifier is a certificate policy
    for that CA. Each policy in a SET certificate may have these

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    qualifiers: (a) a URL where a copy of the policy statement may be
    found; (b) an electronic mail address where a copy of the policy
    statement may be found; (c) a hash result of the policy statement,
    computed using the indicated algorithm; and (d) a statement
    declaring any disclaimers associated with the issuing of the
    certificate.
 $ SET Secure Electronic Transaction(trademark) or SET(trademark)
    (N) A protocol developed jointly by MasterCard International and
    Visa International and published as an open standard to provide
    confidentiality of transaction information, payment integrity, and
    authentication of transaction participants for payment card
    transactions over unsecured networks, such as the Internet. [SET1]
    (See: acquirer, brand, cardholder, dual signature, electronic
    commerce, IOTP, issuer, merchant, payment gateway, third party.)
    Tutorial: This term and acronym are trademarks of SETCo.
    MasterCard and Visa announced the SET standard on 1 February 1996.
 $ SETCo
    (O) Abbreviation of "SET Secure Electronic Transaction LLC",
    formed on 19 December 1997 by MasterCard and Visa for implementing
    the SET Secure Electronic Transaction(trademark) standard. A later
    memorandum of understanding added American Express and JCB Credit
    Card Company as co-owners of SETCo.
 $ SHA, SHA-1, SHA-2
    (N) See: Secure Hash Algorithm.
 $ shared identity
    (I) See: secondary definition under "identity".
 $ shared secret
    (D) Synonym for "cryptographic key" or "password".
    Deprecated Usage: IDOCs that use this term SHOULD state a
    definition for it because the term is used in many ways and could
    easily be misunderstood.
 $ shielded enclosure
    (O) "Room or container designed to attenuate electromagnetic
    radiation, acoustic signals, or emanations." [C4009] (See:
    emanation. Compare: SCIF.)
 $ short title
    (O) "Identifying combination of letters and numbers assigned to
    certain items of COMSEC material to facilitate handling,
    accounting, and controlling." [C4009] (Compare: KMID, long title.)

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 $ shroud
    (D) /verb/ To encrypt a private key, possibly in concert with a
    policy that prevents the key from ever being available in
    cleartext form beyond a certain, well-defined security perimeter.
    [PKC12] (See: encrypt. Compare: seal, wrap.)
    Deprecated Term: IDOCs SHOULD NOT use this term as defined here;
    the definition duplicates the meaning of other, standard terms.
    Instead, use "encrypt" or other terminology that is specific with
    regard to the mechanism being used.
 $ SHS
    (N) See: Secure Hash Standard.
 $ sign
    (I) Create a digital signature for a data object. (See: signer.)
 $ signal analysis
    (I) Gaining indirect knowledge (inference) of communicated data by
    monitoring and analyzing a signal that is emitted by a system and
    that contains the data but is not intended to communicate the
    data. (See: emanation. Compare: traffic analysis.)
 $ signal intelligence
    (I) The science and practice of extracting information from
    signals. (See: signal security.)
 $ signal security
    (N) (I) The science and practice of protecting signals. (See:
    cryptology, security.)
    Tutorial: The term "signal" denotes (a) communication in almost
    any form and also (b) emanations for other purposes, such as
    radar. Signal security is opposed by signal intelligence, and each
    discipline includes opposed sub-disciplines as follows [Kahn]:
    Signal Security                 Signal Intelligence
    ------------------------------  ---------------------------------
    1. Communication Security       1. Communication Intelligence
       1a. Cryptography                1a. Cryptanalysis
       1b. Traffic Security            1b. Traffic Analysis
       1c. Steganography               1c. Detection and Interception
    2. Electronic Security          2. Electronic Intelligence
       2a. Emission Security           2a. Electronic Reconnaissance
       2b. Counter-Countermeasures     2b. Countermeasures
    ------------------------------  ---------------------------------

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 $ signature
    (O) A symbol or process adopted or executed by a system entity
    with present intention to declare that a data object is genuine.
    (See: digital signature, electronic signature.)
 $ signature certificate
    (I) A public-key certificate that contains a public key that is
    intended to be used for verifying digital signatures, rather than
    for encrypting data or performing other cryptographic functions.
    Tutorial: A v3 X.509 public-key certificate may have a "keyUsage"
    extension that indicates the purpose for which the certified
    public key is intended. (See: certificate profile.)
 $ signed receipt
    (I) An S/MIME service [R2634] that (a) provides, to the originator
    of a message, proof of delivery of the message and (b) enables the
    originator to demonstrate to a third party that the recipient was
    able to verify the signature of the original message.
    Tutorial: The receipt is bound to the original message by a
    signature; consequently, the service may be requested only for a
    message that is signed. The receipt sender may optionally also
    encrypt the receipt to provide confidentiality between the receipt
    sender and the receipt recipient.
 $ signer
    (N) A human being or organization entity that uses a private key
    to sign (i.e., create a digital signature on) a data object. [DSG]
 $ SILS
    (N) See: Standards for Interoperable LAN/MAN Security.
 $ simple authentication
    1. (I) An authentication process that uses a password as the
    information needed to verify an identity claimed for an entity.
    (Compare: strong authentication.)
    2. (O) "Authentication by means of simple password arrangements."
    [X509]
 $ Simple Authentication and Security Layer (SASL)
    (I) An Internet specification [R2222, R4422] for adding
    authentication service to connection-based protocols. (Compare:
    EAP, GSS-API.)

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    Tutorial: To use SASL, a protocol includes a command for
    authenticating a user to a server and for optionally negotiating
    protection of subsequent protocol interactions. The command names
    a registered security mechanism. SASL mechanisms include Kerberos,
    GSS-API, S/KEY, and others. Some protocols that use SASL are IMAP4
    and POP3.
 $ Simple Key Management for Internet Protocols (SKIP)
    (I) A key-distribution protocol that uses hybrid encryption to
    convey session keys that are used to encrypt data in IP packets.
    (See:  SKIP reference in [R2356].)
    Tutorial: SKIP was designed by Ashar Aziz and Whitfield Diffie at
    Sun Microsystems and proposed as the standard key management
    protocol for IPsec, but IKE was chosen instead. Although IKE is
    mandatory for an IPsec implementation, the use of SKIP is not
    excluded.
    SKIP uses the Diffie-Hellman-Merkle algorithm (or could use
    another key-agreement algorithm) to generate a key-encrypting key
    for use between two entities. A session key is used with a
    symmetric algorithm to encrypt data in one or more IP packets that
    are to be sent from one entity to the other. A symmetric KEK is
    established and used to encrypt the session key, and the encrypted
    session key is placed in a SKIP header that is added to each IP
    packet that is encrypted with that session key.
 $ Simple Mail Transfer Protocol (SMTP)
    (I) A TCP-based, Application-Layer, Internet Standard protocol
    (RFC 821) for moving electronic mail messages from one computer to
    another.
 $ Simple Network Management Protocol (SNMP)
    (I) A (usually) UDP-based, Application-Layer, Internet Standard
    protocol (RFCs 3410-3418) for conveying management information
    between system components that act as managers and agents.
 $ Simple Public Key Infrastructure (SPKI)
    (I) A set of experimental concepts (RFCs 2692, 2693) that were
    proposed as alternatives to the concepts standardized in PKIX.
 $ simple security property
    (N) /formal model/ Property of a system whereby a subject has read
    access to an object only if the clearance of the subject dominates
    the classification of the object. See: Bell-LaPadula model.

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 $ single sign-on
    1. (I) An authentication subsystem that enables a user to access
    multiple, connected system components (such as separate hosts on a
    network) after a single login at only one of the components. (See:
    Kerberos.)
    2. (O) /Liberty Alliance/ A security subsystem that enables a user
    identity to be authenticated at an identity provider -- i.e., at a
    service that authenticates and asserts the user's identity -- and
    then have that authentication be honored by other service
    providers.
    Tutorial: A single sign-on subsystem typically requires a user to
    log in once at the beginning of a session, and then during the
    session transparently grants access by the user to multiple,
    separately protected hosts, applications, or other system
    resources, without further login action by the user (unless, of
    course, the user logs out). Such a subsystem has the advantages of
    being user friendly and enabling authentication to be managed
    consistently across an entire enterprise. Such a subsystem also
    has the disadvantage of requiring all the accessed components to
    depend on the security of the same authentication information.
 $ singular identity
    (I) See: secondary definition under "identity".
 $ site
    (I) A facility -- i.e., a physical space, room, or building
    together with its physical, personnel, administrative, and other
    safeguards -- in which system functions are performed. (See:
    node.)
 $ situation
    (I) See: security situation.
 $ SKEME
    (I) A key-distribution protocol from which features were adapted
    for IKE. [SKEME]
 $ SKIP
    (I) See: Simple Key Management for Internet Protocols.
 $ SKIPJACK
    (N) A type 2, 64-bit block cipher [SKIP, R2773] with a key size of
    80 bits. (See: CAPSTONE, CLIPPER, FORTEZZA, Key Exchange
    Algorithm.)

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    Tutorial: SKIPJACK was developed by NSA and formerly classified at
    the U.S. DoD "Secret" level. On 23 June 1998, NSA announced that
    SKIPJACK had been declassified.
 $ slot
    (O) /MISSI/ One of the FORTEZZA PC card storage areas that are
    each able to hold an X.509 certificate plus other data, including
    the private key that is associated with a public-key certificate.
 $ smart card
    (I) A credit-card sized device containing one or more integrated
    circuit chips that perform the functions of a computer's central
    processor, memory, and input/output interface. (See: PC card,
    smart token.)
    Usage: Sometimes this term is used rather strictly to mean a card
    that closely conforms to the dimensions and appearance of the kind
    of plastic credit card issued by banks and merchants. At other
    times, the term is used loosely to include cards that are larger
    than credit cards, especially cards that are thicker, such as PC
    cards.
 $ smart token
    (I) A device that conforms to the definition of "smart card"
    except that rather than having the standard dimensions of a credit
    card, the token is packaged in some other form, such as a military
    dog tag or a door key. (See: smart card, cryptographic token.)
 $ SMI
    (I) See: security management infrastructure.
 $ SMTP
    (I) See: Simple Mail Transfer Protocol.
 $ smurf attack
    (D) /slang/ A denial-of-service attack that uses IP broadcast
    addressing to send ICMP ping packets with the intent of flooding a
    system. (See: fraggle attack, ICMP flood.)
    Deprecated Term: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term.
    Derivation: The Smurfs are a fictional race of small, blue
    creatures that were created by a cartoonist. Perhaps the inventor
    of this attack thought that a swarm of ping packets resembled a
    gang of smurfs. (See: Deprecated Usage under "Green Book".)

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    Tutorial: The attacker sends ICMP echo request ("ping") packets
    that appear to originate not from the attacker's own IP address,
    but from the address of the host or router that is the target of
    the attack. Each packet is addressed to an IP broadcast address,
    e.g., to all IP addresses in a given network. Thus, each echo
    request that is sent by the attacker results in many echo
    responses being sent to the target address. This attack can
    disrupt service at a particular host, at the hosts that depend on
    a particular router, or in an entire network.
 $ sneaker net
    (D) /slang/ A process that transfers data between systems only
    manually, under human control; i.e., a data transfer process that
    involves an air gap.
    Deprecated Term: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term.
 $ Snefru
    (N) A public-domain, cryptographic hash function (a.k.a. "The
    Xerox Secure Hash Function") designed by Ralph C. Merkle at Xerox
    Corporation. Snefru can produce either a 128-bit or 256-bit output
    (i.e., hash result). [Schn] (See: Khafre, Khufu.)
 $ sniffing
    (D) /slang/ Synonym for "passive wiretapping"; most often refers
    to capturing and examining the data packets carried on a LAN.
    (See: password sniffing.)
    Deprecated Term: IDOCs SHOULD NOT use this term; it unnecessarily
    duplicates the meaning of a term that is better established. (See:
    Deprecated Usage under "Green Book".
 $ SNMP
    (I) See: Simple Network Management Protocol.
 $ social engineering
    (D) Euphemism for non-technical or low-technology methods, often
    involving trickery or fraud, that are used to attack information
    systems. Example: phishing.
    Deprecated Term: IDOCs SHOULD NOT use this term; it is too vague.
    Instead, use a term that is specific with regard to the means of
    attack, e.g., blackmail, bribery, coercion, impersonation,
    intimidation, lying, or theft.

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 $ SOCKS
    (I) An Internet protocol [R1928] that provides a generalized proxy
    server that enables client-server applications (e.g., TELNET, FTP,
    or HTTP; running over either TCP or UDP) to use the services of a
    firewall.
    Tutorial: SOCKS is layered under the IPS Application Layer and
    above the Transport Layer. When a client inside a firewall wishes
    to establish a connection to an object that is reachable only
    through the firewall, it uses TCP to connect to the SOCKS server,
    negotiates with the server for the authentication method to be
    used, authenticates with the chosen method, and then sends a relay
    request. The SOCKS server evaluates the request, typically based
    on source and destination addresses, and either establishes the
    appropriate connection or denies it.
 $ soft TEMPEST
    (O) The use of software techniques to reduce the radio frequency
    information leakage from computer displays and keyboards. [Kuhn]
    (See: TEMPEST.)
 $ soft token
    (D) A data object that is used to control access or authenticate
    authorization. (See: token.)
    Deprecated Term: IDOCs SHOULD NOT use this term as defined here;
    the definition duplicates the meaning of other, standard terms.
    Instead, use "attribute certificate" or another term that is
    specific with regard to the mechanism being used.
 $ software
    (I) Computer programs (which are stored in and executed by
    computer hardware) and associated data (which also is stored in
    the hardware) that may be dynamically written or modified during
    execution. (Compare: firmware.)
 $ software error
    (I) /threat action/ See: secondary definitions under "corruption",
    "exposure", and "incapacitation".
 $ SORA
    (O) See: SSO-PIN ORA.
 $ source authentication
    (D) Synonym for "data origin authentication" or "peer entity
    authentication". (See: data origin authentication, peer entity
    authentication).

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    Deprecated Term: IDOCs SHOULD NOT use this term because it is
    ambiguous and, in either meaning, duplicates the meaning of
    internationally standardized terms. If the intent is to
    authenticate the original creator or packager of data received,
    then use "data origin authentication". If the intent is to
    authenticate the identity of the sender of data in the current
    instance, then use "peer entity authentication".
 $ source integrity
    (I) The property that data is trustworthy (i.e., worthy of
    reliance or trust), based on the trustworthiness of its sources
    and the trustworthiness of any procedures used for handling data
    in the system. Usage: a.k.a. Biba integrity. (See: integrity.
    Compare: correctness integrity, data integrity.)
    Tutorial: For this kind of integrity, there are formal models of
    unauthorized modification (see: Biba model) that logically
    complement the more familiar models of unauthorized disclosure
    (see: Bell-LaPadula model). In these models, objects are labeled
    to indicate the credibility of the data they contain, and there
    are rules for access control that depend on the labels.
 $ SP3
    (O) See: Security Protocol 3.
 $ SP4
    (O) See: Security Protocol 4.
 $ spam
    1a. (I) /slang verb/ To indiscriminately send unsolicited,
    unwanted, irrelevant, or inappropriate messages, especially
    commercial advertising in mass quantities.
    1b. (I) /slang noun/ Electronic "junk mail". [R2635]
    Deprecated Usage: IDOCs SHOULD NOT use this term in uppercase
    letters, because SPAM(trademark) is a trademark of Hormel Foods
    Corporation. Hormel says, "We do not object to use of this slang
    term [spam] to describe [unsolicited advertising email], although
    we do object to the use of our product image in association with
    that term. Also, if the term is to be used, it SHOULD be used in
    all lower-case letters to distinguish it from our trademark SPAM,
    which SHOULD be used with all uppercase letters." (See: metadata.)
    Tutorial: In sufficient volume, spam can cause denial of service.
    (See: flooding.) According to Hormel, the term was adopted as a
    result of a Monty Python skit in which a group of Vikings sang a
    chorus of 'SPAM, SPAM, SPAM ...' in an increasing crescendo,

Shirey Informational [Page 289] RFC 4949 Internet Security Glossary, Version 2 August 2007

    drowning out other conversation. This lyric became a metaphor for
    the unsolicited advertising messages that threaten to overwhelm
    other discourse on the Internet.
 $ SPD
    (I) See: Security Policy Database.
 $ special access program (SAP)
    (O) /U.S. Government/ "Sensitive program, [that is] approved in
    writing by a head of agency with [i.e., who has] original top
    secret classification authority, [and] that imposes need-to-know
    and access controls beyond those normally provided for access to
    Confidential, Secret, or Top Secret information. The level of
    controls is based on the criticality of the program and the
    assessed hostile intelligence threat. The program may be an
    acquisition program, an intelligence program, or an operations and
    support program." [C4009] (See: formal access approval, SCI.
    Compare: collateral information.)
 $ SPI
    (I) See: Security Parameters Index.
 $ SPKI
    (I) See: Simple Public Key Infrastructure.
 $ split key
    (I) A cryptographic key that is generated and distributed as two
    or more separate data items that individually convey no knowledge
    of the whole key that results from combining the items. (See: dual
    control, split knowledge.)
 $ split knowledge
    1. (I) A security technique in which two or more entities
    separately hold data items that individually do not convey
    knowledge of the information that results from combining the
    items. (See: dual control, split key.)
    2. (O) "A condition under which two or more entities separately
    have key components [that] individually convey no knowledge of the
    plaintext key [that] will be produced when the key components are
    combined in the cryptographic module." [FP140]
 $ spoof
    (I) /threat action/ See: secondary definition under "masquerade".
 $ spoofing attack
    (I) Synonym for "masquerade attack".

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 $ spread spectrum
    (N) A TRANSEC technique that transmits a signal in a bandwidth
    much greater than the transmitted information needs. [F1037]
    Example: frequency hopping.
    Tutorial: Usually uses a sequential, noise-like signal structure
    to spread the normally narrowband information signal over a
    relatively wide band of frequencies. The receiver correlates the
    signals to retrieve the original information signal. This
    technique decreases potential interference to other receivers,
    while achieving data confidentiality and increasing immunity of
    spread spectrum receivers to noise and interference.
 $ spyware
    (D) /slang/ Software that an intruder has installed
    surreptitiously on a networked computer to gather data from that
    computer and send it through the network to the intruder or some
    other interested party. (See: malicious logic, Trojan horse.)
    Deprecated Usage: IDOCs that use this term SHOULD state a
    definition for it because the term is used in many ways and could
    easily be misunderstood.
    Tutorial: Some examples of the types of data that might be
    gathered by spyware are application files, passwords, email
    addresses, usage histories, and keystrokes. Some examples of
    motivations for gathering the data are blackmail, financial fraud,
    identity theft, industrial espionage, market research, and
    voyeurism.
 $ SSH(trademark)
    (N) See: Secure Shell(trademark).
 $ SSL
    (I) See: Secure Sockets Layer.
 $ SSO
    (I) See: system security officer.
 $ SSO PIN
    (O) /MISSI/ One of two PINs that control access to the functions
    and stored data of a FORTEZZA PC card. Knowledge of the SSO PIN
    enables a card user to perform the FORTEZZA functions intended for
    use by an end user and also the functions intended for use by a
    MISSI CA. (See: user PIN.)

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 $ SSO-PIN ORA (SORA)
    (O) /MISSI/ A MISSI organizational RA that operates in a mode in
    which the ORA performs all card management functions and,
    therefore, requires knowledge of the SSO PIN for FORTEZZA PC cards
    issued to end users.
 $ Standards for Interoperable LAN/MAN Security (SILS)
    1. (N) The IEEE 802.10 standards committee. (See: [FP191].)
    2. (N) A set of IEEE standards, which has eight parts: (a) Model,
    including security management, (b) Secure Data Exchange protocol,
    (c) Key Management, (d) [has been incorporated in (a)], (e) SDE
    Over Ethernet 2.0, (f) SDE Sublayer Management, (g) SDE Security
    Labels, and (h) SDE PICS Conformance. Parts b, e, f, g, and h are
    incorporated in IEEE Standard 802.10-1998.
 $ star property
    (N) See: *-property.
 $ Star Trek attack
    (D) /slang/ An attack that penetrates your system where no attack
    has ever gone before.
    Deprecated Usage: IDOCs SHOULD NOT use this term; it is a joke for
    Trekkies. (See: Deprecated Usage under "Green Book".)
 $ static
    (I) /adjective/ Refers to a cryptographic key or other parameter
    that is relatively long-lived. (Compare: ephemeral.)
 $ steganography
    (I) Methods of hiding the existence of a message or other data.
    This is different than cryptography, which hides the meaning of a
    message but does not hide the message itself. Examples: For
    classic, physical methods, see [Kahn]; for modern, digital
    methods, see [John]. (See: cryptology. Compare: concealment
    system, digital watermarking.)
 $ storage channel
    (I) See: covert storage channel.
 $ storage key
    (I) A cryptographic key used by a device for protecting
    information that is being maintained in the device, as opposed to
    protecting information that is being transmitted between devices.
    (See: cryptographic token, token copy. Compare: traffic key.)

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 $ stream cipher
    (I) An encryption algorithm that breaks plain text into a stream
    of successive elements (usually, bits) and encrypts the n-th
    plaintext element with the n-th element of a parallel key stream,
    thus converting the plaintext stream into a ciphertext stream.
    [Schn] (See: block cipher.)
 $ stream integrity service
    (I) A data integrity service that preserves integrity for a
    sequence of data packets, including both (a) bit-by-bit datagram
    integrity of each individual packet in the set and (b) packet-by-
    packet sequential integrity of the set as a whole. (See: data
    integrity. Compare: datagram integrity service.)
    Tutorial: Some internetwork applications need only datagram
    integrity, but others require that an entire stream of packets be
    protected against insertion, reordering, deletion, and delay:
    -  "Insertion": The destination receives an additional packet that
       was not sent by the source.
    -  "Reordering": The destination receives packets in a different
       order than that in which they were sent by the source.
    -  "Deletion": A packet sent by the source is not ever delivered
       to the intended destination.
    -  "Delay": A packet is detained for some period of time at a
       relay, thus hampering and postponing the packet's normal timely
       delivery from source to destination.
 $ strength
    1. (I) /cryptography/ A cryptographic mechanism's level of
    resistance to attacks [R3766]. (See: entropy, strong, work
    factor.)
    2. (N) /Common Criteria/ "Strength of function" is a
    "qualification of a TOE security function expressing the minimum
    efforts assumed necessary to defeat its expected security behavior
    by directly attacking its underlying security mechanisms": (See:
    strong.)
    -  Basic: "A level of the TOE strength of function where analysis
       shows that the function provides adequate protection against
       casual breach of TOE security by attackers possessing a low
       attack potential."
    -  Medium: "... against straightforward or intentional breach ...
       by attackers possessing a moderate attack potential."
    -  High: "... against deliberately planned or organized breach ...
       by attackers possessing a high attack potential."

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 $ strong
    1. (I) /cryptography/ Used to describe a cryptographic algorithm
    that would require a large amount of computational power to defeat
    it. (See: strength, work factor, weak key.)
    2. (I) /COMPUSEC/ Used to describe a security mechanism that would
    be difficult to defeat. (See: strength, work factor.)
 $ strong authentication
    1. (I) An authentication process that uses a cryptographic
    security mechanism -- particularly public-key certificates -- to
    verify the identity claimed for an entity. (Compare: simple
    authentication.)
    2. (O) "Authentication by means of cryptographically derived
    credentials." [X509]
 $ subject
    1a. (I) A process in a computer system that represents a principal
    and that executes with the privileges that have been granted to
    that principal. (Compare: principal, user.)
    1b. (I) /formal model/ A system entity that causes information to
    flow among objects or changes the system state; technically, a
    process-domain pair. A subject may itself be an object relative to
    some other subject; thus, the set of subjects in a system is a
    subset of the set of objects. (See: Bell-LaPadula model, object.)
    2. (I) /digital certificate/ The name (of a system entity) that is
    bound to the data items in a digital certificate; e.g., a DN that
    is bound to a key in a public-key certificate. (See: X.509.)
 $ subject CA
    (D) The CA that is the subject of a cross-certificate issued by
    another CA. [X509] (See: cross-certification.)
    Deprecated Term: IDOCs SHOULD NOT use this term because it is not
    widely known and could be misunderstood. Instead, say "the CA that
    is the subject of the cross-certificate".
 $ subnetwork
    (N) An OSI term for a system of packet relays and connecting links
    that implement OSIRM layer 2 or 3 to provide a communication
    service that interconnects attached end systems. Usually, the
    relays are all of the same type (e.g., X.25 packet switches, or
    interface units in an IEEE 802.3 LAN). (See: gateway, internet,
    router.)

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 $ subordinate CA (SCA)
    1. (I) A CA whose public-key certificate is issued by another
    (superior) CA. (See: certification hierarchy. Compare: cross-
    certification.)
    2. (O) /MISSI/ The fourth-highest (i.e., bottom) level of a MISSI
    certification hierarchy; a MISSI CA whose public-key certificate
    is signed by a MISSI CA rather than by a MISSI PCA. A MISSI SCA is
    the administrative authority for a subunit of an organization,
    established when it is desirable to organizationally distribute or
    decentralize the CA service. The term refers both to that
    authoritative office or role, and to the person who fills that
    office. A MISSI SCA registers end users and issues their
    certificates and may also register ORAs, but may not register
    other CAs. An SCA periodically issues a CRL.
 $ subordinate DN
    (I) An X.500 DN is subordinate to another X.500 DN if it begins
    with a set of attributes that is the same as the entire second DN
    except for the terminal attribute of the second DN (which is
    usually the name of a CA). For example, the DN <C=FooLand, O=Gov,
    OU=Treasurer, CN=DukePinchpenny> is subordinate to the DN
    <C=FooLand, O=Gov, CN=KingFooCA>.
 $ subscriber
    (I) /PKI/ A user that is registered in a PKI and, therefore, can
    be named in the "subject" field of a certificate issued by a CA in
    that PKI. (See: registration, user.)
    Usage: This term is needed to distinguish registered users from
    two other kinds of PKI users:
    -  Users that access the PKI but are not identified to it: For
       example, a relying party may access a PKI repository to obtain
       the certificate of some other party. (See: access.)
    -  Users that do not access the PKI: For example, a relying party
       (see: certificate user) may use a digital certificate that was
       obtained from a database that is not part of the PKI that
       issued the certificate.
 $ substitution
    1. (I) /cryptography/ A method of encryption in which elements of
    the plain text retain their sequential position but are replaced
    by elements of cipher text. (Compare: transposition.)
    2. (I) /threat action/ See: secondary definition under
    "falsification".

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 $ subsystem
    (I) A collection of related system components that together
    perform a system function or deliver a system service.
 $ superencryption
    (I) An encryption operation for which the plaintext input to be
    transformed is the ciphertext output of a previous encryption
    operation. (Compare: hybrid encryption.)
 $ superuser
    (I) /UNIX/ Synonym for "root".
 $ survivability
    (I) The ability of a system to remain in operation or existence
    despite adverse conditions, including natural occurrences,
    accidental actions, and attacks. (Compare: availability,
    reliability.)
 $ swIPe
    (I) An encryption protocol for IP that provides confidentiality,
    integrity, and authentication and can be used for both end-to-end
    and intermediate-hop security. [Ioan] (Compare: IPsec.)
    Tutorial: The swIPe protocol is an IP predecessor that is
    concerned only with encryption mechanisms; policy and key
    management are handled outside the protocol.
 $ syllabary
    (N) /encryption/ A list of individual letters, combinations of
    letters, or syllables, with their equivalent code groups, used for
    spelling out proper names or other unusual words that are not
    present in the basic vocabulary (i.e., are not in the codebook) of
    a code used for encryption.
 $ symmetric cryptography
    (I) A branch of cryptography in which the algorithms use the same
    key for both of two counterpart cryptographic operations (e.g.,
    encryption and decryption). (See: asymmetric cryptography.
    Compare: secret-key cryptography.)
    Tutorial: Symmetric cryptography has been used for thousands of
    years [Kahn]. A modern example is AES.
    Symmetric cryptography has a disadvantage compared to asymmetric
    cryptography with regard to key distribution. For example, when
    Alice wants to ensure confidentiality for data she sends to Bob,
    she encrypts the data with a key, and Bob uses the same key to
    decrypt. However, keeping the shared key secret entails both cost

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    and risk when the key is distributed to both Alice and Bob. (See:
    key distribution, key management.)
 $ symmetric key
    (I) A cryptographic key that is used in a symmetric cryptographic
    algorithm. (See: symmetric cryptography.)
 $ SYN flood
    (I) A denial-of-service attack that sends a large number of TCP
    SYN (synchronize) packets to a host with the intent of disrupting
    the operation of that host. (See: blind attack, flooding.)
    Tutorial: This attack seeks to exploit a vulnerability in the TCP
    specification or in a TCP implementation. Normally, two hosts use
    a three-way exchange of packets to establish a TCP connection: (a)
    host 1 requests a connection by sending a SYN packet to host 2;
    (b) host 2 replies by sending a SYN-ACK (acknowledgement) packet
    to host 1; and (c) host 1 completes the connection by sending an
    ACK packet to host 2. To attack host 2, host 1 can send a series
    of TCP SYNs, each with a different phony source address. ([R2827]
    discusses how to use packet filtering to prevent such attacks from
    being launched from behind an Internet service provider's
    aggregation point.) Host 2 treats each SYN as a request from a
    separate host, replies to each with a SYN-ACK, and waits to
    receive the matching ACKs. (The attacker can use random or
    unreachable sources addresses in the SYN packets, or can use
    source addresses that belong to third parties, that then become
    secondary victims.)
    For each SYN-ACK that is sent, the TCP process in host 2 needs
    some memory space to store state information while waiting for the
    matching ACK to be returned. If the matching ACK never arrives at
    host 2, a timer associated with the pending SYN-ACK will
    eventually expire and release the space. But if host 1 (or a
    cooperating group of hosts) can rapidly send many SYNs to host 2,
    host 2 will need to store state information for many pending SYN-
    ACKs and may run out of space. This can prevent host 2 from
    responding to legitimate connection requests from other hosts or
    even, if there are flaws in host 2's TCP implementation, crash
    when the available space is exhausted.
 $ synchronization
    (I) Any technique by which a receiving (decrypting) cryptographic
    process attains an internal state that matches the transmitting
    (encrypting) process, i.e., has the appropriate keying material to
    process the cipher text and is correctly initialized to do so.

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 $ system
    (I) Synonym for "information system".
    Usage: This is a generic definition, and is the one with which the
    term is used in this Glossary. However, IDOCs that use the term,
    especially IDOCs that are protocol specifications, SHOULD state a
    more specific definition. Also, IDOCs that specify security
    features, services, and assurances need to define which system
    components and system resources are inside the applicable security
    perimeter and which are outside. (See: security architecture.)
 $ system architecture
    (N) The structure of system components, their relationships, and
    the principles and guidelines governing their design and evolution
    over time. [DoD10] (Compare: security architecture.)
 $ system component
    1. (I) A collection of system resources that (a) forms a physical
    or logical part of the system, (b) has specified functions and
    interfaces, and (c) is treated (e.g., by policies or
    specifications) as existing independently of other parts of the
    system. (See: subsystem.)
    2. (O) /ITSEC/ An identifiable and self-contained part of a TOE.
    Usage: Component is a relative term because components may be
    nested; i.e., one component of a system may be a part of another
    component of that system.
    Tutorial: Components can be characterized as follows:
    -  A "physical component" has mass and takes up space.
    -  A "logical component" is an abstraction used to manage and
       coordinate aspects of the physical environment, and typically
       represents a set of states or capabilities of the system.
 $ system entity
    (I) An active part of a system -- a person, a set of persons
    (e.g., some kind of organization), an automated process, or a set
    of processes (see: subsystem) -- that has a specific set of
    capabilities. (Compare: subject, user.)
 $ system high
    (I) The highest security level at which a system operates, or is
    capable of operating, at a particular time or in a particular
    environment. (See: system-high security mode.)

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 $ system-high security mode
    (I) A mode of system operation wherein all users having access to
    the system possess all necessary authorizations (both security
    clearance and formal access approval) for all data handled by the
    system, but some users might not have need-to-know for all the
    data. (See: /system operation/ under "mode", formal access
    approval, protection level, security clearance.)
    Usage: Usually abbreviated as "system-high mode". This mode was
    defined in U.S. DoD policy that applied to system accreditation,
    but the term is widely used outside the Government.
 $ system integrity
    1. (I) An attribute or quality "that a system has when it can
    perform its intended function in a unimpaired manner, free from
    deliberate or inadvertent unauthorized manipulation." [C4009,
    NCS04] (See: recovery, system integrity service.)
    2. (D) "Quality of an [information system] reflecting the logical
    correctness and reliability of the operating system; the logical
    completeness of the hardware and software implementing the
    protection mechanisms; and the consistency of the data structures
    and occurrence of the stored data." [from an earlier version of
    C4009]
    Deprecated Definition: IDOCs SHOULD NOT use definition 2 because
    it mixes several concepts in a potentially misleading way.
    Instead, IDOCs should use the term with definition 1 and,
    depending on what is meant, couple the term with additional, more
    specifically descriptive and informative terms, such as
    "correctness", "reliability", and "data integrity".
 $ system integrity service
    (I) A security service that protects system resources in a
    verifiable manner against unauthorized or accidental change, loss,
    or destruction. (See: system integrity.)
 $ system low
    (I) The lowest security level supported by a system at a
    particular time or in a particular environment. (Compare: system
    high.)
 $ system resource
    (I) Data contained in an information system; or a service provided
    by a system; or a system capacity, such as processing power or
    communication bandwidth; or an item of system equipment (i.e.,

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    hardware, firmware, software, or documentation); or a facility
    that houses system operations and equipment. (See: system
    component.)
 $ system security officer (SSO)
    (I) A person responsible for enforcement or administration of the
    security policy that applies to a system. (Compare: manager,
    operator.)
 $ system user
    (I) A system entity that consumes a product or service provided by
    the system, or that accesses and employs system resources to
    produce a product or service of the system. (See: access, [R2504].
    Compare: authorized user, manager, operator, principal, privileged
    user, subject, subscriber, system entity, unauthorized user.)
    Usage: IDOCs that use this term SHOULD state a definition for it
    because the term is used in many ways and could easily be
    misunderstood:
    -  This term usually refers to an entity that has been authorized
       to access the system, but the term sometimes is used without
       regard for whether access is authorized.
    -  This term usually refers to a living human being acting either
       personally or in an organizational role. However, the term also
       may refer to an automated process in the form of hardware,
       software, or firmware; to a set of persons; or to a set of
       processes.
    -  IDOCs SHOULD NOT use the term to refer to a mixed set
       containing both persons and processes. This exclusion is
       intended to prevent situations that might cause a security
       policy to be interpreted in two different and conflicting ways.
    A system user can be characterized as direct or indirect:
    -  "Passive user": A system entity that is (a) outside the
       system's security perimeter *and* (b) can receive output from
       the system but cannot provide input or otherwise interact with
       the system.
    -  "Active user": A system entity that is (a) inside the system's
       security perimeter *or* (b) can provide input or otherwise
       interact with the system.
 $ TACACS
    (I) See: Terminal Access Controller (TAC) Access Control System.
 $ TACACS+
    (I) A TCP-based protocol that improves on TACACS by separating the
    functions of authentication, authorization, and accounting and by
    encrypting all traffic between the network access server and

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    authentication server. TACACS+ is extensible to allow any
    authentication mechanism to be used with TACACS+ clients.
 $ tamper
    (I) Make an unauthorized modification in a system that alters the
    system's functioning in a way that degrades the security services
    that the system was intended to provide. (See: QUADRANT. Compare:
    secondary definitions under "corruption" and "misuse".)
 $ tamper-evident
    (I) A characteristic of a system component that provides evidence
    that an attack has been attempted on that component or system.
    Usage: Usually involves physical evidence. (See: tamper.)
 $ tamper-resistant
    (I) A characteristic of a system component that provides passive
    protection against an attack. (See: tamper.)
    Usage: Usually involves physical means of protection.
 $ tampering
    (I) /threat action/ See: secondary definitions under "corruption"
    and "misuse".
 $ target of evaluation (TOE)
    (N) /Common Criteria/ An information technology product or system
    that is the subject of a security evaluation, together with the
    product's associated administrator and user documentation.
    (Compare: protection profile.)
    Tutorial: The security characteristics of the target of evaluation
    (TOE) are described in specific terms by a corresponding security
    target, or in more general terms by a protection profile. In
    Common Criteria philosophy, it is important that a TOE be
    evaluated against the specific set of criteria expressed in the
    target. This evaluation consists of rigorous analysis and testing
    performed by an accredited, independent laboratory. The scope of a
    TOE evaluation is set by the EAL and other requirements specified
    in the target. Part of this process is an evaluation of the target
    itself, to ensure that it is correct, complete, and internally
    consistent and can be used as the baseline for the TOE evaluation.
 $ TCB
    (N) See: trusted computing base.
 $ TCC field
    (I) See: Transmission Control Code field.

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 $ TCG
    (N) See: Trusted Computing Group.
 $ TCP
    (I) See: Transmission Control Protocol.
 $ TCP/IP
    (I) Synonym for "Internet Protocol Suite".
 $ TCSEC
    (N) See: Trusted Computer System Evaluation Criteria. (Compare:
    TSEC.)
 $ TDEA
    (I) See: Triple Data Encryption Algorithm.
 $ teardrop attack
    (D) /slang/ A denial-of-service attack that sends improperly
    formed IP packet fragments with the intent of causing the
    destination system to fail.
    Deprecated Term: IDOCs that use this term SHOULD state a
    definition for it because the term is often used imprecisely and
    could easily be misunderstood. (See: Deprecated Usage under "Green
    Book".)
 $ technical non-repudiation
    (I) See: (secondary definition under) non-repudiation.
 $ technical security
    (I) Security mechanisms and procedures that are implemented in and
    executed by computer hardware, firmware, or software to provide
    automated protection for a system. (See: security architecture.
    Compare: administrative security.)
 $ Telecommunications Security Word System (TSEC)
    (O) /U.S. Government/ A terminology for designating
    telecommunication security equipment. (Compare: TCSEC.)
    Tutorial: A TSEC designator has the following parts:
    -  Prefix "TSEC/" for items and systems, or suffix "/TSEC" for
       assemblies. (Often omitted when the context is clear.)
    -  First letter, for function: "C" COMSEC equipment system, "G"
       general purpose, "K" cryptographic, "H" crypto-ancillary, "M"
       manufacturing, "N" noncryptographic, "S" special purpose.
    -  Second letter, for type or purpose: "G" key generation, "I"
       data transmission, "L" literal conversion, "N" signal
       conversion, "O" multipurpose, "P" materials production, "S"

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       special purpose, "T" testing or checking, "U" television, "W"
       teletypewriter, "X" facsimile, "Y" speech.
    -  Optional third letter, used only in designations of assemblies,
       for type or purpose: "A" advancing, "B" base or cabinet, "C"
       combining, "D" drawer or panel, "E" strip or chassis, "F" frame
       or rack, "G" key generator, "H" keyboard, "I" translator or
       reader, "J" speech processing, "K" keying or permuting, "L"
       repeater, "M" memory or storage, "O" observation, "P" power
       supply or converter, "R" receiver, "S" synchronizing, "T"
       transmitter, "U" printer, "V" removable COMSEC component, "W"
       logic programmer/programming, "X" special purpose.
    -  Model number, usually two or three digits, assigned
       sequentially within each letter combination (e.g., KG-34, KG-
       84).
    -  Optional suffix letter, used to designate a version. First
       version has no letter, next version has "A" (e.g., KG-84, KG-
       84A), etc.
 $ TELNET
    (I) A TCP-based, Application-Layer, Internet Standard protocol
    (RFC 854) for remote login from one host to another.
 $ TEMPEST
    1. (N) Short name for technology and methods for protecting
    against data compromise due to electromagnetic emanations from
    electrical and electronic equipment. [Army, Russ] (See:
    inspectable space, soft TEMPEST, TEMPEST zone. Compare: QUADRANT)
    2. (O) /U.S. Government/ "Short name referring to investigation,
    study, and control of compromising emanations from IS equipment."
    [C4009]
    Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
    "electromagnetic emanations security"; instead, use EMSEC. Also,
    the term is NOT an acronym for Transient Electromagnetic Pulse
    Surveillance Technology.
    Tutorial: The U.S. Federal Government issues security policies
    that (a) state specifications and standards for techniques to
    reduce the strength of emanations from systems and reduce the
    ability of unauthorized parties to receive and make use of
    emanations and (b) state rules for applying those techniques.
    Other nations presumably do the same.
 $ TEMPEST zone
    (O) "Designated area [i.e., a physical volume] within a facility
    where equipment with appropriate TEMPEST characteristics ... may

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    be operated." [C4009] (See: emanation security, TEMPEST. Compare:
    control zone, inspectable space.)
    Tutorial: The strength of an electromagnetic signal decreases in
    proportion to the square of the distance between the source and
    the receiver. Therefore, EMSEC for electromagnetic signals can be
    achieved by a combination of (a) reducing the strength of
    emanations to a defined level and (b) establishing around that
    equipment an appropriately sized physical buffer zone from which
    unauthorized entities are excluded. By making the zone large
    enough, it is possible to limit the signal strength available to
    entities outside the zone to a level lower than can be received
    and read with known, state-of-the-art methods. Typically, the need
    for and size of a TEMPEST zone established by a security policy
    depends not only on the measured level of signal emitted by
    equipment, but also on the perceived threat level in the
    equipment's environment.
 $ Terminal Access Controller (TAC) Access Control System (TACACS)
    (I) A UDP-based authentication and access control protocol [R1492]
    in which a network access server receives an identifier and
    password from a remote terminal and passes them to a separate
    authentication server for verification. (See: TACACS+.)
    Tutorial: TACACS can provide service not only for network access
    servers but also routers and other networked computing devices via
    one or more centralized authentication servers. TACACS was
    originally developed for ARPANET and has evolved for use in
    commercial equipment.
 $ TESS
    (I) See: The Exponential Encryption System.
 $ The Exponential Encryption System (TESS)
    (I) A system of separate but cooperating cryptographic mechanisms
    and functions for the secure authenticated exchange of
    cryptographic keys, the generation of digital signatures, and the
    distribution of public keys. TESS uses asymmetric cryptography,
    based on discrete exponentiation, and a structure of self-
    certified public keys. [R1824]
 $ theft
    (I) /threat action/ See: secondary definitions under
    "interception" and "misappropriation".
 $ threat
    1a. (I) A potential for violation of security, which exists when
    there is an entity, circumstance, capability, action, or event

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    that could cause harm. (See: dangling threat, INFOCON level,
    threat action, threat agent, threat consequence. Compare: attack,
    vulnerability.)
    1b. (N) Any circumstance or event with the potential to adversely
    affect a system through unauthorized access, destruction,
    disclosure, or modification of data, or denial of service. [C4009]
    (See: sensitive information.)
    Usage: (a) Frequently misused with the meaning of either "threat
    action" or "vulnerability". (b) In some contexts, "threat" is used
    more narrowly to refer only to intelligent threats; for example,
    see definition 2 below. (c) In some contexts, "threat" is used
    more broadly to cover both definition 1 and other concepts, such
    as in definition 3 below.
    Tutorial: A threat is a possible danger that might exploit a
    vulnerability. Thus, a threat may be intentional or not:
    -  "Intentional threat": A possibility of an attack by an
       intelligent entity (e.g., an individual cracker or a criminal
       organization).
    -  "Accidental threat": A possibility of human error or omission,
       unintended equipment malfunction, or natural disaster (e.g.,
       fire, flood, earthquake, windstorm, and other causes listed in
       [FP031]).
    The Common Criteria characterizes a threat in terms of (a) a
    threat agent, (b) a presumed method of attack, (c) any
    vulnerabilities that are the foundation for the attack, and (d)
    the system resource that is attacked. That characterization agrees
    with the definitions in this Glossary (see: diagram under
    "attack").
    2. (O) The technical and operational ability of a hostile entity
    to detect, exploit, or subvert a friendly system and the
    demonstrated, presumed, or inferred intent of that entity to
    conduct such activity.
    Tutorial: To be likely to launch an attack, an adversary must have
    (a) a motive to attack, (b) a method or technical ability to make
    the attack, and (c) an opportunity to appropriately access the
    targeted system.
    3. (D) "An indication of an impending undesirable event." [Park]
    Deprecated Definition: IDOCs SHOULD NOT use this term with
    definition 3 because the definition is ambiguous; the definition
    was intended to include the following three meanings:

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  1. "Potential threat": A possible security violation; i.e., the

same as definition 1.

  1. "Active threat": An expression of intent to violate security.

(Context usually distinguishes this meaning from the previous

       one.)
    -  "Accomplished threat" or "actualized threat": That is, a threat
       action. Deprecated Usage: IDOCs SHOULD NOT use the term
       "threat" with this meaning; instead, use "threat action".
 $ threat action
    (I) A realization of a threat, i.e., an occurrence in which system
    security is assaulted as the result of either an accidental event
    or an intentional act. (See: attack, threat, threat consequence.)
    Tutorial: A complete security architecture deals with both
    intentional acts (i.e., attacks) and accidental events [FP031].
    (See: various kinds of threat actions defined under the four kinds
    of "threat consequence".)
 $ threat agent
    (I) A system entity that performs a threat action, or an event
    that results in a threat action.
 $ threat analysis
    (I) An analysis of the threat actions that might affect a system,
    primarily emphasizing their probability of occurrence but also
    considering their resulting threat consequences. Example: RFC
    3833. (Compare: risk analysis.)
 $ threat consequence
    (I) A security violation that results from a threat action.
    Tutorial: The four basic types of threat consequence are
    "unauthorized disclosure", "deception", "disruption", and
    "usurpation". (See main Glossary entries of each of these four
    terms for lists of the types of threat actions that can result in
    these consequences.)
 $ thumbprint
    1. (I) A pattern of curves formed by the ridges on the tip of a
    thumb. (See: biometric authentication, fingerprint.)
    2. (D) Synonym for some type of "hash result". (See: biometric
    authentication. Compare: fingerprint.)
    Deprecated Usage: IDOCs SHOULD NOT use this term with definition 2
    because that meaning mixes concepts in a potentially misleading
    way.

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 $ ticket
    (I) Synonym for "capability token".
    Tutorial: A ticket is usually granted by a centralized access
    control server (ticket-granting agent) to authorize access to a
    system resource for a limited time. Tickets can be implemented
    with either symmetric cryptography (see: Kerberos) or asymmetric
    cryptography (see: attribute certificate).
 $ tiger team
    (O) A group of evaluators employed by a system's managers to
    perform penetration tests on the system.
    Deprecated Usage: It is likely that other cultures use different
    metaphors for this concept. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
    Usage under "Green Book".)
 $ time stamp
    1. (I) /noun/ With respect to a data object, a label or marking in
    which is recorded the time (time of day or other instant of
    elapsed time) at which the label or marking was affixed to the
    data object. (See: Time-Stamp Protocol.)
    2. (O) /noun/ "With respect to a recorded network event, a data
    field in which is recorded the time (time of day or other instant
    of elapsed time) at which the event took place." [A1523]
    Tutorial: A time stamp can be used as evidence to prove that a
    data object existed (or that an event occurred) at or before a
    particular time. For example, a time stamp might be used to prove
    that a digital signature based on a private key was created while
    the corresponding public-key certificate was valid, i.e., before
    the certificate either expired or was revoked. Establishing this
    proof would enable the certificate to be used after its expiration
    or revocation, to verify a signature that was created earlier.
    This kind of proof is required as part of implementing PKI
    services, such as non-repudiation service, and long-term security
    services, such as audit.
 $ Time-Stamp Protocol
    (I) An Internet protocol (RFC 3161) that specifies how a client
    requests and receives a time stamp from a server for a data object
    held by the client.
    Tutorial: The protocol describes the format of (a) a request sent
    to a time-stamp authority and (b) the response that is returned
    containing a time stamp. The authority creates the stamp by

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    concatenating (a) a hash value of the input data object with (b) a
    UTC time value and other parameters (policy OID, serial number,
    indication of time accuracy, nonce, DN of the authority, and
    various extensions), and then signing that dataset with the
    authority's private key as specified in CMS. Such an authority
    typically would operate as a trusted third-party service, but
    other operational models might be used.
 $ timing channel
    (I) See: covert timing channel.
 $ TKEY
    (I) A mnemonic referring to an Internet protocol (RFC 2930) for
    establishing a shared secret key between a DNS resolver and a DNS
    name server. (See: TSIG.)
 $ TLS
    (I) See: Transport Layer Security.
 $ TLSP
    (N) See: Transport Layer Security Protocol.
 $ TOE
    (N) See: target of evaluation.
 $ token
    1. (I) /cryptography/ See: cryptographic token. (Compare: dongle.)
    2. (I) /access control/ An object that is used to control access
    and is passed between cooperating entities in a protocol that
    synchronizes use of a shared resource. Usually, the entity that
    currently holds the token has exclusive access to the resource.
    (See: capability token.)
    Usage: This term is heavily overloaded in the computing
    literature; therefore, IDOCs SHOULD NOT use this term with any
    definition other than 1 or 2.
    3a. (D) /authentication/ A data object or a physical device used
    to verify an identity in an authentication process.
    3b. (D) /U.S. Government/ Something that the claimant in an
    authentication process (i.e., the entity that claims an identity)
    possesses and controls, and uses to prove the claim during the
    verification step of the process. [SP63]
    Deprecated usage: IDOCs SHOULD NOT use this term with definitions
    3a and 3b; instead, use more specifically descriptive and

Shirey Informational [Page 308] RFC 4949 Internet Security Glossary, Version 2 August 2007

    informative terms such as "authentication information" or
    "cryptographic token", depending on what is meant.
    NIST defines four types of claimant tokens for electronic
    authentication in an information system [SP63]. IDOCs SHOULD NOT
    use these four NIST terms; they mix concepts in potentially
    confusing ways and duplicate the meaning of better-established
    terms. These four terms can be avoided by using more specifically
    descriptive terms as follows:
    -  NIST "hard token": A hardware device that contains a protected
       cryptographic key. (This is a type of "cryptographic token",
       and the key is a type of "authentication information".)
    -  NIST "one-time password device token": A personal hardware
       device that generates one-time passwords. (One-time passwords
       are typically generated cryptographically. Therefore, this is a
       type of "cryptographic token", and the key is a type of
       "authentication information".)
    -  NIST "soft token": A cryptographic key that typically is stored
       on disk or some other magnetic media. (The key is a type of
       "authentication information"; "authentication key" would be a
       better description.)
    -  NIST "password token": A secret data value that the claimant
       memorizes. (This is a "password" that is being used as
       "authentication information".)
 $ token backup
    (I) A token management operation that stores sufficient
    information in a database (e.g., in a CAW) to recreate or restore
    a security token (e.g., a smart card) if it is lost or damaged.
 $ token copy
    (I) A token management operation that copies all the personality
    information from one security token to another. However, unlike in
    a token restore operation, the second token is initialized with
    its own, different local security values such as PINs and storage
    keys.
 $ token management
    (I) The process that includes initializing security tokens (e.g.,
    "smart card"), loading data into the tokens, and controlling the
    tokens during their lifecycle. May include performing key
    management and certificate management functions; generating and
    installing PINs; loading user personality data; performing card
    backup, card copy, and card restore operations; and updating
    firmware.

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 $ token restore
    (I) A token management operation that loads a security token with
    data for the purpose of recreating (duplicating) the contents
    previously held by that or another token. (See: recovery.)
 $ token storage key
    (I) A cryptographic key used to protect data that is stored on a
    security token.
 $ top CA
    (I) Synonym for "root" in a certification hierarchy. (See: apex
    trust anchor.)
 $ top-level specification
    (I) "A non-procedural description of system behavior at the most
    abstract level; typically a functional specification that omits
    all implementation details." [NCS04] (See: formal top-level
    specification, Tutorial under "security policy".)
    Tutorial: A top-level specification is at a level of abstraction
    below "security model" and above "security architecture" (see:
    Tutorial under "security policy").
    A top-level specification may be descriptive or formal:
    -  "Descriptive top-level specification": One that is written in a
       natural language like English or an informal design notation.
    -  "Formal top-level specification": One that is written in a
       formal mathematical language to enable theorems to be proven
       that show that the specification correctly implements a set of
       formal requirements or a formal security model. (See:
       correctness proof.)
 $ TPM
    (N) See: Trusted Platform Module.
 $ traceback
    (I) Identification of the source of a data packet. (See:
    masquerade, network weaving.)
 $ tracker
    (N) An attack technique for achieving unauthorized disclosure from
    a statistical database. [Denns] (See: Tutorial under "inference
    control".)
 $ traffic analysis
    1. (I) Gaining knowledge of information by inference from
    observable characteristics of a data flow, even if the information
    is not directly available (e.g., when the data is encrypted).

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    These characteristics include the identities and locations of the
    source(s) and destination(s) of the flow, and the flow's presence,
    amount, frequency, and duration of occurrence. The object of the
    analysis might be information in SDUs, information in the PCI, or
    both. (See: inference, traffic-flow confidentiality, wiretapping.
    Compare: signal analysis.)
    2. (O) "The inference of information from observation of traffic
    flows (presence, absence, amount, direction, and frequency)."
    [I7498-2]
 $ traffic-flow analysis
    (I) Synonym for "traffic analysis".
 $ traffic-flow confidentiality (TFC)
    1. (I) A data confidentiality service to protect against traffic
    analysis. (See: communications cover.)
    2. (O) "A confidentiality service to protect against traffic
    analysis." [I7498-2]
    Tutorial: Confidentiality concerns involve both direct and
    indirect disclosure of data, and the latter includes traffic
    analysis. However, operational considerations can make TFC
    difficult to achieve. For example, if Alice sends a product idea
    to Bob in an email message, she wants data confidentiality for the
    message's content, and she might also want to conceal the
    destination of the message to hide Bob's identity from her
    competitors. However, the identity of the intended recipient, or
    at least a network address for that recipient, needs to be made
    available to the mail system. Thus, complex forwarding schemes may
    be needed to conceal the ultimate destination as the message
    travels through the open Internet (see: onion routing).
    Later, if Alice uses an ATM during a clandestine visit to
    negotiate with Bob, she might prefer that her bank conceal the
    origin of her transaction, because knowledge of the ATM's location
    might allow a competitor to infer Bob's identity. The bank, on the
    other hand, might prefer to protect only Alice's PIN (see:
    selective-field confidentiality).
    A TFC service can be either full or partial:
    -  "Full TFC": This type of service conceals all traffic
       characteristics.
    -  "Partial TFC": This type of service either (a) conceals some
       but not all of the characteristics or (b) does not completely
       conceal some characteristic.

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    On point-to-point data links, full TFC can be provided by
    enciphering all PDUs and also generating a continuous, random data
    stream to seamlessly fill all gaps between PDUs. To a wiretapper,
    the link then appears to be carrying an unbroken stream of
    enciphered data. In other cases -- including on a shared or
    broadcast medium, or end-to-end in a network -- only partial TFC
    is possible, and that may require a combination of techniques. For
    example, a LAN that uses "carrier sense multiple access with
    collision detection" (CSMA/CD; a.k.a. "listen while talk") to
    control access to the medium, relies on detecting intervals of
    silence, which prevents using full TFC. Partial TFC can be
    provided on that LAN by measures such as adding spurious PDUs,
    padding PDUs to a constant size, or enciphering addresses just
    above the Physical Layer; but these measures reduce the efficiency
    with which the LAN can carry traffic. At higher protocol layers,
    SDUs can be protected, but addresses and other items of PCI must
    be visible at the layers below.
 $ traffic key
    (I) A cryptographic key used by a device for protecting
    information that is being transmitted between devices, as opposed
    to protecting information that being is maintained in the device.
    (Compare: storage key.)
 $ traffic padding
    (I) "The generation of spurious instances of communication,
    spurious data units, and/or spurious data within data units."
    [I7498-2]
 $ tranquility property
    (N) /formal model/ Property of a system whereby the security level
    of an object cannot change while the object is being processed by
    the system. (See: Bell-LaPadula model.)
 $ transaction
    1. (I) A unit of interaction between an external entity and a
    system, or between components within a system, that involves a
    series of system actions or events.
    2. (O) "A discrete event between user and systems that supports a
    business or programmatic purpose." [M0404]
    Tutorial: To maintain secure state, transactions need to be
    processed coherently and reliably. Usually, they need to be
    designed to be atomic, consistent, isolated, and durable [Gray]:
    -  "Atomic": All actions and events that comprise the transaction
       are guaranteed to be completed successfully, or else the result
       is as if none at all were executed.

Shirey Informational [Page 312] RFC 4949 Internet Security Glossary, Version 2 August 2007

  1. "Consistent": The transaction satisfies correctness constraints

defined for the data that is being processed.

  1. "Isolated": If two transactions are performed concurrently,

they do not interfere with each other, and it appears as though

       the system performs one at a time.
    -  "Durable": System state and transaction semantics survive
       system failures.
 $ TRANSEC
    (I) See: transmission security.
 $ Transmission Control Code field (TCC field)
    (I) A data field that provides a means to segregate traffic and
    define controlled communities of interest in the security option
    (option type = 130) of IPv4's datagram header format. The TCC
    values are alphanumeric trigraphs assigned by the U.S. Government
    as specified in RFC 791.
 $ Transmission Control Protocol (TCP)
    (I) An Internet Standard, Transport-Layer protocol (RFC 793) that
    reliably delivers a sequence of datagrams from one computer to
    another in a computer network. (See: TCP/IP.)
    Tutorial: TCP is designed to fit into a layered suite of protocols
    that support internetwork applications. TCP assumes it can obtain
    a simple but potentially unreliable end-to-end datagram service
    (such as IP) from the lower-layer protocols.
 $ transmission security (TRANSEC)
    (I) COMSEC measures that protect communications from interception
    and exploitation by means other than cryptanalysis. Example:
    frequency hopping. (Compare: anti-jam, traffic flow
    confidentiality.)
 $ Transport Layer
    See: Internet Protocol Suite, OSIRM.
 $ Transport Layer Security (TLS)
    (I) TLS is an Internet protocol [R4346] that is based on, and very
    similar to, SSL Version 3.0. (Compare: TLSP.)
    Tutorial: The TLS protocol is misnamed. The name misleadingly
    suggests that TLS is situated in the IPS Transport Layer, but TLS
    is always layered above a reliable Transport-Layer protocol
    (usually TCP) and either layered immediately below or integrated
    with an Application-Layer protocol (often HTTP).

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 $ Transport Layer Security Protocol (TLSP)
    (N) An end-to-end encryption protocol (ISO 10736) that provides
    security services at the bottom of OSIRM Layer 4, i.e., directly
    above Layer 3. (Compare: TLS.)
    Tutorial: TLSP evolved directly from SP4.
 $ transport mode
    (I) One of two ways to apply AH or ESP to protect data packets; in
    this mode, the IPsec protocol encapsulates (i.e., the protection
    applies to) the packets of an IPS Transport-Layer protocol (e.g.,
    TCP, UDP), which normally is carried directly above IP in an IPS
    protocol stack. (Compare: tunnel mode.)
    Tutorial: An IPsec transport-mode security association is always
    between two hosts; neither end has the role of a security gateway.
    Whenever either end of an IPsec security association is a security
    gateway, the association is required to be in tunnel mode.
 $ transposition
    (I) /cryptography/ A method of encryption in which elements of the
    plain text retain their original form but undergo some change in
    their sequential position. (Compare: substitution.)
 $ trap door
    (I) Synonym for "back door".
 $ trespass
    (I) /threat action/ See: secondary definition under "intrusion".
 $ Triple Data Encryption Algorithm
    (I) A block cipher that transforms each 64-bit plaintext block by
    applying the DEA three successive times, using either two or three
    different keys for an effective key length of 112 or 168 bits.
    [A9052, SP67]
    Example: A variation proposed for IPsec's ESP uses a 168-bit key,
    consisting of three independent 56-bit values used by the DEA, and
    a 64-bit initialization vector. Each datagram contains an IV to
    ensure that each received datagram can be decrypted even when
    other datagrams are dropped or a sequence of datagrams is
    reordered in transit. [R1851]
 $ triple-wrapped
    (I) /S-MIME/ Data that has been signed with a digital signature,
    then encrypted, and then signed again. [R2634]

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 $ Trojan horse
    (I) A computer program that appears to have a useful function, but
    also has a hidden and potentially malicious function that evades
    security mechanisms, sometimes by exploiting legitimate
    authorizations of a system entity that invokes the program. (See:
    malware, spyware. Compare: logic bomb, virus, worm.)
 $ trust
    1. (I) /information system/ A feeling of certainty (sometimes
    based on inconclusive evidence) either (a) that the system will
    not fail or (b) that the system meets its specifications (i.e.,
    the system does what it claims to do and does not perform unwanted
    functions). (See: trust level, trusted system, trustworthy system.
    Compare: assurance.)
    Tutorial: Components of a system can be grouped into three classes
    of trust [Gass]:
    -  "Trusted": The component is responsible for enforcing security
       policy on other components; the system's security depends on
       flawless operation of the component. (See: trusted process.)
    -  "Benign": The component is not responsible for enforcing
       security policy, but it has sensitive authorizations. It must
       be trusted not to intentionally violate security policy, but
       security violations are assumed to be accidental and not likely
       to affect overall system security.
    -  "Untrusted": The component is of unknown or suspicious
       provenance and must be treated as deliberately malicious. (See:
       malicious logic.)
    2. (I) /PKI/ A relationship between a certificate user and a CA in
    which the user acts according to the assumption that the CA
    creates only valid digital certificates.
    Tutorial: "Generally, an entity is said to 'trust' a second entity
    when the first entity makes the assumption that the second entity
    will behave exactly as the first entity expects. This trust may
    apply only for some specific function. The key role of trust in
    [X.509] is to describe the relationship between an entity [i.e., a
    certificate user] and a [CA]; an entity shall be certain that it
    can trust the CA to create only valid and reliable certificates."
    [X509]
 $ trust anchor
    (I) /PKI/ An established point of trust (usually based on the
    authority of some person, office, or organization) from which a
    certificate user begins the validation of a certification path.
    (See: apex trust anchor, path validation, trust anchor CA, trust
    anchor certificate, trust anchor key.)

Shirey Informational [Page 315] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Usage: IDOCs that use this term SHOULD state a definition for it
    because it is used in various ways in existing IDOCs and other PKI
    literature. The literature almost always uses this term in a sense
    that is equivalent to this definition, but usage often differs
    with regard to what constitutes the point of trust.
    Tutorial: A trust anchor may be defined as being based on a public
    key, a CA, a public-key certificate, or some combination or
    variation of those:
  1. 1. A public key as a point of trust: Although a certification

path is defined as beginning with a "sequence of public-key

       certificates", an implementation of a path validation process
       might not explicitly handle a root certificate as part of the
       path, but instead begin the process by using a trusted root key
       to verify the signature on a certificate that was issued by the
       root.
       Therefore, "trust anchor" is sometimes defined as just a public
       key. (See: root key, trust anchor key, trusted key.)
  1. 2. A CA as a point of trust: A trusted public key is just one

of the data elements needed for path validation; the IPS path

       validation algorithm [R3280] also needs the name of the CA to
       which that key belongs, i.e., the DN of the issuer of the first
       X.509 certificate to be validated on the path. (See: issue.)
       Therefore, "trust anchor" is sometimes defined as either just a
       CA (where some public key is implied) or as a CA together with
       a specified public key belonging to that CA. (See: root, trust
       anchor CA, trusted CA.)
       Example: "A public key and the name of a [CA] that is used to
       validate the first certificate in a sequence of certificates.
       The trust anchor public key is used to verify the signature on
       a certificate issued by a trust anchor [CA]." [SP57]
  1. 3. A public-key certificate as a point of trust: Besides the

trusted CA's public key and name, the path validation algorithm

       needs to know the digital signature algorithm and any
       associated parameters with which the public key is used, and
       also any constraints that have been placed on the set of paths
       that may be validated using the key. All of this information is
       available from a CA's public-key certificate.
       Therefore, "trust anchor" is sometimes defined as a public-key
       certificate of a CA. (See: root certificate, trust anchor
       certificate, trusted certificate.)

Shirey Informational [Page 316] RFC 4949 Internet Security Glossary, Version 2 August 2007

  1. 4. Combinations: Combinations and variations of the first three

definitions are also used in the PKI literature.

       Example: "trust anchor information". The IPS standard for path
       validation [R3280] specifies the information that describes "a
       CA that serves as a trust anchor for the certification path.
       The trust anchor information includes: (a) the trusted issuer
       name, (b) the trusted public key algorithm, (c) the trusted
       public key, and (d) optionally, the trusted public key
       parameters associated with the public key. The trust anchor
       information may be provided to the path processing procedure in
       the form of a self-signed certificate. The trusted anchor
       information is trusted because it was delivered to the path
       processing procedure by some trustworthy out-of-band procedure.
       If the trusted public key algorithm requires parameters, then
       the parameters are provided along with the trusted public key."
 $ trust anchor CA
    (I) A CA that is the subject of a trust anchor certificate or
    otherwise establishes a trust anchor key. (See: root, trusted CA.)
    Tutorial: The selection of a CA to be a trust anchor is a matter
    of policy. Some of the possible choices include (a) the top CA in
    a hierarchical PKI, (b) the CA that issued the verifier's own
    certificate, or (c) any other CA in a network PKI. Different
    applications may rely on different trust anchors, or may accept
    paths that begin with any of a set of trust anchors. The IPS path
    validation algorithm is the same, regardless of the choice.
 $ trust anchor certificate
    (I) A public-key certificate that is used to provide the first
    public key in a certification path. (See: root certificate, trust
    anchor, trusted certificate.)
 $ trust anchor key
    (I) A public key that is used as the first public key in a
    certification path. (See: root key, trust anchor, trusted public
    key.)
 $ trust anchor information
    (I) See: secondary definition under "trust anchor".
 $ trust chain
    (D) Synonym for "certification path". (See: trust anchor, trusted
    certificate.)

Shirey Informational [Page 317] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Deprecated Term: IDOCs SHOULD NOT use this term, because it
    unnecessarily duplicates the meaning of the internationally
    standardized term.
    Also, the term mixes concepts in a potentially misleading way.
    Having "trust" involves factors unrelated to simply verifying
    signatures and performing other tests as specified by a standard
    algorithm for path validation (e.g., RFC 3280). Thus, even if a
    user is able to validate a certification path algorithmically, the
    user still might distrust one of the CAs that issued certificates
    in that path or distrust some other aspects of the PKI.
 $ trust-file PKI
    (I) A non-hierarchical PKI in which each certificate user has its
    own local file (which is used by application software) of trust
    anchors, i.e., either public keys or public-key certificates that
    the user trusts as starting points for certification paths. (See:
    trust anchor, web of trust. Compare: hierarchical PKI, mesh PKI.)
    Example: Popular browsers are distributed with an initial file of
    trust anchor certificates, which often are self-signed
    certificates. Users can add certificates to the file or delete
    from it. The file may be directly managed by the user, or the
    user's organization may manage it from a centralized server.
 $ trust hierarchy
    (D) Synonym for "certification hierarchy".
    Deprecated Usage: IDOCs SHOULD NOT use this term because it mixes
    concepts in a potentially misleading way, and because a trust
    hierarchy could be implemented in other ways. (See: trust, trust
    chain, web of trust.)
 $ trust level
    (N) A characterization of a standard of security protection to be
    met by an information system. (See: Common Criteria, TCSEC.)
    Tutorial: A trust level is based not only on (a) the presence of
    security mechanisms, but also on the use of (b) systems
    engineering discipline to properly structure the system and (c)
    implementation analysis to ensure that the system provides an
    appropriate degree of trust.
 $ trusted
    (I) See: secondary definition under "trust".

Shirey Informational [Page 318] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ trusted CA
    (I) A CA upon which a certificate user relies as issuing valid
    certificates; especially a CA that is used as a trust anchor CA.
    (See: certification path, root, trust anchor CA, validation.)
    Tutorial. This trust is transitive to the extent that the X.509
    certificate extensions permit; that is, if a trusted CA issues a
    certificate to another CA, a user that trusts the first CA also
    trusts the second CA if the user succeeds in validating the
    certificate path (see: path validation).
 $ trusted certificate
    (I) A digital certificate that a certificate user accepts as being
    valid "a priori", i.e., without testing the certificate to
    validate it as the final certificate on a certification path;
    especially a certificate that is used as a trust anchor
    certificate. (See: certification path, root certificate, trust
    anchor certificate, trust-file PKI, validation.)
    Tutorial: The acceptance of a certificate as trusted is a matter
    of policy and choice. Usually, a certificate is accepted as
    trusted because the user obtained it by reliable, out-of-band
    means that cause the user to believe the certificate accurately
    binds its subject's name to the subject's public key or other
    attribute values. Many choices are possible; e.g., a trusted
    public-key certificate might be (a) the root certificate in a
    hierarchical PKI, (b) the certificate of the CA that issued the
    user's own certificate in a mesh PKI, or (c) a certificate
    provided with an application that uses a trust-file PKI.
 $ Trusted Computer System Evaluation Criteria (TCSEC)
    (N) A standard for evaluating the security provided by operating
    systems [CSC1, DoD1]. Known as the "Orange Book" because of the
    color of its cover; first document in the Rainbow Series. (See:
    Common Criteria, Deprecated Usage under "Green Book", Orange Book,
    trust level, trusted system. Compare: TSEC.)
    Tutorial: The TCSEC defines classes of hierarchically ordered
    assurance levels for rating computer systems. From highest to
    lowest, the classes are as follows:
    -  Division A:  Verified protection.
         Beyond A1    Beyond current technology. (See: beyond A1.)
         Class  A1    Verified design. (See: SCOMP.)
    -  Division B:  Mandatory protection.
         Class  B3    Security domains.
         Class  B2    Structured protection. (See: Multics.)
         Class  B1    Labeled security protection.

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  1. Division C: Discretionary protection.

Class C2 Controlled access protection.

         Class  C1    Discretionary security protection.
    -  Division D:  Minimal protection, i.e., has been evaluated but
       does not meet the requirements for a higher evaluation class.
 $ trusted computing base (TCB)
    (N) "The totality of protection mechanisms within a computer
    system, including hardware, firmware, and software, the
    combination of which is responsible for enforcing a security
    policy." [NCS04] (See: "trusted" under "trust". Compare: TPM.)
 $ Trusted Computing Group (TCG)
    (N) A not-for-profit, industry standards organization formed to
    develop, define, and promote open standards for hardware-enabled
    trusted computing and security technologies, including hardware
    building blocks and software interfaces, across multiple
    platforms, peripherals, and devices. (See: TPM, trusted system.
    Compare: TSIG.)
 $ trusted distribution
    (I) /COMPUSEC/ "A trusted method for distributing the TCB
    hardware, software, and firmware components, both originals and
    updates, that provides methods for protecting the TCB from
    modification during distribution and for detection of any changes
    to the TCB that may occur." [NCS04] (See: code signing,
    configuration control.)
 $ trusted key
    (D) Abbreviation for "trusted public key" and also for other types
    of keys. (See: root key, trust anchor key.)
    Deprecated Usage: IDOCs SHOULD either (a) state a definition for
    this term or (b) use a different, less ambiguous term. This term
    is ambiguous when it stands alone; e.g., it could refer to a
    trusted public key or to a private key or symmetric key that is
    believed to be secure (i.e., not compromised).
 $ trusted path
    1a. (I) /COMPUSEC/ A mechanism by which a computer system user can
    communicate directly and reliably with the TCB and that can only
    be activated by the user or the TCB and cannot be imitated by
    untrusted software within the computer. [NCS04]
    1b. (I) /COMSEC/ A mechanism by which a person or process can
    communicate directly with a cryptographic module and that can only
    be activated by the person, process, or module, and cannot be
    imitated by untrusted software within the module. [FP140]

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 $ Trusted Platform Module (TPM)
    (N) The name of a specification, published by the TCG, for a
    microcontroller that can store secured information; and also the
    general name of implementations of that specification. (Compare:
    TCB.)
 $ trusted process
    (I) A system component that has privileges that enable it to
    affect the state of system security and that can, therefore,
    through incorrect or malicious execution, violate the system's
    security policy. (See: privileged process, trusted system.)
 $ trusted public key
    (I) A public key upon which a user relies; especially a public key
    that is used as a trust anchor key. (See: certification path, root
    key, trust anchor key, validation.)
    Tutorial: A trusted public key could be (a) the root key in a
    hierarchical PKI, (b) the key of the CA that issued the user's own
    certificate in a mesh PKI, or (c) any key accepted by the user in
    a trust-file PKI.
 $ trusted recovery
    (I) A process that, after a system has experienced a failure or an
    attack, restores the system to normal operation (or to a secure
    state) without causing a security compromise. (See: recovery.)
 $ trusted subnetwork
    (I) A subnetwork containing hosts and routers that trust each
    other not to engage in active or passive attacks. (There also is
    an assumption that the underlying communication channels, such as
    telephone lines or a LAN, are protected from attack.)
 $ trusted system
    1. (I) /information system/ A system that operates as expected,
    according to design and policy, doing what is required -- despite
    environmental disruption, human user and operator errors, and
    attacks by hostile parties -- and not doing other things [NRC98].
    (See: trust level, trusted process. Compare: trustworthy.)
    2. (N) /multilevel secure/ "A [trusted system is a] system that
    employs sufficient hardware and software assurance measures to
    allow its use for simultaneous processing of a range of sensitive
    or classified information." [NCS04] (See: multilevel security
    mode.)

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 $ Trusted Systems Interoperability Group (TSIG)
    (N) A forum of computer vendors, system integrators, and users
    devoted to promoting interoperability of trusted computer systems.
    (See: trusted system. Compare: TCG.)
 $ trustworthy system
    1. (I) A system that not only is trusted, but also warrants that
    trust because the system's behavior can be validated in some
    convincing way, such as through formal analysis or code review.
    (See: trust. Compare: trusted.)
    2. (O) /Digital Signature Guidelines/ "Computer hardware,
    software, and procedures that: (a) are reasonably secure from
    intrusion and misuse; (b) provide a reasonably reliable level of
    availability, reliability, and correct operation; (c) are
    reasonably suited to performing their intended functions; and (d)
    adhere to generally accepted security principles." [DSG]
 $ TSEC
    (O) See: Telecommunications Security Nomenclature System.
    (Compare: TCSEC.)
 $ TSIG
    1. (N) See: Trusted System Interoperability Group.
    2. (I) A mnemonic (presumed to be derived from "Transaction
    SIGnature") referring to an Internet protocol (RFC 2845) for data
    origin authentication and data integrity for certain DNS
    operations. (See: TKEY.)
 $ tunnel
    1. (I) A communication channel created in a computer network by
    encapsulating (i.e., layering) a communication protocol's data
    packets in (i.e., above) a second protocol that normally would be
    carried above, or at the same layer as, the first one. (See: L2TP,
    tunnel mode, VPN. Compare: covert channel.)
    Tutorial: Tunneling can involve almost any two IPS protocol
    layers. For example, a TCP connection between two hosts could
    conceivably be carried above SMTP (i.e., in SMTP messages) as a
    covert channel to evade access controls that a security gateway
    applies to the normal TCP layer that is below SMTP.
    Usually, however, a tunnel is a logical point-to-point link --
    i.e., an OSIRM Layer 2 connection -- created by encapsulating the
    Layer 2 protocol in one of the following three types of IPS
    protocols: (a) an IPS Transport-Layer protocol (such as TCP), (b)
    an IPS Network-Layer or Internet-Layer protocol (such as IP), or

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    (c) another Layer 2 protocol. In many cases, the encapsulation is
    accomplished with an extra, intermediate protocol (i.e., a
    "tunneling protocol"; e.g., L2TP) that is layered below the
    tunneled Layer 2 protocol and above the encapsulating protocol.
    Tunneling can be used to move data between computers that use a
    protocol not supported by the network connecting them. Tunneling
    also can enable a computer network to use the services of a second
    network as though the second network were a set of point-to-point
    links between the first network's nodes. (See: VPN.)
    2. (O) /SET/ The name of a SET private extension that indicates
    whether the CA or the payment gateway supports passing encrypted
    messages to the cardholder through the merchant. If so, the
    extension lists OIDs of symmetric encryption algorithms that are
    supported.
 $ tunnel mode
    (I) One of two ways to apply the IPsec protocols (AH and ESP) to
    protect data packets; in this mode, the IPsec protocol
    encapsulates (i.e., the protection applies to) IP packets, rather
    than the packets of higher-layer protocols. (See: tunnel. Compare:
    transport mode.)
    Tutorial: Each end of a tunnel-mode security association may be
    either a host or a security gateway. Whenever either end of an
    IPsec security association is a security gateway, the association
    is required to be in tunnel mode.
 $ two-person control
    (I) The close surveillance and control of a system, a process, or
    materials (especially with regard to cryptography) at all times by
    a minimum of two appropriately authorized persons, each capable of
    detecting incorrect and unauthorized procedures with respect to
    the tasks to be performed and each familiar with established
    security requirements. (See: dual control, no-lone zone.)
 $ Twofish
    (O) A symmetric, 128-bit block cipher with variable key length
    (128, 192, or 256 bits), developed by Counterpane Labs as a
    candidate for the AES. (See: Blowfish.)
 $ type 0 product
    (O) /cryptography, U.S. Government/ Classified cryptographic
    equipment endorsed by NSA for use (when appropriately keyed) in
    electronically distributing bulk keying material.

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 $ type 1 key
    (O) /cryptography, U.S. Government/ "Generated and distributed
    under the auspices of NSA for use in a cryptographic device for
    the protection of classified and sensitive national security
    information." [C4009]
 $ type 1 product
    (O) /cryptography, U.S. Government/ "Cryptographic equipment,
    assembly or component classified or certified by NSA for
    encrypting and decrypting classified and sensitive national
    security information when appropriately keyed. Developed using
    established NSA business processes and containing NSA approved
    algorithms. Used to protect systems requiring the most stringent
    protection mechanisms." [C4009]
    Tutorial: The current definition of this term is less specific
    than an earlier version: "Classified or controlled cryptographic
    item endorsed by the NSA for securing classified and sensitive
    U.S. Government information, when appropriately keyed. The term
    refers only to products, and not to information, key, services, or
    controls. Type 1 products contain classified NSA algorithms. They
    are available to U.S. Government users, their contractors, and
    federally sponsored non-U.S. Government activities subject to
    export restrictions in accordance with International Traffic in
    Arms Regulation." [from an earlier version of C4009] (See: ITAR.)
 $ type 2 key
    (O) /cryptography, U.S. Government/ "Generated and distributed
    under the auspices of NSA for use in a cryptographic device for
    the protection of unclassified national security information."
    [C4009]
 $ type 2 product
    (O) /cryptography, U.S. Government/ "Cryptographic equipment,
    assembly, or component certified by NSA for encrypting or
    decrypting sensitive national security information when
    appropriately keyed. Developed using established NSA business
    processes and containing NSA approved algorithms. Used to protect
    systems requiring protection mechanisms exceeding best commercial
    practices including systems used for the protection of
    unclassified national security information." [C4009]
    Tutorial: The current definition of this term is less specific
    than an earlier version: "Unclassified cryptographic equipment,
    assembly, or component, endorsed by the NSA, for use in national
    security systems as defined in Title 40 U.S.C. Section 1452."
    [from an earlier version of C4009] (See: national security system.
    Compare: EUCI.)

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 $ type 3 key
    (O) /cryptography, U.S. Government/ "Used in a cryptographic
    device for the protection of unclassified sensitive information,
    even if used in a Type 1 or Type 2 product." [C4009]
 $ type 3 product
    (O) /cryptography, U.S. Government/ "Unclassified cryptographic
    equipment, assembly, or component used, when appropriately keyed,
    for encrypting or decrypting unclassified sensitive U.S.
    Government or commercial information, and to protect systems
    requiring protection mechanisms consistent with standard
    commercial practices. Developed using established commercial
    standards and containing NIST approved cryptographic
    algorithms/modules or successfully evaluated by the National
    Information Assurance Partnership (NIAP)." [C4009]
 $ type 4 key
    (O) /cryptography, U.S. Government/ "Used by a cryptographic
    device in support of its Type 4 functionality; i.e., any provision
    of key that lacks U.S. Government endorsement or oversight."
    [C4009]
 $ type 4 product
    (O) /cryptography, U.S. Government/ "Unevaluated commercial
    cryptographic equipment, assemblies, or components that neither
    NSA nor NIST certify for any Government usage. These products are
    typically delivered as part of commercial offerings and are
    commensurate with the vendor's commercial practices. These
    products may contain either vendor proprietary algorithms,
    algorithms registered by NIST, or algorithms registered by NIST
    and published in a FIPS." [C4009]
 $ UDP
    (I) See: User Datagram Protocol.
 $ UDP flood
    (I) A denial-of-service attack that takes advantage of (a) one
    system's UDP test function that generates a series of characters
    for each packet it receives and (b) another system's UPD test
    function that echoes any character it receives; the attack
    connects (a) to (b) to cause a nonstop flow of data between the
    two systems. (See: flooding.)
 $ unauthorized disclosure
    (I) A circumstance or event whereby an entity gains access to
    information for which the entity is not authorized.

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    Tutorial: This type of threat consequence can be caused by the
    following types of threat actions: exposure, interception,
    inference, and intrusion. Some methods of protecting against this
    consequence include access control, flow control, and inference
    control. (See: data confidentiality.)
 $ unauthorized user
    (I) /access control/ A system entity that accesses a system
    resource for which the entity has not received an authorization.
    (See: user. Compare: authorized user, insider, outsider.)
    Usage: IDOCs that use this term SHOULD state a definition for it
    because the term is used in many ways and could easily be
    misunderstood.
 $ uncertainty
    (N) An information-theoretic measure (usually stated as a number
    of bits) of the minimum amount of plaintext information that needs
    to be recovered from cipher text to learn the entire plain text
    that was encrypted. [SP63] (See: entropy.)
 $ unclassified
    (I) Not classified. (Compare: FOUO.)
 $ unencrypted
    (I) Not encrypted.
 $ unforgeable
    (I) /cryptography/ The property of a cryptographic data structure
    (i.e., a data structure that is defined using one or more
    cryptographic functions, e.g., "digital certificate") that makes
    it computationally infeasible to construct (i.e., compute) an
    unauthorized but correct value of the structure without having
    knowledge of one of more keys.
    Tutorial: This definition is narrower than general English usage,
    where "unforgeable" means unable to be fraudulently created or
    duplicated. In that broader sense, anyone can forge a digital
    certificate containing any set of data items whatsoever by
    generating the to-be-signed certificate and signing it with any
    private key whatsoever. But for PKI purposes, the forged data
    structure is invalid if it is not signed with the true private key
    of the claimed issuer; thus, the forgery will be detected when a
    certificate user uses the true public key of the claimed issuer to
    verify the signature.

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 $ uniform resource identifier (URI)
    (I) A type of formatted identifier (RFC 3986) that encapsulates
    the name of an Internet object, and labels it with an
    identification of the name space, thus producing a member of the
    universal set of names in registered name spaces and of addresses
    referring to registered protocols or name spaces.
    Example: HTML uses URIs to identify the target of hyperlinks.
    Usage: "A URI can be classified as a locator (see: URL), a name
    (see: URN), or both. ... Instances of URIs from any given scheme
    may have the characteristics of names or locators or both, often
    depending on the persistence and care in the assignment of
    identifiers by the naming authority, rather than on any quality of
    the scheme." IDOCs SHOULD "use the general term 'URI' rather than
    the more restrictive terms 'URL' and 'URN'." (RFC 3986)
 $ uniform resource locator (URL)
    (I) A URI that describes the access method and location of an
    information resource object on the Internet. (See: Usage under
    "URI". Compare: URN.)
    Tutorial: The term URL "refers to the subset of URIs that, besides
    identifying a resource, provide a means of locating the resource
    by describing its primary access mechanism (e.g., its network
    'location')." (RFC 3986)
    A URL provides explicit instructions on how to access the named
    object. For example,
    "ftp://bbnarchive.bbn.com/foo/bar/picture/cambridge.zip" is a URL.
    The part before the colon specifies the access scheme or protocol,
    and the part after the colon is interpreted according to that
    access method. Usually, two slashes after the colon indicate the
    host name of a server (written as a domain name). In an FTP or
    HTTP URL, the host name is followed by the path name of a file on
    the server. The last (optional) part of a URL may be either a
    fragment identifier that indicates a position in the file, or a
    query string.
 $ uniform resource name (URN)
    (I) A URI with the properties of a name. (See: Usage under "URI".
    Compare: URL.)
    Tutorial: The term URN "has been used historically to refer to
    both URIs under the "urn" scheme (RFC 2141), which are required to
    remain globally unique and persistent even when the resource
    ceases to exist or becomes unavailable, and to any other URI with
    the properties of a name." (RFC 3986)

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 $ untrusted
    (I) See: secondary definition under "trust".
 $ untrusted process
    1. (I) A system component that is not able to affect the state of
    system security through incorrect or malicious operation. Example:
    A component that has its operations confined by a security kernel.
    (See: trusted process.)
    2. (I) A system component that (a) has not been evaluated or
    examined for adherence to a specified security policy and,
    therefore, (b) must be assumed to contain logic that might attempt
    to circumvent system security.
 $ UORA
    (O) See: user-PIN ORA.
 $ update
    See: "certificate update" and "key update".
 $ upgrade
    (I) /data security/ Increase the classification level of data
    without changing the information content of the data. (See:
    classify, downgrade, regrade.)
 $ URI
    (I) See: uniform resource identifier.
 $ URL
    (I) See: uniform resource locator.
 $ URN
    (I) See: uniform resource name.
 $ user
    See: system user.
    Usage: IDOCs that use this term SHOULD state a definition for it
    because the term is used in many ways and could easily be
    misunderstood.
 $ user authentication service
    (I) A security service that verifies the identity claimed by an
    entity that attempts to access the system. (See: authentication,
    user.)

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 $ User Datagram Protocol (UDP)
    (I) An Internet Standard, Transport-Layer protocol (RFC 768) that
    delivers a sequence of datagrams from one computer to another in a
    computer network. (See: UPD flood.)
    Tutorial: UDP assumes that IP is the underlying protocol. UDP
    enables application programs to send transaction-oriented data to
    other programs with minimal protocol mechanism. UDP does not
    provide reliable delivery, flow control, sequencing, or other end-
    to-end service guarantees that TCP does.
 $ user identifier
    (I) See: identifier.
 $ user identity
    (I) See: identity.
 $ user PIN
    (O) /MISSI/ One of two PINs that control access to the functions
    and stored data of a FORTEZZA PC card. Knowledge of the user PIN
    enables a card user to perform the FORTEZZA functions that are
    intended for use by an end user. (See: PIN. Compare: SSO PIN.)
 $ user-PIN ORA (UORA)
    (O) /MISSI/ A MISSI organizational RA that operates in a mode in
    which the ORA performs only the subset of card management
    functions that are possible with knowledge of the user PIN for a
    FORTEZZA PC card. (See: no-PIN ORA, SSO-PIN ORA.)
 $ usurpation
    (I) A circumstance or event that results in control of system
    services or functions by an unauthorized entity. This type of
    threat consequence can be caused by the following types of threat
    actions: misappropriation, misuse. (See: access control.)
 $ UTCTime
    (N) The ASN.1 data type "UTCTime" contains a calendar date
    (YYMMDD) and a time to a precision of either one minute (HHMM) or
    one second (HHMMSS), where the time is either (a) Coordinated
    Universal Time or (b) the local time followed by an offset that
    enables Coordinated Universal Time to be calculated. (See:
    Coordinated Universal Time. Compare: GeneralizedTime.)
    Usage: If you care about centuries or millennia, you probably need
    to use the GeneralizedTime data type instead of UTCTime.

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 $ v1 certificate
    (N) An abbreviation that ambiguously refers to either an "X.509
    public-key certificate in version 1 format" or an "X.509 attribute
    certificate in version 1 format".
    Deprecated Usage: IDOCs MAY use this term as an abbreviation of
    "version 1 X.509 public-key certificate", but only after using the
    full term at the first instance. Otherwise, the term is ambiguous,
    because X.509 specifies both v1 public-key certificates and v1
    attribute certificates. (See: X.509 attribute certificate, X.509
    public-key certificate.)
 $ v1 CRL
    (N) Abbreviation of "X.509 CRL in version 1 format".
    Usage: IDOCs MAY use this abbreviation, but SHOULD use the full
    term at its first occurrence and define the abbreviation there.
 $ v2 certificate
    (N) Abbreviation of "X.509 public-key certificate in version 2
    format".
    Usage: IDOCs MAY use this abbreviation, but SHOULD use the full
    term at its first occurrence and define the abbreviation there.
 $ v2 CRL
    (N) Abbreviation of "X.509 CRL in version 2 format".
    Usage: IDOCs MAY use this abbreviation, but SHOULD use the full
    term at its first occurrence and define the abbreviation there.
 $ v3 certificate
    (N) Abbreviation of "X.509 public-key certificate in version 3
    format".
    Usage: IDOCs MAY use this abbreviation, but SHOULD use the full
    term at its first occurrence and define the abbreviation there.
 $ valid certificate
    1. (I) A digital certificate that can be validated successfully.
    (See: validate, verify.)
    2. (I) A digital certificate for which the binding of the data
    items can be trusted.
 $ valid signature
    (D) Synonym for "verified signature".

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    Deprecated Term: IDOCs SHOULD NOT use this synonym. This Glossary
    recommends saying "validate the certificate" and "verify the
    signature"; therefore, it would be inconsistent to say that a
    signature is "valid". (See: validate, verify.)
 $ validate
    1. (I) Establish the soundness or correctness of a construct.
    Example: certificate validation. (See: validate vs. verify.)
    2. (I) To officially approve something, sometimes in relation to a
    standard. Example: NIST validates cryptographic modules for
    conformance with [FP140].
 $ validate vs. verify
    Usage: To ensure consistency and align with ordinary English
    usage, IDOCs SHOULD comply with the following two rules:
    -  Rule 1: Use "validate" when referring to a process intended to
       establish the soundness or correctness of a construct (e.g.,
       "certificate validation"). (See: validate.)
    -  Rule 2: Use "verify" when referring to a process intended to
       test or prove the truth or accuracy of a fact or value (e.g.,
       "authenticate"). (See: verify.)
    Tutorial: The Internet security community sometimes uses these two
    terms inconsistently, especially in a PKI context. Most often,
    however, we say "verify the signature" but say "validate the
    certificate". That is, we "verify" atomic truths but "validate"
    data structures, relationships, and systems that are composed of
    or depend on verified items. This usage has a basis in Latin:
    The word "valid" derives from a Latin word that means "strong".
    Thus, to validate means to check that a construct is sound. For
    example, a certificate user validates a public-key certificate to
    establish trust in the binding that the certificate asserts
    between an identity and a key. This can include checking various
    aspects of the certificate's construction, such as verifying the
    digital signature on the certificate by performing calculations,
    verifying that the current time is within the certificate's
    validity period, and validating a certification path involving
    additional certificates.
    The word "verify" derives from a Latin word that means "true".
    Thus, to verify means to check the truth of an assertion by
    examining evidence or performing tests. For example, to verify an
    identity, an authentication process examines identification
    information that is presented or generated. To validate a
    certificate, a certificate user verifies the digital signature on
    the certificate by performing calculations, verifies that the

Shirey Informational [Page 331] RFC 4949 Internet Security Glossary, Version 2 August 2007

    current time is within the certificate's validity period, and may
    need to validate a certification path involving additional
    certificates.
 $ validation
    (I) See: validate vs. verify.
 $ validity period
    (I) /PKI/ A data item in a digital certificate that specifies the
    time period for which the binding between data items (especially
    between the subject name and the public key value in a public-key
    certificate) is valid, except if the certificate appears on a CRL
    or the key appears on a CKL. (See: cryptoperiod, key lifetime.)
 $ value-added network (VAN)
    (I) A computer network or subnetwork (usually a commercial
    enterprise) that transmits, receives, and stores EDI transactions
    on behalf of its users.
    Tutorial: A VAN may also provide additional services, ranging from
    EDI format translation, to EDI-to-FAX conversion, to integrated
    business systems.
 $ VAN
    (I) See: value-added network.
 $ verification
    1. (I) /authentication/ The process of examining information to
    establish the truth of a claimed fact or value. (See: validate vs.
    verify, verify. Compare: authentication.)
    2. (N) /COMPUSEC/ The process of comparing two levels of system
    specification for proper correspondence, such as comparing a
    security model with a top-level specification, a top-level
    specification with source code, or source code with object code.
    [NCS04]
 $ verified design
    (O) See: TCSEC Class A1.
 $ verify
    (I) To test or prove the truth or accuracy of a fact or value.
    (See: validate vs. verify, verification. Compare: authenticate.)
 $ vet
    (I) /verb/ To examine or evaluate thoroughly. (Compare:
    authenticate, identity proofing, validate, verify.)

Shirey Informational [Page 332] RFC 4949 Internet Security Glossary, Version 2 August 2007

 $ violation
    See: security violation.
 $ virtual private network (VPN)
    (I) A restricted-use, logical (i.e., artificial or simulated)
    computer network that is constructed from the system resources of
    a relatively public, physical (i.e., real) network (e.g., the
    Internet), often by using encryption (located at hosts or
    gateways), and often by tunneling links of the virtual network
    across the real network. (See: tunnel.)
    Tutorial: A VPN is generally less expensive to build and operate
    than a dedicated real network, because the virtual network shares
    the cost of system resources with other users of the underlying
    real network. For example, if a corporation has LANs at several
    different sites, each connected to the Internet by a firewall, the
    corporation could create a VPN by using encrypted tunnels to
    connect from firewall to firewall across the Internet.
 $ virus
    (I) A self-replicating (and usually hidden) section of computer
    software (usually malicious logic) that propagates by infecting --
    i.e., inserting a copy of itself into and becoming part of --
    another program. A virus cannot run by itself; it requires that
    its host program be run to make the virus active.
 $ Visa Cash
    (O) A smartcard-based electronic money system that incorporates
    cryptography and can be used to make payments via the Internet.
    (See: IOTP.)
 $ volatile media
    (I) Storage media that require an external power supply to
    maintain stored information. (Compare: non-volatile media,
    permanent storage.)
 $ VPN
    (I) See: virtual private network.
 $ vulnerability
    (I) A flaw or weakness in a system's design, implementation, or
    operation and management that could be exploited to violate the
    system's security policy. (See: harden.)
    Tutorial: A system can have three types of vulnerabilities: (a)
    vulnerabilities in design or specification; (b) vulnerabilities in
    implementation; and (c) vulnerabilities in operation and
    management. Most systems have one or more vulnerabilities, but

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    this does not mean that the systems are too flawed to use. Not
    every threat results in an attack, and not every attack succeeds.
    Success depends on the degree of vulnerability, the strength of
    attacks, and the effectiveness of any countermeasures in use. If
    the attacks needed to exploit a vulnerability are very difficult
    to carry out, then the vulnerability may be tolerable. If the
    perceived benefit to an attacker is small, then even an easily
    exploited vulnerability may be tolerable. However, if the attacks
    are well understood and easily made, and if the vulnerable system
    is employed by a wide range of users, then it is likely that there
    will be enough motivation for someone to launch an attack.
 $ W3
    (D) Synonym for WWW.
    Deprecated Abbreviation: This abbreviation could be confused with
    W3C; use "WWW" instead.
 $ W3C
    (N) See: World Wide Web Consortium.
 $ war dialer
    (I) /slang/ A computer program that automatically dials a series
    of telephone numbers to find lines connected to computer systems,
    and catalogs those numbers so that a cracker can try to break the
    systems.
    Deprecated Usage: IDOCs that use this term SHOULD state a
    definition for it because the term could confuse international
    readers.
 $ Wassenaar Arrangement
    (N) The Wassenaar Arrangement on Export Controls for Conventional
    Arms and Dual-Use Goods and Technologies is a global, multilateral
    agreement approved by 33 countries in July 1996 to contribute to
    regional and international security and stability, by promoting
    information exchange concerning, and greater responsibility in,
    transfers of arms and dual-use items, thus preventing
    destabilizing accumulations. (See: International Traffic in Arms
    Regulations.)
    Tutorial: The Arrangement began operations in September 1996 with
    headquarters in Vienna. The participating countries were
    Argentina, Australia, Austria, Belgium, Bulgaria, Canada, Czech
    Republic, Denmark, Finland, France, Germany, Greece, Hungary,
    Ireland, Italy, Japan, Luxembourg, Netherlands, New Zealand,
    Norway, Poland, Portugal, Republic of Korea, Romania, Russian

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    Federation, Slovak Republic, Spain, Sweden, Switzerland, Turkey,
    Ukraine, United Kingdom, and United States.
    Participating countries seek through their national policies to
    ensure that transfers do not contribute to the development or
    enhancement of military capabilities that undermine the goals of
    the arrangement, and are not diverted to support such
    capabilities. The countries maintain effective export controls for
    items on the agreed lists, which are reviewed periodically to
    account for technological developments and experience gained.
    Through transparency and exchange of views and information,
    suppliers of arms and dual-use items can develop common
    understandings of the risks associated with their transfer and
    assess the scope for coordinating national control policies to
    combat these risks. Members provide semi-annual notification of
    arms transfers, covering seven categories derived from the UN
    Register of Conventional Arms. Members also report transfers or
    denials of transfers of certain controlled dual-use items.
    However, the decision to transfer or deny transfer of any item is
    the sole responsibility of each participating country. All
    measures undertaken with respect to the arrangement are in
    accordance with national legislation and policies and are
    implemented on the basis of national discretion.
 $ watermarking
    See: digital watermarking.
 $ weak key
    (I) In the context of a particular cryptographic algorithm, a key
    value that provides poor security. (See: strong.)
    Example: The DEA has four "weak keys" [Schn] for which encryption
    produces the same result as decryption. It also has ten pairs of
    "semi-weak keys" [Schn] (a.k.a. "dual keys" [FP074]) for which
    encryption with one key in the pair produces the same result as
    decryption with the other key.
 $ web, Web
    1. (I) /not capitalized/ IDOCs SHOULD NOT capitalize "web" when
    using the term (usually as an adjective) to refer generically to
    technology -- such as web browsers, web servers, HTTP, and HTML --
    that is used in the Web or similar networks.
    2. (I) /capitalized/ IDOCs SHOULD capitalize "Web" when using the
    term (as either a noun or an adjective) to refer specifically to
    the World Wide Web. (Similarly, see: internet.)

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    Usage: IDOCs SHOULD NOT use "web" or "Web" in a way that might
    confuse these definitions with the PGP "web of trust". When using
    Web as an abbreviation for "World Wide Web", IDOCs SHOULD fully
    spell out the term at the first instance of usage.
 $ web of trust
    (D) /PGP/ A PKI architecture in which each certificate user
    defines their own trust anchor(s) by depending on personal
    relationships. (See: trust anchor. Compare: hierarchical PKI, mesh
    PKI.)
    Deprecated Usage: IDOCs SHOULD NOT use this term except with
    reference to PGP. This term mixes concepts in potentially
    misleading ways; e.g., this architecture does not depend on World
    Wide Web technology. Instead of this term, IDOCs MAY use "trust-
    file PKI". (See: web, Web).
    Tutorial: This type of architecture does not usually include
    public repositories of certificates. Instead, each certificate
    user builds their own, private repository of trusted public keys
    by making personal judgments about being able to trust certain
    people to be holding properly certified keys of other people. It
    is this set of person-to-person relationships from which the
    architecture gets its name.
 $ web server
    (I) A software process that runs on a host computer connected to a
    network and responds to HTTP requests made by client web browsers.
 $ WEP
    (N) See: Wired Equivalency Protocol.
 $ Wired Equivalent Privacy (WEP)
    (N) A cryptographic protocol that is defined in the IEEE 802.11
    standard and encapsulates the packets on wireless LANs. Usage:
    a.k.a. "Wired Equivalency Protocol".
    Tutorial: The WEP design, which uses RC4 to encrypt both the plain
    text and a CRC, has been shown to be flawed in multiple ways; and
    it also has often suffered from flawed implementation and
    management.
 $ wiretapping
    (I) An attack that intercepts and accesses information contained
    in a data flow in a communication system. (See: active
    wiretapping, end-to-end encryption, passive wiretapping, secondary
    definition under "interception".)

Shirey Informational [Page 336] RFC 4949 Internet Security Glossary, Version 2 August 2007

    Usage: Although the term originally referred to making a
    mechanical connection to an electrical conductor that links two
    nodes, it is now used to refer to accessing information from any
    sort of medium used for a link or even from a node, such as a
    gateway or subnetwork switch.
    Tutorial: Wiretapping can be characterized according to intent:
    -  "Active wiretapping" attempts to alter the data or otherwise
       affect the flow.
    -  "Passive wiretapping" only attempts to observe the data flow
       and gain knowledge of information contained in it.
 $ work factor
    1a. (I) /COMPUSEC/ The estimated amount of effort or time that can
    be expected to be expended by a potential intruder to penetrate a
    system, or defeat a particular countermeasure, when using
    specified amounts of expertise and resources. (See: brute force,
    impossible, strength.)
    1b. (I) /cryptography/ The estimated amount of computing power and
    time needed to break a cryptographic system. (See: brute force,
    impossible, strength.)
 $ World Wide Web ("the Web", WWW)
    (N) The global, hypermedia-based collection of information and
    services that is available on Internet servers and is accessed by
    browsers using Hypertext Transfer Protocol and other information
    retrieval mechanisms. (See: web vs. Web, [R2084].)
 $ World Wide Web Consortium (W3C)
    (N) Created in October 1994 to develop and standardize protocols
    to promote the evolution and interoperability of the Web, and now
    consisting of hundreds of member organizations (commercial firms,
    governmental agencies, schools, and others).
    Tutorial: W3C Recommendations are developed through a process
    similar to that of the standards published by other organizations,
    such as the IETF. The W3 Recommendation Track (i.e., standards
    track) has four levels of increasing maturity: Working, Candidate
    Recommendation, Proposed Recommendation, and W3C Recommendation.
    W3C Recommendations are similar to the standards published by
    other organizations. (Compare: Internet Standard, ISO.)
 $ worm
    (I) A computer program that can run independently, can propagate a
    complete working version of itself onto other hosts on a network,
    and may consume system resources destructively. (See: mobile code,
    Morris Worm, virus.)

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 $ wrap
    1. (N) To use cryptography to provide data confidentiality service
    for keying material. (See: encrypt, wrapping algorithm, wrapping
    key. Compare: seal, shroud.)
    2. (D) To use cryptography to provide data confidentiality service
    for data in general.
    Deprecated Usage: IDOCs SHOULD NOT use this term with definition 2
    because that duplicates the meaning of the more widely understood
    "encrypt".
 $ wrapping algorithm
    (N) An encryption algorithm that is specifically intended for use
    in encrypting keys. (See: KEK, wrap.)
 $ wrapping key
    (N) Synonym for "KEK". (See: encrypt. Compare: seal, shroud.)
 $ write
    (I) /security model/ A system operation that causes a flow of
    information from a subject to an object. (See: access mode.
    Compare: read.)
 $ WWW
    (I) See: World Wide Web.
 $ X.400
    (N) An ITU-T Recommendation [X400] that is one part of a joint
    ITU-T/ISO multi-part standard (X.400-X.421) that defines the
    Message Handling Systems. (The ISO equivalent is IS 10021, parts
    1-7.) (See: Message Handling Systems.)
 $ X.500
    (N) An ITU-T Recommendation [X500] that is one part of a joint
    ITU-T/ISO multi-part standard (X.500-X.525) that defines the X.500
    Directory, a conceptual collection of systems that provide
    distributed directory capabilities for OSI entities, processes,
    applications, and services. (The ISO equivalent is IS 9594-1 and
    related standards, IS 9594-x.) (See: directory vs. Directory,
    X.509.)
    Tutorial: The X.500 Directory is structured as a tree (the
    Directory Information Tree), and information is stored in
    directory entries. Each entry is a collection of information about
    one object, and each object has a DN. A directory entry is
    composed of attributes, each with a type and one or more values.
    For example, if a PKI uses the Directory to distribute

Shirey Informational [Page 338] RFC 4949 Internet Security Glossary, Version 2 August 2007

    certificates, then the X.509 public-key certificate of an end user
    is normally stored as a value of an attribute of type
    "userCertificate" in the Directory entry that has the DN that is
    the subject of the certificate.
 $ X.509
    (N) An ITU-T Recommendation [X509] that defines a framework to
    provide and support data origin authentication and peer entity
    authentication, including formats for X.509 public-key
    certificates, X.509 attribute certificates, and X.509 CRLs. (The
    ISO equivalent is IS 9498-4.) (See: X.500.)
    Tutorial: X.509 describes two "levels" of authentication: "simple
    authentication" and "strong authentication". It recommends, "While
    simple authentication offers some limited protection against
    unauthorized access, only strong authentication should be used as
    the basis for providing secure services."
 $ X.509 attribute certificate
    (N) An attribute certificate in the version 1 (v1) format defined
    by X.509. (The v1 designation for an X.509 attribute certificate
    is disjoint from the v1 designation for an X.509 public-key
    certificate, and from the v1 designation for an X.509 CRL.)
    Tutorial: An X.509 attribute certificate has a "subject" field,
    but the attribute certificate is a separate data structure from
    that subject's public-key certificate. A subject may have multiple
    attribute certificates associated with each of its public-key
    certificates, and an attribute certificate may be issued by a
    different CA than the one that issued the associated public-key
    certificate.
    An X.509 attribute certificate contains a sequence of data items
    and has a digital signature that is computed from that sequence.
    Besides the signature, an attribute certificate contains items 1
    through 9 listed below:
    1. version                 Identifies v1.
    2. subject                 Is one of the following:
       2a. baseCertificateID   Issuer and serial number of an
                               X.509 public-key certificate.
       2b. subjectName         DN of the subject.
    3. issuer                  DN of the issuer (the CA who signed).
    4. signature               OID of algorithm that signed the cert.
    5. serialNumber            Certificate serial number;
                               an integer assigned by the issuer.
    6. attCertValidityPeriod   Validity period; a pair of UTCTime
                               values: "not before" and "not after".

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    7. attributes              Sequence of attributes describing the
                               subject.
    8. issuerUniqueId          Optional, when a DN is not sufficient.
    9. extensions              Optional.
 $ X.509 certificate
    (N) Synonym for "X.509 public-key certificate".
    Usage: IDOCs MAY use this term as an abbreviation of "X.509
    public-key certificate", but only after using the full term at the
    first instance. Otherwise, the term is ambiguous, because X.509
    specifies both public-key certificates and attribute certificates.
    (See: X.509 attribute certificate, X.509 public-key certificate.)
    Deprecated Usage: IDOCs SHOULD NOT use this term as an
    abbreviation of "X.509 attribute certificate", because the term is
    much more commonly used to mean "X.509 public-key certificate"
    and, therefore, is likely to be misunderstood.
 $ X.509 certificate revocation list (CRL)
    (N) A CRL in one of the formats defined by X.509 -- version 1 (v1)
    or version 2 (v2). (The v1 and v2 designations for an X.509 CRL
    are disjoint from the v1 and v2 designations for an X.509 public-
    key certificate, and from the v1 designation for an X.509
    attribute certificate.) (See: certificate revocation.)
    Usage: IDOCs SHOULD NOT refer to an X.509 CRL as a digital
    certificate; however, note that an X.509 CRL does meet this
    Glossary's definition of "digital certificate". That is, like a
    digital certificate, an X.509 CRL makes an assertion and is signed
    by a CA. But instead of binding a key or other attributes to a
    subject, an X.509 CRL asserts that certain previously issued,
    X.509 certificates have been revoked.
    Tutorial: An X.509 CRL contains a sequence of data items and has a
    digital signature computed on that sequence. Besides the
    signature, both v1 and v2 contain items 2 through 6b listed below.
    Version 2 contains item 1 and may optionally contain 6c and 7.
    1. version                 Optional. If present, identifies v2.
    2. signature               OID of the algorithm that signed CRL.
    3. issuer                  DN of the issuer (the CA who signed).
    4. thisUpdate              A UTCTime value.
    5. nextUpdate              A UTCTime value.
    6. revokedCertificates     3-tuples of 6a, 6b, and (optional) 6c:
       6a. userCertificate     A certificate's serial number.
       6b. revocationDate      UTCTime value for the revocation date.
       6c. crlEntryExtensions  Optional.

Shirey Informational [Page 340] RFC 4949 Internet Security Glossary, Version 2 August 2007

    7. crlExtensions           Optional.
 $ X.509 public-key certificate
    (N) A public-key certificate in one of the formats defined by
    X.509 -- version 1 (v1), version 2 (v2), or version 3 (v3). (The
    v1 and v2 designations for an X.509 public-key certificate are
    disjoint from the v1 and v2 designations for an X.509 CRL, and
    from the v1 designation for an X.509 attribute certificate.)
    Tutorial: An X.509 public-key certificate contains a sequence of
    data items and has a digital signature computed on that sequence.
    Besides the signature, all three versions contain items 1 through
    7 listed below. Only v2 and v3 certificates may also contain items
    8 and 9, and only v3 may contain item 10.
    1. version                 Identifies v1, v2, or v3.
    2. serialNumber            Certificate serial number;
                               an integer assigned by the issuer.
    3. signature               OID of algorithm that was used to
                               sign the certificate.
    4. issuer                  DN of the issuer (the CA who signed).
    5. validity                Validity period; a pair of UTCTime
                               values: "not before" and "not after".
    6. subject                 DN of entity who owns the public key.
    7. subjectPublicKeyInfo    Public key value and algorithm OID.
    8. issuerUniqueIdentifier  Defined for v2, v3; optional.
    9. subjectUniqueIdentifier Defined for v2, v2; optional.
    10. extensions             Defined only for v3; optional.
 $ X9
    (N) See: "Accredited Standards Committee X9" under "ANSI".
 $ XML
    (N) See: Extensible Markup Language.
 $ XML-Signature.
    (N) A W3C Recommendation (i.e., approved standard) that specifies
    XML syntax and processing rules for creating and representing
    digital signatures (based on asymmetric cryptography) that can be
    applied to any digital content (i.e., any data object) including
    other XML material.
 $ Yellow Book
    (D) /slang/ Synonym for "Computer Security Requirements: Guidance
    for Applying the [U.S.] Department of Defense Trusted Computer
    System Evaluation Criteria in Specific Environments" [CSC3] (See:
    "first law" under "Courtney's laws".)

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    Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
    that or any other document. Instead, use the full proper name of
    the document or, in subsequent references, a conventional
    abbreviation. (See: Deprecated Usage under "Green Book", Rainbow
    Series.)
 $ zero-knowledge proof
    (I) /cryptography/ A proof-of-possession protocol whereby a system
    entity can prove possession of some information to another entity,
    without revealing any of that information. (See: proof-of-
    possession protocol.)
 $ zeroize
    1. (I) Synonym for "erase". (See: sanitize.) Usage: Particularly
    with regard to erasing keys that are stored in a cryptographic
    module.
    2. (O) Erase electronically stored data by altering the contents
    of the data storage so as to prevent the recovery of the data.
    [FP140]
    3. (O) "To remove or eliminate the key from a cryptoequipment or
    fill device." [C4009]
    Usage: The phrase "zeroize the device" normally is used to mean
    erasing all keys stored in the device, but sometimes means erasing
    all keying material in the device, or all cryptographic
    information in the device, or even all sensitive information in
    the device.
 $ zombie
    (I) /slang/ An Internet host computer that has been
    surreptitiously penetrated by an intruder that installed malicious
    daemon software to cause the host to operate as an accomplice in
    attacking other hosts, particularly in distributed attacks that
    attempt denial of service through flooding.
    Deprecated Usage: Other cultures likely use different metaphorical
    terms (such as "robot") for this concept, and some use this term
    for different concepts. Therefore, to avoid international
    misunderstanding, IDOCs SHOULD NOT use this term. Instead, use
    "compromised, coopted computer" or other explicitly descriptive
    terminology. (See: Deprecated Usage under "Green Book".)
 $ zone of control
    (O) /EMSEC/ Synonym for "inspectable space". [C4009] (See:
    TEMPEST.)

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5. Security Considerations

 This document mainly defines security terms and recommends how to use
 them. It also provides limited tutorial information about security
 aspects of Internet protocols, but it does not describe in detail the
 vulnerabilities of, or threats to, specific protocols and does not
 definitively describe mechanisms that protect specific protocols.

6. Normative Reference

 [R2119]  Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", BCP 14, RFC 2119, March 1997.

7. Informative References

 This Glossary focuses on the Internet Standards Process. Therefore,
 this set of informative references emphasizes international,
 governmental, and industrial standards documents. Some RFCs that are
 especially relevant to Internet security are mentioned in Glossary
 entries in square brackets (e.g., "[R1457]" in the entry for
 "security label") and are listed here; some other RFCs are mentioned
 in parentheses (e.g., "(RFC 959)" in the entry for "File Transport
 Protocol") but are not listed here.
 [A1523]  American National Standards Institute, "American National
          Standard Telecom Glossary", ANSI T1.523-2001.
 [A3092]  ---, "American National Standard Data Encryption Algorithm",
          ANSI X3.92-1981, 30 December 1980.
 [A9009]  ---, "Financial Institution Message Authentication
          (Wholesale)", ANSI X9.9-1986, 15 August 1986.
 [A9017]  ---, "Financial Institution Key Management (Wholesale)",
          X9.17, 4 April 1985. (Defines procedures for manual and
          automated management of keying material and uses DES to
          provide key management for a variety of operational
          environments.)
 [A9042]  ---, "Public key Cryptography for the Financial Service
          Industry: Agreement of Symmetric Keys Using Diffie-Hellman
          and MQV Algorithms", X9.42, 29 January 1999. (See: Diffie-
          Hellman-Merkle.)
 [A9052]  ---, "Triple Data Encryption Algorithm Modes of Operation",
          X9.52-1998, ANSI approval 9 November 1998.

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 [A9062]  ---, "Public Key Cryptography for the Financial Services
          Industry: The Elliptic Curve Digital Signature Algorithm
          (ECDSA)", X9.62-1998, ANSI approval 7 January 1999.
 [A9063]  ---, "Public Key Cryptography for the Financial Services
          Industry: Key Agreement and Key Transport Using Elliptic
          Curve Cryptography", X9.63-2001.
 [ACM]    Association for Computing Machinery, "Communications of the
          ACM", July 1998 issue with: M. Yeung, "Digital
          Watermarking"; N. Memom and P. Wong, "Protecting Digital
          Media Content"; and S. Craver, B.-L. Yeo, and M. Yeung,
          "Technical Trials and Legal Tribulations".
 [Ande]   Anderson, J., "Computer Security Technology Planning Study",
          ESD-TR-73-51, Vols. I and II, USAF Electronics Systems Div.,
          Bedford, MA, October 1972. (Available as AD-758206/772806,
          National Technical Information Service, Springfield, VA.)
 [ANSI]   American National Standards Institute, "Role Based Access
          Control", Secretariat, Information Technology Industry
          Council, BSR INCITS 359, DRAFT, 10 November 2003.
 [Army]   U.S. Army Corps of Engineers, "Electromagnetic Pulse (EMP)
          and Tempest Protection for Facilities", EP 1110-3-2, 31
          December 1990.
 [B1822]  Bolt Baranek and Newman Inc., "Appendix H: Interfacing a
          Host to a Private Line Interface", in "Specifications for
          the Interconnection of a Host and an IMP", BBN Report No.
          1822, revised, December 1983.
 [B4799]  ---, "A History of the Arpanet: The First Decade", BBN
          Report No. 4799, April 1981.
 [Bell]   Bell, D. and L. LaPadula, "Secure Computer Systems:
          Mathematical Foundations and Model", M74-244, The MITRE
          Corporation, Bedford, MA, May 1973. (Available as AD-771543,
          National Technical Information Service, Springfield, VA.)
 [Biba]   K. Biba, "Integrity Considerations for Secure Computer
          Systems", ESD-TR-76-372, USAF Electronic Systems Division,
          Bedford, MA, April 1977.
 [BN89]   Brewer, D. and M. Nash, "The Chinese wall security policy",
          in "Proceedings of IEEE Symposium on Security and Privacy",
          May 1989, pp. 205-214.

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 [BS7799] British Standards Institution, "Information Security
          Management, Part 1: Code of Practice for Information
          Security Management", BS 7799-1:1999, 15 May 1999.
  1. –, "Information Security Management, Part 2: Specification

for Information Security Management Systems", BS 7799-

          2:1999, 15 May 1999.
 [C4009]  Committee on National Security Systems (U.S. Government),
          "National Information Assurance (IA) Glossary", CNSS
          Instruction No. 4009, revised June 2006.
 [CCIB]   Common Criteria Implementation Board, "Common Criteria for
          Information Technology Security Evaluation, Part 1:
          Introduction and General Model", version 2.0, CCIB-98-026,
          May 1998.
 [Chau]   D. Chaum, "Untraceable Electronic Mail, Return Addresses,
          and Digital Pseudonyms", in "Communications of the ACM",
          vol. 24, no. 2, February 1981, pp. 84-88.
 [Cheh]   Cheheyl, M., Gasser, M., Huff, G., and J. Millen, "Verifying
          Security", in "ACM Computing Surveys", vol. 13, no. 3,
          September 1981, pp. 279-339.
 [Chris]  Chrissis, M. et al, 1993. "SW-CMM [Capability Maturity Model
          for Software Version", Release 3.0, Software Engineering
          Institute, Carnegie Mellon University, August 1996.
 [CIPSO]  Trusted Systems Interoperability Working Group, "Common IP
          Security Option", version 2.3, 9 March 1993.
 [Clark]  Clark, D. and D. Wilson, "A Comparison of Commercial and
          Military computer Security Policies", in "Proceedings of the
          IEEE Symposium on Security and Privacy", April 1987, pp.
          184-194.
 [Cons]   NSA, "Consistency Instruction Manual for Development of U.S.
          Government Protection Profiles for Use in Basic Robustness
          Environments", Release 2.0, 1 March 2004
 [CORBA]  Object Management Group, Inc., "CORBAservices: Common Object
          Service Specification", December 1998.
 [CSC1]   U.S. DoD Computer Security Center, "Department of Defense
          Trusted Computer System Evaluation Criteria", CSC-STD-001-
          83, 15 August 1983. (Superseded by [DoD1].)

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 [CSC2]   ---, "Department of Defense Password Management Guideline",
          CSC-STD-002-85, 12 April 1985.
 [CSC3]   ---, "Computer Security Requirements: Guidance for Applying
          the Department of Defense Trusted Computer System Evaluation
          Criteria in Specific Environments", CSC-STD-003-85, 25 June
          1985.
 [CSOR]   U.S. Department of Commerce, "General Procedures for
          Registering Computer Security Objects", National Institute
          of Standards Interagency Report 5308, December 1993.
 [Daem]   Daemen, J. and V. Rijmen, "Rijndael, the advanced encryption
          standard", in "Dr. Dobb's Journal", vol. 26, no. 3, March
          2001, pp. 137-139.
 [DC6/9]  Director of Central Intelligence, "Physical Security
          Standards for Sensitive Compartmented Information
          Facilities", DCI Directive 6/9, 18 November 2002.
 [Denn]   Denning, D., "A Lattice Model of Secure Information Flow",
          in "Communications of the ACM", vol. 19, no. 5, May 1976,
          pp. 236-243.
 [Denns]  Denning, D. and P. Denning, "Data Security", in "ACM
          Computing Surveys", vol. 11, no. 3, September 1979, pp. 227-
          249.
 [DH76]   Diffie, W. and M. Hellman, "New Directions in Cryptography",
          in "IEEE Transactions on Information Theory", vol. IT-22,
          no. 6, November 1976, pp. 644-654. (See: Diffie-Hellman-
          Merkle.)
 [DoD1]   U.S. DoD, "Department of Defense Trusted Computer System
          Evaluation Criteria", DoD 5200.28-STD, 26 December 1985.
          (Supersedes [CSC1].) (Superseded by DoD Directive 8500.1.)
 [DoD4]   ---, "NSA Key Recovery Assessment Criteria", 8 June 1998.
 [DoD5]   ---, Directive 5200.1, "DoD Information Security Program",
          13 December 1996.
 [DoD6]   ---, "Department of Defense Technical Architecture Framework
          for Information Management, Volume 6: Department of Defense
          (DoD) Goal Security Architecture", Defense Information
          Systems Agency, Center for Standards, version 3.0, 15 April
          1996.

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 [DoD7]   ---, "X.509 Certificate Policy for the United States
          Department of Defense", version 7, 18 December 2002.
          (Superseded by [DoD9].)
 [DoD9]   ---, "X.509 Certificate Policy for the United States
          Department of Defense", version 9, 9 February 2005.
 [DoD10]  ---, "DoD Architecture Framework, Version 1: Deskbook", 9
          February 2004.
 [DSG]    American Bar Association, "Digital Signature Guidelines:
          Legal Infrastructure for Certification Authorities and
          Secure Electronic Commerce", Chicago, IL, 1 August 1996.
          (See: [PAG].)
 [ElGa]   El Gamal, T., "A Public-Key Cryptosystem and a Signature
          Scheme Based on Discrete Logarithms", in "IEEE Transactions
          on Information Theory", vol. IT-31, no. 4, 1985, pp. 469-
          472.
 [EMV1]   Europay International S.A., MasterCard International
          Incorporated, and Visa International Service Association,
          "EMV '96 Integrated Circuit Card Specification for Payment
          Systems", version 3.1.1, 31 May 1998.
 [EMV2]   ---, "EMV '96 Integrated Circuit Card Terminal Specification
          for Payment Systems", version 3.1.1, 31 May 1998.
 [EMV3]   ---, "EMV '96 Integrated Circuit Card Application
          Specification for Payment Systems", version 3.1.1, 31 May
          1998.
 [F1037]  U.S. General Services Administration, "Glossary of
          Telecommunications Terms", FED STD 1037C, 7 August 1996.
 [For94]  Ford, W., "Computer Communications Security: Principles,
          Standard Protocols and Techniques", ISBN 0-13-799453-2,
          1994.
 [For97]  --- and M. Baum, "Secure Electronic Commerce: Building the
          Infrastructure for Digital Signatures and Encryption", ISBN
          0-13-476342-4, 1994.
 [FP001]  U.S. Department of Commerce, "Code for Information
          Interchange", Federal Information Processing Standards
          Publication (FIPS PUB) 1, 1 November 1968.

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 [FP031]  ---, "Guidelines for Automatic Data Processing Physical
          Security and Risk Management", FIPS PUB 31, June 1974.
 [FP039]  ---, "Glossary for Computer Systems Security", FIPS PUB 39,
          15 February 1976.
 [FP041]  ---, "Computer Security Guidelines for Implementing the
          Privacy Act of 1974", FIPS PUB 41, 30 May 1975.
 [FP046]  ---, "Data Encryption Standard (DES)", FIPS PUB 46-3, 25
          October 1999.
 [FP074]  ---, "Data Encryption Standard (DES)", FIPS PUB 46-3, 25
          October 1999.
 [FP081]  ---, "DES Modes of Operation", FIPS PUB 81, 2 December 1980.
 [FP087]  ---, "Guidelines for ADP Contingency Planning", FIPS PUB 87,
          27 March 1981.
 [FP102]  ---, "Guideline for Computer Security Certification and
          Accreditation", FIPS PUB 102, 27 September 1983.
 [FP113]  ---, "Computer Data Authentication", FIPS PUB 113, 30 May
          1985.
 [FP140]  ---, "Security Requirements for Cryptographic Modules", FIPS
          PUB 140-2, 25 May 2001; with change notice 4, 3 December
          2002.
 [FP151]  ---, "Portable Operating System Interface (POSIX) -- System
          Application Program Interface [C Language]", FIPS PUB 151-2,
          12 May 1993
 [FP180]  ---, "Secure Hash Standard", FIPS PUB 180-2, August 2000;
          with change notice 1, 25 February 2004.
 [FP185]  ---, "Escrowed Encryption Standard", FIPS PUB 185, 9
          February 1994.
 [FP186]  ---, "Digital Signature Standard (DSS)", FIPS PUB 186-2, 27
          June 2000; with change notice 1, 5 October 2001.
 [FP188]  ---, "Standard Security Label for Information Transfer",
          FIPS PUB 188, 6 September 1994.
 [FP191]  ---, "Guideline for the Analysis of Local Area Network
          Security", FIPS PUB 191, 9 November 1994.

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 [FP197]  ---, "Advanced Encryption Standard", FIPS PUB 197, 26
          November 2001.
 [FP199]  ---, "Standards for Security Categorization of Federal
          Information and Information Systems ", FIPS PUB 199,
          December 2003.
 [FPKI]   ---, "Public Key Infrastructure (PKI) Technical
          Specifications: Part A -- Technical Concept of Operations",
          NIST, 4 September 1998.
 [Gass]   Gasser, M., "Building a Secure Computer System", Van
          Nostrand Reinhold Company, New York, 1988, ISBN 0-442-
          23022-2.
 [Gray]   Gray, J. and A. Reuter, "Transaction Processing: Concepts
          and Techniques", Morgan Kaufmann Publishers, Inc., 1993.
 [Hafn]   Hafner, K. and M. Lyon, "Where Wizards Stay Up Late: The
          Origins of the Internet", Simon & Schuster, New York, 1996.
 [Huff]   Huff, G., "Trusted Computer Systems -- Glossary", MTR 8201,
          The MITRE Corporation, March 1981.
 [I3166]  International Standards Organization, "Codes for the
          Representation of Names of Countries and Their Subdivisions,
          Part 1: Country Codes", ISO 3166-1:1997.
  1. –, "Codes for the Representation of Names of Countries and

Their Subdivisions, Part 2: Country Subdivision Codes",

          ISO/DIS 3166-2.
  1. –, "Codes for the Representation of Names of Countries and

Their Subdivisions, Part 3: Codes for Formerly Used Names of

          Countries", ISO/DIS 3166-3.
 [I7498-1] ---, "Information Processing Systems -- Open Systems
          Interconnection Reference Model, [Part 1:] Basic Reference
          Model", ISO/IEC 7498-1. (Equivalent to ITU-T Recommendation
          X.200.)
 [I7498-2] ---, "Information Processing Systems -- Open Systems
          Interconnection Reference Model, Part 2: Security
          Architecture", ISO/IEC 7499-2.
 [I7498-4] ---, "Information Processing Systems -- Open Systems
          Interconnection Reference Model, Part 4: Management
          Framework", ISO/IEC 7498-4.

Shirey Informational [Page 349] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [I7812]  ---, "Identification cards -- Identification of Issuers,
          Part 1: Numbering System", ISO/IEC 7812-1:1993
  1. –, "Identification cards – Identification of Issuers,

Part 2: Application and Registration Procedures", ISO/IEC

          7812-2:1993.
 [I8073]  ---, "Information Processing Systems -- Open Systems
          Interconnection, Transport Protocol Specification", ISO IS
          8073.
 [I8327]  ---, "Information Processing Systems -- Open Systems
          Interconnection, Session Protocol Specification", ISO IS
          8327.
 [I8473]  ---, "Information Processing Systems -- Open Systems
          Interconnection, Protocol for Providing the Connectionless
          Network Service", ISO IS 8473.
 [I8802-2] ---, "Information Processing Systems -- Local Area
          Networks, Part 2: Logical Link Control", ISO IS 8802-2.
          (Equivalent to IEEE 802.2.)
 [I8802-3] ---, "Information Processing Systems -- Local Area
          Networks, Part 3: Carrier Sense Multiple Access with
          Collision Detection (CSMA/CD) Access Method and Physical
          Layer Specifications", ISO IS 8802-3. (Equivalent to IEEE
          802.3.)
 [I8823]  ---, "Information Processing Systems -- Open Systems
          Interconnection -- Connection-Oriented Presentation Protocol
          Specification", ISO IS 8823.
 [I9945]  "Portable Operating System Interface for Computer
          Environments", ISO/IEC 9945-1: 1990.
 [IATF]   NSA, "Information Assurance Technical Framework", Release 3,
          NSA, September 2000. (See: IATF.)
 [IDSAN]  ---, "Intrusion Detection System Analyzer Protection
          Profile", version 1.1, NSA, 10 December 2001.
 [IDSSC]  ---, "Intrusion Detection System Scanner Protection
          Profile", version 1.1, NSA, 10 December 2001.
 [IDSSE]  ---, "Intrusion Detection System Sensor Protection Profile",
          version 1.1, NSA, 10 December 2001.

Shirey Informational [Page 350] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [IDSSY]  ---, "Intrusion Detection System", version 1.4, NSA, 4
          February 2002.
 [Ioan]   Ioannidis, J. and M. Blaze, "The Architecture and
          Implementation of Network Layer Security in UNIX", in "UNIX
          Security IV Symposium", October 1993, pp. 29-39.
 [ITSEC]  "Information Technology Security Evaluation Criteria
          (ITSEC): Harmonised Criteria of France, Germany, the
          Netherlands, and the United Kingdom", version 1.2, U.K.
          Department of Trade and Industry, June 1991.
 [JP1]    U.S. DoD, "Department of Defense Dictionary of Military and
          Associated Terms", Joint Publication 1-02, as amended
          through 13 June 2007.
 [John]   Johnson, N. and S. Jajodia, "Exploring Steganography; Seeing
          the Unseen", in "IEEE Computer", February 1998, pp. 26-34.
 [Kahn]   Kahn, D., "The Codebreakers: The Story of Secret Writing",
          The Macmillan Company, New York, 1967.
 [Knut]   Knuth, D., Chapter 3 ("Random Numbers") of Volume 2
          ("Seminumerical Algorithms") of "The Art of Computer
          Programming", Addison-Wesley, Reading, MA, 1969.
 [Kuhn]   Kuhn, M. and R. Anderson, "Soft Tempest: Hidden Data
          Transmission Using Electromagnetic Emanations", in David
          Aucsmith, ed., "Information Hiding, Second International
          Workshop, IH'98", Portland, Oregon, USA, 15-17 April 1998,
          LNCS 1525, Springer-Verlag, ISBN 3-540-65386-4, pp. 124-142.
 [Land]   Landwehr, C., "Formal Models for Computer Security", in "ACM
          Computing Surveys", vol. 13, no. 3, September 1981, pp. 247-
          278.
 [Larm]   Larmouth, J., "ASN.1 Complete", Open System Solutions, 1999
          (a freeware book).
 [M0404]  U.S. Office of Management and Budget, "E-Authentication
          Guidance for Federal Agencies", Memorandum M-04-04, 16
          December 2003.
 [Mene]   Menezes, A. et al, "Some Key Agreement Protocols Providing
          Implicit Authentication", in "The 2nd Workshop on Selected
          Areas in Cryptography", 1995.

Shirey Informational [Page 351] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [Moor]   Moore, A. et al, "Attack Modeling for Information Security
          and Survivability", Carnegie Mellon University / Software
          Engineering Institute, CMU/SEI-2001-TN-001, March 2001.
 [Murr]   Murray, W., "Courtney's Laws of Security", in "Infosecurity
          News", March/April 1993, p. 65.
 [N4001]  National Security Telecommunications and Information System
          Security Committee, "Controlled Cryptographic Items",
          NSTISSI No. 4001, 25 March 1985.
 [N4006]  ---, "Controlled Cryptographic Items", NSTISSI No. 4006, 2
          December 1991.
 [N7003]  ---, "Protective Distribution Systems", NSTISSI No. 7003, 13
          December 1996.
 [NCS01]  National Computer Security Center, "A Guide to Understanding
          Audit in Trusted Systems", NCSC-TG-001, 1 June 1988. (See:
          Rainbow Series.)
 [NCS03]  ---, "Information System Security Policy Guideline", I942-
          TR-003, version 1, July 1994. (See: Rainbow Series.)
 [NCS04]  ---, "Glossary of Computer Security Terms", NCSC-TG-004,
          version 1, 21 October 1988. (See: Rainbow Series.)
 [NCS05]  ---, "Trusted Network Interpretation of the Trusted Computer
          System Evaluation Criteria", NCSC-TG-005, version 1, 31 July
          1987. (See: Rainbow Series.)
 [NCS25]  ---, "A Guide to Understanding Data Remanence in Automated
          Information Systems", NCSC-TG-025, version 2, September
          1991. (See: Rainbow Series.)
 [NCSSG]  National Computer Security Center, "COMPUSECese: Computer
          Security Glossary", NCSC-WA-001-85, Edition 1, 1 October
          1985. (See: Rainbow Series.)
 [NRC91]  National Research Council, "Computers At Risk: Safe
          Computing in the Information Age", National Academy Press,
          1991.
 [NRC98]  Schneider, F., ed., "Trust in Cyberspace", National Research
          Council, National Academy of Sciences, 1998.
 [Padl]   Padlipsky, M., "The Elements of Networking Style", 1985,
          ISBN 0-13-268111-0.

Shirey Informational [Page 352] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [PAG]    American Bar Association, "PKI Assessment Guidelines",
          version 1.0, 10 May 2002. (See: [DSG].)
 [Park]   Parker, D., "Computer Security Management", ISBN 0-8359-
          0905-0, 1981
 [Perr]   Perrine, T. et al, "An Overview of the Kernelized Secure
          Operating System (KSOS)", in "Proceedings of the 7th DoD/NBS
          Computer Security Conference", 24-26 September 1984.
 [PGP]    Garfinkel, S.. "PGP: Pretty Good Privacy", O'Reilly &
          Associates, Inc., Sebastopol, CA, 1995.
 [PKCS]   Kaliski Jr., B., "An Overview of the PKCS Standards", RSA
          Data Security, Inc., 3 June 1991.
 [PKC05]  RSA Laboratories, "PKCS #5: Password-Based Encryption
          Standard ", version 1.5, 1 November 1993. (See: RFC 2898.)
 [PKC07]  ---, "PKCS #7: Cryptographic Message Syntax Standard",
          version 1.5, 1 November 1993. (See: RFC 2315.)
 [PKC10]  ---, "PKCS #10: Certification Request Syntax Standard",
          version 1.0, 1 November 1993.
 [PKC11]  ---, "PKCS #11: Cryptographic Token Interface Standard",
          version 1.0, 28 April 1995.
 [PKC12]  ---, "PKCS #12: Personal Information Exchange Syntax",
          version 1.0, 24 June 1995.
 [R1108]  Kent, S., "U.S. Department of Defense Security Options for
          the Internet Protocol", RFC 1108, November 1991.
 [R1135]  Reynolds, J., "The Helminthiasis of the Internet", RFC 1135,
          December 1989
 [R1208]  Jacobsen, O. and D. Lynch, "A Glossary of Networking Terms",
          RFC 1208, March 1991.
 [R1281]  Pethia, R., Crocker, S., and B. Fraser, "Guidelines for
          Secure Operation of the Internet", RFC 1281, November 1991.
 [R1319]  Kaliski, B., "The MD2 Message-Digest Algorithm", RFC 1319,
          April 1992.
 [R1320]  Rivest, R., "The MD4 Message-Digest Algorithm", RFC 1320,
          April 1992.

Shirey Informational [Page 353] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [R1321]  ---, "The MD5 Message-Digest Algorithm", RFC 1321, April
          1992.
 [R1334]  Lloyd, B. and W. Simpson, "PPP Authentication Protocols",
          RFC 1334, October 1992.
 [R1413]  St. Johns, M., "Identification Protocol", RFC 1413, February
          1993.
 [R1421]  Linn, J., "Privacy Enhancement for Internet Electronic Mail,
          Part I: Message Encryption and Authentication Procedures",
          RFC 1421, February 1993.
 [R1422]  Kent, S., "Privacy Enhancement for Internet Electronic Mail,
          Part II: Certificate-Based Key Management", RFC 1422,
          February 1993.
 [R1455]  Eastlake 3rd, D., "Physical Link Security Type of Service",
          RFC 1455, May 1993.
 [R1457]  Housley, R., "Security Label Framework for the Internet",
          RFC 1457, May 1993.
 [R1492]  Finseth, C., "An Access Control Protocol, Sometimes Called
          TACACS", RFC 1492, July 1993.
 [R1507]  Kaufman, C., "DASS: Distributed Authentication Security
          Service", RFC 1507, September 1993.
 [R1731]  Myers, J., "IMAP4 Authentication Mechanisms", RFC 1731,
          December 1994.
 [R1734]  ---, "POP3 AUTHentication Command", RFC 1734, Dec, 1994.
 [R1760]  Haller, N., "The S/KEY One-Time Password System", RFC 1760,
          February 1995.
 [R1824]  Danisch, H., "The Exponential Security System TESS: An
          Identity-Based Cryptographic Protocol for Authenticated Key-
          Exchange (E.I.S.S.-Report 1995/4)", RFC 1824, August 1995.
 [R1828]  Metzger, P. and W. Simpson, "IP Authentication using Keyed
          MD5", RFC 1828, August 1995.
 [R1829]  Karn, P., Metzger, P., and W. Simpson, "The ESP DES-CBC
          Transform", RFC 1829, August 1995.

Shirey Informational [Page 354] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [R1848]  Crocker, S., Freed, N., Galvin, J., and S. Murphy, "MIME
          Object Security Services", RFC 1848, October 1995.
 [R1851]  Karn, P., Metzger, P., and W. Simpson, "The ESP Triple DES
          Transform", RFC 1851, September 1995.
 [R1928]  Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and L.
          Jones, "SOCKS Protocol Version 5", RFC 1928, March 1996.
 [R1958]  Carpenter, B., "Architectural Principles of the Internet",
          RFC 1958, June 1996.
 [R1983]  Malkin, G., "Internet Users' Glossary", FYI 18, RFC 1983,
          August 1996.
 [R1994]  Simpson, W., "PPP Challenge Handshake Authentication
          Protocol (CHAP)", RFC 1994, August 1996.
 [R2078]  Linn, J., "Generic Security Service Application Program
          Interface, Version 2", RFC 2078, January 1997. (Superseded
          by RFC 2743.)
 [R2084]  Bossert, G., Cooper, S., and W. Drummond, "Considerations
          for Web Transaction Security", RFC 2084, January 1997.
 [R2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
          Hashing for Message Authentication", RFC 2104, February
          1997.
 [R2144]  Adams, C., "The CAST-128 Encryption Algorithm", RFC 2144,
          May 1997.
 [R2179]  Gwinn, A., "Network Security For Trade Shows", RFC 2179,
          July 1997.
 [R2195]  Klensin, J., Catoe, R., and P. Krumviede, "IMAP/POP
          AUTHorize Extension for Simple Challenge/Response", RFC
          2195, September 1997.
 [R2196]  Fraser, B., "Site Security Handbook", FYI 8, RFC 2196,
          September 1997.
 [R2202]  Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and HMAC-
          SHA-1", RFC 2202, Sep. 1997.
 [R2222]  Myers, J., "Simple Authentication and Security Layer
          (SASL)", RFC 2222, October 1997.

Shirey Informational [Page 355] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [R2289]  Haller, N., Metz, C., Nesser, P., and M. Straw, "A One-Time
          Password System", STD 61, RFC 2289, February 1998.
 [R2323]  Ramos, A., "IETF Identification and Security Guidelines",
          RFC 2323, 1 April 1998. (Intended for humorous entertainment
          -- "please laugh loud and hard" -- and does not contain
          serious security information.)
 [R2350]  Brownlee, N. and E. Guttman, "Expectations for Computer
          Security Incident Response", BCP 21, RFC 2350, June 1998.
 [R2356]  Montenegro, G. and V. Gupta, "Sun's SKIP Firewall Traversal
          for Mobile IP", RFC 2356, June 1998.
 [R2401]  Kent, S. and R. Atkinson, "Security Architecture for the
          Internet Protocol", RFC 2401, November 1998.
 [R2402]  ---, "IP Authentication Header", RFC 2402, November 1998.
 [R2403]  Madson, C. and R. Glenn, "The Use of HMAC-MD5-96 within ESP
          and AH", RFC 2403, November 1998.
 [R2404]  ---, "The Use of HMAC-SHA-1-96 within ESP and AH", RFC 2404,
          November 1998.
 [R2405]  Madson, C. and N. Doraswamy, "The ESP DES-CBC Cipher
          Algorithm With Explicit IV", RFC 2405, November 1998.
 [R2406]  Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
          (ESP)", RFC 2406, November 1998.
 [R2407]  Piper, D. "The Internet IP Security Domain of Interpretation
          for ISAKMP", RFC 2407, November 1998.
 [R2408]  Maughan, D., Schertler, M., Schneider, M., and J. Turner,
          "Internet Security Association and Key Management Protocol
          (ISAKMP)", RFC 2408, November 1998.
 [R2410]  Glenn, R. and S. Kent, "The NULL Encryption Algorithm and
          Its Use With IPsec", RFC 2410, November 1998.
 [R2412]  Orman, H., "The OAKLEY Key Determination Protocol", RFC
          2412, November 1998.
 [R2451]  Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher
          Algorithms", RFC 2451, November 1998.

Shirey Informational [Page 356] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [R2504]  Guttman, E., Leong, L., and G. Malkin, "Users' Security
          Handbook", RFC 2504, February 1999.
 [R2560]  Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
          Adams, "X.509 Internet Public Key Infrastructure Online
          Certificate Status Protocol - OCSP", RFC 2560, June 1999.
 [R2612]  Adams, C. and J. Gilchrist, "The CAST-256 Encryption
          Algorithm", RFC 2612, June 1999.
 [R2628]  Smyslov, V., "Simple Cryptographic Program Interface (Crypto
          API)", RFC 2628, June 1999.
 [R2631]  Rescorla, E., "Diffie-Hellman Key Agreement Method", RFC
          2631, June 1999. (See: Diffie-Hellman-Merkle.)
 [R2634]  Hoffman, P., "Enhanced Security Services for S/MIME", RFC
          2634, June 1999.
 [R2635]  Hambridge, S. and A. Lunde, "DON'T SPEW: A Set of Guidelines
          for Mass Unsolicited Mailings and Postings", RFC 2635, June
          1999.
 [R2660]  Rescorla, E. and A. Schiffman, "The Secure HyperText
          Transfer Protocol", RFC 2660, August 1999.
 [R2743]  Linn, J., "Generic Security Service Application Program
          Interface Version 2, Update 1", RFC 2743, January 2000.
 [R2773]  Housley, R., Yee, P., and W. Nace, "Encryption using KEA and
          SKIPJACK", RFC 2773, February 2000.
 [R2801]  Burdett, D., "Internet Open Trading Protocol - IOTP, Version
          1.0", RFC 2801, April 2000.
 [R2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
          Defeating Denial of Service Attacks which employ IP Source
          Address Spoofing", BCP 38, RFC 2827, May 2000.
 [R2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote
          Authentication Dial In User Service (RADIUS)", RFC 2865,
          June 2000.
 [R3060]  Moore, B., Ellesson, E., Strassner, J., and A. Westerinen,
          "Policy Core Information Model -- Version 1 Specification",
          RFC 3060, February 2001.

Shirey Informational [Page 357] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [R3198]  Westerinen, A., Schnizlein, J., Strassner, J., Scherling,
          M., Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry,
          J., and S. Waldbusser, "Terminology for Policy-Based
          Management", RFC 3198, November 2001.
 [R3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
          X.509 Public Key Infrastructure Certificate and Certificate
          Revocation List (CRL) Profile", RFC 3280, April 2002.
 [R3547]  Baugher, M., Weis, B., Hardjono, T., and H. Harney, "Group
          Domain of Interpretation", RFC 3547, July 2003.
 [R3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text
          on Security Considerations", RFC 3552, July 2003.
 [R3647]  Chokhani, S., Ford, W., Sabett, R., Merrill, C., and S. Wu,
          "Internet X.509 Public Key Infrastructure Certificate Policy
          and Certification Practices Framework", RFC 3647, November
          2003.
 [R3739]  Santesson, S., Nystrom, M., and T. Polk, "Internet X.509
          Public Key Infrastructure: Qualified Certificates Profile",
          RFC 3739, March 2004.
 [R3740]  Hardjono, T. and B. Weis, "The Multicast Group Security
          Architecture", RFC 3740, March 2004.
 [R3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
          Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
          3748, June 2004.
 [R3766]  Orman, H. and P. Hoffman, "Determining Strengths For Public
          Keys Used For Exchanging Symmetric Keys", BCP 86, RFC 3766,
          April 2004.
 [R3820]  Tuecke, S., Welch, V., Engert, D., Pearlman, L., and M.
          Thompson, "Internet X.509 Public Key Infrastructure (PKI)
          Proxy Certificate Profile", RFC 3820, June 2004.
 [R3851]  Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
          (S/MIME) Version 3.1 Message Specification", RFC 3851, July
          2004.
 [R3871]  Jones, G., "Operational Security Requirements for Large
          Internet Service Provider (ISP) IP Network Infrastructure",
          RFC 3871, September 2004.

Shirey Informational [Page 358] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [R4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
          Rose, "DNS Security Introduction and Requirements", RFC
          4033, March 2005.
 [R4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
          Rose, "Resource Records for the DNS Security Extensions",
          RFC 4034,  March 2005.
 [R4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
          Rose, "Protocol Modifications for the DNS Security
          Extensions", RFC 4035, March 2005.
 [R4086]  Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness
          Requirements for Security", BCP 106, RFC 4086, June 2005.
 [R4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
          Kerberos Network Authentication Service (V5)", RFC 4120,
          July 2005.
 [R4158]  Cooper, M., Dzambasow, Y., Hesse, P., Joseph, S., and R.
          Nicholas, "Internet X.509 Public Key Infrastructure:
          Certification Path Building", RFC 4158, September 2005.
 [R4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen, "Internet
          X.509 Public Key Infrastructure Certificate Management
          Protocol (CMP)", RFC 4210, September 2005.
 [R4301]  Kent, S. and K. Seo, "Security Architecture for the Internet
          Protocol", RFC 4301, December 2005.
 [R4302]  Kent, S., "IP Authentication Header", RFC 4302, December
          2005.
 [R4303]  Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
          4303, December 2005.
 [R4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC
          4306, December 2005.
 [R4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
          (TLS) Protocol Version 1.1", RFC 4346, April 2006.
 [R4422]  Melnikov, A. and K. Zeilenga, "Simple Authentication and
          Security Layer (SASL)", RFC 4422, June 2006.

Shirey Informational [Page 359] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [Raym]   Raymond, E., ed., "The On-Line Hacker Jargon File", version
          4.0.0, 24 July 1996. (See: http://www.catb.org/~esr/jargon
          for the latest version. Also, "The New Hacker's Dictionary",
          3rd edition, MIT Press, September 1996, ISBN 0-262-68092-0.)
 [Roge]   Rogers, H., "An Overview of the CANEWARE Program", in
          "Proceedings of the 10th National Computer Security
          Conference", NIST and NCSC, September 1987.
 [RSA78]  Rivest, R., A. Shamir, and L. Adleman, "A Method for
          Obtaining Digital Signatures and Public-Key Cryptosystems",
          in "Communications of the ACM", vol. 21, no. 2, February
          1978, pp. 120-126.
 [RSCG]   NSA, "Router Security Configuration Guide: Principles and
          Guidance for Secure Configuration of IP Routers, with
          Detailed Instructions for Cisco Systems Routers", version
          1.1c, C4-040R-02, 15 December 2005, available at
          http://www.nsa.gov/snac/routers/C4-040R-02.pdf.
 [Russ]   Russell, D. et al, Chapter 10 ("TEMPEST") of "Computer
          Security Basics", ISBN 0-937175-71-4, 1991.
 [SAML]   Organization for the Advancement of Structured Information
          Standards (OASIS), "Assertions and Protocol for the OASIS
          Security Assertion Markup Language (SAML)", version 1.1, 2
          September 2003.
 [Sand]   Sandhu, R. et al, "Role-Based Access Control Models", in
          "IEEE Computer", vol. 29, no. 2, February 1996, pp. 38-47.
 [Schn]   Schneier, B., "Applied Cryptography Second Edition", John
          Wiley & Sons, Inc., New York, 1996.
 [SDNS3]  U.S. DoD, NSA, "Secure Data Network Systems, Security
          Protocol 3 (SP3)", document SDN.301, Revision 1.5, 15 May
          1989.
 [SDNS4]  ---, "Secure Data Network Systems, Security Protocol 4
          (SP4)", document SDN.401, Revision 1.2, 12 July 1988.
 [SDNS7]  ---, "Secure Data Network Systems, Message Security Protocol
          (MSP)", SDN.701, Revision 4.0, 7 June 1996, with
          "Corrections to Message Security Protocol, SDN.701, Rev 4.0,
          96-06-07", 30 Aug, 1996.

Shirey Informational [Page 360] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [SET1]   MasterCard and Visa, "SET Secure Electronic Transaction
          Specification, Book 1: Business Description", version 1.0,
          31 May 1997.
 [SET2]   ---, "SET Secure Electronic Transaction Specification, Book
          2: Programmer's Guide", version 1.0, 31 May 1997.
 [SKEME]  Krawczyk, H., "SKEME: A Versatile Secure Key Exchange
          Mechanism for Internet", in "Proceedings of the 1996
          Symposium on Network and Distributed Systems Security".
 [SKIP]   "SKIPJACK and KEA Algorithm Specifications", version 2.0, 22
          May 1998, and "Clarification to the SKIPJACK Algorithm
          Specification", 9 May 2002 (available from NIST Computer
          Security Resource Center).
 [SP12]   NIST, "An Introduction to Computer Security: The NIST
          Handbook", Special Publication 800-12.
 [SP14]   Swanson, M. et al (NIST), "Generally Accepted Principles and
          Practices for Security Information Technology Systems",
          Special Publication 800-14, September 1996.
 [SP15]   Burr, W. et al (NIST), "Minimum Interoperability
          Specification for PKI Components (MISPC), Version 1",
          Special Publication 800-15, September 1997.
 [SP22]   Rukhin, A. et al (NIST), "A Statistical Test Suite for
          Random and Pseudorandom Number Generators for Cryptographic
          Applications", Special Publication 800-15, 15 May 2001.
 [SP27]   Stoneburner, G. et al (NIST), "Engineering Principles for
          Information Technology Security (A Baseline for Achieving
          Security)", Special Publication 800-27 Rev A, June 2004.
 [SP28]   Jansen, W. (NIST), "Guidelines on Active Content and Mobile
          Code", Special Publication 800-28, October 2001.
 [SP30]   Stoneburner, G. et al (NIST), "Risk Management Guide for
          Information Technology Systems", Special Publication 800-30,
          October 2001.
 [SP31]   Bace, R. et al (NIST), "Intrusion Detection Systems",
          Special Publication 800-31.
 [SP32]   Kuhn, D. (NIST), "Introduction to Public Key Technology and
          the Federal PKI Infrastructure ", Special Publication
          800-32, 26 February 2001.

Shirey Informational [Page 361] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [SP33]   Stoneburner, G. (NIST), "Underlying Technical Models for
          Information Technology Security", Special Publication
          800-33, December 2001.
 [SP37]   Ross, R. et al (NIST), "Guide for the Security Certification
          and Accreditation of Federal Information Systems", Special
          Publication 800-37, May 2004.
 [SP38A]  Dworkin, M. (NIST), "Recommendation for Block Cipher Modes
          of Operation: Methods and Techniques", Special Publication
          800-38A, 2001 Edition, December 2001.
 [SP38B]  ---, "Recommendation for Block Cipher Modes of Operation:
          The CMAC Mode for Authentication", Special Publication
          800-38B, May 2005.
 [SP38C]  ---, "Recommendation for Block Cipher Modes of Operation:
          The CCM Mode for Authentication and Confidentiality",
          Special Publication 800-38C, May 2004.
 [SP41]   Wack, J. et al (NIST), "Guidelines on Firewalls and Firewall
          Policy", Special Publication 800-41, January 2002.
 [SP42]   ---, "Guideline on Network Security Testing", Special
          Publication 800-42, October 2003.
 [SP56]   NIST, "Recommendations on Key Establishment Schemes", Draft
          2.0, Special Publication 800-63, January 2003.
 [SP57]   ---, "Recommendation for Key Management", Part 1 "General
          Guideline" and Part 2 "Best Practices for Key Management
          Organization", Special Publication 800-57, DRAFT, January
          2003.
 [SP61]   Grance, T. et al (NIST), "Computer Security Incident
          Handling Guide", Special Publication 800-57, January 2003.
 [SP63]   Burr, W. et al (NIST), "Electronic Authentication
          Guideline", Special Publication 800-63, June 2004
 [SP67]   Barker, W. (NIST), "Recommendation for the Triple Data
          Encryption Algorithm (TDEA) Block Cipher", Special
          Publication 800-67, May 2004
 [Stal]   Stallings, W., "Local Networks", 1987, ISBN 0-02-415520-9.

Shirey Informational [Page 362] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [Stei]   Steiner, J. et al, "Kerberos: An Authentication Service for
          Open Network Systems", in "Usenix Conference Proceedings",
          February 1988.
 [Weis]   Weissman, C., "Blacker: Security for the DDN: Examples of A1
          Security Engineering Trades", in "Symposium on Security and
          Privacy", IEEE Computer Society Press, May 1992, pp. 286-
          292.
 [X400]   International Telecommunications Union -- Telecommunication
          Standardization Sector (formerly "CCITT"), Recommendation
          X.400, "Message Handling Services: Message Handling System
          and Service Overview".
 [X419]   ---, "Message Handling Systems: Protocol Specifications",
          ITU-T Recommendation X.419. (Equivalent to ISO 10021-6).
 [X420]   ---, "Message Handling Systems: Interpersonal Messaging
          System", ITU-T Recommendation X.420. (Equivalent to ISO
          10021-7.).
 [X500]   ---, Recommendation X.500, "Information Technology -- Open
          Systems Interconnection -- The Directory: Overview of
          Concepts, Models, and Services". (Equivalent to ISO 9594-1.)
 [X501]   ---, Recommendation X.501, "Information Technology -- Open
          Systems Interconnection -- The Directory: Models".
 [X509]   ---, Recommendation X.509, "Information Technology -- Open
          Systems Interconnection -- The Directory: Authentication
          Framework", COM 7-250-E Revision 1, 23 February 2001.
          (Equivalent to ISO 9594-8.)
 [X519]   ---, Recommendation X.519, "Information Technology -- Open
          Systems Interconnection -- The Directory: Protocol
          Specifications".
 [X520]   ---, Recommendation X.520, "Information Technology -- Open
          Systems Interconnection -- The Directory: Selected Attribute
          Types".
 [X680]   ---, Recommendation X.680, "Information Technology --
          Abstract Syntax Notation One (ASN.1) -- Specification of
          Basic Notation", 15 November 1994. (Equivalent to ISO/IEC
          8824-1.)

Shirey Informational [Page 363] RFC 4949 Internet Security Glossary, Version 2 August 2007

 [X690]   ---, Recommendation X.690, "Information Technology -- ASN.1
          Encoding Rules -- Specification of Basic Encoding Rules
          (BER), Canonical Encoding Rules (CER) and Distinguished
          Encoding Rules (DER)", 15 November 1994. (Equivalent to
          ISO/IEC 8825-1.)

7. Acknowledgments

 George Huff had a good idea! [Huff]

Author's Address

 Dr. Robert W. Shirey
 3516 N. Kensington St.
 Arlington, Virginia  22207-1328
 USA
 EMail: rwshirey4949@verizon.net

Shirey Informational [Page 364] RFC 4949 Internet Security Glossary, Version 2 August 2007

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