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rfc:rfc3280

Network Working Group R. Housley Request for Comments: 3280 RSA Laboratories Obsoletes: 2459 W. Polk Category: Standards Track NIST

                                                               W. Ford
                                                              VeriSign
                                                               D. Solo
                                                             Citigroup
                                                            April 2002
              Internet X.509 Public Key Infrastructure
     Certificate and Certificate Revocation List (CRL) Profile

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

 This memo profiles the X.509 v3 certificate and X.509 v2 Certificate
 Revocation List (CRL) for use in the Internet.  An overview of this
 approach and model are provided as an introduction.  The X.509 v3
 certificate format is described in detail, with additional
 information regarding the format and semantics of Internet name
 forms.  Standard certificate extensions are described and two
 Internet-specific extensions are defined.  A set of required
 certificate extensions is specified.  The X.509 v2 CRL format is
 described in detail, and required extensions are defined.  An
 algorithm for X.509 certification path validation is described.  An
 ASN.1 module and examples are provided in the appendices.

Table of Contents

 1  Introduction  . . . . . . . . . . . . . . . . . . . . . .   4
 2  Requirements and Assumptions  . . . . . . . . . . . . . .   5
 2.1  Communication and Topology  . . . . . . . . . . . . . .   6
 2.2  Acceptability Criteria  . . . . . . . . . . . . . . . .   6
 2.3  User Expectations . . . . . . . . . . . . . . . . . . .   7
 2.4  Administrator Expectations  . . . . . . . . . . . . . .   7
 3  Overview of Approach  . . . . . . . . . . . . . . . . . .   7

Housley, et. al. Standards Track [Page 1] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 3.1  X.509 Version 3 Certificate . . . . . . . . . . . . . .   8
 3.2  Certification Paths and Trust . . . . . . . . . . . . .   9
 3.3  Revocation  . . . . . . . . . . . . . . . . . . . . . .  11
 3.4  Operational Protocols . . . . . . . . . . . . . . . . .  13
 3.5  Management Protocols  . . . . . . . . . . . . . . . . .  13
 4  Certificate and Certificate Extensions Profile  . . . . .  14
 4.1  Basic Certificate Fields  . . . . . . . . . . . . . . .  15
 4.1.1  Certificate Fields  . . . . . . . . . . . . . . . . .  16
 4.1.1.1  tbsCertificate  . . . . . . . . . . . . . . . . . .  16
 4.1.1.2  signatureAlgorithm  . . . . . . . . . . . . . . . .  16
 4.1.1.3  signatureValue  . . . . . . . . . . . . . . . . . .  16
 4.1.2  TBSCertificate  . . . . . . . . . . . . . . . . . . .  17
 4.1.2.1  Version . . . . . . . . . . . . . . . . . . . . . .  17
 4.1.2.2  Serial number . . . . . . . . . . . . . . . . . . .  17
 4.1.2.3  Signature . . . . . . . . . . . . . . . . . . . . .  18
 4.1.2.4  Issuer  . . . . . . . . . . . . . . . . . . . . . .  18
 4.1.2.5  Validity  . . . . . . . . . . . . . . . . . . . . .  22
 4.1.2.5.1  UTCTime . . . . . . . . . . . . . . . . . . . . .  22
 4.1.2.5.2  GeneralizedTime . . . . . . . . . . . . . . . . .  22
 4.1.2.6  Subject . . . . . . . . . . . . . . . . . . . . . .  23
 4.1.2.7  Subject Public Key Info . . . . . . . . . . . . . .  24
 4.1.2.8  Unique Identifiers  . . . . . . . . . . . . . . . .  24
 4.1.2.9 Extensions . . . . . . . . . . . . . . . . . . . . .  24
 4.2  Certificate Extensions  . . . . . . . . . . . . . . . .  24
 4.2.1  Standard Extensions . . . . . . . . . . . . . . . . .  25
 4.2.1.1  Authority Key Identifier  . . . . . . . . . . . . .  26
 4.2.1.2  Subject Key Identifier  . . . . . . . . . . . . . .  27
 4.2.1.3  Key Usage . . . . . . . . . . . . . . . . . . . . .  28
 4.2.1.4  Private Key Usage Period  . . . . . . . . . . . . .  29
 4.2.1.5  Certificate Policies  . . . . . . . . . . . . . . .  30
 4.2.1.6  Policy Mappings . . . . . . . . . . . . . . . . . .  33
 4.2.1.7  Subject Alternative Name  . . . . . . . . . . . . .  33
 4.2.1.8  Issuer Alternative Name . . . . . . . . . . . . . .  36
 4.2.1.9  Subject Directory Attributes  . . . . . . . . . . .  36
 4.2.1.10  Basic Constraints  . . . . . . . . . . . . . . . .  36
 4.2.1.11  Name Constraints . . . . . . . . . . . . . . . . .  37
 4.2.1.12  Policy Constraints . . . . . . . . . . . . . . . .  40
 4.2.1.13  Extended Key Usage . . . . . . . . . . . . . . . .  40
 4.2.1.14  CRL Distribution Points  . . . . . . . . . . . . .  42
 4.2.1.15  Inhibit Any-Policy . . . . . . . . . . . . . . . .  44
 4.2.1.16  Freshest CRL . . . . . . . . . . . . . . . . . . .  44
 4.2.2  Internet Certificate Extensions . . . . . . . . . . .  45
 4.2.2.1  Authority Information Access  . . . . . . . . . . .  45
 4.2.2.2  Subject Information Access  . . . . . . . . . . . .  46
 5  CRL and CRL Extensions Profile  . . . . . . . . . . . . .  48
 5.1  CRL Fields  . . . . . . . . . . . . . . . . . . . . . .  49
 5.1.1  CertificateList Fields  . . . . . . . . . . . . . . .  50
 5.1.1.1  tbsCertList . . . . . . . . . . . . . . . . . . . .  50

Housley, et. al. Standards Track [Page 2] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 5.1.1.2  signatureAlgorithm  . . . . . . . . . . . . . . . .  50
 5.1.1.3  signatureValue  . . . . . . . . . . . . . . . . . .  51
 5.1.2  Certificate List "To Be Signed" . . . . . . . . . . .  51
 5.1.2.1  Version . . . . . . . . . . . . . . . . . . . . . .  52
 5.1.2.2  Signature . . . . . . . . . . . . . . . . . . . . .  52
 5.1.2.3  Issuer Name . . . . . . . . . . . . . . . . . . . .  52
 5.1.2.4  This Update . . . . . . . . . . . . . . . . . . . .  52
 5.1.2.5  Next Update . . . . . . . . . . . . . . . . . . . .  53
 5.1.2.6  Revoked Certificates  . . . . . . . . . . . . . . .  53
 5.1.2.7  Extensions  . . . . . . . . . . . . . . . . . . . .  53
 5.2  CRL Extensions  . . . . . . . . . . . . . . . . . . . .  53
 5.2.1  Authority Key Identifier  . . . . . . . . . . . . . .  54
 5.2.2  Issuer Alternative Name . . . . . . . . . . . . . . .  54
 5.2.3  CRL Number  . . . . . . . . . . . . . . . . . . . . .  55
 5.2.4  Delta CRL Indicator . . . . . . . . . . . . . . . . .  55
 5.2.5  Issuing Distribution Point  . . . . . . . . . . . . .  58
 5.2.6  Freshest CRL  . . . . . . . . . . . . . . . . . . . .  59
 5.3  CRL Entry Extensions  . . . . . . . . . . . . . . . . .  60
 5.3.1  Reason Code . . . . . . . . . . . . . . . . . . . . .  60
 5.3.2  Hold Instruction Code . . . . . . . . . . . . . . . .  61
 5.3.3  Invalidity Date . . . . . . . . . . . . . . . . . . .  62
 5.3.4  Certificate Issuer  . . . . . . . . . . . . . . . . .  62
 6  Certificate Path Validation . . . . . . . . . . . . . . .  62
 6.1  Basic Path Validation . . . . . . . . . . . . . . . . .  63
 6.1.1  Inputs  . . . . . . . . . . . . . . . . . . . . . . .  66
 6.1.2  Initialization  . . . . . . . . . . . . . . . . . . .  67
 6.1.3  Basic Certificate Processing  . . . . . . . . . . . .  70
 6.1.4  Preparation for Certificate i+1 . . . . . . . . . . .  75
 6.1.5  Wrap-up procedure . . . . . . . . . . . . . . . . . .  78
 6.1.6  Outputs . . . . . . . . . . . . . . . . . . . . . . .  80
 6.2  Extending Path Validation . . . . . . . . . . . . . . .  80
 6.3  CRL Validation  . . . . . . . . . . . . . . . . . . . .  81
 6.3.1  Revocation Inputs . . . . . . . . . . . . . . . . . .  82
 6.3.2  Initialization and Revocation State Variables . . . .  82
 6.3.3  CRL Processing  . . . . . . . . . . . . . . . . . . .  83
 7  References  . . . . . . . . . . . . . . . . . . . . . . .  86
 8  Intellectual Property Rights  . . . . . . . . . . . . . .  88
 9  Security Considerations . . . . . . . . . . . . . . . . .  89
 Appendix A.  ASN.1 Structures and OIDs . . . . . . . . . . .  92
 A.1 Explicitly Tagged Module, 1988 Syntax  . . . . . . . . .  92
 A.2 Implicitly Tagged Module, 1988 Syntax  . . . . . . . . . 105
 Appendix B.  ASN.1 Notes . . . . . . . . . . . . . . . . . . 112
 Appendix C.  Examples  . . . . . . . . . . . . . . . . . . . 115
 C.1  DSA Self-Signed Certificate . . . . . . . . . . . . . . 115
 C.2  End Entity Certificate Using DSA  . . . . . . . . . . . 119
 C.3  End Entity Certificate Using RSA  . . . . . . . . . . . 122
 C.4  Certificate Revocation List . . . . . . . . . . . . . . 126
 Author Addresses . . . . . . . . . . . . . . . . . . . . . . 128

Housley, et. al. Standards Track [Page 3] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 Full Copyright Statement . . . . . . . . . . . . . . . . . . 129

1 Introduction

 This specification is one part of a family of standards for the X.509
 Public Key Infrastructure (PKI) for the Internet.
 This specification profiles the format and semantics of certificates
 and certificate revocation lists (CRLs) for the Internet PKI.
 Procedures are described for processing of certification paths in the
 Internet environment.  Finally, ASN.1 modules are provided in the
 appendices for all data structures defined or referenced.
 Section 2 describes Internet PKI requirements, and the assumptions
 which affect the scope of this document.  Section 3 presents an
 architectural model and describes its relationship to previous IETF
 and ISO/IEC/ITU-T standards.  In particular, this document's
 relationship with the IETF PEM specifications and the ISO/IEC/ITU-T
 X.509 documents are described.
 Section 4 profiles the X.509 version 3 certificate, and section 5
 profiles the X.509 version 2 CRL.  The profiles include the
 identification of ISO/IEC/ITU-T and ANSI extensions which may be
 useful in the Internet PKI.  The profiles are presented in the 1988
 Abstract Syntax Notation One (ASN.1) rather than the 1997 ASN.1
 syntax used in the most recent ISO/IEC/ITU-T standards.
 Section 6 includes certification path validation procedures.  These
 procedures are based upon the ISO/IEC/ITU-T definition.
 Implementations are REQUIRED to derive the same results but are not
 required to use the specified procedures.
 Procedures for identification and encoding of public key materials
 and digital signatures are defined in [PKIXALGS].  Implementations of
 this specification are not required to use any particular
 cryptographic algorithms.  However, conforming implementations which
 use the algorithms identified in [PKIXALGS] MUST identify and encode
 the public key materials and digital signatures as described in that
 specification.
 Finally, three appendices are provided to aid implementers.  Appendix
 A contains all ASN.1 structures defined or referenced within this
 specification.  As above, the material is presented in the 1988
 ASN.1.  Appendix B contains notes on less familiar features of the
 ASN.1 notation used within this specification.  Appendix C contains
 examples of a conforming certificate and a conforming CRL.

Housley, et. al. Standards Track [Page 4] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 This specification obsoletes RFC 2459.  This specification differs
 from RFC 2459 in five basic areas:
  • To promote interoperable implementations, a detailed algorithm

for certification path validation is included in section 6.1 of

    this specification; RFC 2459 provided only a high-level
    description of path validation.
  • An algorithm for determining the status of a certificate using

CRLs is provided in section 6.3 of this specification. This

    material was not present in RFC 2459.
  • To accommodate new usage models, detailed information describing

the use of delta CRLs is provided in Section 5 of this

    specification.
  • Identification and encoding of public key materials and digital

signatures are not included in this specification, but are now

    described in a companion specification [PKIXALGS].
  • Four additional extensions are specified: three certificate

extensions and one CRL extension. The certificate extensions are

    subject info access, inhibit any-policy, and freshest CRL.  The
    freshest CRL extension is also defined as a CRL extension.
  • Throughout the specification, clarifications have been

introduced to enhance consistency with the ITU-T X.509

    specification.  X.509 defines the certificate and CRL format as
    well as many of the extensions that appear in this specification.
    These changes were introduced to improve the likelihood of
    interoperability between implementations based on this
    specification with implementations based on the ITU-T
    specification.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119.

2 Requirements and Assumptions

 The goal of this specification is to develop a profile to facilitate
 the use of X.509 certificates within Internet applications for those
 communities wishing to make use of X.509 technology.  Such
 applications may include WWW, electronic mail, user authentication,
 and IPsec.  In order to relieve some of the obstacles to using X.509

Housley, et. al. Standards Track [Page 5] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 certificates, this document defines a profile to promote the
 development of certificate management systems; development of
 application tools; and interoperability determined by policy.
 Some communities will need to supplement, or possibly replace, this
 profile in order to meet the requirements of specialized application
 domains or environments with additional authorization, assurance, or
 operational requirements.  However, for basic applications, common
 representations of frequently used attributes are defined so that
 application developers can obtain necessary information without
 regard to the issuer of a particular certificate or certificate
 revocation list (CRL).
 A certificate user should review the certificate policy generated by
 the certification authority (CA) before relying on the authentication
 or non-repudiation services associated with the public key in a
 particular certificate.  To this end, this standard does not
 prescribe legally binding rules or duties.
 As supplemental authorization and attribute management tools emerge,
 such as attribute certificates, it may be appropriate to limit the
 authenticated attributes that are included in a certificate.  These
 other management tools may provide more appropriate methods of
 conveying many authenticated attributes.

2.1 Communication and Topology

 The users of certificates will operate in a wide range of
 environments with respect to their communication topology, especially
 users of secure electronic mail.  This profile supports users without
 high bandwidth, real-time IP connectivity, or high connection
 availability.  In addition, the profile allows for the presence of
 firewall or other filtered communication.
 This profile does not assume the deployment of an X.500 Directory
 system or a LDAP directory system.  The profile does not prohibit the
 use of an X.500 Directory or a LDAP directory; however, any means of
 distributing certificates and certificate revocation lists (CRLs) may
 be used.

2.2 Acceptability Criteria

 The goal of the Internet Public Key Infrastructure (PKI) is to meet
 the needs of deterministic, automated identification, authentication,
 access control, and authorization functions.  Support for these
 services determines the attributes contained in the certificate as
 well as the ancillary control information in the certificate such as
 policy data and certification path constraints.

Housley, et. al. Standards Track [Page 6] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

2.3 User Expectations

 Users of the Internet PKI are people and processes who use client
 software and are the subjects named in certificates.  These uses
 include readers and writers of electronic mail, the clients for WWW
 browsers, WWW servers, and the key manager for IPsec within a router.
 This profile recognizes the limitations of the platforms these users
 employ and the limitations in sophistication and attentiveness of the
 users themselves.  This manifests itself in minimal user
 configuration responsibility (e.g., trusted CA keys, rules), explicit
 platform usage constraints within the certificate, certification path
 constraints which shield the user from many malicious actions, and
 applications which sensibly automate validation functions.

2.4 Administrator Expectations

 As with user expectations, the Internet PKI profile is structured to
 support the individuals who generally operate CAs.  Providing
 administrators with unbounded choices increases the chances that a
 subtle CA administrator mistake will result in broad compromise.
 Also, unbounded choices greatly complicate the software that process
 and validate the certificates created by the CA.

3 Overview of Approach

 Following is a simplified view of the architectural model assumed by
 the PKIX specifications.
 The components in this model are:
 end entity: user of PKI certificates and/or end user system that is
             the subject of a certificate;
 CA:         certification authority;
 RA:         registration authority, i.e., an optional system to which
             a CA delegates certain management functions;
 CRL issuer: an optional system to which a CA delegates the
             publication of certificate revocation lists;
 repository: a system or collection of distributed systems that stores
             certificates and CRLs and serves as a means of
             distributing these certificates and CRLs to end entities.
 Note that an Attribute Authority (AA) might also choose to delegate
 the publication of CRLs to a CRL issuer.

Housley, et. al. Standards Track [Page 7] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 +---+
 | C |                       +------------+
 | e | <-------------------->| End entity |
 | r |       Operational     +------------+
 | t |       transactions          ^
 | i |      and management         |  Management
 | f |       transactions          |  transactions        PKI
 | i |                             |                     users
 | c |                             v
 | a | =======================  +--+------------+  ==============
 | t |                          ^               ^
 | e |                          |               |         PKI
 |   |                          v               |      management
 | & |                       +------+           |       entities
 |   | <---------------------|  RA  |<----+     |
 | C |  Publish certificate  +------+     |     |
 | R |                                    |     |
 | L |                                    |     |
 |   |                                    v     v
 | R |                                +------------+
 | e | <------------------------------|     CA     |
 | p |   Publish certificate          +------------+
 | o |   Publish CRL                     ^      ^
 | s |                                   |      |  Management
 | i |                +------------+     |      |  transactions
 | t | <--------------| CRL Issuer |<----+      |
 | o |   Publish CRL  +------------+            v
 | r |                                      +------+
 | y |                                      |  CA  |
 +---+                                      +------+
                    Figure 1 - PKI Entities

3.1 X.509 Version 3 Certificate

 Users of a public key require confidence that the associated private
 key is owned by the correct remote subject (person or system) with
 which an encryption or digital signature mechanism will be used.
 This confidence is obtained through the use of public key
 certificates, which are data structures that bind public key values
 to subjects.  The binding is asserted by having a trusted CA
 digitally sign each certificate.  The CA may base this assertion upon
 technical means (a.k.a., proof of possession through a challenge-
 response protocol), presentation of the private key, or on an
 assertion by the subject.  A certificate has a limited valid lifetime
 which is indicated in its signed contents.  Because a certificate's
 signature and timeliness can be independently checked by a
 certificate-using client, certificates can be distributed via

Housley, et. al. Standards Track [Page 8] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 untrusted communications and server systems, and can be cached in
 unsecured storage in certificate-using systems.
 ITU-T X.509 (formerly CCITT X.509) or ISO/IEC 9594-8, which was first
 published in 1988 as part of the X.500 Directory recommendations,
 defines a standard certificate format [X.509].  The certificate
 format in the 1988 standard is called the version 1 (v1) format.
 When X.500 was revised in 1993, two more fields were added, resulting
 in the version 2 (v2) format.
 The Internet Privacy Enhanced Mail (PEM) RFCs, published in 1993,
 include specifications for a public key infrastructure based on X.509
 v1 certificates [RFC 1422].  The experience gained in attempts to
 deploy RFC 1422 made it clear that the v1 and v2 certificate formats
 are deficient in several respects.  Most importantly, more fields
 were needed to carry information which PEM design and implementation
 experience had proven necessary.  In response to these new
 requirements, ISO/IEC, ITU-T and ANSI X9 developed the X.509 version
 3 (v3) certificate format.  The v3 format extends the v2 format by
 adding provision for additional extension fields.  Particular
 extension field types may be specified in standards or may be defined
 and registered by any organization or community.  In June 1996,
 standardization of the basic v3 format was completed [X.509].
 ISO/IEC, ITU-T, and ANSI X9 have also developed standard extensions
 for use in the v3 extensions field [X.509][X9.55].  These extensions
 can convey such data as additional subject identification
 information, key attribute information, policy information, and
 certification path constraints.
 However, the ISO/IEC, ITU-T, and ANSI X9 standard extensions are very
 broad in their applicability.  In order to develop interoperable
 implementations of X.509 v3 systems for Internet use, it is necessary
 to specify a profile for use of the X.509 v3 extensions tailored for
 the Internet.  It is one goal of this document to specify a profile
 for Internet WWW, electronic mail, and IPsec applications.
 Environments with additional requirements may build on this profile
 or may replace it.

3.2 Certification Paths and Trust

 A user of a security service requiring knowledge of a public key
 generally needs to obtain and validate a certificate containing the
 required public key.  If the public key user does not already hold an
 assured copy of the public key of the CA that signed the certificate,
 the CA's name, and related information (such as the validity period
 or name constraints), then it might need an additional certificate to
 obtain that public key.  In general, a chain of multiple certificates

Housley, et. al. Standards Track [Page 9] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 may be needed, comprising a certificate of the public key owner (the
 end entity) signed by one CA, and zero or more additional
 certificates of CAs signed by other CAs.  Such chains, called
 certification paths, are required because a public key user is only
 initialized with a limited number of assured CA public keys.
 There are different ways in which CAs might be configured in order
 for public key users to be able to find certification paths.  For
 PEM, RFC 1422 defined a rigid hierarchical structure of CAs.  There
 are three types of PEM certification authority:
    (a)  Internet Policy Registration Authority (IPRA):  This
    authority, operated under the auspices of the Internet Society,
    acts as the root of the PEM certification hierarchy at level 1.
    It issues certificates only for the next level of authorities,
    PCAs.  All certification paths start with the IPRA.
    (b)  Policy Certification Authorities (PCAs):  PCAs are at level 2
    of the hierarchy, each PCA being certified by the IPRA.  A PCA
    shall establish and publish a statement of its policy with respect
    to certifying users or subordinate certification authorities.
    Distinct PCAs aim to satisfy different user needs.  For example,
    one PCA (an organizational PCA) might support the general
    electronic mail needs of commercial organizations, and another PCA
    (a high-assurance PCA) might have a more stringent policy designed
    for satisfying legally binding digital signature requirements.
    (c)  Certification Authorities (CAs):  CAs are at level 3 of the
    hierarchy and can also be at lower levels.  Those at level 3 are
    certified by PCAs.  CAs represent, for example, particular
    organizations, particular organizational units (e.g., departments,
    groups, sections), or particular geographical areas.
 RFC 1422 furthermore has a name subordination rule which requires
 that a CA can only issue certificates for entities whose names are
 subordinate (in the X.500 naming tree) to the name of the CA itself.
 The trust associated with a PEM certification path is implied by the
 PCA name.  The name subordination rule ensures that CAs below the PCA
 are sensibly constrained as to the set of subordinate entities they
 can certify (e.g., a CA for an organization can only certify entities
 in that organization's name tree).  Certificate user systems are able
 to mechanically check that the name subordination rule has been
 followed.
 The RFC 1422 uses the X.509 v1 certificate formats.  The limitations
 of X.509 v1 required imposition of several structural restrictions to
 clearly associate policy information or restrict the utility of
 certificates.  These restrictions included:

Housley, et. al. Standards Track [Page 10] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (a)  a pure top-down hierarchy, with all certification paths
    starting from IPRA;
    (b)  a naming subordination rule restricting the names of a CA's
    subjects; and
    (c)  use of the PCA concept, which requires knowledge of
    individual PCAs to be built into certificate chain verification
    logic.  Knowledge of individual PCAs was required to determine if
    a chain could be accepted.
 With X.509 v3, most of the requirements addressed by RFC 1422 can be
 addressed using certificate extensions, without a need to restrict
 the CA structures used.  In particular, the certificate extensions
 relating to certificate policies obviate the need for PCAs and the
 constraint extensions obviate the need for the name subordination
 rule.  As a result, this document supports a more flexible
 architecture, including:
    (a)  Certification paths start with a public key of a CA in a
    user's own domain, or with the public key of the top of a
    hierarchy.  Starting with the public key of a CA in a user's own
    domain has certain advantages.  In some environments, the local
    domain is the most trusted.
    (b)  Name constraints may be imposed through explicit inclusion of
    a name constraints extension in a certificate, but are not
    required.
    (c)  Policy extensions and policy mappings replace the PCA
    concept, which permits a greater degree of automation.  The
    application can determine if the certification path is acceptable
    based on the contents of the certificates instead of a priori
    knowledge of PCAs.  This permits automation of certification path
    processing.

3.3 Revocation

 When a certificate is issued, it is expected to be in use for its
 entire validity period.  However, various circumstances may cause a
 certificate to become invalid prior to the expiration of the validity
 period.  Such circumstances include change of name, change of
 association between subject and CA (e.g., an employee terminates
 employment with an organization), and compromise or suspected
 compromise of the corresponding private key.  Under such
 circumstances, the CA needs to revoke the certificate.

Housley, et. al. Standards Track [Page 11] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 X.509 defines one method of certificate revocation.  This method
 involves each CA periodically issuing a signed data structure called
 a certificate revocation list (CRL).  A CRL is a time stamped list
 identifying revoked certificates which is signed by a CA or CRL
 issuer and made freely available in a public repository.  Each
 revoked certificate is identified in a CRL by its certificate serial
 number.  When a certificate-using system uses a certificate (e.g.,
 for verifying a remote user's digital signature), that system not
 only checks the certificate signature and validity but also acquires
 a suitably-recent CRL and checks that the certificate serial number
 is not on that CRL.  The meaning of "suitably-recent" may vary with
 local policy, but it usually means the most recently-issued CRL.  A
 new CRL is issued on a regular periodic basis (e.g., hourly, daily,
 or weekly).  An entry is added to the CRL as part of the next update
 following notification of revocation.  An entry MUST NOT be removed
 from the CRL until it appears on one regularly scheduled CRL issued
 beyond the revoked certificate's validity period.
 An advantage of this revocation method is that CRLs may be
 distributed by exactly the same means as certificates themselves,
 namely, via untrusted servers and untrusted communications.
 One limitation of the CRL revocation method, using untrusted
 communications and servers, is that the time granularity of
 revocation is limited to the CRL issue period.  For example, if a
 revocation is reported now, that revocation will not be reliably
 notified to certificate-using systems until all currently issued CRLs
 are updated -- this may be up to one hour, one day, or one week
 depending on the frequency that CRLs are issued.
 As with the X.509 v3 certificate format, in order to facilitate
 interoperable implementations from multiple vendors, the X.509 v2 CRL
 format needs to be profiled for Internet use.  It is one goal of this
 document to specify that profile.  However, this profile does not
 require the issuance of CRLs.  Message formats and protocols
 supporting on-line revocation notification are defined in other PKIX
 specifications.  On-line methods of revocation notification may be
 applicable in some environments as an alternative to the X.509 CRL.
 On-line revocation checking may significantly reduce the latency
 between a revocation report and the distribution of the information
 to relying parties.  Once the CA accepts a revocation report as
 authentic and valid, any query to the on-line service will correctly
 reflect the certificate validation impacts of the revocation.
 However, these methods impose new security requirements: the
 certificate validator needs to trust the on-line validation service
 while the repository does not need to be trusted.

Housley, et. al. Standards Track [Page 12] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

3.4 Operational Protocols

 Operational protocols are required to deliver certificates and CRLs
 (or status information) to certificate using client systems.
 Provisions are needed for a variety of different means of certificate
 and CRL delivery, including distribution procedures based on LDAP,
 HTTP, FTP, and X.500.  Operational protocols supporting these
 functions are defined in other PKIX specifications.  These
 specifications may include definitions of message formats and
 procedures for supporting all of the above operational environments,
 including definitions of or references to appropriate MIME content
 types.

3.5 Management Protocols

 Management protocols are required to support on-line interactions
 between PKI user and management entities.  For example, a management
 protocol might be used between a CA and a client system with which a
 key pair is associated, or between two CAs which cross-certify each
 other.  The set of functions which potentially need to be supported
 by management protocols include:
    (a)  registration:  This is the process whereby a user first makes
    itself known to a CA (directly, or through an RA), prior to that
    CA issuing  a certificate or certificates for that user.
    (b)  initialization:  Before a client system can operate securely
    it is necessary to install key materials which have the
    appropriate relationship with keys stored elsewhere in the
    infrastructure.  For example, the client needs to be securely
    initialized with the public key and other assured information of
    the trusted CA(s), to be used in validating certificate paths.
    Furthermore, a client typically needs to be initialized with its
    own key pair(s).
    (c)  certification:  This is the process in which a CA issues a
    certificate for a user's public key, and returns that certificate
    to the user's client system and/or posts that certificate in a
    repository.
    (d)  key pair recovery:  As an option, user client key materials
    (e.g., a user's private key used for encryption purposes) may be
    backed up by a CA or a key backup system.  If a user needs to
    recover these backed up key materials (e.g., as a result of a
    forgotten password or a lost key chain file), an on-line protocol
    exchange may be needed to support such recovery.

Housley, et. al. Standards Track [Page 13] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (e)  key pair update:  All key pairs need to be updated regularly,
    i.e., replaced with a new key pair, and new certificates issued.
    (f)  revocation request:  An authorized person advises a CA of an
    abnormal situation requiring certificate revocation.
    (g)  cross-certification:  Two CAs exchange information used in
    establishing a cross-certificate.  A cross-certificate is a
    certificate issued by one CA to another CA which contains a CA
    signature key used for issuing certificates.
 Note that on-line protocols are not the only way of implementing the
 above functions.  For all functions there are off-line methods of
 achieving the same result, and this specification does not mandate
 use of on-line protocols.  For example, when hardware tokens are
 used, many of the functions may be achieved as part of the physical
 token delivery.  Furthermore, some of the above functions may be
 combined into one protocol exchange.  In particular, two or more of
 the registration, initialization, and certification functions can be
 combined into one protocol exchange.
 The PKIX series of specifications defines a set of standard message
 formats supporting the above functions.  The protocols for conveying
 these messages in different environments (e.g., e-mail, file
 transfer, and WWW) are described in those specifications.

4 Certificate and Certificate Extensions Profile

 This section presents a profile for public key certificates that will
 foster interoperability and a reusable PKI.  This section is based
 upon the X.509 v3 certificate format and the standard certificate
 extensions defined in [X.509].  The ISO/IEC and ITU-T documents use
 the 1997 version of ASN.1; while this document uses the 1988 ASN.1
 syntax, the encoded certificate and standard extensions are
 equivalent.  This section also defines private extensions required to
 support a PKI for the Internet community.
 Certificates may be used in a wide range of applications and
 environments covering a broad spectrum of interoperability goals and
 a broader spectrum of operational and assurance requirements.  The
 goal of this document is to establish a common baseline for generic
 applications requiring broad interoperability and limited special
 purpose requirements.  In particular, the emphasis will be on
 supporting the use of X.509 v3 certificates for informal Internet
 electronic mail, IPsec, and WWW applications.

Housley, et. al. Standards Track [Page 14] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

4.1 Basic Certificate Fields

 The X.509 v3 certificate basic syntax is as follows.  For signature
 calculation, the data that is to be signed is encoded using the ASN.1
 distinguished encoding rules (DER) [X.690].  ASN.1 DER encoding is a
 tag, length, value encoding system for each element.
 Certificate  ::=  SEQUENCE  {
      tbsCertificate       TBSCertificate,
      signatureAlgorithm   AlgorithmIdentifier,
      signatureValue       BIT STRING  }
 TBSCertificate  ::=  SEQUENCE  {
      version         [0]  EXPLICIT Version DEFAULT v1,
      serialNumber         CertificateSerialNumber,
      signature            AlgorithmIdentifier,
      issuer               Name,
      validity             Validity,
      subject              Name,
      subjectPublicKeyInfo SubjectPublicKeyInfo,
      issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
                           -- If present, version MUST be v2 or v3
      subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
                           -- If present, version MUST be v2 or v3
      extensions      [3]  EXPLICIT Extensions OPTIONAL
                           -- If present, version MUST be v3
      }
 Version  ::=  INTEGER  {  v1(0), v2(1), v3(2)  }
 CertificateSerialNumber  ::=  INTEGER
 Validity ::= SEQUENCE {
      notBefore      Time,
      notAfter       Time }
 Time ::= CHOICE {
      utcTime        UTCTime,
      generalTime    GeneralizedTime }
 UniqueIdentifier  ::=  BIT STRING
 SubjectPublicKeyInfo  ::=  SEQUENCE  {
      algorithm            AlgorithmIdentifier,
      subjectPublicKey     BIT STRING  }
 Extensions  ::=  SEQUENCE SIZE (1..MAX) OF Extension

Housley, et. al. Standards Track [Page 15] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 Extension  ::=  SEQUENCE  {
      extnID      OBJECT IDENTIFIER,
      critical    BOOLEAN DEFAULT FALSE,
      extnValue   OCTET STRING  }
 The following items describe the X.509 v3 certificate for use in the
 Internet.

4.1.1 Certificate Fields

 The Certificate is a SEQUENCE of three required fields.  The fields
 are described in detail in the following subsections.

4.1.1.1 tbsCertificate

 The field contains the names of the subject and issuer, a public key
 associated with the subject, a validity period, and other associated
 information.  The fields are described in detail in section 4.1.2;
 the tbsCertificate usually includes extensions which are described in
 section 4.2.

4.1.1.2 signatureAlgorithm

 The signatureAlgorithm field contains the identifier for the
 cryptographic algorithm used by the CA to sign this certificate.
 [PKIXALGS] lists supported signature algorithms, but other signature
 algorithms MAY also be supported.
 An algorithm identifier is defined by the following ASN.1 structure:
 AlgorithmIdentifier  ::=  SEQUENCE  {
      algorithm               OBJECT IDENTIFIER,
      parameters              ANY DEFINED BY algorithm OPTIONAL  }
 The algorithm identifier is used to identify a cryptographic
 algorithm.  The OBJECT IDENTIFIER component identifies the algorithm
 (such as DSA with SHA-1).  The contents of the optional parameters
 field will vary according to the algorithm identified.
 This field MUST contain the same algorithm identifier as the
 signature field in the sequence tbsCertificate (section 4.1.2.3).

4.1.1.3 signatureValue

 The signatureValue field contains a digital signature computed upon
 the ASN.1 DER encoded tbsCertificate.  The ASN.1 DER encoded
 tbsCertificate is used as the input to the signature function.  This

Housley, et. al. Standards Track [Page 16] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 signature value is encoded as a BIT STRING and included in the
 signature field.  The details of this process are specified for each
 of algorithms listed in [PKIXALGS].
 By generating this signature, a CA certifies the validity of the
 information in the tbsCertificate field.  In particular, the CA
 certifies the binding between the public key material and the subject
 of the certificate.

4.1.2 TBSCertificate

 The sequence TBSCertificate contains information associated with the
 subject of the certificate and the CA who issued it.  Every
 TBSCertificate contains the names of the subject and issuer, a public
 key associated with the subject, a validity period, a version number,
 and a serial number; some MAY contain optional unique identifier
 fields.  The remainder of this section describes the syntax and
 semantics of these fields.  A TBSCertificate usually includes
 extensions.  Extensions for the Internet PKI are described in Section
 4.2.

4.1.2.1 Version

 This field describes the version of the encoded certificate.  When
 extensions are used, as expected in this profile, version MUST be 3
 (value is 2).  If no extensions are present, but a UniqueIdentifier
 is present, the version SHOULD be 2 (value is 1); however version MAY
 be 3.  If only basic fields are present, the version SHOULD be 1 (the
 value is omitted from the certificate as the default value); however
 the version MAY be 2 or 3.
 Implementations SHOULD be prepared to accept any version certificate.
 At a minimum, conforming implementations MUST recognize version 3
 certificates.
 Generation of version 2 certificates is not expected by
 implementations based on this profile.

4.1.2.2 Serial number

 The serial number MUST be a positive integer assigned by the CA to
 each certificate.  It MUST be unique for each certificate issued by a
 given CA (i.e., the issuer name and serial number identify a unique
 certificate).  CAs MUST force the serialNumber to be a non-negative
 integer.

Housley, et. al. Standards Track [Page 17] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 Given the uniqueness requirements above, serial numbers can be
 expected to contain long integers.  Certificate users MUST be able to
 handle serialNumber values up to 20 octets.  Conformant CAs MUST NOT
 use serialNumber values longer than 20 octets.
 Note: Non-conforming CAs may issue certificates with serial numbers
 that are negative, or zero.  Certificate users SHOULD be prepared to
 gracefully handle such certificates.

4.1.2.3 Signature

 This field contains the algorithm identifier for the algorithm used
 by the CA to sign the certificate.
 This field MUST contain the same algorithm identifier as the
 signatureAlgorithm field in the sequence Certificate (section
 4.1.1.2).  The contents of the optional parameters field will vary
 according to the algorithm identified.  [PKIXALGS] lists the
 supported signature algorithms, but other signature algorithms MAY
 also be supported.

4.1.2.4 Issuer

 The issuer field identifies the entity who has signed and issued the
 certificate.  The issuer field MUST contain a non-empty distinguished
 name (DN).  The issuer field is defined as the X.501 type Name
 [X.501].  Name is defined by the following ASN.1 structures:
 Name ::= CHOICE {
   RDNSequence }
 RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
 RelativeDistinguishedName ::=
   SET OF AttributeTypeAndValue
 AttributeTypeAndValue ::= SEQUENCE {
   type     AttributeType,
   value    AttributeValue }
 AttributeType ::= OBJECT IDENTIFIER
 AttributeValue ::= ANY DEFINED BY AttributeType

Housley, et. al. Standards Track [Page 18] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 DirectoryString ::= CHOICE {
       teletexString           TeletexString (SIZE (1..MAX)),
       printableString         PrintableString (SIZE (1..MAX)),
       universalString         UniversalString (SIZE (1..MAX)),
       utf8String              UTF8String (SIZE (1..MAX)),
       bmpString               BMPString (SIZE (1..MAX)) }
 The Name describes a hierarchical name composed of attributes, such
 as country name, and corresponding values, such as US.  The type of
 the component AttributeValue is determined by the AttributeType; in
 general it will be a DirectoryString.
 The DirectoryString type is defined as a choice of PrintableString,
 TeletexString, BMPString, UTF8String, and UniversalString.  The
 UTF8String encoding [RFC 2279] is the preferred encoding, and all
 certificates issued after December 31, 2003 MUST use the UTF8String
 encoding of DirectoryString (except as noted below).  Until that
 date, conforming CAs MUST choose from the following options when
 creating a distinguished name, including their own:
    (a)  if the character set is sufficient, the string MAY be
    represented as a PrintableString;
    (b)  failing (a), if the BMPString character set is sufficient the
    string MAY be represented as a BMPString; and
    (c)  failing (a) and (b), the string MUST be represented as a
    UTF8String.  If (a) or (b) is satisfied, the CA MAY still choose
    to represent the string as a UTF8String.
 Exceptions to the December 31, 2003 UTF8 encoding requirements are as
 follows:
    (a)  CAs MAY issue "name rollover" certificates to support an
    orderly migration to UTF8String encoding.  Such certificates would
    include the CA's UTF8String encoded name as issuer and and the old
    name encoding as subject, or vice-versa.
    (b)  As stated in section 4.1.2.6, the subject field MUST be
    populated with a non-empty distinguished name matching the
    contents of the issuer field in all certificates issued by the
    subject CA regardless of encoding.
 The TeletexString and UniversalString are included for backward
 compatibility, and SHOULD NOT be used for certificates for new
 subjects.  However, these types MAY be used in certificates where the
 name was previously established.  Certificate users SHOULD be
 prepared to receive certificates with these types.

Housley, et. al. Standards Track [Page 19] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 In addition, many legacy implementations support names encoded in the
 ISO 8859-1 character set (Latin1String) [ISO 8859-1] but tag them as
 TeletexString.  TeletexString encodes a larger character set than ISO
 8859-1, but it encodes some characters differently.  Implementations
 SHOULD be prepared to handle both encodings.
 As noted above, distinguished names are composed of attributes.  This
 specification does not restrict the set of attribute types that may
 appear in names.  However, conforming implementations MUST be
 prepared to receive certificates with issuer names containing the set
 of attribute types defined below.  This specification RECOMMENDS
 support for additional attribute types.
 Standard sets of attributes have been defined in the X.500 series of
 specifications [X.520].  Implementations of this specification MUST
 be prepared to receive the following standard attribute types in
 issuer and subject (section 4.1.2.6) names:
  • country,
  • organization,
  • organizational-unit,
  • distinguished name qualifier,
  • state or province name,
  • common name (e.g., "Susan Housley"), and
  • serial number.
 In addition, implementations of this specification SHOULD be prepared
 to receive the following standard attribute types in issuer and
 subject names:
  • locality,
  • title,
  • surname,
  • given name,
  • initials,
  • pseudonym, and
  • generation qualifier (e.g., "Jr.", "3rd", or "IV").
 The syntax and associated object identifiers (OIDs) for these
 attribute types are provided in the ASN.1 modules in Appendix A.
 In addition, implementations of this specification MUST be prepared
 to receive the domainComponent attribute, as defined in [RFC 2247].
 The Domain Name System (DNS) provides a hierarchical resource
 labeling system.  This attribute provides a convenient mechanism for
 organizations that wish to use DNs that parallel their DNS names.
 This is not a replacement for the dNSName component of the

Housley, et. al. Standards Track [Page 20] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 alternative name field.  Implementations are not required to convert
 such names into DNS names.  The syntax and associated OID for this
 attribute type is provided in the ASN.1 modules in Appendix A.
 Certificate users MUST be prepared to process the issuer
 distinguished name and subject distinguished name (section 4.1.2.6)
 fields to perform name chaining for certification path validation
 (section 6).  Name chaining is performed by matching the issuer
 distinguished name in one certificate with the subject name in a CA
 certificate.
 This specification requires only a subset of the name comparison
 functionality specified in the X.500 series of specifications.
 Conforming implementations are REQUIRED to implement the following
 name comparison rules:
    (a)  attribute values encoded in different types (e.g.,
    PrintableString and BMPString) MAY be assumed to represent
    different strings;
    (b) attribute values in types other than PrintableString are case
    sensitive (this permits matching of attribute values as binary
    objects);
    (c)  attribute values in PrintableString are not case sensitive
    (e.g., "Marianne Swanson" is the same as "MARIANNE SWANSON"); and
    (d)  attribute values in PrintableString are compared after
    removing leading and trailing white space and converting internal
    substrings of one or more consecutive white space characters to a
    single space.
 These name comparison rules permit a certificate user to validate
 certificates issued using languages or encodings unfamiliar to the
 certificate user.
 In addition, implementations of this specification MAY use these
 comparison rules to process unfamiliar attribute types for name
 chaining.  This allows implementations to process certificates with
 unfamiliar attributes in the issuer name.
 Note that the comparison rules defined in the X.500 series of
 specifications indicate that the character sets used to encode data
 in distinguished names are irrelevant.  The characters themselves are
 compared without regard to encoding.  Implementations of this profile
 are permitted to use the comparison algorithm defined in the X.500
 series.  Such an implementation will recognize a superset of name
 matches recognized by the algorithm specified above.

Housley, et. al. Standards Track [Page 21] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

4.1.2.5 Validity

 The certificate validity period is the time interval during which the
 CA warrants that it will maintain information about the status of the
 certificate.  The field is represented as a SEQUENCE of two dates:
 the date on which the certificate validity period begins (notBefore)
 and the date on which the certificate validity period ends
 (notAfter).  Both notBefore and notAfter may be encoded as UTCTime or
 GeneralizedTime.
 CAs conforming to this profile MUST always encode certificate
 validity dates through the year 2049 as UTCTime; certificate validity
 dates in 2050 or later MUST be encoded as GeneralizedTime.
 The validity period for a certificate is the period of time from
 notBefore through notAfter, inclusive.

4.1.2.5.1 UTCTime

 The universal time type, UTCTime, is a standard ASN.1 type intended
 for representation of dates and time.  UTCTime specifies the year
 through the two low order digits and time is specified to the
 precision of one minute or one second.  UTCTime includes either Z
 (for Zulu, or Greenwich Mean Time) or a time differential.
 For the purposes of this profile, UTCTime values MUST be expressed
 Greenwich Mean Time (Zulu) and MUST include seconds (i.e., times are
 YYMMDDHHMMSSZ), even where the number of seconds is zero.  Conforming
 systems MUST interpret the year field (YY) as follows:
    Where YY is greater than or equal to 50, the year SHALL be
    interpreted as 19YY; and
    Where YY is less than 50, the year SHALL be interpreted as 20YY.

4.1.2.5.2 GeneralizedTime

 The generalized time type, GeneralizedTime, is a standard ASN.1 type
 for variable precision representation of time.  Optionally, the
 GeneralizedTime field can include a representation of the time
 differential between local and Greenwich Mean Time.
 For the purposes of this profile, GeneralizedTime values MUST be
 expressed Greenwich Mean Time (Zulu) and MUST include seconds (i.e.,
 times are YYYYMMDDHHMMSSZ), even where the number of seconds is zero.
 GeneralizedTime values MUST NOT include fractional seconds.

Housley, et. al. Standards Track [Page 22] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

4.1.2.6 Subject

 The subject field identifies the entity associated with the public
 key stored in the subject public key field.  The subject name MAY be
 carried in the subject field and/or the subjectAltName extension.  If
 the subject is a CA (e.g., the basic constraints extension, as
 discussed in 4.2.1.10, is present and the value of cA is TRUE), then
 the subject field MUST be populated with a non-empty distinguished
 name matching the contents of the issuer field (section 4.1.2.4) in
 all certificates issued by the subject CA.  If the subject is a CRL
 issuer (e.g., the key usage extension, as discussed in 4.2.1.3, is
 present and the value of cRLSign is TRUE) then the subject field MUST
 be populated with a non-empty distinguished name matching the
 contents of the issuer field (section 4.1.2.4) in all CRLs issued by
 the subject CRL issuer.  If subject naming information is present
 only in the subjectAltName extension (e.g., a key bound only to an
 email address or URI), then the subject name MUST be an empty
 sequence and the subjectAltName extension MUST be critical.
 Where it is non-empty, the subject field MUST contain an X.500
 distinguished name (DN).  The DN MUST be unique for each subject
 entity certified by the one CA as defined by the issuer name field.
 A CA MAY issue more than one certificate with the same DN to the same
 subject entity.
 The subject name field is defined as the X.501 type Name.
 Implementation requirements for this field are those defined for the
 issuer field (section 4.1.2.4).  When encoding attribute values of
 type DirectoryString, the encoding rules for the issuer field MUST be
 implemented.  Implementations of this specification MUST be prepared
 to receive subject names containing the attribute types required for
 the issuer field.  Implementations of this specification SHOULD be
 prepared to receive subject names containing the recommended
 attribute types for the issuer field.  The syntax and associated
 object identifiers (OIDs) for these attribute types are provided in
 the ASN.1 modules in Appendix A.  Implementations of this
 specification MAY use these comparison rules to process unfamiliar
 attribute types (i.e., for name chaining).  This allows
 implementations to process certificates with unfamiliar attributes in
 the subject name.
 In addition, legacy implementations exist where an RFC 822 name is
 embedded in the subject distinguished name as an EmailAddress
 attribute.  The attribute value for EmailAddress is of type IA5String
 to permit inclusion of the character '@', which is not part of the
 PrintableString character set.  EmailAddress attribute values are not
 case sensitive (e.g., "fanfeedback@redsox.com" is the same as
 "FANFEEDBACK@REDSOX.COM").

Housley, et. al. Standards Track [Page 23] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 Conforming implementations generating new certificates with
 electronic mail addresses MUST use the rfc822Name in the subject
 alternative name field (section 4.2.1.7) to describe such identities.
 Simultaneous inclusion of the EmailAddress attribute in the subject
 distinguished name to support legacy implementations is deprecated
 but permitted.

4.1.2.7 Subject Public Key Info

 This field is used to carry the public key and identify the algorithm
 with which the key is used (e.g., RSA, DSA, or Diffie-Hellman).  The
 algorithm is identified using the AlgorithmIdentifier structure
 specified in section 4.1.1.2.  The object identifiers for the
 supported algorithms and the methods for encoding the public key
 materials (public key and parameters) are specified in [PKIXALGS].

4.1.2.8 Unique Identifiers

 These fields MUST only appear if the version is 2 or 3 (section
 4.1.2.1).  These fields MUST NOT appear if the version is 1.  The
 subject and issuer unique identifiers are present in the certificate
 to handle the possibility of reuse of subject and/or issuer names
 over time.  This profile RECOMMENDS that names not be reused for
 different entities and that Internet certificates not make use of
 unique identifiers.  CAs conforming to this profile SHOULD NOT
 generate certificates with unique identifiers.  Applications
 conforming to this profile SHOULD be capable of parsing unique
 identifiers.

4.1.2.9 Extensions

 This field MUST only appear if the version is 3 (section 4.1.2.1).
 If present, this field is a SEQUENCE of one or more certificate
 extensions.  The format and content of certificate extensions in the
 Internet PKI is defined in section 4.2.

4.2 Certificate Extensions

 The extensions defined for X.509 v3 certificates provide methods for
 associating additional attributes with users or public keys and for
 managing a certification hierarchy.  The X.509 v3 certificate format
 also allows communities to define private extensions to carry
 information unique to those communities.  Each extension in a
 certificate is designated as either critical or non-critical.  A
 certificate using system MUST reject the certificate if it encounters
 a critical extension it does not recognize; however, a non-critical
 extension MAY be ignored if it is not recognized.  The following
 sections present recommended extensions used within Internet

Housley, et. al. Standards Track [Page 24] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 certificates and standard locations for information.  Communities may
 elect to use additional extensions; however, caution ought to be
 exercised in adopting any critical extensions in certificates which
 might prevent use in a general context.
 Each extension includes an OID and an ASN.1 structure.  When an
 extension appears in a certificate, the OID appears as the field
 extnID and the corresponding ASN.1 encoded structure is the value of
 the octet string extnValue.  A certificate MUST NOT include more than
 one instance of a particular extension.  For example, a certificate
 may contain only one authority key identifier extension (section
 4.2.1.1).  An extension includes the boolean critical, with a default
 value of FALSE.  The text for each extension specifies the acceptable
 values for the critical field.
 Conforming CAs MUST support key identifiers (sections 4.2.1.1 and
 4.2.1.2), basic constraints (section 4.2.1.10), key usage (section
 4.2.1.3), and certificate policies (section 4.2.1.5) extensions.  If
 the CA issues certificates with an empty sequence for the subject
 field, the CA MUST support the subject alternative name extension
 (section 4.2.1.7).  Support for the remaining extensions is OPTIONAL.
 Conforming CAs MAY support extensions that are not identified within
 this specification; certificate issuers are cautioned that marking
 such extensions as critical may inhibit interoperability.
 At a minimum, applications conforming to this profile MUST recognize
 the following extensions: key usage (section 4.2.1.3), certificate
 policies (section 4.2.1.5), the subject alternative name (section
 4.2.1.7), basic constraints (section 4.2.1.10), name constraints
 (section 4.2.1.11), policy constraints (section 4.2.1.12), extended
 key usage (section 4.2.1.13), and inhibit any-policy (section
 4.2.1.15).
 In addition, applications conforming to this profile SHOULD recognize
 the authority and subject key identifier (sections 4.2.1.1 and
 4.2.1.2), and policy mapping (section 4.2.1.6) extensions.

4.2.1 Standard Extensions

 This section identifies standard certificate extensions defined in
 [X.509] for use in the Internet PKI.  Each extension is associated
 with an OID defined in [X.509].  These OIDs are members of the id-ce
 arc, which is defined by the following:
 id-ce   OBJECT IDENTIFIER ::=  { joint-iso-ccitt(2) ds(5) 29 }

Housley, et. al. Standards Track [Page 25] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

4.2.1.1 Authority Key Identifier

 The authority key identifier extension provides a means of
 identifying the public key corresponding to the private key used to
 sign a certificate.  This extension is used where an issuer has
 multiple signing keys (either due to multiple concurrent key pairs or
 due to changeover).  The identification MAY be based on either the
 key identifier (the subject key identifier in the issuer's
 certificate) or on the issuer name and serial number.
 The keyIdentifier field of the authorityKeyIdentifier extension MUST
 be included in all certificates generated by conforming CAs to
 facilitate certification path construction.  There is one exception;
 where a CA distributes its public key in the form of a "self-signed"
 certificate, the authority key identifier MAY be omitted.  The
 signature on a self-signed certificate is generated with the private
 key associated with the certificate's subject public key.  (This
 proves that the issuer possesses both the public and private keys.)
 In this case, the subject and authority key identifiers would be
 identical, but only the subject key identifier is needed for
 certification path building.
 The value of the keyIdentifier field SHOULD be derived from the
 public key used to verify the certificate's signature or a method
 that generates unique values.  Two common methods for generating key
 identifiers from the public key, and one common method for generating
 unique values, are described in section 4.2.1.2.  Where a key
 identifier has not been previously established, this specification
 RECOMMENDS use of one of these methods for generating keyIdentifiers.
 Where a key identifier has been previously established, the CA SHOULD
 use the previously established identifier.
 This profile RECOMMENDS support for the key identifier method by all
 certificate users.
 This extension MUST NOT be marked critical.
 id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 35 }
 AuthorityKeyIdentifier ::= SEQUENCE {
    keyIdentifier             [0] KeyIdentifier           OPTIONAL,
    authorityCertIssuer       [1] GeneralNames            OPTIONAL,
    authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL  }
 KeyIdentifier ::= OCTET STRING

Housley, et. al. Standards Track [Page 26] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

4.2.1.2 Subject Key Identifier

 The subject key identifier extension provides a means of identifying
 certificates that contain a particular public key.
 To facilitate certification path construction, this extension MUST
 appear in all conforming CA certificates, that is, all certificates
 including the basic constraints extension (section 4.2.1.10) where
 the value of cA is TRUE.  The value of the subject key identifier
 MUST be the value placed in the key identifier field of the Authority
 Key Identifier extension (section 4.2.1.1) of certificates issued by
 the subject of this certificate.
 For CA certificates, subject key identifiers SHOULD be derived from
 the public key or a method that generates unique values.  Two common
 methods for generating key identifiers from the public key are:
    (1) The keyIdentifier is composed of the 160-bit SHA-1 hash of the
    value of the BIT STRING subjectPublicKey (excluding the tag,
    length, and number of unused bits).
    (2) The keyIdentifier is composed of a four bit type field with
    the value 0100 followed by the least significant 60 bits of the
    SHA-1 hash of the value of the BIT STRING subjectPublicKey
    (excluding the tag, length, and number of unused bit string bits).
 One common method for generating unique values is a monotonically
 increasing sequence of integers.
 For end entity certificates, the subject key identifier extension
 provides a means for identifying certificates containing the
 particular public key used in an application.  Where an end entity
 has obtained multiple certificates, especially from multiple CAs, the
 subject key identifier provides a means to quickly identify the set
 of certificates containing a particular public key.  To assist
 applications in identifying the appropriate end entity certificate,
 this extension SHOULD be included in all end entity certificates.
 For end entity certificates, subject key identifiers SHOULD be
 derived from the public key.  Two common methods for generating key
 identifiers from the public key are identified above.
 Where a key identifier has not been previously established, this
 specification RECOMMENDS use of one of these methods for generating
 keyIdentifiers.  Where a key identifier has been previously
 established, the CA SHOULD use the previously established identifier.
 This extension MUST NOT be marked critical.

Housley, et. al. Standards Track [Page 27] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::=  { id-ce 14 }
 SubjectKeyIdentifier ::= KeyIdentifier

4.2.1.3 Key Usage

 The key usage extension defines the purpose (e.g., encipherment,
 signature, certificate signing) of the key contained in the
 certificate.  The usage restriction might be employed when a key that
 could be used for more than one operation is to be restricted.  For
 example, when an RSA key should be used only to verify signatures on
 objects other than public key certificates and CRLs, the
 digitalSignature and/or nonRepudiation bits would be asserted.
 Likewise, when an RSA key should be used only for key management, the
 keyEncipherment bit would be asserted.
 This extension MUST appear in certificates that contain public keys
 that are used to validate digital signatures on other public key
 certificates or CRLs.  When this extension appears, it SHOULD be
 marked critical.
    id-ce-keyUsage OBJECT IDENTIFIER ::=  { id-ce 15 }
    KeyUsage ::= BIT STRING {
         digitalSignature        (0),
         nonRepudiation          (1),
         keyEncipherment         (2),
         dataEncipherment        (3),
         keyAgreement            (4),
         keyCertSign             (5),
         cRLSign                 (6),
         encipherOnly            (7),
         decipherOnly            (8) }
 Bits in the KeyUsage type are used as follows:
    The digitalSignature bit is asserted when the subject public key
    is used with a digital signature mechanism to support security
    services other than certificate signing (bit 5), or CRL signing
    (bit 6).  Digital signature mechanisms are often used for entity
    authentication and data origin authentication with integrity.
    The nonRepudiation bit is asserted when the subject public key is
    used to verify digital signatures used to provide a non-
    repudiation service which protects against the signing entity
    falsely denying some action, excluding certificate or CRL signing.
    In the case of later conflict, a reliable third party may
    determine the authenticity of the signed data.

Housley, et. al. Standards Track [Page 28] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    Further distinctions between the digitalSignature and
    nonRepudiation bits may be provided in specific certificate
    policies.
    The keyEncipherment bit is asserted when the subject public key is
    used for key transport.  For example, when an RSA key is to be
    used for key management, then this bit is set.
    The dataEncipherment bit is asserted when the subject public key
    is used for enciphering user data, other than cryptographic keys.
    The keyAgreement bit is asserted when the subject public key is
    used for key agreement.  For example, when a Diffie-Hellman key is
    to be used for key management, then this bit is set.
    The keyCertSign bit is asserted when the subject public key is
    used for verifying a signature on public key certificates.  If the
    keyCertSign bit is asserted, then the cA bit in the basic
    constraints extension (section 4.2.1.10) MUST also be asserted.
    The cRLSign bit is asserted when the subject public key is used
    for verifying a signature on certificate revocation list (e.g., a
    CRL, delta CRL, or an ARL).  This bit MUST be asserted in
    certificates that are used to verify signatures on CRLs.
    The meaning of the encipherOnly bit is undefined in the absence of
    the keyAgreement bit.  When the encipherOnly bit is asserted and
    the keyAgreement bit is also set, the subject public key may be
    used only for enciphering data while performing key agreement.
    The meaning of the decipherOnly bit is undefined in the absence of
    the keyAgreement bit.  When the decipherOnly bit is asserted and
    the keyAgreement bit is also set, the subject public key may be
    used only for deciphering data while performing key agreement.
 This profile does not restrict the combinations of bits that may be
 set in an instantiation of the keyUsage extension.  However,
 appropriate values for keyUsage extensions for particular algorithms
 are specified in [PKIXALGS].

4.2.1.4 Private Key Usage Period

 This extension SHOULD NOT be used within the Internet PKI.  CAs
 conforming to this profile MUST NOT generate certificates that
 include a critical private key usage period extension.

Housley, et. al. Standards Track [Page 29] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 The private key usage period extension allows the certificate issuer
 to specify a different validity period for the private key than the
 certificate.  This extension is intended for use with digital
 signature keys.  This extension consists of two optional components,
 notBefore and notAfter.  The private key associated with the
 certificate SHOULD NOT be used to sign objects before or after the
 times specified by the two components, respectively.  CAs conforming
 to this profile MUST NOT generate certificates with private key usage
 period extensions unless at least one of the two components is
 present and the extension is non-critical.
 Where used, notBefore and notAfter are represented as GeneralizedTime
 and MUST be specified and interpreted as defined in section
 4.1.2.5.2.
 id-ce-privateKeyUsagePeriod OBJECT IDENTIFIER ::=  { id-ce 16 }
 PrivateKeyUsagePeriod ::= SEQUENCE {
      notBefore       [0]     GeneralizedTime OPTIONAL,
      notAfter        [1]     GeneralizedTime OPTIONAL }

4.2.1.5 Certificate Policies

 The certificate policies extension contains a sequence of one or more
 policy information terms, each of which consists of an object
 identifier (OID) and optional qualifiers.  Optional qualifiers, which
 MAY be present, are not expected to change the definition of the
 policy.
 In an end entity certificate, these policy information terms indicate
 the policy under which the certificate has been issued and the
 purposes for which the certificate may be used.  In a CA certificate,
 these policy information terms limit the set of policies for
 certification paths which include this certificate.  When a CA does
 not wish to limit the set of policies for certification paths which
 include this certificate, it MAY assert the special policy anyPolicy,
 with a value of { 2 5 29 32 0 }.
 Applications with specific policy requirements are expected to have a
 list of those policies which they will accept and to compare the
 policy OIDs in the certificate to that list.  If this extension is
 critical, the path validation software MUST be able to interpret this
 extension (including the optional qualifier), or MUST reject the
 certificate.
 To promote interoperability, this profile RECOMMENDS that policy
 information terms consist of only an OID.  Where an OID alone is
 insufficient, this profile strongly recommends that use of qualifiers

Housley, et. al. Standards Track [Page 30] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 be limited to those identified in this section.  When qualifiers are
 used with the special policy anyPolicy, they MUST be limited to the
 qualifiers identified in this section.
 This specification defines two policy qualifier types for use by
 certificate policy writers and certificate issuers.  The qualifier
 types are the CPS Pointer and User Notice qualifiers.
 The CPS Pointer qualifier contains a pointer to a Certification
 Practice Statement (CPS) published by the CA.  The pointer is in the
 form of a URI.  Processing requirements for this qualifier are a
 local matter.  No action is mandated by this specification regardless
 of the criticality value asserted for the extension.
 User notice is intended for display to a relying party when a
 certificate is used.  The application software SHOULD display all
 user notices in all certificates of the certification path used,
 except that if a notice is duplicated only one copy need be
 displayed.  To prevent such duplication, this qualifier SHOULD only
 be present in end entity certificates and CA certificates issued to
 other organizations.
 The user notice has two optional fields: the noticeRef field and the
 explicitText field.
    The noticeRef field, if used, names an organization and
    identifies, by number, a particular textual statement prepared by
    that organization.  For example, it might identify the
    organization "CertsRUs" and notice number 1.  In a typical
    implementation, the application software will have a notice file
    containing the current set of notices for CertsRUs; the
    application will extract the notice text from the file and display
    it.  Messages MAY be multilingual, allowing the software to select
    the particular language message for its own environment.
    An explicitText field includes the textual statement directly in
    the certificate.  The explicitText field is a string with a
    maximum size of 200 characters.
 If both the noticeRef and explicitText options are included in the
 one qualifier and if the application software can locate the notice
 text indicated by the noticeRef option, then that text SHOULD be
 displayed; otherwise, the explicitText string SHOULD be displayed.
 Note: While the explicitText has a maximum size of 200 characters,
 some non-conforming CAs exceed this limit.  Therefore, certificate
 users SHOULD gracefully handle explicitText with more than 200
 characters.

Housley, et. al. Standards Track [Page 31] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 id-ce-certificatePolicies OBJECT IDENTIFIER ::=  { id-ce 32 }
 anyPolicy OBJECT IDENTIFIER ::= { id-ce-certificate-policies 0 }
 certificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation
 PolicyInformation ::= SEQUENCE {
      policyIdentifier   CertPolicyId,
      policyQualifiers   SEQUENCE SIZE (1..MAX) OF
                              PolicyQualifierInfo OPTIONAL }
 CertPolicyId ::= OBJECT IDENTIFIER
 PolicyQualifierInfo ::= SEQUENCE {
      policyQualifierId  PolicyQualifierId,
      qualifier          ANY DEFINED BY policyQualifierId }
  1. - policyQualifierIds for Internet policy qualifiers
 id-qt          OBJECT IDENTIFIER ::=  { id-pkix 2 }
 id-qt-cps      OBJECT IDENTIFIER ::=  { id-qt 1 }
 id-qt-unotice  OBJECT IDENTIFIER ::=  { id-qt 2 }
 PolicyQualifierId ::=
      OBJECT IDENTIFIER ( id-qt-cps | id-qt-unotice )
 Qualifier ::= CHOICE {
      cPSuri           CPSuri,
      userNotice       UserNotice }
 CPSuri ::= IA5String
 UserNotice ::= SEQUENCE {
      noticeRef        NoticeReference OPTIONAL,
      explicitText     DisplayText OPTIONAL}
 NoticeReference ::= SEQUENCE {
      organization     DisplayText,
      noticeNumbers    SEQUENCE OF INTEGER }
 DisplayText ::= CHOICE {
      ia5String        IA5String      (SIZE (1..200)),
      visibleString    VisibleString  (SIZE (1..200)),
      bmpString        BMPString      (SIZE (1..200)),
      utf8String       UTF8String     (SIZE (1..200)) }

Housley, et. al. Standards Track [Page 32] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

4.2.1.6 Policy Mappings

 This extension is used in CA certificates.  It lists one or more
 pairs of OIDs; each pair includes an issuerDomainPolicy and a
 subjectDomainPolicy.  The pairing indicates the issuing CA considers
 its issuerDomainPolicy equivalent to the subject CA's
 subjectDomainPolicy.
 The issuing CA's users might accept an issuerDomainPolicy for certain
 applications.  The policy mapping defines the list of policies
 associated with the subject CA that may be accepted as comparable to
 the issuerDomainPolicy.
 Each issuerDomainPolicy named in the policy mapping extension SHOULD
 also be asserted in a certificate policies extension in the same
 certificate.  Policies SHOULD NOT be mapped either to or from the
 special value anyPolicy (section 4.2.1.5).
 This extension MAY be supported by CAs and/or applications, and it
 MUST be non-critical.
 id-ce-policyMappings OBJECT IDENTIFIER ::=  { id-ce 33 }
 PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
      issuerDomainPolicy      CertPolicyId,
      subjectDomainPolicy     CertPolicyId }

4.2.1.7 Subject Alternative Name

 The subject alternative names extension allows additional identities
 to be bound to the subject of the certificate.  Defined options
 include an Internet electronic mail address, a DNS name, an IP
 address, and a uniform resource identifier (URI).  Other options
 exist, including completely local definitions.  Multiple name forms,
 and multiple instances of each name form, MAY be included.  Whenever
 such identities are to be bound into a certificate, the subject
 alternative name (or issuer alternative name) extension MUST be used;
 however, a DNS name MAY be represented in the subject field using the
 domainComponent attribute as described in section 4.1.2.4.
 Because the subject alternative name is considered to be definitively
 bound to the public key, all parts of the subject alternative name
 MUST be verified by the CA.
 Further, if the only subject identity included in the certificate is
 an alternative name form (e.g., an electronic mail address), then the
 subject distinguished name MUST be empty (an empty sequence), and the

Housley, et. al. Standards Track [Page 33] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 subjectAltName extension MUST be present.  If the subject field
 contains an empty sequence, the subjectAltName extension MUST be
 marked critical.
 When the subjectAltName extension contains an Internet mail address,
 the address MUST be included as an rfc822Name.  The format of an
 rfc822Name is an "addr-spec" as defined in RFC 822 [RFC 822].  An
 addr-spec has the form "local-part@domain".  Note that an addr-spec
 has no phrase (such as a common name) before it, has no comment (text
 surrounded in parentheses) after it, and is not surrounded by "<" and
 ">".  Note that while upper and lower case letters are allowed in an
 RFC 822 addr-spec, no significance is attached to the case.
 When the subjectAltName extension contains a iPAddress, the address
 MUST be stored in the octet string in "network byte order," as
 specified in RFC 791 [RFC 791].  The least significant bit (LSB) of
 each octet is the LSB of the corresponding byte in the network
 address.  For IP Version 4, as specified in RFC 791, the octet string
 MUST contain exactly four octets.  For IP Version 6, as specified in
 RFC 1883, the octet string MUST contain exactly sixteen octets [RFC
 1883].
 When the subjectAltName extension contains a domain name system
 label, the domain name MUST be stored in the dNSName (an IA5String).
 The name MUST be in the "preferred name syntax," as specified by RFC
 1034 [RFC 1034].  Note that while upper and lower case letters are
 allowed in domain names, no signifigance is attached to the case.  In
 addition, while the string " " is a legal domain name, subjectAltName
 extensions with a dNSName of " " MUST NOT be used.  Finally, the use
 of the DNS representation for Internet mail addresses (wpolk.nist.gov
 instead of wpolk@nist.gov) MUST NOT be used; such identities are to
 be encoded as rfc822Name.
 Note: work is currently underway to specify domain names in
 international character sets.  Such names will likely not be
 accommodated by IA5String.  Once this work is complete, this profile
 will be revisited and the appropriate functionality will be added.
 When the subjectAltName extension contains a URI, the name MUST be
 stored in the uniformResourceIdentifier (an IA5String).  The name
 MUST NOT be a relative URL, and it MUST follow the URL syntax and
 encoding rules specified in [RFC 1738].  The name MUST include both a
 scheme (e.g., "http" or "ftp") and a scheme-specific-part.  The
 scheme-specific-part MUST include a fully qualified domain name or IP
 address as the host.

Housley, et. al. Standards Track [Page 34] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 As specified in [RFC 1738], the scheme name is not case-sensitive
 (e.g., "http" is equivalent to "HTTP").  The host part is also not
 case-sensitive, but other components of the scheme-specific-part may
 be case-sensitive.  When comparing URIs, conforming implementations
 MUST compare the scheme and host without regard to case, but assume
 the remainder of the scheme-specific-part is case sensitive.
 When the subjectAltName extension contains a DN in the directoryName,
 the DN MUST be unique for each subject entity certified by the one CA
 as defined by the issuer name field.  A CA MAY issue more than one
 certificate with the same DN to the same subject entity.
 The subjectAltName MAY carry additional name types through the use of
 the otherName field.  The format and semantics of the name are
 indicated through the OBJECT IDENTIFIER in the type-id field.  The
 name itself is conveyed as value field in otherName.  For example,
 Kerberos [RFC 1510] format names can be encoded into the otherName,
 using using a Kerberos 5 principal name OID and a SEQUENCE of the
 Realm and the PrincipalName.
 Subject alternative names MAY be constrained in the same manner as
 subject distinguished names using the name constraints extension as
 described in section 4.2.1.11.
 If the subjectAltName extension is present, the sequence MUST contain
 at least one entry.  Unlike the subject field, conforming CAs MUST
 NOT issue certificates with subjectAltNames containing empty
 GeneralName fields.  For example, an rfc822Name is represented as an
 IA5String.  While an empty string is a valid IA5String, such an
 rfc822Name is not permitted by this profile.  The behavior of clients
 that encounter such a certificate when processing a certificication
 path is not defined by this profile.
 Finally, the semantics of subject alternative names that include
 wildcard characters (e.g., as a placeholder for a set of names) are
 not addressed by this specification.  Applications with specific
 requirements MAY use such names, but they must define the semantics.
 id-ce-subjectAltName OBJECT IDENTIFIER ::=  { id-ce 17 }
 SubjectAltName ::= GeneralNames
 GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

Housley, et. al. Standards Track [Page 35] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 GeneralName ::= CHOICE {
      otherName                       [0]     OtherName,
      rfc822Name                      [1]     IA5String,
      dNSName                         [2]     IA5String,
      x400Address                     [3]     ORAddress,
      directoryName                   [4]     Name,
      ediPartyName                    [5]     EDIPartyName,
      uniformResourceIdentifier       [6]     IA5String,
      iPAddress                       [7]     OCTET STRING,
      registeredID                    [8]     OBJECT IDENTIFIER }
 OtherName ::= SEQUENCE {
      type-id    OBJECT IDENTIFIER,
      value      [0] EXPLICIT ANY DEFINED BY type-id }
 EDIPartyName ::= SEQUENCE {
      nameAssigner            [0]     DirectoryString OPTIONAL,
      partyName               [1]     DirectoryString }

4.2.1.8 Issuer Alternative Names

 As with 4.2.1.7, this extension is used to associate Internet style
 identities with the certificate issuer.  Issuer alternative names
 MUST be encoded as in 4.2.1.7.
 Where present, this extension SHOULD NOT be marked critical.
 id-ce-issuerAltName OBJECT IDENTIFIER ::=  { id-ce 18 }
 IssuerAltName ::= GeneralNames

4.2.1.9 Subject Directory Attributes

 The subject directory attributes extension is used to convey
 identification attributes (e.g., nationality) of the subject.  The
 extension is defined as a sequence of one or more attributes.  This
 extension MUST be non-critical.
 id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::=  { id-ce 9 }
 SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

4.2.1.10 Basic Constraints

 The basic constraints extension identifies whether the subject of the
 certificate is a CA and the maximum depth of valid certification
 paths that include this certificate.

Housley, et. al. Standards Track [Page 36] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 The cA boolean indicates whether the certified public key belongs to
 a CA.  If the cA boolean is not asserted, then the keyCertSign bit in
 the key usage extension MUST NOT be asserted.
 The pathLenConstraint field is meaningful only if the cA boolean is
 asserted and the key usage extension asserts the keyCertSign bit
 (section 4.2.1.3).  In this case, it gives the maximum number of non-
 self-issued intermediate certificates that may follow this
 certificate in a valid certification path.  A certificate is self-
 issued if the DNs that appear in the subject and issuer fields are
 identical and are not empty.  (Note: The last certificate in the
 certification path is not an intermediate certificate, and is not
 included in this limit.  Usually, the last certificate is an end
 entity certificate, but it can be a CA certificate.)  A
 pathLenConstraint of zero indicates that only one more certificate
 may follow in a valid certification path.  Where it appears, the
 pathLenConstraint field MUST be greater than or equal to zero.  Where
 pathLenConstraint does not appear, no limit is imposed.
 This extension MUST appear as a critical extension in all CA
 certificates that contain public keys used to validate digital
 signatures on certificates.  This extension MAY appear as a critical
 or non-critical extension in CA certificates that contain public keys
 used exclusively for purposes other than validating digital
 signatures on certificates.  Such CA certificates include ones that
 contain public keys used exclusively for validating digital
 signatures on CRLs and ones that contain key management public keys
 used with certificate enrollment protocols.  This extension MAY
 appear as a critical or non-critical extension in end entity
 certificates.
 CAs MUST NOT include the pathLenConstraint field unless the cA
 boolean is asserted and the key usage extension asserts the
 keyCertSign bit.
 id-ce-basicConstraints OBJECT IDENTIFIER ::=  { id-ce 19 }
 BasicConstraints ::= SEQUENCE {
      cA                      BOOLEAN DEFAULT FALSE,
      pathLenConstraint       INTEGER (0..MAX) OPTIONAL }

4.2.1.11 Name Constraints

 The name constraints extension, which MUST be used only in a CA
 certificate, indicates a name space within which all subject names in
 subsequent certificates in a certification path MUST be located.
 Restrictions apply to the subject distinguished name and apply to
 subject alternative names.  Restrictions apply only when the

Housley, et. al. Standards Track [Page 37] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 specified name form is present.  If no name of the type is in the
 certificate, the certificate is acceptable.
 Name constraints are not applied to certificates whose issuer and
 subject are identical (unless the certificate is the final
 certificate in the path).  (This could prevent CAs that use name
 constraints from employing self-issued certificates to implement key
 rollover.)
 Restrictions are defined in terms of permitted or excluded name
 subtrees.  Any name matching a restriction in the excludedSubtrees
 field is invalid regardless of information appearing in the
 permittedSubtrees.  This extension MUST be critical.
 Within this profile, the minimum and maximum fields are not used with
 any name forms, thus minimum MUST be zero, and maximum MUST be
 absent.
 For URIs, the constraint applies to the host part of the name.  The
 constraint MAY specify a host or a domain.  Examples would be
 "foo.bar.com";  and ".xyz.com".  When the the constraint begins with
 a period, it MAY be expanded with one or more subdomains.  That is,
 the constraint ".xyz.com" is satisfied by both abc.xyz.com and
 abc.def.xyz.com.  However, the constraint ".xyz.com" is not satisfied
 by "xyz.com".  When the constraint does not begin with a period, it
 specifies a host.
 A name constraint for Internet mail addresses MAY specify a
 particular mailbox, all addresses at a particular host, or all
 mailboxes in a domain.  To indicate a particular mailbox, the
 constraint is the complete mail address.  For example, "root@xyz.com"
 indicates the root mailbox on the host "xyz.com".  To indicate all
 Internet mail addresses on a particular host, the constraint is
 specified as the host name.  For example, the constraint "xyz.com" is
 satisfied by any mail address at the host "xyz.com".  To specify any
 address within a domain, the constraint is specified with a leading
 period (as with URIs).  For example, ".xyz.com" indicates all the
 Internet mail addresses in the domain "xyz.com", but not Internet
 mail addresses on the host "xyz.com".
 DNS name restrictions are expressed as foo.bar.com.  Any DNS name
 that can be constructed by simply adding to the left hand side of the
 name satisfies the name constraint.  For example, www.foo.bar.com
 would satisfy the constraint but foo1.bar.com would not.
 Legacy implementations exist where an RFC 822 name is embedded in the
 subject distinguished name in an attribute of type EmailAddress
 (section 4.1.2.6).  When rfc822 names are constrained, but the

Housley, et. al. Standards Track [Page 38] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 certificate does not include a subject alternative name, the rfc822
 name constraint MUST be applied to the attribute of type EmailAddress
 in the subject distinguished name.  The ASN.1 syntax for EmailAddress
 and the corresponding OID are supplied in Appendix A.
 Restrictions of the form directoryName MUST be applied to the subject
 field in the certificate and to the subjectAltName extensions of type
 directoryName.  Restrictions of the form x400Address MUST be applied
 to subjectAltName extensions of type x400Address.
 When applying restrictions of the form directoryName, an
 implementation MUST compare DN attributes.  At a minimum,
 implementations MUST perform the DN comparison rules specified in
 Section 4.1.2.4.  CAs issuing certificates with a restriction of the
 form directoryName SHOULD NOT rely on implementation of the full ISO
 DN name comparison algorithm.  This implies name restrictions MUST be
 stated identically to the encoding used in the subject field or
 subjectAltName extension.
 The syntax of iPAddress MUST be as described in section 4.2.1.7 with
 the following additions specifically for Name Constraints.  For IPv4
 addresses, the ipAddress field of generalName MUST contain eight (8)
 octets, encoded in the style of RFC 1519 (CIDR) to represent an
 address range [RFC 1519].  For IPv6 addresses, the ipAddress field
 MUST contain 32 octets similarly encoded.  For example, a name
 constraint for "class C" subnet 10.9.8.0 is represented as the octets
 0A 09 08 00 FF FF FF 00, representing the CIDR notation
 10.9.8.0/255.255.255.0.
 The syntax and semantics for name constraints for otherName,
 ediPartyName, and registeredID are not defined by this specification.
    id-ce-nameConstraints OBJECT IDENTIFIER ::=  { id-ce 30 }
    NameConstraints ::= SEQUENCE {
         permittedSubtrees       [0]     GeneralSubtrees OPTIONAL,
         excludedSubtrees        [1]     GeneralSubtrees OPTIONAL }
    GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree
    GeneralSubtree ::= SEQUENCE {
         base                    GeneralName,
         minimum         [0]     BaseDistance DEFAULT 0,
         maximum         [1]     BaseDistance OPTIONAL }
    BaseDistance ::= INTEGER (0..MAX)

Housley, et. al. Standards Track [Page 39] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

4.2.1.12 Policy Constraints

 The policy constraints extension can be used in certificates issued
 to CAs.  The policy constraints extension constrains path validation
 in two ways.  It can be used to prohibit policy mapping or require
 that each certificate in a path contain an acceptable policy
 identifier.
 If the inhibitPolicyMapping field is present, the value indicates the
 number of additional certificates that may appear in the path before
 policy mapping is no longer permitted.  For example, a value of one
 indicates that policy mapping may be processed in certificates issued
 by the subject of this certificate, but not in additional
 certificates in the path.
 If the requireExplicitPolicy field is present, the value of
 requireExplicitPolicy indicates the number of additional certificates
 that may appear in the path before an explicit policy is required for
 the entire path.  When an explicit policy is required, it is
 necessary for all certificates in the path to contain an acceptable
 policy identifier in the certificate policies extension.  An
 acceptable policy identifier is the identifier of a policy required
 by the user of the certification path or the identifier of a policy
 which has been declared equivalent through policy mapping.
 Conforming CAs MUST NOT issue certificates where policy constraints
 is a empty sequence.  That is, at least one of the
 inhibitPolicyMapping field or the requireExplicitPolicy field MUST be
 present.  The behavior of clients that encounter a empty policy
 constraints field is not addressed in this profile.
 This extension MAY be critical or non-critical.
 id-ce-policyConstraints OBJECT IDENTIFIER ::=  { id-ce 36 }
 PolicyConstraints ::= SEQUENCE {
      requireExplicitPolicy           [0] SkipCerts OPTIONAL,
      inhibitPolicyMapping            [1] SkipCerts OPTIONAL }
 SkipCerts ::= INTEGER (0..MAX)

4.2.1.13 Extended Key Usage

 This extension indicates one or more purposes for which the certified
 public key may be used, in addition to or in place of the basic
 purposes indicated in the key usage extension.  In general, this
 extension will appear only in end entity certificates.  This
 extension is defined as follows:

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 id-ce-extKeyUsage OBJECT IDENTIFIER ::= { id-ce 37 }
 ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId
 KeyPurposeId ::= OBJECT IDENTIFIER
 Key purposes may be defined by any organization with a need.  Object
 identifiers used to identify key purposes MUST be assigned in
 accordance with IANA or ITU-T Recommendation X.660 [X.660].
 This extension MAY, at the option of the certificate issuer, be
 either critical or non-critical.
 If the extension is present, then the certificate MUST only be used
 for one of the purposes indicated.  If multiple purposes are
 indicated the application need not recognize all purposes indicated,
 as long as the intended purpose is present.  Certificate using
 applications MAY require that a particular purpose be indicated in
 order for the certificate to be acceptable to that application.
 If a CA includes extended key usages to satisfy such applications,
 but does not wish to restrict usages of the key, the CA can include
 the special keyPurposeID anyExtendedKeyUsage.  If the
 anyExtendedKeyUsage keyPurposeID is present, the extension SHOULD NOT
 be critical.
 If a certificate contains both a key usage extension and an extended
 key usage extension, then both extensions MUST be processed
 independently and the certificate MUST only be used for a purpose
 consistent with both extensions.  If there is no purpose consistent
 with both extensions, then the certificate MUST NOT be used for any
 purpose.
 The following key usage purposes are defined:
 anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }
 id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }
 id-kp-serverAuth             OBJECT IDENTIFIER ::= { id-kp 1 }
 -- TLS WWW server authentication
 -- Key usage bits that may be consistent: digitalSignature,
 -- keyEncipherment or keyAgreement
 id-kp-clientAuth             OBJECT IDENTIFIER ::= { id-kp 2 }
 -- TLS WWW client authentication
 -- Key usage bits that may be consistent: digitalSignature
 -- and/or keyAgreement

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 id-kp-codeSigning             OBJECT IDENTIFIER ::= { id-kp 3 }
 -- Signing of downloadable executable code
 -- Key usage bits that may be consistent: digitalSignature
 id-kp-emailProtection         OBJECT IDENTIFIER ::= { id-kp 4 }
 -- E-mail protection
 -- Key usage bits that may be consistent: digitalSignature,
 -- nonRepudiation, and/or (keyEncipherment or keyAgreement)
 id-kp-timeStamping            OBJECT IDENTIFIER ::= { id-kp 8 }
 -- Binding the hash of an object to a time
 -- Key usage bits that may be consistent: digitalSignature
 -- and/or nonRepudiation
 id-kp-OCSPSigning            OBJECT IDENTIFIER ::= { id-kp 9 }
 -- Signing OCSP responses
 -- Key usage bits that may be consistent: digitalSignature
 -- and/or nonRepudiation

4.2.1.14 CRL Distribution Points

 The CRL distribution points extension identifies how CRL information
 is obtained.  The extension SHOULD be non-critical, but this profile
 RECOMMENDS support for this extension by CAs and applications.
 Further discussion of CRL management is contained in section 5.
 The cRLDistributionPoints extension is a SEQUENCE of
 DistributionPoint.  A DistributionPoint consists of three fields,
 each of which is optional: distributionPoint, reasons, and cRLIssuer.
 While each of these fields is optional, a DistributionPoint MUST NOT
 consist of only the reasons field; either distributionPoint or
 cRLIssuer MUST be present.  If the certificate issuer is not the CRL
 issuer, then the cRLIssuer field MUST be present and contain the Name
 of the CRL issuer.  If the certificate issuer is also the CRL issuer,
 then the cRLIssuer field MUST be omitted and the distributionPoint
 field MUST be present.  If the distributionPoint field is omitted,
 cRLIssuer MUST be present and include a Name corresponding to an
 X.500 or LDAP directory entry where the CRL is located.
 When the distributionPoint field is present, it contains either a
 SEQUENCE of general names or a single value, nameRelativeToCRLIssuer.
 If the cRLDistributionPoints extension contains a general name of
 type URI, the following semantics MUST be assumed: the URI is a
 pointer to the current CRL for the associated reasons and will be
 issued by the associated cRLIssuer.  The expected values for the URI
 are those defined in 4.2.1.7.  Processing rules for other values are
 not defined by this specification.

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 If the DistributionPointName contains multiple values, each name
 describes a different mechanism to obtain the same CRL.  For example,
 the same CRL could be available for retrieval through both LDAP and
 HTTP.
 If the DistributionPointName contains the single value
 nameRelativeToCRLIssuer, the value provides a distinguished name
 fragment.  The fragment is appended to the X.500 distinguished name
 of the CRL issuer to obtain the distribution point name.  If the
 cRLIssuer field in the DistributionPoint is present, then the name
 fragment is appended to the distinguished name that it contains;
 otherwise, the name fragment is appended to the certificate issuer
 distinguished name.  The DistributionPointName MUST NOT use the
 nameRealtiveToCRLIssuer alternative when cRLIssuer contains more than
 one distinguished name.
 If the DistributionPoint omits the reasons field, the CRL MUST
 include revocation information for all reasons.
 The cRLIssuer identifies the entity who signs and issues the CRL.  If
 present, the cRLIssuer MUST contain at least one an X.500
 distinguished name (DN), and MAY also contain other name forms.
 Since the cRLIssuer is compared to the CRL issuer name, the X.501
 type Name MUST follow the encoding rules for the issuer name field in
 the certificate (section 4.1.2.4).
 id-ce-cRLDistributionPoints OBJECT IDENTIFIER ::=  { id-ce 31 }
 CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint
 DistributionPoint ::= SEQUENCE {
      distributionPoint       [0]     DistributionPointName OPTIONAL,
      reasons                 [1]     ReasonFlags OPTIONAL,
      cRLIssuer               [2]     GeneralNames OPTIONAL }
 DistributionPointName ::= CHOICE {
      fullName                [0]     GeneralNames,
      nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }

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 ReasonFlags ::= BIT STRING {
      unused                  (0),
      keyCompromise           (1),
      cACompromise            (2),
      affiliationChanged      (3),
      superseded              (4),
      cessationOfOperation    (5),
      certificateHold         (6),
      privilegeWithdrawn      (7),
      aACompromise            (8) }

4.2.1.15 Inhibit Any-Policy

 The inhibit any-policy extension can be used in certificates issued
 to CAs.  The inhibit any-policy indicates that the special anyPolicy
 OID, with the value { 2 5 29 32 0 }, is not considered an explicit
 match for other certificate policies.  The value indicates the number
 of additional certificates that may appear in the path before
 anyPolicy is no longer permitted.  For example, a value of one
 indicates that anyPolicy may be processed in certificates issued by
 the subject of this certificate, but not in additional certificates
 in the path.
 This extension MUST be critical.
 id-ce-inhibitAnyPolicy OBJECT IDENTIFIER ::=  { id-ce 54 }
 InhibitAnyPolicy ::= SkipCerts
 SkipCerts ::= INTEGER (0..MAX)

4.2.1.16 Freshest CRL (a.k.a. Delta CRL Distribution Point)

 The freshest CRL extension identifies how delta CRL information is
 obtained.  The extension MUST be non-critical.  Further discussion of
 CRL management is contained in section 5.
 The same syntax is used for this extension and the
 cRLDistributionPoints extension, and is described in section
 4.2.1.14.  The same conventions apply to both extensions.
 id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }
 FreshestCRL ::= CRLDistributionPoints

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4.2.2 Private Internet Extensions

 This section defines two extensions for use in the Internet Public
 Key Infrastructure.  These extensions may be used to direct
 applications to on-line information about the issuing CA or the
 subject.  As the information may be available in multiple forms, each
 extension is a sequence of IA5String values, each of which represents
 a URI.  The URI implicitly specifies the location and format of the
 information and the method for obtaining the information.
 An object identifier is defined for the private extension.  The
 object identifier associated with the private extension is defined
 under the arc id-pe within the arc id-pkix.  Any future extensions
 defined for the Internet PKI are also expected to be defined under
 the arc id-pe.
    id-pkix  OBJECT IDENTIFIER  ::=
             { iso(1) identified-organization(3) dod(6) internet(1)
                     security(5) mechanisms(5) pkix(7) }
    id-pe  OBJECT IDENTIFIER  ::=  { id-pkix 1 }

4.2.2.1 Authority Information Access

 The authority information access extension indicates 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.  (The location of CRLs is not
 specified in this extension; that information is provided by the
 cRLDistributionPoints extension.)  This extension may be included in
 end entity or CA certificates, and it MUST be non-critical.
 id-pe-authorityInfoAccess OBJECT IDENTIFIER ::= { id-pe 1 }
 AuthorityInfoAccessSyntax  ::=
         SEQUENCE SIZE (1..MAX) OF AccessDescription
 AccessDescription  ::=  SEQUENCE {
         accessMethod          OBJECT IDENTIFIER,
         accessLocation        GeneralName  }
 id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }
 id-ad-caIssuers OBJECT IDENTIFIER ::= { id-ad 2 }
 id-ad-ocsp OBJECT IDENTIFIER ::= { id-ad 1 }

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 Each entry in the sequence AuthorityInfoAccessSyntax describes the
 format and location of additional information provided by the CA that
 issued the certificate in which this extension appears.  The type and
 format of the information is specified by the accessMethod field; the
 accessLocation field specifies the location of the information.  The
 retrieval mechanism may be implied by the accessMethod or specified
 by accessLocation.
 This profile defines two accessMethod OIDs: id-ad-caIssuers and
 id-ad-ocsp.
 The id-ad-caIssuers OID is used when the additional information lists
 CAs that have issued certificates superior to the CA that issued the
 certificate containing this extension.  The referenced CA issuers
 description is intended to aid certificate users in the selection of
 a certification path that terminates at a point trusted by the
 certificate user.
 When id-ad-caIssuers appears as accessMethod, the accessLocation
 field describes the referenced description server and the access
 protocol to obtain the referenced description.  The accessLocation
 field is defined as a GeneralName, which can take several forms.
 Where the information is available via http, ftp, or ldap,
 accessLocation MUST be a uniformResourceIdentifier.  Where the
 information is available via the Directory Access Protocol (DAP),
 accessLocation MUST be a directoryName.  The entry for that
 directoryName contains CA certificates in the crossCertificatePair
 attribute.  When the information is available via electronic mail,
 accessLocation MUST be an rfc822Name.  The semantics of other
 id-ad-caIssuers accessLocation name forms are not defined.
 The id-ad-ocsp OID is used when revocation information for the
 certificate containing this extension is available using the Online
 Certificate Status Protocol (OCSP) [RFC 2560].
 When id-ad-ocsp appears as accessMethod, the accessLocation field is
 the location of the OCSP responder, using the conventions defined in
 [RFC 2560].
 Additional access descriptors may be defined in other PKIX
 specifications.

4.2.2.2 Subject Information Access

 The subject information access extension indicates how to access
 information and services for the subject of the certificate in which
 the extension appears.  When the subject is a CA, information and
 services may include certificate validation services and CA policy

Housley, et. al. Standards Track [Page 46] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 data.  When the subject is an end entity, the information describes
 the type of services offered and how to access them.  In this case,
 the contents of this extension are defined in the protocol
 specifications for the suported services.  This extension may be
 included in subject or CA certificates, and it MUST be non-critical.
 id-pe-subjectInfoAccess OBJECT IDENTIFIER ::= { id-pe 11 }
 SubjectInfoAccessSyntax  ::=
         SEQUENCE SIZE (1..MAX) OF AccessDescription
 AccessDescription  ::=  SEQUENCE {
         accessMethod          OBJECT IDENTIFIER,
         accessLocation        GeneralName  }
 Each entry in the sequence SubjectInfoAccessSyntax describes the
 format and location of additional information provided by the subject
 of the certificate in which this extension appears.  The type and
 format of the information is specified by the accessMethod field; the
 accessLocation field specifies the location of the information.  The
 retrieval mechanism may be implied by the accessMethod or specified
 by accessLocation.
 This profile defines one access method to be used when the subject is
 a CA, and one access method to be used when the subject is an end
 entity.  Additional access methods may be defined in the future in
 the protocol specifications for other services.
 The id-ad-caRepository OID is used when the subject is a CA, and
 publishes its certificates and CRLs (if issued) in a repository.  The
 accessLocation field is defined as a GeneralName, which can take
 several forms.  Where the information is available via http, ftp, or
 ldap, accessLocation MUST be a uniformResourceIdentifier.  Where the
 information is available via the directory access protocol (dap),
 accessLocation MUST be a directoryName.  When the information is
 available via electronic mail, accessLocation MUST be an rfc822Name.
 The semantics of other name forms of of accessLocation (when
 accessMethod is id-ad-caRepository) are not defined by this
 specification.
 The id-ad-timeStamping OID is used when the subject offers
 timestamping services using the Time Stamp Protocol defined in
 [PKIXTSA].  Where the timestamping services are available via http or
 ftp, accessLocation MUST be a uniformResourceIdentifier.  Where the
 timestamping services are available via electronic mail,
 accessLocation MUST be an rfc822Name.  Where timestamping services

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 are available using TCP/IP, the dNSName or ipAddress name forms may
 be used.  The semantics of other name forms of accessLocation (when
 accessMethod is id-ad-timeStamping) are not defined by this
 specification.
 Additional access descriptors may be defined in other PKIX
 specifications.
 id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }
 id-ad-caRepository OBJECT IDENTIFIER ::= { id-ad 5 }
 id-ad-timeStamping OBJECT IDENTIFIER ::= { id-ad 3 }

5 CRL and CRL Extensions Profile

 As discussed above, one goal of this X.509 v2 CRL profile is to
 foster the creation of an interoperable and reusable Internet PKI.
 To achieve this goal, guidelines for the use of extensions are
 specified, and some assumptions are made about the nature of
 information included in the CRL.
 CRLs may be used in a wide range of applications and environments
 covering a broad spectrum of interoperability goals and an even
 broader spectrum of operational and assurance requirements.  This
 profile establishes a common baseline for generic applications
 requiring broad interoperability.  The profile defines a set of
 information that can be expected in every CRL.  Also, the profile
 defines common locations within the CRL for frequently used
 attributes as well as common representations for these attributes.
 CRL issuers issue CRLs.  In general, the CRL issuer is the CA.  CAs
 publish CRLs to provide status information about the certificates
 they issued.  However, a CA may delegate this responsibility to
 another trusted authority.  Whenever the CRL issuer is not the CA
 that issued the certificates, the CRL is referred to as an indirect
 CRL.
 Each CRL has a particular scope.  The CRL scope is the set of
 certificates that could appear on a given CRL.  For example, the
 scope could be "all certificates issued by CA X", "all CA
 certificates issued by CA X", "all certificates issued by CA X that
 have been revoked for reasons of key compromise and CA compromise",
 or could be a set of certificates based on arbitrary local
 information, such as "all certificates issued to the NIST employees
 located in Boulder".

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 A complete CRL lists all unexpired certificates, within its scope,
 that have been revoked for one of the revocation reasons covered by
 the CRL scope.  The CRL issuer MAY also generate delta CRLs.  A delta
 CRL only lists those certificates, within its scope, whose revocation
 status has changed since the issuance of a referenced complete CRL.
 The referenced complete CRL is referred to as a base CRL.  The scope
 of a delta CRL MUST be the same as the base CRL that it references.
 This profile does not define any private Internet CRL extensions or
 CRL entry extensions.
 Environments with additional or special purpose requirements may
 build on this profile or may replace it.
 Conforming CAs are not required to issue CRLs if other revocation or
 certificate status mechanisms are provided.  When CRLs are issued,
 the CRLs MUST be version 2 CRLs, include the date by which the next
 CRL will be issued in the nextUpdate field (section 5.1.2.5), include
 the CRL number extension (section 5.2.3), and include the authority
 key identifier extension (section 5.2.1).  Conforming applications
 that support CRLs are REQUIRED to process both version 1 and version
 2 complete CRLs that provide revocation information for all
 certificates issued by one CA.  Conforming applications are NOT
 REQUIRED to support processing of delta CRLs, indirect CRLs, or CRLs
 with a scope other than all certificates issued by one CA.

5.1 CRL Fields

 The X.509 v2 CRL syntax is as follows.  For signature calculation,
 the data that is to be signed is ASN.1 DER encoded.  ASN.1 DER
 encoding is a tag, length, value encoding system for each element.
 CertificateList  ::=  SEQUENCE  {
      tbsCertList          TBSCertList,
      signatureAlgorithm   AlgorithmIdentifier,
      signatureValue       BIT STRING  }

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 TBSCertList  ::=  SEQUENCE  {
      version                 Version OPTIONAL,
                                   -- if present, MUST be v2
      signature               AlgorithmIdentifier,
      issuer                  Name,
      thisUpdate              Time,
      nextUpdate              Time OPTIONAL,
      revokedCertificates     SEQUENCE OF SEQUENCE  {
           userCertificate         CertificateSerialNumber,
           revocationDate          Time,
           crlEntryExtensions      Extensions OPTIONAL
                                         -- if present, MUST be v2
                                }  OPTIONAL,
      crlExtensions           [0]  EXPLICIT Extensions OPTIONAL
                                         -- if present, MUST be v2
                                }
  1. - Version, Time, CertificateSerialNumber, and Extensions
  2. - are all defined in the ASN.1 in section 4.1
  1. - AlgorithmIdentifier is defined in section 4.1.1.2
 The following items describe the use of the X.509 v2 CRL in the
 Internet PKI.

5.1.1 CertificateList Fields

 The CertificateList is a SEQUENCE of three required fields.  The
 fields are described in detail in the following subsections.

5.1.1.1 tbsCertList

 The first field in the sequence is the tbsCertList.  This field is
 itself a sequence containing the name of the issuer, issue date,
 issue date of the next list, the optional list of revoked
 certificates, and optional CRL extensions.  When there are no revoked
 certificates, the revoked certificates list is absent.  When one or
 more certificates are revoked, each entry on the revoked certificate
 list is defined by a sequence of user certificate serial number,
 revocation date, and optional CRL entry extensions.

5.1.1.2 signatureAlgorithm

 The signatureAlgorithm field contains the algorithm identifier for
 the algorithm used by the CRL issuer to sign the CertificateList.
 The field is of type AlgorithmIdentifier, which is defined in section
 4.1.1.2.  [PKIXALGS] lists the supported algorithms for this
 specification, but other signature algorithms MAY also be supported.

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 This field MUST contain the same algorithm identifier as the
 signature field in the sequence tbsCertList (section 5.1.2.2).

5.1.1.3 signatureValue

 The signatureValue field contains a digital signature computed upon
 the ASN.1 DER encoded tbsCertList.  The ASN.1 DER encoded tbsCertList
 is used as the input to the signature function.  This signature value
 is encoded as a BIT STRING and included in the CRL signatureValue
 field.  The details of this process are specified for each of the
 supported algorithms in [PKIXALGS].
 CAs that are also CRL issuers MAY use one private key to digitally
 sign certificates and CRLs, or MAY use separate private keys to
 digitally sign certificates and CRLs.  When separate private keys are
 employed, each of the public keys associated with these private keys
 is placed in a separate certificate, one with the keyCertSign bit set
 in the key usage extension, and one with the cRLSign bit set in the
 key usage extension (section 4.2.1.3).  When separate private keys
 are employed, certificates issued by the CA contain one authority key
 identifier, and the corresponding CRLs contain a different authority
 key identifier.  The use of separate CA certificates for validation
 of certificate signatures and CRL signatures can offer improved
 security characteristics; however, it imposes a burden on
 applications, and it might limit interoperability.  Many applications
 construct a certification path, and then validate the certification
 path (section 6).  CRL checking in turn requires a separate
 certification path to be constructed and validated for the CA's CRL
 signature validation certificate.  Applications that perform CRL
 checking MUST support certification path validation when certificates
 and CRLs are digitally signed with the same CA private key.  These
 applications SHOULD support certification path validation when
 certificates and CRLs are digitally signed with different CA private
 keys.

5.1.2 Certificate List "To Be Signed"

 The certificate list to be signed, or TBSCertList, is a sequence of
 required and optional fields.  The required fields identify the CRL
 issuer, the algorithm used to sign the CRL, the date and time the CRL
 was issued, and the date and time by which the CRL issuer will issue
 the next CRL.
 Optional fields include lists of revoked certificates and CRL
 extensions.  The revoked certificate list is optional to support the
 case where a CA has not revoked any unexpired certificates that it

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 has issued.  The profile requires conforming CRL issuers to use the
 CRL number and authority key identifier CRL extensions in all CRLs
 issued.

5.1.2.1 Version

 This optional field describes the version of the encoded CRL.  When
 extensions are used, as required by this profile, this field MUST be
 present and MUST specify version 2 (the integer value is 1).

5.1.2.2 Signature

 This field contains the algorithm identifier for the algorithm used
 to sign the CRL.  [PKIXALGS] lists OIDs for the most popular
 signature algorithms used in the Internet PKI.
 This field MUST contain the same algorithm identifier as the
 signatureAlgorithm field in the sequence CertificateList (section
 5.1.1.2).

5.1.2.3 Issuer Name

 The issuer name identifies the entity who has signed and issued the
 CRL.  The issuer identity is carried in the issuer name field.
 Alternative name forms may also appear in the issuerAltName extension
 (section 5.2.2).  The issuer name field MUST contain an X.500
 distinguished name (DN).  The issuer name field is defined as the
 X.501 type Name, and MUST follow the encoding rules for the issuer
 name field in the certificate (section 4.1.2.4).

5.1.2.4 This Update

 This field indicates the issue date of this CRL.  ThisUpdate may be
 encoded as UTCTime or GeneralizedTime.
 CRL issuers conforming to this profile MUST encode thisUpdate as
 UTCTime for dates through the year 2049.  CRL issuers conforming to
 this profile MUST encode thisUpdate as GeneralizedTime for dates in
 the year 2050 or later.
 Where encoded as UTCTime, thisUpdate MUST be specified and
 interpreted as defined in section 4.1.2.5.1.  Where encoded as
 GeneralizedTime, thisUpdate MUST be specified and interpreted as
 defined in section 4.1.2.5.2.

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5.1.2.5 Next Update

 This field indicates the date by which the next CRL will be issued.
 The next CRL could be issued before the indicated date, but it will
 not be issued any later than the indicated date.  CRL issuers SHOULD
 issue CRLs with a nextUpdate time equal to or later than all previous
 CRLs.  nextUpdate may be encoded as UTCTime or GeneralizedTime.
 This profile requires inclusion of nextUpdate in all CRLs issued by
 conforming CRL issuers.  Note that the ASN.1 syntax of TBSCertList
 describes this field as OPTIONAL, which is consistent with the ASN.1
 structure defined in [X.509].  The behavior of clients processing
 CRLs which omit nextUpdate is not specified by this profile.
 CRL issuers conforming to this profile MUST encode nextUpdate as
 UTCTime for dates through the year 2049.  CRL issuers conforming to
 this profile MUST encode nextUpdate as GeneralizedTime for dates in
 the year 2050 or later.
 Where encoded as UTCTime, nextUpdate MUST be specified and
 interpreted as defined in section 4.1.2.5.1.  Where encoded as
 GeneralizedTime, nextUpdate MUST be specified and interpreted as
 defined in section 4.1.2.5.2.

5.1.2.6 Revoked Certificates

 When there are no revoked certificates, the revoked certificates list
 MUST be absent.  Otherwise, revoked certificates are listed by their
 serial numbers.  Certificates revoked by the CA are uniquely
 identified by the certificate serial number.  The date on which the
 revocation occurred is specified.  The time for revocationDate MUST
 be expressed as described in section 5.1.2.4. Additional information
 may be supplied in CRL entry extensions; CRL entry extensions are
 discussed in section 5.3.

5.1.2.7 Extensions

 This field may only appear if the version is 2 (section 5.1.2.1).  If
 present, this field is a sequence of one or more CRL extensions.  CRL
 extensions are discussed in section 5.2.

5.2 CRL Extensions

 The extensions defined by ANSI X9, ISO/IEC, and ITU-T for X.509 v2
 CRLs [X.509] [X9.55] provide methods for associating additional
 attributes with CRLs.  The X.509 v2 CRL format also allows
 communities to define private extensions to carry information unique
 to those communities.  Each extension in a CRL may be designated as

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 critical or non-critical.  A CRL validation MUST fail if it
 encounters a critical extension which it does not know how to
 process.  However, an unrecognized non-critical extension may be
 ignored.  The following subsections present those extensions used
 within Internet CRLs.  Communities may elect to include extensions in
 CRLs which are not defined in this specification.  However, caution
 should be exercised in adopting any critical extensions in CRLs which
 might be used in a general context.
 Conforming CRL issuers are REQUIRED to include the authority key
 identifier (section 5.2.1) and the CRL number (section 5.2.3)
 extensions in all CRLs issued.

5.2.1 Authority Key Identifier

 The authority key identifier extension provides a means of
 identifying the public key corresponding to the private key used to
 sign a CRL.  The identification can be based on either the key
 identifier (the subject key identifier in the CRL signer's
 certificate) or on the issuer name and serial number.  This extension
 is especially useful where an issuer has more than one signing key,
 either due to multiple concurrent key pairs or due to changeover.
 Conforming CRL issuers MUST use the key identifier method, and MUST
 include this extension in all CRLs issued.
 The syntax for this CRL extension is defined in section 4.2.1.1.

5.2.2 Issuer Alternative Name

 The issuer alternative names extension allows additional identities
 to be associated with the issuer of the CRL.  Defined options include
 an rfc822 name (electronic mail address), a DNS name, an IP address,
 and a URI.  Multiple instances of a name and multiple name forms may
 be included.  Whenever such identities are used, the issuer
 alternative name extension MUST be used; however, a DNS name MAY be
 represented in the issuer field using the domainComponent attribute
 as described in section 4.1.2.4.
 The issuerAltName extension SHOULD NOT be marked critical.
 The OID and syntax for this CRL extension are defined in section
 4.2.1.8.

Housley, et. al. Standards Track [Page 54] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

5.2.3 CRL Number

 The CRL number is a non-critical CRL extension which conveys a
 monotonically increasing sequence number for a given CRL scope and
 CRL issuer.  This extension allows users to easily determine when a
 particular CRL supersedes another CRL.  CRL numbers also support the
 identification of complementary complete CRLs and delta CRLs.  CRL
 issuers conforming to this profile MUST include this extension in all
 CRLs.
 If a CRL issuer generates delta CRLs in addition to complete CRLs for
 a given scope, the complete CRLs and delta CRLs MUST share one
 numbering sequence.  If a delta CRL and a complete CRL that cover the
 same scope are issued at the same time, they MUST have the same CRL
 number and provide the same revocation information.  That is, the
 combination of the delta CRL and an acceptable complete CRL MUST
 provide the same revocation information as the simultaneously issued
 complete CRL.
 If a CRL issuer generates two CRLs (two complete CRLs, two delta
 CRLs, or a complete CRL and a delta CRL) for the same scope at
 different times, the two CRLs MUST NOT have the same CRL number.
 That is, if the this update field (section 5.1.2.4) in the two CRLs
 are not identical, the CRL numbers MUST be different.
 Given the requirements above, CRL numbers can be expected to contain
 long integers.  CRL verifiers MUST be able to handle CRLNumber values
 up to 20 octets.  Conformant CRL issuers MUST NOT use CRLNumber
 values longer than 20 octets.
 id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }
 CRLNumber ::= INTEGER (0..MAX)

5.2.4 Delta CRL Indicator

 The delta CRL indicator is a critical CRL extension that identifies a
 CRL as being a delta CRL.  Delta CRLs contain updates to revocation
 information previously distributed, rather than all the information
 that would appear in a complete CRL.  The use of delta CRLs can
 significantly reduce network load and processing time in some
 environments.  Delta CRLs are generally smaller than the CRLs they
 update, so applications that obtain delta CRLs consume less network
 bandwidth than applications that obtain the corresponding complete
 CRLs.  Applications which store revocation information in a format
 other than the CRL structure can add new revocation information to
 the local database without reprocessing information.

Housley, et. al. Standards Track [Page 55] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 The delta CRL indicator extension contains the single value of type
 BaseCRLNumber.  The CRL number identifies the CRL, complete for a
 given scope, that was used as the starting point in the generation of
 this delta CRL.  A conforming CRL issuer MUST publish the referenced
 base CRL as a complete CRL.  The delta CRL contains all updates to
 the revocation status for that same scope.  The combination of a
 delta CRL plus the referenced base CRL is equivalent to a complete
 CRL, for the applicable scope, at the time of publication of the
 delta CRL.
 When a conforming CRL issuer generates a delta CRL, the delta CRL
 MUST include a critical delta CRL indicator extension.
 When a delta CRL is issued, it MUST cover the same set of reasons and
 the same set of certificates that were covered by the base CRL it
 references.  That is, the scope of the delta CRL MUST be the same as
 the scope of the complete CRL referenced as the base.  The referenced
 base CRL and the delta CRL MUST omit the issuing distribution point
 extension or contain identical issuing distribution point extensions.
 Further, the CRL issuer MUST use the same private key to sign the
 delta CRL and any complete CRL that it can be used to update.
 An application that supports delta CRLs can construct a CRL that is
 complete for a given scope by combining a delta CRL for that scope
 with either an issued CRL that is complete for that scope or a
 locally constructed CRL that is complete for that scope.
 When a delta CRL is combined with a complete CRL or a locally
 constructed CRL, the resulting locally constructed CRL has the CRL
 number specified in the CRL number extension found in the delta CRL
 used in its construction.  In addition, the resulting locally
 constructed CRL has the thisUpdate and nextUpdate times specified in
 the corresponding fields of the delta CRL used in its construction.
 In addition, the locally constructed CRL inherits the issuing
 distribution point from the delta CRL.
 A complete CRL and a delta CRL MAY be combined if the following four
 conditions are satisfied:
    (a)  The complete CRL and delta CRL have the same issuer.
    (b)  The complete CRL and delta CRL have the same scope.  The two
    CRLs have the same scope if either of the following conditions are
    met:
       (1)  The issuingDistributionPoint extension is omitted from
       both the complete CRL and the delta CRL.

Housley, et. al. Standards Track [Page 56] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

       (2)  The issuingDistributionPoint extension is present in both
       the complete CRL and the delta CRL, and the values for each of
       the fields in the extensions are the same in both CRLs.
    (c)  The CRL number of the complete CRL is equal to or greater
    than the BaseCRLNumber specified in the delta CRL.  That is, the
    complete CRL contains (at a minimum) all the revocation
    information held by the referenced base CRL.
    (d)  The CRL number of the complete CRL is less than the CRL
    number of the delta CRL.  That is, the delta CRL follows the
    complete CRL in the numbering sequence.
 CRL issuers MUST ensure that the combination of a delta CRL and any
 appropriate complete CRL accurately reflects the current revocation
 status.  The CRL issuer MUST include an entry in the delta CRL for
 each certificate within the scope of the delta CRL whose status has
 changed since the generation of the referenced base CRL:
    (a)  If the certificate is revoked for a reason included in the
    scope of the CRL, list the certificate as revoked.
    (b)  If the certificate is valid and was listed on the referenced
    base CRL or any subsequent CRL with reason code certificateHold,
    and the reason code certificateHold is included in the scope of
    the CRL, list the certificate with the reason code removeFromCRL.
    (c)  If the certificate is revoked for a reason outside the scope
    of the CRL, but the certificate was listed on the referenced base
    CRL or any subsequent CRL with a reason code included in the scope
    of this CRL, list the certificate as revoked but omit the reason
    code.
    (d)  If the certificate is revoked for a reason outside the scope
    of the CRL and the certificate was neither listed on the
    referenced base CRL nor any subsequent CRL with a reason code
    included in the scope of this CRL, do not list the certificate on
    this CRL.
 The status of a certificate is considered to have changed if it is
 revoked, placed on hold, released from hold, or if its revocation
 reason changes.
 It is appropriate to list a certificate with reason code
 removeFromCRL on a delta CRL even if the certificate was not on hold
 in the referenced base CRL.  If the certificate was placed on hold in

Housley, et. al. Standards Track [Page 57] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 any CRL issued after the base but before this delta CRL and then
 released from hold, it MUST be listed on the delta CRL with
 revocation reason removeFromCRL.
 A CRL issuer MAY optionally list a certificate on a delta CRL with
 reason code removeFromCRL if the notAfter time specified in the
 certificate precedes the thisUpdate time specified in the delta CRL
 and the certificate was listed on the referenced base CRL or in any
 CRL issued after the base but before this delta CRL.
 If a certificate revocation notice first appears on a delta CRL, then
 it is possible for the certificate validity period to expire before
 the next complete CRL for the same scope is issued.  In this case,
 the revocation notice MUST be included in all subsequent delta CRLs
 until the revocation notice is included on at least one explicitly
 issued complete CRL for this scope.
 An application that supports delta CRLs MUST be able to construct a
 current complete CRL by combining a previously issued complete CRL
 and the most current delta CRL.  An application that supports delta
 CRLs MAY also be able to construct a current complete CRL by
 combining a previously locally constructed complete CRL and the
 current delta CRL.  A delta CRL is considered to be the current one
 if the current time is between the times contained in the thisUpdate
 and nextUpdate fields.  Under some circumstances, the CRL issuer may
 publish one or more delta CRLs before indicated by the nextUpdate
 field.  If more than one current delta CRL for a given scope is
 encountered, the application SHOULD consider the one with the latest
 value in thisUpdate to be the most current one.
 id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }
 BaseCRLNumber ::= CRLNumber

5.2.5 Issuing Distribution Point

 The issuing distribution point is a critical CRL extension that
 identifies the CRL distribution point and scope for a particular CRL,
 and it indicates whether the CRL covers revocation for end entity
 certificates only, CA certificates only, attribute certificates only,
 or a limited set of reason codes.  Although the extension is
 critical, conforming implementations are not required to support this
 extension.

Housley, et. al. Standards Track [Page 58] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 The CRL is signed using the CRL issuer's private key.  CRL
 Distribution Points do not have their own key pairs.  If the CRL is
 stored in the X.500 Directory, it is stored in the Directory entry
 corresponding to the CRL distribution point, which may be different
 than the Directory entry of the CRL issuer.
 The reason codes associated with a distribution point MUST be
 specified in onlySomeReasons.  If onlySomeReasons does not appear,
 the distribution point MUST contain revocations for all reason codes.
 CAs may use CRL distribution points to partition the CRL on the basis
 of compromise and routine revocation.  In this case, the revocations
 with reason code keyCompromise (1), cACompromise (2), and
 aACompromise (8) appear in one distribution point, and the
 revocations with other reason codes appear in another distribution
 point.
 If the distributionPoint field is present and contains a URI, the
 following semantics MUST be assumed: the object is a pointer to the
 most current CRL issued by this CRL issuer.  The URI schemes ftp,
 http, mailto [RFC1738] and ldap [RFC1778] are defined for this
 purpose.  The URI MUST be an absolute pathname, not a relative
 pathname, and MUST specify the host.
 If the distributionPoint field is absent, the CRL MUST contain
 entries for all revoked unexpired certificates issued by the CRL
 issuer, if any, within the scope of the CRL.
 The CRL issuer MUST assert the indirectCRL boolean, if the scope of
 the CRL includes certificates issued by authorities other than the
 CRL issuer.  The authority responsible for each entry is indicated by
 the certificate issuer CRL entry extension (section 5.3.4).
 id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }
 issuingDistributionPoint ::= SEQUENCE {
      distributionPoint          [0] DistributionPointName OPTIONAL,
      onlyContainsUserCerts      [1] BOOLEAN DEFAULT FALSE,
      onlyContainsCACerts        [2] BOOLEAN DEFAULT FALSE,
      onlySomeReasons            [3] ReasonFlags OPTIONAL,
      indirectCRL                [4] BOOLEAN DEFAULT FALSE,
      onlyContainsAttributeCerts [5] BOOLEAN DEFAULT FALSE }

5.2.6 Freshest CRL (a.k.a. Delta CRL Distribution Point)

 The freshest CRL extension identifies how delta CRL information for
 this complete CRL is obtained.  The extension MUST be non-critical.
 This extension MUST NOT appear in delta CRLs.

Housley, et. al. Standards Track [Page 59] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 The same syntax is used for this extension as the
 cRLDistributionPoints certificate extension, and is described in
 section 4.2.1.14.  However, only the distribution point field is
 meaningful in this context.  The reasons and CRLIssuer fields MUST be
 omitted from this CRL extension.
 Each distribution point name provides the location at which a delta
 CRL for this complete CRL can be found.  The scope of these delta
 CRLs MUST be the same as the scope of this complete CRL.  The
 contents of this CRL extension are only used to locate delta CRLs;
 the contents are not used to validate the CRL or the referenced delta
 CRLs.  The encoding conventions defined for distribution points in
 section 4.2.1.14 apply to this extension.
 id-ce-freshestCRL OBJECT IDENTIFIER ::=  { id-ce 46 }
 FreshestCRL ::= CRLDistributionPoints

5.3 CRL Entry Extensions

 The CRL entry extensions defined by ISO/IEC, ITU-T, and ANSI X9 for
 X.509 v2 CRLs provide methods for associating additional attributes
 with CRL entries [X.509] [X9.55].  The X.509 v2 CRL format also
 allows communities to define private CRL entry extensions to carry
 information unique to those communities.  Each extension in a CRL
 entry may be designated as critical or non-critical.  A CRL
 validation MUST fail if it encounters a critical CRL entry extension
 which it does not know how to process.  However, an unrecognized non-
 critical CRL entry extension may be ignored.  The following
 subsections present recommended extensions used within Internet CRL
 entries and standard locations for information.  Communities may
 elect to use additional CRL entry extensions; however, caution should
 be exercised in adopting any critical extensions in CRL entries which
 might be used in a general context.
 All CRL entry extensions used in this specification are non-critical.
 Support for these extensions is optional for conforming CRL issuers
 and applications.  However, CRL issuers SHOULD include reason codes
 (section 5.3.1) and invalidity dates (section 5.3.3) whenever this
 information is available.

5.3.1 Reason Code

 The reasonCode is a non-critical CRL entry extension that identifies
 the reason for the certificate revocation.  CRL issuers are strongly
 encouraged to include meaningful reason codes in CRL entries;
 however, the reason code CRL entry extension SHOULD be absent instead
 of using the unspecified (0) reasonCode value.

Housley, et. al. Standards Track [Page 60] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 id-ce-cRLReason OBJECT IDENTIFIER ::= { id-ce 21 }
  1. - reasonCode ::= { CRLReason }
 CRLReason ::= ENUMERATED {
      unspecified             (0),
      keyCompromise           (1),
      cACompromise            (2),
      affiliationChanged      (3),
      superseded              (4),
      cessationOfOperation    (5),
      certificateHold         (6),
      removeFromCRL           (8),
      privilegeWithdrawn      (9),
      aACompromise           (10) }

5.3.2 Hold Instruction Code

 The hold instruction code is a non-critical CRL entry extension that
 provides a registered instruction identifier which indicates the
 action to be taken after encountering a certificate that has been
 placed on hold.
 id-ce-holdInstructionCode OBJECT IDENTIFIER ::= { id-ce 23 }
 holdInstructionCode ::= OBJECT IDENTIFIER
 The following instruction codes have been defined.  Conforming
 applications that process this extension MUST recognize the following
 instruction codes.
 holdInstruction    OBJECT IDENTIFIER ::=
                  { iso(1) member-body(2) us(840) x9-57(10040) 2 }
 id-holdinstruction-none   OBJECT IDENTIFIER ::= {holdInstruction 1}
 id-holdinstruction-callissuer
                           OBJECT IDENTIFIER ::= {holdInstruction 2}
 id-holdinstruction-reject OBJECT IDENTIFIER ::= {holdInstruction 3}
 Conforming applications which encounter an id-holdinstruction-
 callissuer MUST call the certificate issuer or reject the
 certificate.  Conforming applications which encounter an id-
 holdinstruction-reject MUST reject the certificate.  The hold
 instruction id-holdinstruction-none is semantically equivalent to the
 absence of a holdInstructionCode, and its use is strongly deprecated
 for the Internet PKI.

Housley, et. al. Standards Track [Page 61] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

5.3.3 Invalidity Date

 The invalidity date is a non-critical CRL entry extension that
 provides the date on which it is known or suspected that the private
 key was compromised or that the certificate otherwise became invalid.
 This date may be earlier than the revocation date in the CRL entry,
 which is the date at which the CA processed the revocation.  When a
 revocation is first posted by a CRL issuer in a CRL, the invalidity
 date may precede the date of issue of earlier CRLs, but the
 revocation date SHOULD NOT precede the date of issue of earlier CRLs.
 Whenever this information is available, CRL issuers are strongly
 encouraged to share it with CRL users.
 The GeneralizedTime values included in this field MUST be expressed
 in Greenwich Mean Time (Zulu), and MUST be specified and interpreted
 as defined in section 4.1.2.5.2.
 id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }
 invalidityDate ::=  GeneralizedTime

5.3.4 Certificate Issuer

 This CRL entry extension identifies the certificate issuer associated
 with an entry in an indirect CRL, that is, a CRL that has the
 indirectCRL indicator set in its issuing distribution point
 extension.  If this extension is not present on the first entry in an
 indirect CRL, the certificate issuer defaults to the CRL issuer.  On
 subsequent entries in an indirect CRL, if this extension is not
 present, the certificate issuer for the entry is the same as that for
 the preceding entry.  This field is defined as follows:
 id-ce-certificateIssuer   OBJECT IDENTIFIER ::= { id-ce 29 }
 certificateIssuer ::=     GeneralNames
 If used by conforming CRL issuers, this extension MUST always be
 critical.  If an implementation ignored this extension it could not
 correctly attribute CRL entries to certificates.  This specification
 RECOMMENDS that implementations recognize this extension.

6 Certification Path Validation

 Certification path validation procedures for the Internet PKI are
 based on the algorithm supplied in [X.509].  Certification path
 processing verifies the binding between the subject distinguished
 name and/or subject alternative name and subject public key.  The
 binding is limited by constraints which are specified in the

Housley, et. al. Standards Track [Page 62] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 certificates which comprise the path and inputs which are specified
 by the relying party.  The basic constraints and policy constraints
 extensions allow the certification path processing logic to automate
 the decision making process.
 This section describes an algorithm for validating certification
 paths.  Conforming implementations of this specification are not
 required to implement this algorithm, but MUST provide functionality
 equivalent to the external behavior resulting from this procedure.
 Any algorithm may be used by a particular implementation so long as
 it derives the correct result.
 In section 6.1, the text describes basic path validation.  Valid
 paths begin with certificates issued by a trust anchor.  The
 algorithm requires the public key of the CA, the CA's name, and any
 constraints upon the set of paths which may be validated using this
 key.
 The selection of a trust anchor is a matter of policy: it could be
 the top CA in a hierarchical PKI; the CA that issued the verifier's
 own certificate(s); or any other CA in a network PKI.  The path
 validation procedure is the same regardless of the choice of trust
 anchor.  In addition, different applications may rely on different
 trust anchor, or may accept paths that begin with any of a set of
 trust anchor.
 Section 6.2 describes methods for using the path validation algorithm
 in specific implementations.  Two specific cases are discussed: the
 case where paths may begin with one of several trusted CAs; and where
 compatibility with the PEM architecture is required.
 Section 6.3 describes the steps necessary to determine if a
 certificate is revoked or on hold status when CRLs are the revocation
 mechanism used by the certificate issuer.

6.1 Basic Path Validation

 This text describes an algorithm for X.509 path processing.  A
 conformant implementation MUST include an X.509 path processing
 procedure that is functionally equivalent to the external behavior of
 this algorithm.  However, support for some of the certificate
 extensions processed in this algorithm are OPTIONAL for compliant
 implementations.  Clients that do not support these extensions MAY
 omit the corresponding steps in the path validation algorithm.

Housley, et. al. Standards Track [Page 63] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 For example, clients are NOT REQUIRED to support the policy mapping
 extension.  Clients that do not support this extension MAY omit the
 path validation steps where policy mappings are processed.  Note that
 clients MUST reject the certificate if it contains an unsupported
 critical extension.
 The algorithm presented in this section validates the certificate
 with respect to the current date and time.  A conformant
 implementation MAY also support validation with respect to some point
 in the past.  Note that mechanisms are not available for validating a
 certificate with respect to a time outside the certificate validity
 period.
 The trust anchor is an input to the algorithm.  There is no
 requirement that the same trust anchor be used to validate all
 certification paths.  Different trust anchors MAY be used to validate
 different paths, as discussed further in Section 6.2.
 The primary goal of path validation is to verify the binding between
 a subject distinguished name or a subject alternative name and
 subject public key, as represented in the end entity certificate,
 based on the public key of the trust anchor.  This requires obtaining
 a sequence of certificates that support that binding.  The procedure
 performed to obtain this sequence of certificates is outside the
 scope of this specification.
 To meet this goal, the path validation process verifies, among other
 things, that a prospective certification path (a sequence of n
 certificates) satisfies the following conditions:
    (a)  for all x in {1, ..., n-1}, the subject of certificate x is
    the issuer of certificate x+1;
    (b)  certificate 1 is issued by the trust anchor;
    (c)  certificate n is the certificate to be validated; and
    (d)  for all x in {1, ..., n}, the certificate was valid at the
    time in question.
 When the trust anchor is provided in the form of a self-signed
 certificate, this self-signed certificate is not included as part of
 the prospective certification path.  Information about trust anchors
 are provided as inputs to the certification path validation algorithm
 (section 6.1.1).

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 A particular certification path may not, however, be appropriate for
 all applications.  Therefore, an application MAY augment this
 algorithm to further limit the set of valid paths.  The path
 validation process also determines the set of certificate policies
 that are valid for this path, based on the certificate policies
 extension, policy mapping extension, policy constraints extension,
 and inhibit any-policy extension.  To achieve this, the path
 validation algorithm constructs a valid policy tree.  If the set of
 certificate policies that are valid for this path is not empty, then
 the result will be a valid policy tree of depth n, otherwise the
 result will be a null valid policy tree.
 A certificate is self-issued if the DNs that appear in the subject
 and issuer fields are identical and are not empty.  In general, the
 issuer and subject of the certificates that make up a path are
 different for each certificate.  However, a CA may issue a
 certificate to itself to support key rollover or changes in
 certificate policies.  These self-issued certificates are not counted
 when evaluating path length or name constraints.
 This section presents the algorithm in four basic steps: (1)
 initialization, (2) basic certificate processing, (3) preparation for
 the next certificate, and (4) wrap-up.  Steps (1) and (4) are
 performed exactly once.  Step (2) is performed for all certificates
 in the path.  Step (3) is performed for all certificates in the path
 except the final certificate.  Figure 2 provides a high-level
 flowchart of this algorithm.

Housley, et. al. Standards Track [Page 65] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

                         +-------+
                         | START |
                         +-------+
                             |
                             V
                     +----------------+
                     | Initialization |
                     +----------------+
                             |
                             +<--------------------+
                             |                     |
                             V                     |
                     +----------------+            |
                     |  Process Cert  |            |
                     +----------------+            |
                             |                     |
                             V                     |
                     +================+            |
                     |  IF Last Cert  |            |
                     |    in Path     |            |
                     +================+            |
                       |            |              |
                  THEN |            | ELSE         |
                       V            V              |
            +----------------+ +----------------+  |
            |    Wrap up     | |  Prepare for   |  |
            +----------------+ |   Next Cert    |  |
                    |          +----------------+  |
                    V               |              |
                +-------+           +--------------+
                | STOP  |
                +-------+
       Figure 2.  Certification Path Processing Flowchart

6.1.1 Inputs

 This algorithm assumes the following seven inputs are provided to the
 path processing logic:
    (a)  a prospective certification path of length n.
    (b)  the current date/time.

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    (c)  user-initial-policy-set:  A set of certificate policy
    identifiers naming the policies that are acceptable to the
    certificate user.  The user-initial-policy-set contains the
    special value any-policy if the user is not concerned about
    certificate policy.
    (d)  trust anchor information, describing a CA that serves as a
    trust anchor for the certification path.  The trust anchor
    information includes:
       (1)  the trusted issuer name,
       (2)  the trusted public key algorithm,
       (3)  the trusted public key, and
       (4)  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.
    (e) initial-policy-mapping-inhibit, which indicates if policy
    mapping is allowed in the certification path.
    (f) initial-explicit-policy, which indicates if the path must be
    valid for at least one of the certificate policies in the user-
    initial-policy-set.
    (g) initial-any-policy-inhibit, which indicates whether the
    anyPolicy OID should be processed if it is included in a
    certificate.

6.1.2 Initialization

 This initialization phase establishes eleven state variables based
 upon the seven inputs:
    (a)  valid_policy_tree:  A tree of certificate policies with their
    optional qualifiers; each of the leaves of the tree represents a
    valid policy at this stage in the certification path validation.
    If valid policies exist at this stage in the certification path
    validation, the depth of the tree is equal to the number of

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    certificates in the chain that have been processed.  If valid
    policies do not exist at this stage in the certification path
    validation, the tree is set to NULL.  Once the tree is set to
    NULL, policy processing ceases.
    Each node in the valid_policy_tree includes four data objects: the
    valid policy, a set of associated policy qualifiers, a set of one
    or more expected policy values, and a criticality indicator.  If
    the node is at depth x, the components of the node have the
    following semantics:
       (1)  The valid_policy is a single policy OID representing a
       valid policy for the path of length x.
       (2)  The qualifier_set is a set of policy qualifiers associated
       with the valid policy in certificate x.
       (3)  The criticality_indicator indicates whether the
       certificate policy extension in certificate x was marked as
       critical.
       (4)  The expected_policy_set contains one or more policy OIDs
       that would satisfy this policy in the certificate x+1.
    The initial value of the valid_policy_tree is a single node with
    valid_policy anyPolicy, an empty qualifier_set, an
    expected_policy_set with the single value anyPolicy, and a
    criticality_indicator of FALSE.  This node is considered to be at
    depth zero.
    Figure 3 is a graphic representation of the initial state of the
    valid_policy_tree.  Additional figures will use this format to
    describe changes in the valid_policy_tree during path processing.
            +----------------+
            |   anyPolicy    |   <---- valid_policy
            +----------------+
            |       {}       |   <---- qualifier_set
            +----------------+
            |     FALSE      |   <---- criticality_indicator
            +----------------+
            |  {anyPolicy}   |   <---- expected_policy_set
            +----------------+
    Figure 3.  Initial value of the valid_policy_tree state variable

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    (b) permitted_subtrees:  A set of root names for each name type
    (e.g., X.500 distinguished names, email addresses, or ip
    addresses) defining a set of subtrees within which all subject
    names in subsequent certificates in the certification path MUST
    fall.  This variable includes a set for each name type: the
    initial value for the set for Distinguished Names is the set of
    all Distinguished names; the initial value for the set of RFC822
    names is the set of all RFC822 names, etc.
    (c) excluded_subtrees:  A set of root names for each name type
    (e.g., X.500 distinguished names, email addresses, or ip
    addresses) defining a set of subtrees within which no subject name
    in subsequent certificates in the certification path may fall.
    This variable includes a set for each name type, and the initial
    value for each set is empty.
    (d) explicit_policy: an integer which indicates if a non-NULL
    valid_policy_tree is required. The integer indicates the number of
    non-self-issued certificates to be processed before this
    requirement is imposed.  Once set, this variable may be decreased,
    but may not be increased. That is, if a certificate in the path
    requires a non-NULL valid_policy_tree, a later certificate can not
    remove this requirement. If initial-explicit-policy is set, then
    the initial value is 0, otherwise the initial value is n+1.
    (e) inhibit_any-policy: an integer which indicates whether the
    anyPolicy policy identifier is considered a match. The integer
    indicates the number of non-self-issued certificates to be
    processed before the anyPolicy OID, if asserted in a certificate,
    is ignored. Once set, this variable may be decreased, but may not
    be increased. That is, if a certificate in the path inhibits
    processing of anyPolicy, a later certificate can not permit it.
    If initial-any-policy-inhibit is set, then the initial value is 0,
    otherwise the initial value is n+1.
    (f) policy_mapping: an integer which indicates if policy mapping
    is permitted.  The integer indicates the number of non-self-issued
    certificates to be processed before policy mapping is inhibited.
    Once set, this variable may be decreased, but may not be
    increased. That is, if a certificate in the path specifies policy
    mapping is not permitted, it can not be overridden by a later
    certificate. If initial-policy-mapping-inhibit is set, then the
    initial value is 0, otherwise the initial value is n+1.
    (g) working_public_key_algorithm: the digital signature algorithm
    used to verify the signature of a certificate.  The
    working_public_key_algorithm is initialized from the trusted
    public key algorithm provided in the trust anchor information.

Housley, et. al. Standards Track [Page 69] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (h) working_public_key: the public key used to verify the
    signature of a certificate.  The working_public_key is initialized
    from the trusted public key provided in the trust anchor
    information.
    (i) working_public_key_parameters:  parameters associated with the
    current public key, that may be required to verify a signature
    (depending upon the algorithm).  The working_public_key_parameters
    variable is initialized from the trusted public key parameters
    provided in the trust anchor information.
    (j) working_issuer_name:  the issuer distinguished name expected
    in the next certificate in the chain.  The working_issuer_name is
    initialized to the trusted issuer provided in the trust anchor
    information.
    (k) max_path_length:  this integer is initialized to n, is
    decremented for each non-self-issued certificate in the path, and
    may be reduced to the value in the path length constraint field
    within the basic constraints extension of a CA certificate.
 Upon completion of the initialization steps, perform the basic
 certificate processing steps specified in 6.1.3.

6.1.3 Basic Certificate Processing

 The basic path processing actions to be performed for certificate i
 (for all i in [1..n]) are listed below.
    (a)  Verify the basic certificate information.  The certificate
    MUST satisfy each of the following:
       (1)  The certificate was signed with the
       working_public_key_algorithm using the working_public_key and
       the working_public_key_parameters.
       (2)  The certificate validity period includes the current time.
       (3)  At the current time, the certificate is not revoked and is
       not on hold status.  This may be determined by obtaining the
       appropriate CRL (section 6.3), status information, or by out-
       of-band mechanisms.
       (4)  The certificate issuer name is the working_issuer_name.

Housley, et. al. Standards Track [Page 70] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (b)  If certificate i is self-issued and it is not the final
    certificate in the path, skip this step for certificate i.
    Otherwise, verify that the subject name is within one of the
    permitted_subtrees for X.500 distinguished names, and verify that
    each of the alternative names in the subjectAltName extension
    (critical or non-critical) is within one of the permitted_subtrees
    for that name type.
    (c)  If certificate i is self-issued and it is not the final
    certificate in the path, skip this step for certificate i.
    Otherwise, verify that the subject name is not within one of the
    excluded_subtrees for X.500 distinguished names, and verify that
    each of the alternative names in the subjectAltName extension
    (critical or non-critical) is not within one of the
    excluded_subtrees for that name type.
    (d)  If the certificate policies extension is present in the
    certificate and the valid_policy_tree is not NULL, process the
    policy information by performing the following steps in order:
       (1)  For each policy P not equal to anyPolicy in the
       certificate policies extension, let P-OID denote the OID in
       policy P and P-Q denote the qualifier set for policy P.
       Perform the following steps in order:
          (i)  If the valid_policy_tree includes a node of depth i-1
          where P-OID is in the expected_policy_set, create a child
          node as follows: set the valid_policy to OID-P; set the
          qualifier_set to P-Q, and set the expected_policy_set to
          {P-OID}.
          For example, consider a valid_policy_tree with a node of
          depth i-1 where the expected_policy_set is {Gold, White}.
          Assume the certificate policies Gold and Silver appear in
          the certificate policies extension of certificate i.  The
          Gold policy is matched but the Silver policy is not.  This
          rule will generate a child node of depth i for the Gold
          policy. The result is shown as Figure 4.

Housley, et. al. Standards Track [Page 71] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

                           +-----------------+
                           |       Red       |
                           +-----------------+
                           |       {}        |
                           +-----------------+   node of depth i-1
                           |      FALSE      |
                           +-----------------+
                           |  {Gold, White}  |
                           +-----------------+
                                    |
                                    |
                                    |
                                    V
                           +-----------------+
                           |      Gold       |
                           +-----------------+
                           |       {}        |
                           +-----------------+ node of depth i
                           |  uninitialized  |
                           +-----------------+
                           |     {Gold}      |
                           +-----------------+
                  Figure 4.  Processing an exact match
          (ii)  If there was no match in step (i) and the
          valid_policy_tree includes a node of depth i-1 with the
          valid policy anyPolicy, generate a child node with the
          following values: set the valid_policy to P-OID; set the
          qualifier_set to P-Q, and set the expected_policy_set to
          {P-OID}.
          For example, consider a valid_policy_tree with a node of
          depth i-1 where the valid_policy is anyPolicy.  Assume the
          certificate policies Gold and Silver appear in the
          certificate policies extension of certificate i.  The Gold
          policy does not have a qualifier, but the Silver policy has
          the qualifier Q-Silver.  If Gold and Silver were not matched
          in (i) above, this rule will generate two child nodes of
          depth i, one for each policy.  The result is shown as Figure
          5.

Housley, et. al. Standards Track [Page 72] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

                           +-----------------+
                           |    anyPolicy    |
                           +-----------------+
                           |       {}        |
                           +-----------------+ node of depth i-1
                           |      FALSE      |
                           +-----------------+
                           |   {anyPolicy}   |
                           +-----------------+
                              /           \
                             /             \
                            /               \
                           /                 \
             +-----------------+          +-----------------+
             |      Gold       |          |     Silver      |
             +-----------------+          +-----------------+
             |       {}        |          |   {Q-Silver}    |
             +-----------------+ nodes of +-----------------+
             | uninitialized   | depth i  | uninitialized   |
             +-----------------+          +-----------------+
             |     {Gold}      |          |    {Silver}     |
             +-----------------+          +-----------------+
             Figure 5.  Processing unmatched policies when a leaf node
             specifies anyPolicy
       (2)  If the certificate policies extension includes the policy
       anyPolicy with the qualifier set AP-Q and either (a)
       inhibit_any-policy is greater than 0 or (b) i<n and the
       certificate is self-issued, then:
       For each node in the valid_policy_tree of depth i-1, for each
       value in the expected_policy_set (including anyPolicy) that
       does not appear in a child node, create a child node with the
       following values: set the valid_policy to the value from the
       expected_policy_set in the parent node; set the qualifier_set
       to AP-Q, and set the expected_policy_set to the value in the
       valid_policy from this node.
       For example, consider a valid_policy_tree with a node of depth
       i-1 where the expected_policy_set is {Gold, Silver}.  Assume
       anyPolicy appears in the certificate policies extension of
       certificate i, but Gold and Silver do not.  This rule will
       generate two child nodes of depth i, one for each policy.  The
       result is shown below as Figure 6.

Housley, et. al. Standards Track [Page 73] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

                        +-----------------+
                        |      Red        |
                        +-----------------+
                        |       {}        |
                        +-----------------+ node of depth i-1
                        |      FALSE      |
                        +-----------------+
                        |  {Gold, Silver} |
                        +-----------------+
                           /           \
                          /             \
                         /               \
                        /                 \
          +-----------------+          +-----------------+
          |      Gold       |          |     Silver      |
          +-----------------+          +-----------------+
          |       {}        |          |       {}        |
          +-----------------+ nodes of +-----------------+
          |  uninitialized  | depth i  |  uninitialized  |
          +-----------------+          +-----------------+
          |     {Gold}      |          |    {Silver}     |
          +-----------------+          +-----------------+
       Figure 6.  Processing unmatched policies when the certificate
       policies extension specifies anyPolicy
       (3)  If there is a node in the valid_policy_tree of depth i-1
       or less without any child nodes, delete that node.  Repeat this
       step until there are no nodes of depth i-1 or less without
       children.
       For example, consider the valid_policy_tree shown in Figure 7
       below.  The two nodes at depth i-1 that are marked with an 'X'
       have no children, and are deleted.  Applying this rule to the
       resulting tree will cause the node at depth i-2 that is marked
       with an 'Y' to be deleted.  The following application of the
       rule does not cause any nodes to be deleted, and this step is
       complete.

Housley, et. al. Standards Track [Page 74] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

                            +-----------+
                            |           | node of depth i-3
                            +-----------+
                            /     |     \
                           /      |      \
                          /       |       \
              +-----------+ +-----------+ +-----------+
              |           | |           | |     Y     | nodes of
              +-----------+ +-----------+ +-----------+ depth i-2
              /   \               |             |
             /     \              |             |
            /       \             |             |
 +-----------+ +-----------+ +-----------+ +-----------+ nodes of
 |           | |     X     | |           | |    X      |  depth
 +-----------+ +-----------+ +-----------+ +-----------+   i-1
       |                      /    |    \
       |                     /     |     \
       |                    /      |      \
 +-----------+ +-----------+ +-----------+ +-----------+ nodes of
 |           | |           | |           | |           |  depth
 +-----------+ +-----------+ +-----------+ +-----------+   i
        Figure 7.  Pruning the valid_policy_tree
       (4)  If the certificate policies extension was marked as
       critical, set the criticality_indicator in all nodes of depth i
       to TRUE.  If the certificate policies extension was not marked
       critical, set the criticality_indicator in all nodes of depth i
       to FALSE.
    (e)  If the certificate policies extension is not present, set the
    valid_policy_tree to NULL.
    (f)  Verify that either explicit_policy is greater than 0 or the
    valid_policy_tree is not equal to NULL;
 If any of steps (a), (b), (c), or (f) fails, the procedure
 terminates, returning a failure indication and an appropriate reason.
 If i is not equal to n, continue by performing the preparatory steps
 listed in 6.1.4.  If i is equal to n, perform the wrap-up steps
 listed in 6.1.5.

6.1.4 Preparation for Certificate i+1

 To prepare for processing of certificate i+1, perform the following
 steps for certificate i:

Housley, et. al. Standards Track [Page 75] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (a)  If a policy mapping extension is present, verify that the
    special value anyPolicy does not appear as an issuerDomainPolicy
    or a subjectDomainPolicy.
    (b)  If a policy mapping extension is present, then for each
    issuerDomainPolicy ID-P in the policy mapping extension:
       (1)  If the policy_mapping variable is greater than 0, for each
       node in the valid_policy_tree of depth i where ID-P is the
       valid_policy, set expected_policy_set to the set of
       subjectDomainPolicy values that are specified as equivalent to
       ID-P by the policy mapping extension.
       If no node of depth i in the valid_policy_tree has a
       valid_policy of ID-P but there is a node of depth i with a
       valid_policy of anyPolicy, then generate a child node of the
       node of depth i-1 that has a valid_policy of anyPolicy as
       follows:
          (i)  set the valid_policy to ID-P;
          (ii)  set the qualifier_set to the qualifier set of the
          policy anyPolicy in the certificate policies extension of
          certificate i;
          (iii)  set the criticality_indicator to the criticality of
          the certificate policies extension of certificate i;
          (iv)  and set the expected_policy_set to the set of
          subjectDomainPolicy values that are specified as equivalent
          to ID-P by the policy mappings extension.
       (2)  If the policy_mapping variable is equal to 0:
          (i)  delete each node of depth i in the valid_policy_tree
          where ID-P is the valid_policy.
          (ii)  If there is a node in the valid_policy_tree of depth
          i-1 or less without any child nodes, delete that node.
          Repeat this step until there are no nodes of depth i-1 or
          less without children.
    (c)  Assign the certificate subject name to working_issuer_name.
    (d)  Assign the certificate subjectPublicKey to
    working_public_key.

Housley, et. al. Standards Track [Page 76] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (e)  If the subjectPublicKeyInfo field of the certificate contains
    an algorithm field with non-null parameters, assign the parameters
    to the working_public_key_parameters variable.
    If the subjectPublicKeyInfo field of the certificate contains an
    algorithm field with null parameters or parameters are omitted,
    compare the certificate subjectPublicKey algorithm to the
    working_public_key_algorithm.  If the certificate subjectPublicKey
    algorithm and the working_public_key_algorithm are different, set
    the working_public_key_parameters to null.
    (f)  Assign the certificate subjectPublicKey algorithm to the
    working_public_key_algorithm variable.
    (g)  If a name constraints extension is included in the
    certificate, modify the permitted_subtrees and excluded_subtrees
    state variables as follows:
       (1)  If permittedSubtrees is present in the certificate, set
       the permitted_subtrees state variable to the intersection of
       its previous value and the value indicated in the extension
       field.  If permittedSubtrees does not include a particular name
       type, the permitted_subtrees state variable is unchanged for
       that name type.  For example, the intersection of nist.gov and
       csrc.nist.gov is csrc.nist.gov.  And, the intersection of
       nist.gov and rsasecurity.com is the empty set.
       (2)  If excludedSubtrees is present in the certificate, set the
       excluded_subtrees state variable to the union of its previous
       value and the value indicated in the extension field.  If
       excludedSubtrees does not include a particular name type, the
       excluded_subtrees state variable is unchanged for that name
       type.  For example, the union of the name spaces nist.gov and
       csrc.nist.gov is nist.gov.  And, the union of nist.gov and
       rsasecurity.com is both name spaces.
    (h)  If the issuer and subject names are not identical:
       (1)  If explicit_policy is not 0, decrement explicit_policy by
       1.
       (2)  If policy_mapping is not 0, decrement policy_mapping by 1.
       (3)  If inhibit_any-policy is not 0, decrement inhibit_any-
       policy by 1.

Housley, et. al. Standards Track [Page 77] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (i)  If a policy constraints extension is included in the
    certificate, modify the explicit_policy and policy_mapping state
    variables as follows:
       (1)  If requireExplicitPolicy is present and is less than
       explicit_policy, set explicit_policy to the value of
       requireExplicitPolicy.
       (2)  If inhibitPolicyMapping is present and is less than
       policy_mapping, set policy_mapping to the value of
       inhibitPolicyMapping.
    (j)  If the inhibitAnyPolicy extension is included in the
    certificate and is less than inhibit_any-policy, set inhibit_any-
    policy to the value of inhibitAnyPolicy.
    (k)  Verify that the certificate is a CA certificate (as specified
    in a basicConstraints extension or as verified out-of-band).
    (l)  If the certificate was not self-issued, verify that
    max_path_length is greater than zero and decrement max_path_length
    by 1.
    (m)  If pathLengthConstraint is present in the certificate and is
    less than max_path_length, set max_path_length to the value of
    pathLengthConstraint.
    (n)  If a key usage extension is present, verify that the
    keyCertSign bit is set.
    (o)  Recognize and process any other critical extension present in
    the certificate.  Process any other recognized non-critical
    extension present in the certificate.
 If check (a), (k), (l), (n) or (o) fails, the procedure terminates,
 returning a failure indication and an appropriate reason.
 If (a), (k), (l), (n) and (o) have completed successfully, increment
 i and perform the basic certificate processing specified in 6.1.3.

6.1.5 Wrap-up procedure

 To complete the processing of the end entity certificate, perform the
 following steps for certificate n:
    (a)  If certificate n was not self-issued and explicit_policy is
    not 0, decrement explicit_policy by 1.

Housley, et. al. Standards Track [Page 78] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (b)  If a policy constraints extension is included in the
    certificate and requireExplicitPolicy is present and has a value
    of 0, set the explicit_policy state variable to 0.
    (c)  Assign the certificate subjectPublicKey to
    working_public_key.
    (d)  If the subjectPublicKeyInfo field of the certificate contains
    an algorithm field with non-null parameters, assign the parameters
    to the working_public_key_parameters variable.
    If the subjectPublicKeyInfo field of the certificate contains an
    algorithm field with null parameters or parameters are omitted,
    compare the certificate subjectPublicKey algorithm to the
    working_public_key_algorithm.  If the certificate subjectPublicKey
    algorithm and the working_public_key_algorithm are different, set
    the working_public_key_parameters to null.
    (e)  Assign the certificate subjectPublicKey algorithm to the
    working_public_key_algorithm variable.
    (f)  Recognize and process any other critical extension present in
    the certificate n.  Process any other recognized non-critical
    extension present in certificate n.
    (g)  Calculate the intersection of the valid_policy_tree and the
    user-initial-policy-set, as follows:
       (i)  If the valid_policy_tree is NULL, the intersection is
       NULL.
       (ii)  If the valid_policy_tree is not NULL and the user-
       initial-policy-set is any-policy, the intersection is the
       entire valid_policy_tree.
       (iii)  If the valid_policy_tree is not NULL and the user-
       initial-policy-set is not any-policy, calculate the
       intersection of the valid_policy_tree and the user-initial-
       policy-set as follows:
          1.  Determine the set of policy nodes whose parent nodes
          have a valid_policy of anyPolicy.  This is the
          valid_policy_node_set.
          2.  If the valid_policy of any node in the
          valid_policy_node_set is not in the user-initial-policy-set
          and is not anyPolicy, delete this node and all its children.

Housley, et. al. Standards Track [Page 79] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

          3.  If the valid_policy_tree includes a node of depth n with
          the valid_policy anyPolicy and the user-initial-policy-set
          is not any-policy perform the following steps:
             a. Set P-Q to the qualifier_set in the node of depth n
             with valid_policy anyPolicy.
             b. For each P-OID in the user-initial-policy-set that is
             not the valid_policy of a node in the
             valid_policy_node_set, create a child node whose parent
             is the node of depth n-1 with the valid_policy anyPolicy.
             Set the values in the child node as follows: set the
             valid_policy to P-OID; set the qualifier_set to P-Q; copy
             the criticality_indicator from the node of depth n with
             the valid_policy anyPolicy; and set the
             expected_policy_set to {P-OID}.
             c.  Delete the node of depth n with the valid_policy
             anyPolicy.
          4.  If there is a node in the valid_policy_tree of depth n-1
          or less without any child nodes, delete that node.  Repeat
          this step until there are no nodes of depth n-1 or less
          without children.
 If either (1) the value of explicit_policy variable is greater than
 zero, or (2) the valid_policy_tree is not NULL, then path processing
 has succeeded.

6.1.6 Outputs

 If path processing succeeds, the procedure terminates, returning a
 success indication together with final value of the
 valid_policy_tree, the working_public_key, the
 working_public_key_algorithm, and the working_public_key_parameters.

6.2 Using the Path Validation Algorithm

 The path validation algorithm describes the process of validating a
 single certification path.  While each certification path begins with
 a specific trust anchor, there is no requirement that all
 certification paths validated by a particular system share a single
 trust anchor.  An implementation that supports multiple trust anchors
 MAY augment the algorithm presented in section 6.1 to further limit
 the set of valid certification paths which begin with a particular
 trust anchor.  For example, an implementation MAY modify the
 algorithm to apply name constraints to a specific trust anchor during
 the initialization phase, or the application MAY require the presence

Housley, et. al. Standards Track [Page 80] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 of a particular alternative name form in the end entity certificate,
 or the application MAY impose requirements on application-specific
 extensions.  Thus, the path validation algorithm presented in section
 6.1 defines the minimum conditions for a path to be considered valid.
 The selection of one or more trusted CAs is a local decision.  A
 system may provide any one of its trusted CAs as the trust anchor for
 a particular path.  The inputs to the path validation algorithm may
 be different for each path.  The inputs used to process a path may
 reflect application-specific requirements or limitations in the trust
 accorded a particular trust anchor.  For example, a trusted CA may
 only be trusted for a particular certificate policy.  This
 restriction can be expressed through the inputs to the path
 validation procedure.
 It is also possible to specify an extended version of the above
 certification path processing procedure which results in default
 behavior identical to the rules of PEM [RFC 1422].  In this extended
 version, additional inputs to the procedure are a list of one or more
 Policy Certification Authority (PCA) names and an indicator of the
 position in the certification path where the PCA is expected.  At the
 nominated PCA position, the CA name is compared against this list.
 If a recognized PCA name is found, then a constraint of
 SubordinateToCA is implicitly assumed for the remainder of the
 certification path and processing continues.  If no valid PCA name is
 found, and if the certification path cannot be validated on the basis
 of identified policies, then the certification path is considered
 invalid.

6.3 CRL Validation

 This section describes the steps necessary to determine if a
 certificate is revoked or on hold status when CRLs are the revocation
 mechanism used by the certificate issuer.  Conforming implementations
 that support CRLs are not required to implement this algorithm, but
 they MUST be functionally equivalent to the external behavior
 resulting from this procedure.  Any algorithm may be used by a
 particular implementation so long as it derives the correct result.
 This algorithm assumes that all of the needed CRLs are available in a
 local cache.  Further, if the next update time of a CRL has passed,
 the algorithm assumes a mechanism to fetch a current CRL and place it
 in the local CRL cache.
 This algorithm defines a set of inputs, a set of state variables, and
 processing steps that are performed for each certificate in the path.
 The algorithm output is the revocation status of the certificate.

Housley, et. al. Standards Track [Page 81] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

6.3.1 Revocation Inputs

 To support revocation processing, the algorithm requires two inputs:
    (a)  certificate:  The algorithm requires the certificate serial
    number and issuer name to determine whether a certificate is on a
    particular CRL.  The basicConstraints extension is used to
    determine whether the supplied certificate is associated with a CA
    or an end entity.  If present, the algorithm uses the
    cRLDistributionsPoint and freshestCRL extensions to determine
    revocation status.
    (b)  use-deltas:  This boolean input determines whether delta CRLs
    are applied to CRLs.
    Note that implementations supporting legacy PKIs, such as RFC 1422
    and X.509 version 1, will need an additional input indicating
    whether the supplied certificate is associated with a CA or an end
    entity.

6.3.2 Initialization and Revocation State Variables

 To support CRL processing, the algorithm requires the following state
 variables:
    (a)  reasons_mask:  This variable contains the set of revocation
    reasons supported by the CRLs and delta CRLs processed so far.
    The legal members of the set are the possible revocation reason
    values: unspecified, keyCompromise, caCompromise,
    affiliationChanged, superseded, cessationOfOperation,
    certificateHold, privilegeWithdrawn, and aACompromise.  The
    special value all-reasons is used to denote the set of all legal
    members.  This variable is initialized to the empty set.
    (b)  cert_status:  This variable contains the status of the
    certificate.  This variable may be assigned one of the following
    values: unspecified, keyCompromise, caCompromise,
    affiliationChanged, superseded, cessationOfOperation,
    certificateHold, removeFromCRL, privilegeWithdrawn, aACompromise,
    the special value UNREVOKED, or the special value UNDETERMINED.
    This variable is initialized to the special value UNREVOKED.
    (c)  interim_reasons_mask:  This contains the set of revocation
    reasons supported by the CRL or delta CRL currently being
    processed.

Housley, et. al. Standards Track [Page 82] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 Note: In some environments, it is not necessary to check all reason
 codes.  For example, some environments are only concerned with
 caCompromise and keyCompromise for CA certificates.  This algorithm
 checks all reason codes.  Additional processing and state variables
 may be necessary to limit the checking to a subset of the reason
 codes.

6.3.3 CRL Processing

 This algorithm begins by assuming the certificate is not revoked.
 The algorithm checks one or more CRLs until either the certificate
 status is determined to be revoked or sufficient CRLs have been
 checked to cover all reason codes.
 For each distribution point (DP) in the certificate CRL distribution
 points extension, for each corresponding CRL in the local CRL cache,
 while ((reasons_mask is not all-reasons) and (cert_status is
 UNREVOKED)) perform the following:
    (a)  Update the local CRL cache by obtaining a complete CRL, a
    delta CRL, or both, as required:
       (1)  If the current time is after the value of the CRL next
       update field, then do one of the following:
          (i)  If use-deltas is set and either the certificate or the
          CRL contains the freshest CRL extension, obtain a delta CRL
          with the a next update value that is after the current time
          and can be used to update the locally cached CRL as
          specified in section 5.2.4.
          (ii)  Update the local CRL cache with a current complete
          CRL, verify that the current time is before the next update
          value in the new CRL, and continue processing with the new
          CRL.  If use-deltas is set, then obtain the current delta
          CRL that can be used to update the new locally cached
          complete CRL as specified in section 5.2.4.
       (2)  If the current time is before the value of the next update
       field and use-deltas is set, then obtain the current delta CRL
       that can be used to update the locally cached complete CRL as
       specified in section 5.2.4.
    (b)  Verify the issuer and scope of the complete CRL as follows:

Housley, et. al. Standards Track [Page 83] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

       (1)  If the DP includes cRLIssuer, then verify that the issuer
       field in the complete CRL matches cRLIssuer in the DP and that
       the complete CRL contains an issuing distribution point
       extension with the indrectCRL boolean asserted.  Otherwise,
       verify that the CRL issuer matches the certificate issuer.
       (2)  If the complete CRL includes an issuing distribution point
       (IDP) CRL extension check the following:
          (i)  If the distribution point name is present in the IDP
          CRL extension and the distribution field is present in the
          DP, then verify that one of the names in the IDP matches one
          of the names in the DP.  If the distribution point name is
          present in the IDP CRL extension and the distribution field
          is omitted from the DP, then verify that one of the names in
          the IDP matches one of the names in the cRLIssuer field of
          the DP.
          (ii)  If the onlyContainsUserCerts boolean is asserted in
          the IDP CRL extension, verify that the certificate does not
          include the basic constraints extension with the cA boolean
          asserted.
          (iii)  If the onlyContainsCACerts boolean is asserted in the
          IDP CRL extension, verify that the certificate includes the
          basic constraints extension with the cA boolean asserted.
          (iv)  Verify that the onlyContainsAttributeCerts boolean is
          not asserted.
    (c)  If use-deltas is set, verify the issuer and scope of the
    delta CRL as follows:
       (1)  Verify that the delta CRL issuer matches complete CRL
       issuer.
       (2)  If the complete CRL includes an issuing distribution point
       (IDP) CRL extension, verify that the delta CRL contains a
       matching IDP CRL extension.  If the complete CRL omits an IDP
       CRL extension, verify that the delta CRL also omits an IDP CRL
       extension.
       (3)  Verify that the delta CRL authority key identifier
       extension matches complete CRL authority key identifier
       extension.

Housley, et. al. Standards Track [Page 84] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 (d)  Compute the interim_reasons_mask for this CRL as follows:
       (1)  If the issuing distribution point (IDP) CRL extension is
       present and includes onlySomeReasons and the DP includes
       reasons, then set interim_reasons_mask to the intersection of
       reasons in the DP and onlySomeReasons in IDP CRL extension.
       (2)  If the IDP CRL extension includes onlySomeReasons but the
       DP omits reasons, then set interim_reasons_mask to the value of
       onlySomeReasons in IDP CRL extension.
       (3)  If the IDP CRL extension is not present or omits
       onlySomeReasons but the DP includes reasons, then set
       interim_reasons_mask to the value of DP reasons.
       (4)  If the IDP CRL extension is not present or omits
       onlySomeReasons and the DP omits reasons, then set
       interim_reasons_mask to the special value all-reasons.
 (e)  Verify that interim_reasons_mask includes one or more reasons
 that is not included in the reasons_mask.
 (f)  Obtain and validate the certification path for the complete CRL
 issuer.  If a key usage extension is present in the CRL issuer's
 certificate, verify that the cRLSign bit is set.
 (g)  Validate the signature on the complete CRL using the public key
 validated in step (f).
 (h)  If use-deltas is set, then validate the signature on the delta
 CRL using the public key validated in step (f).
 (i)  If use-deltas is set, then search for the certificate on the
 delta CRL.  If an entry is found that matches the certificate issuer
 and serial number as described in section 5.3.4, then set the
 cert_status variable to the indicated reason as follows:
       (1)  If the reason code CRL entry extension is present, set the
       cert_status variable to the value of the reason code CRL entry
       extension.
       (2)  If the reason code CRL entry extension is not present, set
       the cert_status variable to the value unspecified.

Housley, et. al. Standards Track [Page 85] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (j)  If (cert_status is UNREVOKED), then search for the
    certificate on the complete CRL.  If an entry is found that
    matches the certificate issuer and serial number as described in
    section 5.3.4, then set the cert_status variable to the indicated
    reason as described in step (i).
    (k)  If (cert_status is removeFromCRL), then set cert_status to
    UNREVOKED.
 If ((reasons_mask is all-reasons) OR (cert_status is not UNREVOKED)),
 then the revocation status has been determined, so return
 cert_status.
 If the revocation status has not been determined, repeat the process
 above with any available CRLs not specified in a distribution point
 but issued by the certificate issuer.  For the processing of such a
 CRL, assume a DP with both the reasons and the cRLIssuer fields
 omitted and a distribution point name of the certificate issuer.
 That is, the sequence of names in fullName is generated from the
 certificate issuer field as well as the certificate issuerAltName
 extension.  If the revocation status remains undetermined, then
 return the cert_status UNDETERMINED.

7 References

 [ISO 10646] ISO/IEC 10646-1:1993.  International Standard --
             Information technology -- Universal Multiple-Octet Coded
             Character Set (UCS) -- Part 1: Architecture and Basic
             Multilingual Plane.
 [RFC 791]   Postel, J.,  "Internet Protocol", STD 5, RFC 791,
             September 1981.
 [RFC 822]   Crocker, D., "Standard for the format of ARPA Internet
             text messages", STD 11, RFC 822, August 1982.
 [RFC 1034]  Mockapetris, P., "Domain Names - Concepts and
             Facilities", STD 13, RFC 1034, November 1987.
 [RFC 1422]  Kent, S., "Privacy Enhancement for Internet Electronic
             Mail: Part II: Certificate-Based Key Management," RFC
             1422, February 1993.
 [RFC 1423]  Balenson, D., "Privacy Enhancement for Internet
             Electronic Mail: Part III: Algorithms, Modes, and
             Identifiers," RFC 1423, February 1993.

Housley, et. al. Standards Track [Page 86] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 [RFC 1510]  Kohl, J. and C. Neuman, "The Kerberos Network
             Authentication Service (V5)," RFC 1510, September 1993.
 [RFC 1519]  Fuller, V., T. Li, J. Yu and K. Varadhan, "Classless
             Inter-Domain Routing (CIDR): An Address Assignment and
             Aggregation Strategy", RFC 1519, September 1993.
 [RFC 1738]  Berners-Lee, T., L. Masinter and M. McCahill, "Uniform
             Resource Locators (URL)", RFC 1738, December 1994.
 [RFC 1778]  Howes, T., S. Kille, W. Yeong and C. Robbins, "The String
             Representation of Standard Attribute Syntaxes," RFC 1778,
             March 1995.
 [RFC 1883]  Deering, S. and R. Hinden.  "Internet Protocol, Version 6
             (IPv6) Specification", RFC 1883, December 1995.
 [RFC 2044]  F. Yergeau, F., "UTF-8, a transformation format of
             Unicode and ISO 10646", RFC 2044, October 1996.
 [RFC 2119]  Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC 2247]  Kille, S., M. Wahl, A. Grimstad, R. Huber and S.
             Sataluri, "Using Domains in LDAP/X.500 Distinguished
             Names", RFC 2247, January 1998.
 [RFC 2252]  Wahl, M., A. Coulbeck, T. Howes and S. Kille,
             "Lightweight Directory Access Protocol (v3):  Attribute
             Syntax Definitions", RFC 2252, December 1997.
 [RFC 2277]  Alvestrand, H., "IETF Policy on Character Sets and
             Languages", BCP 18, RFC 2277, January 1998.
 [RFC 2279]  Yergeau, F., "UTF-8, a transformation format of ISO
             10646", RFC 2279, January 1998.
 [RFC 2459]  Housley, R., W. Ford, W. Polk and D. Solo, "Internet
             X.509 Public Key Infrastructure: Certificate and CRL
             Profile", RFC 2459, January 1999.
 [RFC 2560]  Myers, M., R. Ankney, A. Malpani, S. Galperin and C.
             Adams, "Online Certificate Status Protocal - OCSP", June
             1999.
 [SDN.701]   SDN.701, "Message Security Protocol 4.0", Revision A,
             1997-02-06.

Housley, et. al. Standards Track [Page 87] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 [X.501]     ITU-T Recommendation X.501: Information Technology - Open
             Systems Interconnection - The Directory: Models, 1993.
 [X.509]     ITU-T Recommendation X.509 (1997 E): Information
             Technology - Open Systems Interconnection - The
             Directory: Authentication Framework, June 1997.
 [X.520]     ITU-T Recommendation X.520: Information Technology - Open
             Systems Interconnection - The Directory: Selected
             Attribute Types, 1993.
 [X.660]     ITU-T Recommendation X.660 Information Technology - ASN.1
             encoding rules: Specification of Basic Encoding Rules
             (BER), Canonical Encoding Rules (CER) and Distinguished
             Encoding Rules (DER), 1997.
 [X.690]     ITU-T Recommendation X.690 Information Technology - Open
             Systems Interconnection - Procedures for the operation of
             OSI Registration Authorities: General procedures, 1992.
 [X9.55]     ANSI X9.55-1995, Public Key Cryptography For The
             Financial Services Industry: Extensions To Public Key
             Certificates And Certificate Revocation Lists, 8
             December, 1995.
 [PKIXALGS]  Bassham, L., Polk, W. and R. Housley, "Algorithms and
             Identifiers for the Internet X.509 Public Key
             Infrastructure Certificate and Certificate Revocation
             Lists (CRL) Profile", RFC 3279, April 2002.
 [PKIXTSA]   Adams, C., Cain, P., Pinkas, D. and R. Zuccherato,
             "Internet X.509 Public Key Infrastructure Time-Stamp
             Protocol (TSP)", RFC 3161, August 2001.

8 Intellectual Property Rights

 The IETF has been notified of intellectual property rights claimed in
 regard to some or all of the specification contained in this
 document.  For more information consult the online list of claimed
 rights (see http://www.ietf.org/ipr.html).
 The IETF takes no position regarding the validity or scope of any
 intellectual property or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; neither does it represent that it
 has made any effort to identify any such rights.  Information on the
 IETF's procedures with respect to rights in standards-track and

Housley, et. al. Standards Track [Page 88] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 standards-related documentation can be found in BCP 11.  Copies of
 claims of rights made available for publication and any assurances of
 licenses to be made available, or the result of an attempt made to
 obtain a general license or permission for the use of such
 proprietary rights by implementors or users of this specification can
 be obtained from the IETF Secretariat.

9 Security Considerations

 The majority of this specification is devoted to the format and
 content of certificates and CRLs.  Since certificates and CRLs are
 digitally signed, no additional integrity service is necessary.
 Neither certificates nor CRLs need be kept secret, and unrestricted
 and anonymous access to certificates and CRLs has no security
 implications.
 However, security factors outside the scope of this specification
 will affect the assurance provided to certificate users.  This
 section highlights critical issues to be considered by implementers,
 administrators, and users.
 The procedures performed by CAs and RAs to validate the binding of
 the subject's identity to their public key greatly affect the
 assurance that ought to be placed in the certificate.  Relying
 parties might wish to review the CA's certificate practice statement.
 This is particularly important when issuing certificates to other
 CAs.
 The use of a single key pair for both signature and other purposes is
 strongly discouraged.  Use of separate key pairs for signature and
 key management provides several benefits to the users.  The
 ramifications associated with loss or disclosure of a signature key
 are different from loss or disclosure of a key management key.  Using
 separate key pairs permits a balanced and flexible response.
 Similarly, different validity periods or key lengths for each key
 pair may be appropriate in some application environments.
 Unfortunately, some legacy applications (e.g., SSL) use a single key
 pair for signature and key management.
 The protection afforded private keys is a critical security factor.
 On a small scale, failure of users to protect their private keys will
 permit an attacker to masquerade as them, or decrypt their personal
 information.  On a larger scale, compromise of a CA's private signing
 key may have a catastrophic effect.  If an attacker obtains the
 private key unnoticed, the attacker may issue bogus certificates and
 CRLs.  Existence of bogus certificates and CRLs will undermine
 confidence in the system.  If such a compromise is detected, all
 certificates issued to the compromised CA MUST be revoked, preventing

Housley, et. al. Standards Track [Page 89] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 services between its users and users of other CAs.  Rebuilding after
 such a compromise will be problematic, so CAs are advised to
 implement a combination of strong technical measures (e.g., tamper-
 resistant cryptographic modules) and appropriate management
 procedures (e.g., separation of duties) to avoid such an incident.
 Loss of a CA's private signing key may also be problematic.  The CA
 would not be able to produce CRLs or perform normal key rollover.
 CAs SHOULD maintain secure backup for signing keys.  The security of
 the key backup procedures is a critical factor in avoiding key
 compromise.
 The availability and freshness of revocation information affects the
 degree of assurance that ought to be placed in a certificate.  While
 certificates expire naturally, events may occur during its natural
 lifetime which negate the binding between the subject and public key.
 If revocation information is untimely or unavailable, the assurance
 associated with the binding is clearly reduced.  Relying parties
 might not be able to process every critical extension that can appear
 in a CRL.  CAs SHOULD take extra care when making revocation
 information available only through CRLs that contain critical
 extensions, particularly if support for those extensions is not
 mandated by this profile.  For example, if revocation information is
 supplied using a combination of delta CRLs and full CRLs, and the
 delta CRLs are issued more frequently than the full CRLs, then
 relying parties that cannot handle the critical extensions related to
 delta CRL processing will not be able to obtain the most recent
 revocation information.  Alternatively, if a full CRL is issued
 whenever a delta CRL is issued, then timely revocation information
 will be available to all relying parties.  Similarly, implementations
 of the certification path validation mechanism described in section 6
 that omit revocation checking provide less assurance than those that
 support it.
 The certification path validation algorithm depends on the certain
 knowledge of the public keys (and other information) about one or
 more trusted CAs.  The decision to trust a CA is an important
 decision as it ultimately determines the trust afforded a
 certificate.  The authenticated distribution of trusted CA public
 keys (usually in the form of a "self-signed" certificate) is a
 security critical out-of-band process that is beyond the scope of
 this specification.
 In addition, where a key compromise or CA failure occurs for a
 trusted CA, the user will need to modify the information provided to
 the path validation routine.  Selection of too many trusted CAs makes

Housley, et. al. Standards Track [Page 90] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 the trusted CA information difficult to maintain.  On the other hand,
 selection of only one trusted CA could limit users to a closed
 community of users.
 The quality of implementations that process certificates also affects
 the degree of assurance provided.  The path validation algorithm
 described in section 6 relies upon the integrity of the trusted CA
 information, and especially the integrity of the public keys
 associated with the trusted CAs.  By substituting public keys for
 which an attacker has the private key, an attacker could trick the
 user into accepting false certificates.
 The binding between a key and certificate subject cannot be stronger
 than the cryptographic module implementation and algorithms used to
 generate the signature.  Short key lengths or weak hash algorithms
 will limit the utility of a certificate.  CAs are encouraged to note
 advances in cryptology so they can employ strong cryptographic
 techniques.  In addition, CAs SHOULD decline to issue certificates to
 CAs or end entities that generate weak signatures.
 Inconsistent application of name comparison rules can result in
 acceptance of invalid X.509 certification paths, or rejection of
 valid ones.  The X.500 series of specifications defines rules for
 comparing distinguished names that require comparison of strings
 without regard to case, character set, multi-character white space
 substring, or leading and trailing white space.  This specification
 relaxes these requirements, requiring support for binary comparison
 at a minimum.
 CAs MUST encode the distinguished name in the subject field of a CA
 certificate identically to the distinguished name in the issuer field
 in certificates issued by that CA.  If CAs use different encodings,
 implementations might fail to recognize name chains for paths that
 include this certificate.  As a consequence, valid paths could be
 rejected.
 In addition, name constraints for distinguished names MUST be stated
 identically to the encoding used in the subject field or
 subjectAltName extension.  If not, then name constraints stated as
 excludedSubTrees will not match and invalid paths will be accepted
 and name constraints expressed as permittedSubtrees will not match
 and valid paths will be rejected.  To avoid acceptance of invalid
 paths, CAs SHOULD state name constraints for distinguished names as
 permittedSubtrees wherever possible.

Housley, et. al. Standards Track [Page 91] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

Appendix A. Psuedo-ASN.1 Structures and OIDs

 This section describes data objects used by conforming PKI components
 in an "ASN.1-like" syntax.  This syntax is a hybrid of the 1988 and
 1993 ASN.1 syntaxes.  The 1988 ASN.1 syntax is augmented with 1993
 UNIVERSAL Types UniversalString, BMPString and UTF8String.
 The ASN.1 syntax does not permit the inclusion of type statements in
 the ASN.1 module, and the 1993 ASN.1 standard does not permit use of
 the new UNIVERSAL types in modules using the 1988 syntax.  As a
 result, this module does not conform to either version of the ASN.1
 standard.
 This appendix may be converted into 1988 ASN.1 by replacing the
 definitions for the UNIVERSAL Types with the 1988 catch-all "ANY".

A.1 Explicitly Tagged Module, 1988 Syntax

PKIX1Explicit88 { iso(1) identified-organization(3) dod(6) internet(1)

security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18) }

DEFINITIONS EXPLICIT TAGS ::=

BEGIN

– EXPORTS ALL –

– IMPORTS NONE –

– UNIVERSAL Types defined in 1993 and 1998 ASN.1 – and required by this specification

UniversalString ::= [UNIVERSAL 28] IMPLICIT OCTET STRING

  1. - UniversalString is defined in ASN.1:1993

BMPString ::= [UNIVERSAL 30] IMPLICIT OCTET STRING

  1. - BMPString is the subtype of UniversalString and models
  2. - the Basic Multilingual Plane of ISO/IEC/ITU 10646-1

UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING

  1. - The content of this type conforms to RFC 2279.

– PKIX specific OIDs

id-pkix OBJECT IDENTIFIER ::=

       { iso(1) identified-organization(3) dod(6) internet(1)
                  security(5) mechanisms(5) pkix(7) }

Housley, et. al. Standards Track [Page 92] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

– PKIX arcs

id-pe OBJECT IDENTIFIER ::= { id-pkix 1 }

  1. - arc for private certificate extensions

id-qt OBJECT IDENTIFIER ::= { id-pkix 2 }

  1. - arc for policy qualifier types

id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }

  1. - arc for extended key purpose OIDS

id-ad OBJECT IDENTIFIER ::= { id-pkix 48 }

  1. - arc for access descriptors

– policyQualifierIds for Internet policy qualifiers

id-qt-cps OBJECT IDENTIFIER ::= { id-qt 1 }

  1. - OID for CPS qualifier

id-qt-unotice OBJECT IDENTIFIER ::= { id-qt 2 }

  1. - OID for user notice qualifier

– access descriptor definitions

id-ad-ocsp OBJECT IDENTIFIER ::= { id-ad 1 } id-ad-caIssuers OBJECT IDENTIFIER ::= { id-ad 2 } id-ad-timeStamping OBJECT IDENTIFIER ::= { id-ad 3 } id-ad-caRepository OBJECT IDENTIFIER ::= { id-ad 5 }

– attribute data types

Attribute ::= SEQUENCE {

    type              AttributeType,
    values    SET OF AttributeValue }
          -- at least one value is required

AttributeType ::= OBJECT IDENTIFIER

AttributeValue ::= ANY

AttributeTypeAndValue ::= SEQUENCE {

      type    AttributeType,
      value   AttributeValue }

– suggested naming attributes: Definition of the following – information object set may be augmented to meet local – requirements. Note that deleting members of the set may – prevent interoperability with conforming implementations. – presented in pairs: the AttributeType followed by the – type definition for the corresponding AttributeValue –Arc for standard naming attributes id-at OBJECT IDENTIFIER ::= { joint-iso-ccitt(2) ds(5) 4 }

Housley, et. al. Standards Track [Page 93] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

– Naming attributes of type X520name

id-at-name AttributeType ::= { id-at 41 } id-at-surname AttributeType ::= { id-at 4 } id-at-givenName AttributeType ::= { id-at 42 } id-at-initials AttributeType ::= { id-at 43 } id-at-generationQualifier AttributeType ::= { id-at 44 }

X520name ::= CHOICE {

    teletexString     TeletexString   (SIZE (1..ub-name)),
    printableString   PrintableString (SIZE (1..ub-name)),
    universalString   UniversalString (SIZE (1..ub-name)),
    utf8String        UTF8String      (SIZE (1..ub-name)),
    bmpString         BMPString       (SIZE (1..ub-name)) }

– Naming attributes of type X520CommonName

id-at-commonName AttributeType ::= { id-at 3 }

X520CommonName ::= CHOICE {

    teletexString     TeletexString   (SIZE (1..ub-common-name)),
    printableString   PrintableString (SIZE (1..ub-common-name)),
    universalString   UniversalString (SIZE (1..ub-common-name)),
    utf8String        UTF8String      (SIZE (1..ub-common-name)),
    bmpString         BMPString       (SIZE (1..ub-common-name)) }

– Naming attributes of type X520LocalityName

id-at-localityName AttributeType ::= { id-at 7 }

X520LocalityName ::= CHOICE {

    teletexString     TeletexString   (SIZE (1..ub-locality-name)),
    printableString   PrintableString (SIZE (1..ub-locality-name)),
    universalString   UniversalString (SIZE (1..ub-locality-name)),
    utf8String        UTF8String      (SIZE (1..ub-locality-name)),
    bmpString         BMPString       (SIZE (1..ub-locality-name)) }

– Naming attributes of type X520StateOrProvinceName

id-at-stateOrProvinceName AttributeType ::= { id-at 8 }

X520StateOrProvinceName ::= CHOICE {

    teletexString     TeletexString   (SIZE (1..ub-state-name)),
    printableString   PrintableString (SIZE (1..ub-state-name)),
    universalString   UniversalString (SIZE (1..ub-state-name)),
    utf8String        UTF8String      (SIZE (1..ub-state-name)),
    bmpString         BMPString       (SIZE(1..ub-state-name)) }

Housley, et. al. Standards Track [Page 94] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

– Naming attributes of type X520OrganizationName

id-at-organizationName AttributeType ::= { id-at 10 }

X520OrganizationName ::= CHOICE {

    teletexString     TeletexString
                        (SIZE (1..ub-organization-name)),
    printableString   PrintableString
                        (SIZE (1..ub-organization-name)),
    universalString   UniversalString
                        (SIZE (1..ub-organization-name)),
    utf8String        UTF8String
                        (SIZE (1..ub-organization-name)),
    bmpString         BMPString
                        (SIZE (1..ub-organization-name))  }

– Naming attributes of type X520OrganizationalUnitName

id-at-organizationalUnitName AttributeType ::= { id-at 11 }

X520OrganizationalUnitName ::= CHOICE {

    teletexString     TeletexString
                        (SIZE (1..ub-organizational-unit-name)),
    printableString   PrintableString
                        (SIZE (1..ub-organizational-unit-name)),
    universalString   UniversalString
                        (SIZE (1..ub-organizational-unit-name)),
    utf8String        UTF8String
                        (SIZE (1..ub-organizational-unit-name)),
    bmpString         BMPString
                        (SIZE (1..ub-organizational-unit-name)) }

– Naming attributes of type X520Title

id-at-title AttributeType ::= { id-at 12 }

X520Title ::= CHOICE {

    teletexString     TeletexString   (SIZE (1..ub-title)),
    printableString   PrintableString (SIZE (1..ub-title)),
    universalString   UniversalString (SIZE (1..ub-title)),
    utf8String        UTF8String      (SIZE (1..ub-title)),
    bmpString         BMPString       (SIZE (1..ub-title)) }

– Naming attributes of type X520dnQualifier

id-at-dnQualifier AttributeType ::= { id-at 46 }

X520dnQualifier ::= PrintableString

Housley, et. al. Standards Track [Page 95] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

– Naming attributes of type X520countryName (digraph from IS 3166)

id-at-countryName AttributeType ::= { id-at 6 }

X520countryName ::= PrintableString (SIZE (2))

– Naming attributes of type X520SerialNumber

id-at-serialNumber AttributeType ::= { id-at 5 }

X520SerialNumber ::= PrintableString (SIZE (1..ub-serial-number))

– Naming attributes of type X520Pseudonym

id-at-pseudonym AttributeType ::= { id-at 65 }

X520Pseudonym ::= CHOICE {

 teletexString     TeletexString   (SIZE (1..ub-pseudonym)),
 printableString   PrintableString (SIZE (1..ub-pseudonym)),
 universalString   UniversalString (SIZE (1..ub-pseudonym)),
 utf8String        UTF8String      (SIZE (1..ub-pseudonym)),
 bmpString         BMPString       (SIZE (1..ub-pseudonym)) }

– Naming attributes of type DomainComponent (from RFC 2247)

id-domainComponent AttributeType ::=

                        { 0 9 2342 19200300 100 1 25 }

DomainComponent ::= IA5String

– Legacy attributes

pkcs-9 OBJECT IDENTIFIER ::=

     { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) 9 }

id-emailAddress AttributeType ::= { pkcs-9 1 }

EmailAddress ::= IA5String (SIZE (1..ub-emailaddress-length))

– naming data types –

Name ::= CHOICE { – only one possibility for now –

    rdnSequence  RDNSequence }

RDNSequence ::= SEQUENCE OF RelativeDistinguishedName

DistinguishedName ::= RDNSequence

Housley, et. al. Standards Track [Page 96] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

RelativeDistinguishedName ::=

                  SET SIZE (1 .. MAX) OF AttributeTypeAndValue

– Directory string type –

DirectoryString ::= CHOICE {

    teletexString             TeletexString   (SIZE (1..MAX)),
    printableString           PrintableString (SIZE (1..MAX)),
    universalString           UniversalString (SIZE (1..MAX)),
    utf8String              UTF8String      (SIZE (1..MAX)),
    bmpString               BMPString       (SIZE (1..MAX)) }

– certificate and CRL specific structures begin here

Certificate ::= SEQUENCE {

   tbsCertificate       TBSCertificate,
   signatureAlgorithm   AlgorithmIdentifier,
   signature            BIT STRING  }

TBSCertificate ::= SEQUENCE {

   version         [0]  Version DEFAULT v1,
   serialNumber         CertificateSerialNumber,
   signature            AlgorithmIdentifier,
   issuer               Name,
   validity             Validity,
   subject              Name,
   subjectPublicKeyInfo SubjectPublicKeyInfo,
   issuerUniqueID  [1]  IMPLICIT UniqueIdentifier OPTIONAL,
                        -- If present, version MUST be v2 or v3
   subjectUniqueID [2]  IMPLICIT UniqueIdentifier OPTIONAL,
                        -- If present, version MUST be v2 or v3
   extensions      [3]  Extensions OPTIONAL
                        -- If present, version MUST be v3 --  }

Version ::= INTEGER { v1(0), v2(1), v3(2) }

CertificateSerialNumber ::= INTEGER

Validity ::= SEQUENCE {

   notBefore      Time,
   notAfter       Time  }

Time ::= CHOICE {

   utcTime        UTCTime,
   generalTime    GeneralizedTime }

UniqueIdentifier ::= BIT STRING

Housley, et. al. Standards Track [Page 97] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

SubjectPublicKeyInfo ::= SEQUENCE {

   algorithm            AlgorithmIdentifier,
   subjectPublicKey     BIT STRING  }

Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension

Extension ::= SEQUENCE {

   extnID      OBJECT IDENTIFIER,
   critical    BOOLEAN DEFAULT FALSE,
   extnValue   OCTET STRING  }

– CRL structures

CertificateList ::= SEQUENCE {

   tbsCertList          TBSCertList,
   signatureAlgorithm   AlgorithmIdentifier,
   signature            BIT STRING  }

TBSCertList ::= SEQUENCE {

   version                 Version OPTIONAL,
                                -- if present, MUST be v2
   signature               AlgorithmIdentifier,
   issuer                  Name,
   thisUpdate              Time,
   nextUpdate              Time OPTIONAL,
   revokedCertificates     SEQUENCE OF SEQUENCE  {
        userCertificate         CertificateSerialNumber,
        revocationDate          Time,
        crlEntryExtensions      Extensions OPTIONAL
                                       -- if present, MUST be v2
                             }  OPTIONAL,
   crlExtensions           [0] Extensions OPTIONAL }
                                       -- if present, MUST be v2

– Version, Time, CertificateSerialNumber, and Extensions were – defined earlier for use in the certificate structure

AlgorithmIdentifier ::= SEQUENCE {

   algorithm               OBJECT IDENTIFIER,
   parameters              ANY DEFINED BY algorithm OPTIONAL  }
                              -- contains a value of the type
                              -- registered for use with the
                              -- algorithm object identifier value

– X.400 address syntax starts here

Housley, et. al. Standards Track [Page 98] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

ORAddress ::= SEQUENCE {

 built-in-standard-attributes BuiltInStandardAttributes,
 built-in-domain-defined-attributes
                 BuiltInDomainDefinedAttributes OPTIONAL,
 -- see also teletex-domain-defined-attributes
 extension-attributes ExtensionAttributes OPTIONAL }

– Built-in Standard Attributes

BuiltInStandardAttributes ::= SEQUENCE {

 country-name                  CountryName OPTIONAL,
 administration-domain-name    AdministrationDomainName OPTIONAL,
 network-address           [0] IMPLICIT NetworkAddress OPTIONAL,
   -- see also extended-network-address
 terminal-identifier       [1] IMPLICIT TerminalIdentifier OPTIONAL,
 private-domain-name       [2] PrivateDomainName OPTIONAL,
 organization-name         [3] IMPLICIT OrganizationName OPTIONAL,
   -- see also teletex-organization-name
 numeric-user-identifier   [4] IMPLICIT NumericUserIdentifier
                               OPTIONAL,
 personal-name             [5] IMPLICIT PersonalName OPTIONAL,
   -- see also teletex-personal-name
 organizational-unit-names [6] IMPLICIT OrganizationalUnitNames
                               OPTIONAL }
   -- see also teletex-organizational-unit-names

CountryName ::= [APPLICATION 1] CHOICE {

 x121-dcc-code         NumericString
                         (SIZE (ub-country-name-numeric-length)),
 iso-3166-alpha2-code  PrintableString
                         (SIZE (ub-country-name-alpha-length)) }

AdministrationDomainName ::= [APPLICATION 2] CHOICE {

 numeric   NumericString   (SIZE (0..ub-domain-name-length)),
 printable PrintableString (SIZE (0..ub-domain-name-length)) }

NetworkAddress ::= X121Address – see also extended-network-address

X121Address ::= NumericString (SIZE (1..ub-x121-address-length))

TerminalIdentifier ::= PrintableString (SIZE (1..ub-terminal-id-length))

PrivateDomainName ::= CHOICE {

 numeric   NumericString   (SIZE (1..ub-domain-name-length)),
 printable PrintableString (SIZE (1..ub-domain-name-length)) }

Housley, et. al. Standards Track [Page 99] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

OrganizationName ::= PrintableString

                          (SIZE (1..ub-organization-name-length))
-- see also teletex-organization-name

NumericUserIdentifier ::= NumericString

                          (SIZE (1..ub-numeric-user-id-length))

PersonalName ::= SET {

 surname     [0] IMPLICIT PrintableString
                  (SIZE (1..ub-surname-length)),
 given-name  [1] IMPLICIT PrintableString
                  (SIZE (1..ub-given-name-length)) OPTIONAL,
 initials    [2] IMPLICIT PrintableString
                  (SIZE (1..ub-initials-length)) OPTIONAL,
 generation-qualifier [3] IMPLICIT PrintableString
                  (SIZE (1..ub-generation-qualifier-length))
                  OPTIONAL }
-- see also teletex-personal-name

OrganizationalUnitNames ::= SEQUENCE SIZE (1..ub-organizational-units)

                           OF OrganizationalUnitName
-- see also teletex-organizational-unit-names

OrganizationalUnitName ::= PrintableString (SIZE

                  (1..ub-organizational-unit-name-length))

– Built-in Domain-defined Attributes

BuiltInDomainDefinedAttributes ::= SEQUENCE SIZE

                  (1..ub-domain-defined-attributes) OF
                  BuiltInDomainDefinedAttribute

BuiltInDomainDefinedAttribute ::= SEQUENCE {

 type PrintableString (SIZE
                 (1..ub-domain-defined-attribute-type-length)),
 value PrintableString (SIZE
                 (1..ub-domain-defined-attribute-value-length)) }

– Extension Attributes

ExtensionAttributes ::= SET SIZE (1..ub-extension-attributes) OF

             ExtensionAttribute

ExtensionAttribute ::= SEQUENCE {

 extension-attribute-type [0] IMPLICIT INTEGER
                 (0..ub-extension-attributes),
 extension-attribute-value [1]
                 ANY DEFINED BY extension-attribute-type }

Housley, et. al. Standards Track [Page 100] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

– Extension types and attribute values

common-name INTEGER ::= 1

CommonName ::= PrintableString (SIZE (1..ub-common-name-length))

teletex-common-name INTEGER ::= 2

TeletexCommonName ::= TeletexString (SIZE (1..ub-common-name-length))

teletex-organization-name INTEGER ::= 3

TeletexOrganizationName ::=

              TeletexString (SIZE (1..ub-organization-name-length))

teletex-personal-name INTEGER ::= 4

TeletexPersonalName ::= SET {

 surname     [0] IMPLICIT TeletexString
                  (SIZE (1..ub-surname-length)),
 given-name  [1] IMPLICIT TeletexString
                  (SIZE (1..ub-given-name-length)) OPTIONAL,
 initials    [2] IMPLICIT TeletexString
                  (SIZE (1..ub-initials-length)) OPTIONAL,
 generation-qualifier [3] IMPLICIT TeletexString
                  (SIZE (1..ub-generation-qualifier-length))
                  OPTIONAL }

teletex-organizational-unit-names INTEGER ::= 5

TeletexOrganizationalUnitNames ::= SEQUENCE SIZE

    (1..ub-organizational-units) OF TeletexOrganizationalUnitName

TeletexOrganizationalUnitName ::= TeletexString

                (SIZE (1..ub-organizational-unit-name-length))

pds-name INTEGER ::= 7

PDSName ::= PrintableString (SIZE (1..ub-pds-name-length))

physical-delivery-country-name INTEGER ::= 8

PhysicalDeliveryCountryName ::= CHOICE {

 x121-dcc-code NumericString (SIZE

(ub-country-name-numeric-length)),

 iso-3166-alpha2-code PrintableString
                (SIZE (ub-country-name-alpha-length)) }

Housley, et. al. Standards Track [Page 101] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

postal-code INTEGER ::= 9

PostalCode ::= CHOICE {

 numeric-code NumericString (SIZE (1..ub-postal-code-length)),
 printable-code PrintableString (SIZE (1..ub-postal-code-length)) }

physical-delivery-office-name INTEGER ::= 10

PhysicalDeliveryOfficeName ::= PDSParameter

physical-delivery-office-number INTEGER ::= 11

PhysicalDeliveryOfficeNumber ::= PDSParameter

extension-OR-address-components INTEGER ::= 12

ExtensionORAddressComponents ::= PDSParameter

physical-delivery-personal-name INTEGER ::= 13

PhysicalDeliveryPersonalName ::= PDSParameter

physical-delivery-organization-name INTEGER ::= 14

PhysicalDeliveryOrganizationName ::= PDSParameter

extension-physical-delivery-address-components INTEGER ::= 15

ExtensionPhysicalDeliveryAddressComponents ::= PDSParameter

unformatted-postal-address INTEGER ::= 16

UnformattedPostalAddress ::= SET {

 printable-address SEQUENCE SIZE (1..ub-pds-physical-address-lines)
       OF PrintableString (SIZE (1..ub-pds-parameter-length))
       OPTIONAL,
 teletex-string TeletexString
       (SIZE (1..ub-unformatted-address-length)) OPTIONAL }

street-address INTEGER ::= 17

StreetAddress ::= PDSParameter

post-office-box-address INTEGER ::= 18

PostOfficeBoxAddress ::= PDSParameter

poste-restante-address INTEGER ::= 19

Housley, et. al. Standards Track [Page 102] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

PosteRestanteAddress ::= PDSParameter

unique-postal-name INTEGER ::= 20

UniquePostalName ::= PDSParameter

local-postal-attributes INTEGER ::= 21

LocalPostalAttributes ::= PDSParameter

PDSParameter ::= SET {

 printable-string PrintableString
              (SIZE(1..ub-pds-parameter-length)) OPTIONAL,
 teletex-string TeletexString
              (SIZE(1..ub-pds-parameter-length)) OPTIONAL }

extended-network-address INTEGER ::= 22

ExtendedNetworkAddress ::= CHOICE {

 e163-4-address SEQUENCE {
    number      [0] IMPLICIT NumericString
                     (SIZE (1..ub-e163-4-number-length)),
    sub-address [1] IMPLICIT NumericString
                     (SIZE (1..ub-e163-4-sub-address-length))
                     OPTIONAL },
 psap-address [0] IMPLICIT PresentationAddress }

PresentationAddress ::= SEQUENCE {

  pSelector     [0] EXPLICIT OCTET STRING OPTIONAL,
  sSelector     [1] EXPLICIT OCTET STRING OPTIONAL,
  tSelector     [2] EXPLICIT OCTET STRING OPTIONAL,
  nAddresses    [3] EXPLICIT SET SIZE (1..MAX) OF OCTET STRING }

terminal-type INTEGER ::= 23

TerminalType ::= INTEGER {

 telex (3),
 teletex (4),
 g3-facsimile (5),
 g4-facsimile (6),
 ia5-terminal (7),
 videotex (8) } (0..ub-integer-options)

– Extension Domain-defined Attributes

teletex-domain-defined-attributes INTEGER ::= 6

Housley, et. al. Standards Track [Page 103] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

TeletexDomainDefinedAttributes ::= SEQUENCE SIZE

 (1..ub-domain-defined-attributes) OF TeletexDomainDefinedAttribute

TeletexDomainDefinedAttribute ::= SEQUENCE {

      type TeletexString
             (SIZE (1..ub-domain-defined-attribute-type-length)),
      value TeletexString
             (SIZE (1..ub-domain-defined-attribute-value-length)) }

– specifications of Upper Bounds MUST be regarded as mandatory – from Annex B of ITU-T X.411 Reference Definition of MTS Parameter – Upper Bounds

– Upper Bounds ub-name INTEGER ::= 32768 ub-common-name INTEGER ::= 64 ub-locality-name INTEGER ::= 128 ub-state-name INTEGER ::= 128 ub-organization-name INTEGER ::= 64 ub-organizational-unit-name INTEGER ::= 64 ub-title INTEGER ::= 64 ub-serial-number INTEGER ::= 64 ub-match INTEGER ::= 128 ub-emailaddress-length INTEGER ::= 128 ub-common-name-length INTEGER ::= 64 ub-country-name-alpha-length INTEGER ::= 2 ub-country-name-numeric-length INTEGER ::= 3 ub-domain-defined-attributes INTEGER ::= 4 ub-domain-defined-attribute-type-length INTEGER ::= 8 ub-domain-defined-attribute-value-length INTEGER ::= 128 ub-domain-name-length INTEGER ::= 16 ub-extension-attributes INTEGER ::= 256 ub-e163-4-number-length INTEGER ::= 15 ub-e163-4-sub-address-length INTEGER ::= 40 ub-generation-qualifier-length INTEGER ::= 3 ub-given-name-length INTEGER ::= 16 ub-initials-length INTEGER ::= 5 ub-integer-options INTEGER ::= 256 ub-numeric-user-id-length INTEGER ::= 32 ub-organization-name-length INTEGER ::= 64 ub-organizational-unit-name-length INTEGER ::= 32 ub-organizational-units INTEGER ::= 4 ub-pds-name-length INTEGER ::= 16 ub-pds-parameter-length INTEGER ::= 30 ub-pds-physical-address-lines INTEGER ::= 6 ub-postal-code-length INTEGER ::= 16 ub-pseudonym INTEGER ::= 128 ub-surname-length INTEGER ::= 40

Housley, et. al. Standards Track [Page 104] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

ub-terminal-id-length INTEGER ::= 24 ub-unformatted-address-length INTEGER ::= 180 ub-x121-address-length INTEGER ::= 16

– Note - upper bounds on string types, such as TeletexString, are – measured in characters. Excepting PrintableString or IA5String, a – significantly greater number of octets will be required to hold – such a value. As a minimum, 16 octets, or twice the specified – upper bound, whichever is the larger, should be allowed for – TeletexString. For UTF8String or UniversalString at least four – times the upper bound should be allowed.

END

A.2 Implicitly Tagged Module, 1988 Syntax

PKIX1Implicit88 { iso(1) identified-organization(3) dod(6) internet(1)

security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-implicit(19) }

DEFINITIONS IMPLICIT TAGS ::=

BEGIN

– EXPORTS ALL –

IMPORTS

    id-pe, id-kp, id-qt-unotice, id-qt-cps,
    -- delete following line if "new" types are supported --
    BMPString, UTF8String,  -- end "new" types --
    ORAddress, Name, RelativeDistinguishedName,
    CertificateSerialNumber, Attribute, DirectoryString
    FROM PKIX1Explicit88 { iso(1) identified-organization(3)
          dod(6) internet(1) security(5) mechanisms(5) pkix(7)
          id-mod(0) id-pkix1-explicit(18) };

– ISO arc for standard certificate and CRL extensions

id-ce OBJECT IDENTIFIER ::= {joint-iso-ccitt(2) ds(5) 29}

– authority key identifier OID and syntax

id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 35 }

Housley, et. al. Standards Track [Page 105] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

AuthorityKeyIdentifier ::= SEQUENCE {

  keyIdentifier             [0] KeyIdentifier            OPTIONAL,
  authorityCertIssuer       [1] GeneralNames             OPTIONAL,
  authorityCertSerialNumber [2] CertificateSerialNumber  OPTIONAL }
  -- authorityCertIssuer and authorityCertSerialNumber MUST both
  -- be present or both be absent

KeyIdentifier ::= OCTET STRING

– subject key identifier OID and syntax

id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 14 }

SubjectKeyIdentifier ::= KeyIdentifier

– key usage extension OID and syntax

id-ce-keyUsage OBJECT IDENTIFIER ::= { id-ce 15 }

KeyUsage ::= BIT STRING {

   digitalSignature        (0),
   nonRepudiation          (1),
   keyEncipherment         (2),
   dataEncipherment        (3),
   keyAgreement            (4),
   keyCertSign             (5),
   cRLSign                 (6),
   encipherOnly            (7),
   decipherOnly            (8) }

– private key usage period extension OID and syntax

id-ce-privateKeyUsagePeriod OBJECT IDENTIFIER ::= { id-ce 16 }

PrivateKeyUsagePeriod ::= SEQUENCE {

   notBefore       [0]     GeneralizedTime OPTIONAL,
   notAfter        [1]     GeneralizedTime OPTIONAL }
   -- either notBefore or notAfter MUST be present

– certificate policies extension OID and syntax

id-ce-certificatePolicies OBJECT IDENTIFIER ::= { id-ce 32 }

anyPolicy OBJECT IDENTIFIER ::= { id-ce-certificatePolicies 0 }

CertificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

PolicyInformation ::= SEQUENCE {

Housley, et. al. Standards Track [Page 106] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

   policyIdentifier   CertPolicyId,
   policyQualifiers   SEQUENCE SIZE (1..MAX) OF
           PolicyQualifierInfo OPTIONAL }

CertPolicyId ::= OBJECT IDENTIFIER

PolicyQualifierInfo ::= SEQUENCE {

     policyQualifierId  PolicyQualifierId,
     qualifier        ANY DEFINED BY policyQualifierId }

– Implementations that recognize additional policy qualifiers MUST – augment the following definition for PolicyQualifierId

PolicyQualifierId ::=

  OBJECT IDENTIFIER ( id-qt-cps | id-qt-unotice )

– CPS pointer qualifier

CPSuri ::= IA5String

– user notice qualifier

UserNotice ::= SEQUENCE {

   noticeRef        NoticeReference OPTIONAL,
   explicitText     DisplayText OPTIONAL}

NoticeReference ::= SEQUENCE {

   organization     DisplayText,
   noticeNumbers    SEQUENCE OF INTEGER }

DisplayText ::= CHOICE {

   ia5String        IA5String      (SIZE (1..200)),
   visibleString    VisibleString  (SIZE (1..200)),
   bmpString        BMPString      (SIZE (1..200)),
   utf8String       UTF8String     (SIZE (1..200)) }

– policy mapping extension OID and syntax

id-ce-policyMappings OBJECT IDENTIFIER ::= { id-ce 33 }

PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {

   issuerDomainPolicy      CertPolicyId,
   subjectDomainPolicy     CertPolicyId }

– subject alternative name extension OID and syntax

id-ce-subjectAltName OBJECT IDENTIFIER ::= { id-ce 17 }

Housley, et. al. Standards Track [Page 107] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

SubjectAltName ::= GeneralNames

GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

GeneralName ::= CHOICE {

   otherName                       [0]     AnotherName,
   rfc822Name                      [1]     IA5String,
   dNSName                         [2]     IA5String,
   x400Address                     [3]     ORAddress,
   directoryName                   [4]     Name,
   ediPartyName                    [5]     EDIPartyName,
   uniformResourceIdentifier       [6]     IA5String,
   iPAddress                       [7]     OCTET STRING,
   registeredID                    [8]     OBJECT IDENTIFIER }

– AnotherName replaces OTHER-NAME ::= TYPE-IDENTIFIER, as – TYPE-IDENTIFIER is not supported in the '88 ASN.1 syntax

AnotherName ::= SEQUENCE {

   type-id    OBJECT IDENTIFIER,
   value      [0] EXPLICIT ANY DEFINED BY type-id }

EDIPartyName ::= SEQUENCE {

   nameAssigner            [0]     DirectoryString OPTIONAL,
   partyName               [1]     DirectoryString }

– issuer alternative name extension OID and syntax

id-ce-issuerAltName OBJECT IDENTIFIER ::= { id-ce 18 }

IssuerAltName ::= GeneralNames

id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::= { id-ce 9 }

SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

– basic constraints extension OID and syntax

id-ce-basicConstraints OBJECT IDENTIFIER ::= { id-ce 19 }

BasicConstraints ::= SEQUENCE {

   cA                      BOOLEAN DEFAULT FALSE,
   pathLenConstraint       INTEGER (0..MAX) OPTIONAL }

– name constraints extension OID and syntax

id-ce-nameConstraints OBJECT IDENTIFIER ::= { id-ce 30 }

Housley, et. al. Standards Track [Page 108] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

NameConstraints ::= SEQUENCE {

   permittedSubtrees       [0]     GeneralSubtrees OPTIONAL,
   excludedSubtrees        [1]     GeneralSubtrees OPTIONAL }

GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree

GeneralSubtree ::= SEQUENCE {

   base                    GeneralName,
   minimum         [0]     BaseDistance DEFAULT 0,
   maximum         [1]     BaseDistance OPTIONAL }

BaseDistance ::= INTEGER (0..MAX)

– policy constraints extension OID and syntax

id-ce-policyConstraints OBJECT IDENTIFIER ::= { id-ce 36 }

PolicyConstraints ::= SEQUENCE {

   requireExplicitPolicy           [0] SkipCerts OPTIONAL,
   inhibitPolicyMapping            [1] SkipCerts OPTIONAL }

SkipCerts ::= INTEGER (0..MAX)

– CRL distribution points extension OID and syntax

id-ce-cRLDistributionPoints OBJECT IDENTIFIER ::= {id-ce 31}

CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint

DistributionPoint ::= SEQUENCE {

   distributionPoint       [0]     DistributionPointName OPTIONAL,
   reasons                 [1]     ReasonFlags OPTIONAL,
   cRLIssuer               [2]     GeneralNames OPTIONAL }

DistributionPointName ::= CHOICE {

   fullName                [0]     GeneralNames,
   nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }

ReasonFlags ::= BIT STRING {

   unused                  (0),
   keyCompromise           (1),
   cACompromise            (2),
   affiliationChanged      (3),
   superseded              (4),
   cessationOfOperation    (5),
   certificateHold         (6),
   privilegeWithdrawn      (7),
   aACompromise            (8) }

Housley, et. al. Standards Track [Page 109] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

– extended key usage extension OID and syntax

id-ce-extKeyUsage OBJECT IDENTIFIER ::= {id-ce 37}

ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId

KeyPurposeId ::= OBJECT IDENTIFIER

– permit unspecified key uses

anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }

– extended key purpose OIDs

id-kp-serverAuth OBJECT IDENTIFIER ::= { id-kp 1 } id-kp-clientAuth OBJECT IDENTIFIER ::= { id-kp 2 } id-kp-codeSigning OBJECT IDENTIFIER ::= { id-kp 3 } id-kp-emailProtection OBJECT IDENTIFIER ::= { id-kp 4 } id-kp-timeStamping OBJECT IDENTIFIER ::= { id-kp 8 } id-kp-OCSPSigning OBJECT IDENTIFIER ::= { id-kp 9 }

– inhibit any policy OID and syntax

id-ce-inhibitAnyPolicy OBJECT IDENTIFIER ::= { id-ce 54 }

InhibitAnyPolicy ::= SkipCerts

– freshest (delta)CRL extension OID and syntax

id-ce-freshestCRL OBJECT IDENTIFIER ::= { id-ce 46 }

FreshestCRL ::= CRLDistributionPoints

– authority info access

id-pe-authorityInfoAccess OBJECT IDENTIFIER ::= { id-pe 1 }

AuthorityInfoAccessSyntax ::=

      SEQUENCE SIZE (1..MAX) OF AccessDescription

AccessDescription ::= SEQUENCE {

      accessMethod          OBJECT IDENTIFIER,
      accessLocation        GeneralName  }

– subject info access

id-pe-subjectInfoAccess OBJECT IDENTIFIER ::= { id-pe 11 }

Housley, et. al. Standards Track [Page 110] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

SubjectInfoAccessSyntax ::=

      SEQUENCE SIZE (1..MAX) OF AccessDescription

– CRL number extension OID and syntax

id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

CRLNumber ::= INTEGER (0..MAX)

– issuing distribution point extension OID and syntax

id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }

IssuingDistributionPoint ::= SEQUENCE {

   distributionPoint          [0] DistributionPointName OPTIONAL,
   onlyContainsUserCerts      [1] BOOLEAN DEFAULT FALSE,
   onlyContainsCACerts        [2] BOOLEAN DEFAULT FALSE,
   onlySomeReasons            [3] ReasonFlags OPTIONAL,
   indirectCRL                [4] BOOLEAN DEFAULT FALSE,
   onlyContainsAttributeCerts [5] BOOLEAN DEFAULT FALSE }

id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }

BaseCRLNumber ::= CRLNumber

– CRL reasons extension OID and syntax

id-ce-cRLReasons OBJECT IDENTIFIER ::= { id-ce 21 }

CRLReason ::= ENUMERATED {

   unspecified             (0),
   keyCompromise           (1),
   cACompromise            (2),
   affiliationChanged      (3),
   superseded              (4),
   cessationOfOperation    (5),
   certificateHold         (6),
   removeFromCRL           (8),
   privilegeWithdrawn      (9),
   aACompromise           (10) }

– certificate issuer CRL entry extension OID and syntax

id-ce-certificateIssuer OBJECT IDENTIFIER ::= { id-ce 29 }

CertificateIssuer ::= GeneralNames

– hold instruction extension OID and syntax

Housley, et. al. Standards Track [Page 111] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

id-ce-holdInstructionCode OBJECT IDENTIFIER ::= { id-ce 23 }

HoldInstructionCode ::= OBJECT IDENTIFIER

– ANSI x9 holdinstructions

– ANSI x9 arc holdinstruction arc

holdInstruction OBJECT IDENTIFIER ::=

        {joint-iso-itu-t(2) member-body(2) us(840) x9cm(10040) 2}

– ANSI X9 holdinstructions referenced by this standard

id-holdinstruction-none OBJECT IDENTIFIER ::=

              {holdInstruction 1} -- deprecated

id-holdinstruction-callissuer OBJECT IDENTIFIER ::=

              {holdInstruction 2}

id-holdinstruction-reject OBJECT IDENTIFIER ::=

              {holdInstruction 3}

– invalidity date CRL entry extension OID and syntax

id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }

InvalidityDate ::= GeneralizedTime

END

Appendix B. ASN.1 Notes

 CAs MUST force the serialNumber to be a non-negative integer, that
 is, the sign bit in the DER encoding of the INTEGER value MUST be
 zero - this can be done by adding a leading (leftmost) `00'H octet if
 necessary.  This removes a potential ambiguity in mapping between a
 string of octets and an integer value.
 As noted in section 4.1.2.2, serial numbers can be expected to
 contain long integers.  Certificate users MUST be able to handle
 serialNumber values up to 20 octets in length.  Conformant CAs MUST
 NOT use serialNumber values longer than 20 octets.
 As noted in section 5.2.3, CRL numbers can be expected to contain
 long integers.  CRL validators MUST be able to handle cRLNumber
 values up to 20 octets in length.  Conformant CRL issuers MUST NOT
 use cRLNumber values longer than 20 octets.

Housley, et. al. Standards Track [Page 112] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 The construct "SEQUENCE SIZE (1..MAX) OF" appears in several ASN.1
 constructs.  A valid ASN.1 sequence will have zero or more entries.
 The SIZE (1..MAX) construct constrains the sequence to have at least
 one entry.  MAX indicates the upper bound is unspecified.
 Implementations are free to choose an upper bound that suits their
 environment.
 The construct "positiveInt ::= INTEGER (0..MAX)" defines positiveInt
 as a subtype of INTEGER containing integers greater than or equal to
 zero.  The upper bound is unspecified.  Implementations are free to
 select an upper bound that suits their environment.
 The character string type PrintableString supports a very basic Latin
 character set: the lower case letters 'a' through 'z', upper case
 letters 'A' through 'Z', the digits '0' through '9', eleven special
 characters ' = ( ) + , - . / : ? and space.
 Implementers should note that the at sign ('@') and underscore ('_')
 characters are not supported by the ASN.1 type PrintableString.
 These characters often appear in internet addresses.  Such addresses
 MUST be encoded using an ASN.1 type that supports them.  They are
 usually encoded as IA5String in either the emailAddress attribute
 within a distinguished name or the rfc822Name field of GeneralName.
 Conforming implementations MUST NOT encode strings which include
 either the at sign or underscore character as PrintableString.
 The character string type TeletexString is a superset of
 PrintableString.  TeletexString supports a fairly standard (ASCII-
 like) Latin character set, Latin characters with non-spacing accents
 and Japanese characters.
 Named bit lists are BIT STRINGs where the values have been assigned
 names.  This specification makes use of named bit lists in the
 definitions for the key usage, CRL distribution points and freshest
 CRL certificate extensions, as well as the freshest CRL and issuing
 distribution point CRL extensions.  When DER encoding a named bit
 list, trailing zeroes MUST be omitted.  That is, the encoded value
 ends with the last named bit that is set to one.
 The character string type UniversalString supports any of the
 characters allowed by ISO 10646-1 [ISO 10646].  ISO 10646-1 is the
 Universal multiple-octet coded Character Set (UCS).  ISO 10646-1
 specifies the architecture and the "basic multilingual plane" -- a
 large standard character set which includes all major world character
 standards.

Housley, et. al. Standards Track [Page 113] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 The character string type UTF8String was introduced in the 1997
 version of ASN.1, and UTF8String was added to the list of choices for
 DirectoryString in the 2001 version of X.520 [X.520].  UTF8String is
 a universal type and has been assigned tag number 12.  The content of
 UTF8String was defined by RFC 2044 [RFC 2044] and updated in RFC 2279
 [RFC 2279].
 In anticipation of these changes, and in conformance with IETF Best
 Practices codified in RFC 2277 [RFC 2277], IETF Policy on Character
 Sets and Languages, this document includes UTF8String as a choice in
 DirectoryString and the CPS qualifier extensions.
 Implementers should note that the DER encoding of the SET OF values
 requires ordering of the encodings of the values.  In particular,
 this issue arises with respect to distinguished names.
 Implementers should note that the DER encoding of SET or SEQUENCE
 components whose value is the DEFAULT omit the component from the
 encoded certificate or CRL.  For example, a BasicConstraints
 extension whose cA value is FALSE would omit the cA boolean from the
 encoded certificate.
 Object Identifiers (OIDs) are used throughout this specification to
 identify certificate policies, public key and signature algorithms,
 certificate extensions, etc.  There is no maximum size for OIDs.
 This specification mandates support for OIDs which have arc elements
 with values that are less than 2^28, that is, they MUST be between 0
 and 268,435,455, inclusive.  This allows each arc element to be
 represented within a single 32 bit word.  Implementations MUST also
 support OIDs where the length of the dotted decimal (see [RFC 2252],
 section 4.1) string representation can be up to 100 bytes
 (inclusive).  Implementations MUST be able to handle OIDs with up to
 20 elements (inclusive).  CAs SHOULD NOT issue certificates which
 contain OIDs that exceed these requirements.  Likewise, CRL issuers
 SHOULD NOT issue CRLs which contain OIDs that exceed these
 requirements.
 Implementors are warned that the X.500 standards community has
 developed a series of extensibility rules.  These rules determine
 when an ASN.1 definition can be changed without assigning a new
 object identifier (OID).  For example, at least two extension
 definitions included in RFC 2459 [RFC 2459], the predecessor to this
 profile document, have different ASN.1 definitions in this
 specification, but the same OID is used.  If unknown elements appear
 within an extension, and the extension is not marked critical, those
 unknown elements ought to be ignored, as follows:
    (a)  ignore all unknown bit name assignments within a bit string;

Housley, et. al. Standards Track [Page 114] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

    (b)  ignore all unknown named numbers in an ENUMERATED type or
    INTEGER type that is being used in the enumerated style, provided
    the number occurs as an optional element of a SET or SEQUENCE; and
    (c)  ignore all unknown elements in SETs, at the end of SEQUENCEs,
    or in CHOICEs where the CHOICE is itself an optional element of a
    SET or SEQUENCE.
 If an extension containing unexpected values is marked critical, the
 implementation MUST reject the certificate or CRL containing the
 unrecognized extension.

Appendix C. Examples

 This section contains four examples: three certificates and a CRL.
 The first two certificates and the CRL comprise a minimal
 certification path.
 Section C.1 contains an annotated hex dump of a "self-signed"
 certificate issued by a CA whose distinguished name is
 cn=us,o=gov,ou=nist.  The certificate contains a DSA public key with
 parameters, and is signed by the corresponding DSA private key.
 Section C.2 contains an annotated hex dump of an end entity
 certificate.  The end entity certificate contains a DSA public key,
 and is signed by the private key corresponding to the "self-signed"
 certificate in section C.1.
 Section C.3 contains a dump of an end entity certificate which
 contains an RSA public key and is signed with RSA and MD5.  This
 certificate is not part of the minimal certification path.
 Section C.4 contains an annotated hex dump of a CRL.  The CRL is
 issued by the CA whose distinguished name is cn=us,o=gov,ou=nist and
 the list of revoked certificates includes the end entity certificate
 presented in C.2.
 The certificates were processed using Peter Gutman's dumpasn1 utility
 to generate the output.  The source for the dumpasn1 utility is
 available at <http://www.cs.auckland.ac.nz/~pgut001/dumpasn1.c>.  The
 binaries for the certificates and CRLs are available at
 <http://csrc.nist.gov/pki/pkixtools>.

C.1 Certificate

 This section contains an annotated hex dump of a 699 byte version 3
 certificate.  The certificate contains the following information:
 (a)  the serial number is 23 (17 hex);

Housley, et. al. Standards Track [Page 115] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 (b)  the certificate is signed with DSA and the SHA-1 hash algorithm;
 (c)  the issuer's distinguished name is OU=NIST; O=gov; C=US
 (d)  and the subject's distinguished name is OU=NIST; O=gov; C=US
 (e)  the certificate was issued on June 30, 1997 and will expire on
 December 31, 1997;
 (f)  the certificate contains a 1024 bit DSA public key with
 parameters;
 (g)  the certificate contains a subject key identifier extension
 generated using method (1) of section 4.2.1.2; and
 (h)  the certificate is a CA certificate (as indicated through the
 basic constraints extension.)
0 30  699: SEQUENCE {
4 30  635:   SEQUENCE {
8 A0    3:     [0] {

10 02 1: INTEGER 2

        :       }

13 02 1: INTEGER 17 16 30 9: SEQUENCE { 18 06 7: OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)

        :       }

27 30 42: SEQUENCE { 29 31 11: SET { 31 30 9: SEQUENCE { 33 06 3: OBJECT IDENTIFIER countryName (2 5 4 6) 38 13 2: PrintableString 'US'

        :           }
        :         }

42 31 12: SET { 44 30 10: SEQUENCE { 46 06 3: OBJECT IDENTIFIER organizationName (2 5 4 10) 51 13 3: PrintableString 'gov'

        :           }
        :         }

56 31 13: SET { 58 30 11: SEQUENCE { 60 06 3: OBJECT IDENTIFIER

        :             organizationalUnitName (2 5 4 11)

65 13 4: PrintableString 'NIST'

         :           }
         :         }
         :       }

71 30 30: SEQUENCE { 73 17 13: UTCTime '970630000000Z' 88 17 13: UTCTime '971231000000Z'

         :       }

103 30 42: SEQUENCE { 105 31 11: SET {

Housley, et. al. Standards Track [Page 116] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

107 30 9: SEQUENCE { 109 06 3: OBJECT IDENTIFIER countryName (2 5 4 6) 114 13 2: PrintableString 'US'

         :           }
         :         }

118 31 12: SET { 120 30 10: SEQUENCE { 122 06 3: OBJECT IDENTIFIER organizationName (2 5 4 10) 127 13 3: PrintableString 'gov'

         :           }
         :         }

132 31 13: SET { 134 30 11: SEQUENCE { 136 06 3: OBJECT IDENTIFIER

         :             organizationalUnitName (2 5 4 11)

141 13 4: PrintableString 'NIST'

         :           }
         :         }
         :       }

147 30 440: SEQUENCE { 151 30 300: SEQUENCE { 155 06 7: OBJECT IDENTIFIER dsa (1 2 840 10040 4 1) 164 30 287: SEQUENCE { 168 02 129: INTEGER

         :             00 B6 8B 0F 94 2B 9A CE A5 25 C6 F2 ED FC
         :             FB 95 32 AC 01 12 33 B9 E0 1C AD 90 9B BC
         :             48 54 9E F3 94 77 3C 2C 71 35 55 E6 FE 4F
         :             22 CB D5 D8 3E 89 93 33 4D FC BD 4F 41 64
         :             3E A2 98 70 EC 31 B4 50 DE EB F1 98 28 0A
         :             C9 3E 44 B3 FD 22 97 96 83 D0 18 A3 E3 BD
         :             35 5B FF EE A3 21 72 6A 7B 96 DA B9 3F 1E
         :             5A 90 AF 24 D6 20 F0 0D 21 A7 D4 02 B9 1A
         :             FC AC 21 FB 9E 94 9E 4B 42 45 9E 6A B2 48
         :             63 FE 43

300 02 21: INTEGER

         :             00 B2 0D B0 B1 01 DF 0C 66 24 FC 13 92 BA
         :             55 F7 7D 57 74 81 E5

323 02 129: INTEGER

         :             00 9A BF 46 B1 F5 3F 44 3D C9 A5 65 FB 91
         :             C0 8E 47 F1 0A C3 01 47 C2 44 42 36 A9 92
         :             81 DE 57 C5 E0 68 86 58 00 7B 1F F9 9B 77
         :             A1 C5 10 A5 80 91 78 51 51 3C F6 FC FC CC
         :             46 C6 81 78 92 84 3D F4 93 3D 0C 38 7E 1A
         :             5B 99 4E AB 14 64 F6 0C 21 22 4E 28 08 9C
         :             92 B9 66 9F 40 E8 95 F6 D5 31 2A EF 39 A2
         :             62 C7 B2 6D 9E 58 C4 3A A8 11 81 84 6D AF
         :             F8 B4 19 B4 C2 11 AE D0 22 3B AA 20 7F EE
         :             1E 57 18

Housley, et. al. Standards Track [Page 117] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

         :           }
         :         }

455 03 133: BIT STRING 0 unused bits, encapsulates { 459 02 129: INTEGER

         :             00 B5 9E 1F 49 04 47 D1 DB F5 3A DD CA 04
         :             75 E8 DD 75 F6 9B 8A B1 97 D6 59 69 82 D3
         :             03 4D FD 3B 36 5F 4A F2 D1 4E C1 07 F5 D1
         :             2A D3 78 77 63 56 EA 96 61 4D 42 0B 7A 1D
         :             FB AB 91 A4 CE DE EF 77 C8 E5 EF 20 AE A6
         :             28 48 AF BE 69 C3 6A A5 30 F2 C2 B9 D9 82
         :             2B 7D D9 C4 84 1F DE 0D E8 54 D7 1B 99 2E
         :             B3 D0 88 F6 D6 63 9B A7 E2 0E 82 D4 3B 8A
         :             68 1B 06 56 31 59 0B 49 EB 99 A5 D5 81 41
         :             7B C9 55
         :           }
         :       }

591 A3 50: [3] { 593 30 48: SEQUENCE { 595 30 29: SEQUENCE { 597 06 3: OBJECT IDENTIFIER

         :             subjectKeyIdentifier (2 5 29 14)

602 04 22: OCTET STRING, encapsulates { 604 04 20: OCTET STRING

         :                 86 CA A5 22 81 62 EF AD 0A 89 BC AD 72 41
         :                 2C 29 49 F4 86 56
         :               }
         :           }

626 30 15: SEQUENCE { 628 06 3: OBJECT IDENTIFIER basicConstraints (2 5 29 19) 633 01 1: BOOLEAN TRUE 636 04 5: OCTET STRING, encapsulates { 638 30 3: SEQUENCE { 640 01 1: BOOLEAN TRUE

         :                 }
         :               }
         :           }
         :         }
         :       }
         :     }

643 30 9: SEQUENCE { 645 06 7: OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)

         :     }

654 03 47: BIT STRING 0 unused bits, encapsulates { 657 30 44: SEQUENCE { 659 02 20: INTEGER

         :           43 1B CF 29 25 45 C0 4E 52 E7 7D D6 FC B1
         :           66 4C 83 CF 2D 77

681 02 20: INTEGER

Housley, et. al. Standards Track [Page 118] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

         :           0B 5B 9A 24 11 98 E8 F3 86 90 04 F6 08 A9
         :           E1 8D A5 CC 3A D4
         :         }
         :       }
         :   }

C.2 Certificate

 This section contains an annotated hex dump of a 730 byte version 3
 certificate.  The certificate contains the following information:
 (a)  the serial number is 18 (12 hex);
 (b)  the certificate is signed with DSA and the SHA-1 hash algorithm;
 (c)  the issuer's distinguished name is OU=nist; O=gov; C=US
 (d)  and the subject's distinguished name is CN=Tim Polk; OU=nist;
 O=gov; C=US
 (e)  the certificate was valid from July 30, 1997 through December 1,
 1997;
 (f)  the certificate contains a 1024 bit DSA public key;
 (g)  the certificate is an end entity certificate, as the basic
 constraints extension is not present;
 (h)  the certificate contains an authority key identifier extension
 matching the subject key identifier of the certificate in Appendix
 C.1; and
 (i)  the certificate includes one alternative name - an RFC 822
 address of "wpolk@nist.gov".
   0 30  730: SEQUENCE {
   4 30  665:   SEQUENCE {
   8 A0    3:     [0] {
  10 02    1:       INTEGER 2
            :       }
  13 02    1:     INTEGER 18
  16 30    9:     SEQUENCE {
  18 06    7:       OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
            :       }
  27 30   42:     SEQUENCE {
  29 31   11:       SET {
  31 30    9:         SEQUENCE {
  33 06    3:           OBJECT IDENTIFIER countryName (2 5 4 6)
  38 13    2:           PrintableString 'US'
            :           }
            :         }
  42 31   12:       SET {
  44 30   10:         SEQUENCE {
  46 06    3:           OBJECT IDENTIFIER organizationName (2 5 4 10)
  51 13    3:           PrintableString 'gov'
            :           }
            :         }

Housley, et. al. Standards Track [Page 119] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

  56 31   13:       SET {
  58 30   11:         SEQUENCE {
  60 06    3:           OBJECT IDENTIFIER
            :             organizationalUnitName (2 5 4 11)
  65 13    4:           PrintableString 'NIST'
            :           }
            :         }
            :       }
  71 30   30:     SEQUENCE {
  73 17   13:       UTCTime '970730000000Z'
  88 17   13:       UTCTime '971201000000Z'
            :       }
 103 30   61:     SEQUENCE {
 105 31   11:       SET {
 107 30    9:         SEQUENCE {
 109 06    3:           OBJECT IDENTIFIER countryName (2 5 4 6)
 114 13    2:           PrintableString 'US'
            :           }
            :         }
 118 31   12:       SET {
 120 30   10:         SEQUENCE {
 122 06    3:           OBJECT IDENTIFIER organizationName (2 5 4 10)
 127 13    3:           PrintableString 'gov'
            :           }
            :         }
 132 31   13:       SET {
 134 30   11:         SEQUENCE {
 136 06    3:           OBJECT IDENTIFIER
            :             organizationalUnitName (2 5 4 11)
 141 13    4:           PrintableString 'NIST'
            :           }
            :         }
 147 31   17:       SET {
 149 30   15:         SEQUENCE {
 151 06    3:           OBJECT IDENTIFIER commonName (2 5 4 3)
 156 13    8:           PrintableString 'Tim Polk'
            :           }
            :         }
            :       }
 166 30  439:     SEQUENCE {
 170 30  300:       SEQUENCE {
 174 06    7:         OBJECT IDENTIFIER dsa (1 2 840 10040 4 1)
 183 30  287:         SEQUENCE {
 187 02  129:           INTEGER
            :             00 B6 8B 0F 94 2B 9A CE A5 25 C6 F2 ED FC
            :             FB 95 32 AC 01 12 33 B9 E0 1C AD 90 9B BC
            :             48 54 9E F3 94 77 3C 2C 71 35 55 E6 FE 4F
            :             22 CB D5 D8 3E 89 93 33 4D FC BD 4F 41 64

Housley, et. al. Standards Track [Page 120] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

            :             3E A2 98 70 EC 31 B4 50 DE EB F1 98 28 0A
            :             C9 3E 44 B3 FD 22 97 96 83 D0 18 A3 E3 BD
            :             35 5B FF EE A3 21 72 6A 7B 96 DA B9 3F 1E
            :             5A 90 AF 24 D6 20 F0 0D 21 A7 D4 02 B9 1A
            :             FC AC 21 FB 9E 94 9E 4B 42 45 9E 6A B2 48
            :             63 FE 43
 319 02   21:           INTEGER
            :             00 B2 0D B0 B1 01 DF 0C 66 24 FC 13 92 BA
            :             55 F7 7D 57 74 81 E5
 342 02  129:           INTEGER
            :             00 9A BF 46 B1 F5 3F 44 3D C9 A5 65 FB 91
            :             C0 8E 47 F1 0A C3 01 47 C2 44 42 36 A9 92
            :             81 DE 57 C5 E0 68 86 58 00 7B 1F F9 9B 77
            :             A1 C5 10 A5 80 91 78 51 51 3C F6 FC FC CC
            :             46 C6 81 78 92 84 3D F4 93 3D 0C 38 7E 1A
            :             5B 99 4E AB 14 64 F6 0C 21 22 4E 28 08 9C
            :             92 B9 66 9F 40 E8 95 F6 D5 31 2A EF 39 A2
            :             62 C7 B2 6D 9E 58 C4 3A A8 11 81 84 6D AF
            :             F8 B4 19 B4 C2 11 AE D0 22 3B AA 20 7F EE
            :             1E 57 18
            :           }
            :         }
 474 03  132:       BIT STRING 0 unused bits, encapsulates {
 478 02  128:           INTEGER
            :             30 B6 75 F7 7C 20 31 AE 38 BB 7E 0D 2B AB
            :             A0 9C 4B DF 20 D5 24 13 3C CD 98 E5 5F 6C
            :             B7 C1 BA 4A BA A9 95 80 53 F0 0D 72 DC 33
            :             37 F4 01 0B F5 04 1F 9D 2E 1F 62 D8 84 3A
            :             9B 25 09 5A 2D C8 46 8E 2B D4 F5 0D 3B C7
            :             2D C6 6C B9 98 C1 25 3A 44 4E 8E CA 95 61
            :             35 7C CE 15 31 5C 23 13 1E A2 05 D1 7A 24
            :             1C CB D3 72 09 90 FF 9B 9D 28 C0 A1 0A EC
            :             46 9F 0D B8 D0 DC D0 18 A6 2B 5E F9 8F B5
            :             95 BE
            :           }
            :       }
 609 A3   62:     [3] {
 611 30   60:       SEQUENCE {
 613 30   25:         SEQUENCE {
 615 06    3:           OBJECT IDENTIFIER subjectAltName (2 5 29 17)
 620 04   18:           OCTET STRING, encapsulates {
 622 30   16:               SEQUENCE {
 624 81   14:                 [1] 'wpolk@nist.gov'
            :                 }
            :               }
            :           }
 640 30   31:         SEQUENCE {
 642 06    3:           OBJECT IDENTIFIER

Housley, et. al. Standards Track [Page 121] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

            :             authorityKeyIdentifier (2 5 29 35)
 647 04   24:           OCTET STRING, encapsulates {
 649 30   22:               SEQUENCE {
 651 80   20:                 [0]
            :                   86 CA A5 22 81 62 EF AD 0A 89 BC AD 72
            :                   41 2C 29 49 F4 86 56
            :                 }
            :               }
            :           }
            :         }
            :       }
            :     }
 673 30    9:   SEQUENCE {
 675 06    7:     OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)
            :     }
 684 03   48:   BIT STRING 0 unused bits, encapsulates {
 687 30   45:       SEQUENCE {
 689 02   20:         INTEGER
            :           36 97 CB E3 B4 2C E1 BB 61 A9 D3 CC 24 CC
            :           22 92 9F F4 F5 87
 711 02   21:         INTEGER
            :           00 AB C9 79 AF D2 16 1C A9 E3 68 A9 14 10
            :           B4 A0 2E FF 22 5A 73
            :         }
            :       }
            :   }

C.3 End Entity Certificate Using RSA

 This section contains an annotated hex dump of a 654 byte version 3
 certificate.  The certificate contains the following information:
 (a)  the serial number is 256;
 (b)  the certificate is signed with RSA and the SHA-1 hash algorithm;
 (c)  the issuer's distinguished name is OU=NIST; O=gov; C=US
 (d)  and the subject's distinguished name is CN=Tim Polk; OU=NIST;
 O=gov; C=US
 (e)  the certificate was issued on May 21, 1996 at 09:58:26 and
 expired on May 21, 1997 at 09:58:26;
 (f)  the certificate contains a 1024 bit RSA public key;
 (g)  the certificate is an end entity certificate (not a CA
 certificate);
 (h)  the certificate includes an alternative subject name of
 "<http://www.itl.nist.gov/div893/staff/polk/index.html>" and an
 alternative issuer name of "<http://www.nist.gov/>" - both are URLs;
 (i)  the certificate include an authority key identifier extension
 and a certificate policies extension specifying the policy OID
 2.16.840.1.101.3.2.1.48.9; and

Housley, et. al. Standards Track [Page 122] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

 (j)  the certificate includes a critical key usage extension
 specifying that the public key is intended for verification of
 digital signatures.
0 30  654: SEQUENCE {
4 30  503:   SEQUENCE {
8 A0    3:     [0] {

10 02 1: INTEGER 2

         :       }

13 02 2: INTEGER 256 17 30 13: SEQUENCE { 19 06 9: OBJECT IDENTIFIER

         :         sha1withRSAEncryption (1 2 840 113549 1 1 5)

30 05 0: NULL

         :       }

32 30 42: SEQUENCE { 34 31 11: SET { 36 30 9: SEQUENCE { 38 06 3: OBJECT IDENTIFIER countryName (2 5 4 6) 43 13 2: PrintableString 'US'

         :           }
         :         }

47 31 12: SET { 49 30 10: SEQUENCE { 51 06 3: OBJECT IDENTIFIER organizationName (2 5 4 10) 56 13 3: PrintableString 'gov'

         :           }
         :         }

61 31 13: SET { 63 30 11: SEQUENCE { 65 06 3: OBJECT IDENTIFIER

         :             organizationalUnitName (2 5 4 11)

70 13 4: PrintableString 'NIST'

         :           }
         :         }
         :       }

76 30 30: SEQUENCE { 78 17 13: UTCTime '960521095826Z' 93 17 13: UTCTime '970521095826Z'

         :       }

108 30 61: SEQUENCE { 110 31 11: SET { 112 30 9: SEQUENCE { 114 06 3: OBJECT IDENTIFIER countryName (2 5 4 6) 119 13 2: PrintableString 'US'

         :           }
         :         }

123 31 12: SET {

Housley, et. al. Standards Track [Page 123] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

125 30 10: SEQUENCE { 127 06 3: OBJECT IDENTIFIER organizationName (2 5 4 10) 132 13 3: PrintableString 'gov'

         :           }
         :         }

137 31 13: SET { 139 30 11: SEQUENCE { 141 06 3: OBJECT IDENTIFIER

         :             organizationalUnitName (2 5 4 11)

146 13 4: PrintableString 'NIST'

         :           }
         :         }

152 31 17: SET { 154 30 15: SEQUENCE { 156 06 3: OBJECT IDENTIFIER commonName (2 5 4 3) 161 13 8: PrintableString 'Tim Polk'

         :           }
         :         }
         :       }

171 30 159: SEQUENCE { 174 30 13: SEQUENCE { 176 06 9: OBJECT IDENTIFIER

         :           rsaEncryption (1 2 840 113549 1 1 1)

187 05 0: NULL

         :         }

189 03 141: BIT STRING 0 unused bits, encapsulates { 193 30 137: SEQUENCE { 196 02 129: INTEGER

         :               00 E1 6A E4 03 30 97 02 3C F4 10 F3 B5 1E
         :               4D 7F 14 7B F6 F5 D0 78 E9 A4 8A F0 A3 75
         :               EC ED B6 56 96 7F 88 99 85 9A F2 3E 68 77
         :               87 EB 9E D1 9F C0 B4 17 DC AB 89 23 A4 1D
         :               7E 16 23 4C 4F A8 4D F5 31 B8 7C AA E3 1A
         :               49 09 F4 4B 26 DB 27 67 30 82 12 01 4A E9
         :               1A B6 C1 0C 53 8B 6C FC 2F 7A 43 EC 33 36
         :               7E 32 B2 7B D5 AA CF 01 14 C6 12 EC 13 F2
         :               2D 14 7A 8B 21 58 14 13 4C 46 A3 9A F2 16
         :               95 FF 23

328 02 3: INTEGER 65537

         :             }
         :           }
         :       }

333 A3 175: [3] { 336 30 172: SEQUENCE { 339 30 63: SEQUENCE { 341 06 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17) 346 04 56: OCTET STRING, encapsulates { 348 30 54: SEQUENCE {

Housley, et. al. Standards Track [Page 124] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

350 86 52: [6]

         :                   'http://www.itl.nist.gov/div893/staff/'
         :                   'polk/index.html'
         :                 }
         :               }
         :           }

404 30 31: SEQUENCE { 406 06 3: OBJECT IDENTIFIER issuerAltName (2 5 29 18) 411 04 24: OCTET STRING, encapsulates { 413 30 22: SEQUENCE { 415 86 20: [6] 'http://www.nist.gov/'

         :                 }
         :               }
         :           }

437 30 31: SEQUENCE { 439 06 3: OBJECT IDENTIFIER

         :             authorityKeyIdentifier (2 5 29 35)

444 04 24: OCTET STRING, encapsulates { 446 30 22: SEQUENCE { 448 80 20: [0]

         :                   08 68 AF 85 33 C8 39 4A 7A F8 82 93 8E
         :                   70 6A 4A 20 84 2C 32
         :                 }
         :               }
         :           }

470 30 23: SEQUENCE { 472 06 3: OBJECT IDENTIFIER

         :             certificatePolicies (2 5 29 32)

477 04 16: OCTET STRING, encapsulates { 479 30 14: SEQUENCE { 481 30 12: SEQUENCE { 483 06 10: OBJECT IDENTIFIER

         :                            '2 16 840 1 101 3 2 1 48 9'
         :                   }
         :                 }
         :               }
         :           }

495 30 14: SEQUENCE { 497 06 3: OBJECT IDENTIFIER keyUsage (2 5 29 15) 502 01 1: BOOLEAN TRUE 505 04 4: OCTET STRING, encapsulates { 507 03 2: BIT STRING 7 unused bits

         :                 '1'B (bit 0)
         :               }
         :           }
         :         }
         :       }
         :     }

Housley, et. al. Standards Track [Page 125] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

511 30 13: SEQUENCE { 513 06 9: OBJECT IDENTIFIER

         :       sha1withRSAEncryption (1 2 840 113549 1 1 5)

524 05 0: NULL

         :     }

526 03 129: BIT STRING 0 unused bits

         :     1E 07 77 6E 66 B5 B6 B8 57 F0 03 DC 6F 77
         :     6D AF 55 1D 74 E5 CE 36 81 FC 4B C5 F4 47
         :     82 C4 0A 25 AA 8D D6 7D 3A 89 AB 44 34 39
         :     F6 BD 61 1A 78 85 7A B8 1E 92 A2 22 2F CE
         :     07 1A 08 8E F1 46 03 59 36 4A CB 60 E6 03
         :     40 01 5B 2A 44 D6 E4 7F EB 43 5E 74 0A E6
         :     E4 F9 3E E1 44 BE 1F E7 5F 5B 2C 41 8D 08
         :     BD 26 FE 6A A6 C3 2F B2 3B 41 12 6B C1 06
         :     8A B8 4C 91 59 EB 2F 38 20 2A 67 74 20 0B
         :     77 F3
         :   }

C.4 Certificate Revocation List

 This section contains an annotated hex dump of a version 2 CRL with
 one extension (cRLNumber).  The CRL was issued by OU=NIST; O=gov;
 C=US on August 7, 1997; the next scheduled issuance was September 7,
 1997.  The CRL includes one revoked certificates: serial number 18
 (12 hex), which was revoked on July 31, 1997 due to keyCompromise.
 The CRL itself is number 18, and it was signed with DSA and SHA-1.
0 30  203: SEQUENCE {
3 30  140:   SEQUENCE {
6 02    1:     INTEGER 1
9 30    9:     SEQUENCE {

11 06 7: OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)

         :       }

20 30 42: SEQUENCE { 22 31 11: SET { 24 30 9: SEQUENCE { 26 06 3: OBJECT IDENTIFIER countryName (2 5 4 6) 31 13 2: PrintableString 'US'

         :           }
         :         }

35 31 12: SET { 37 30 10: SEQUENCE { 39 06 3: OBJECT IDENTIFIER organizationName (2 5 4 10) 44 13 3: PrintableString 'gov'

         :           }
         :         }

49 31 13: SET { 51 30 11: SEQUENCE {

Housley, et. al. Standards Track [Page 126] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

53 06 3: OBJECT IDENTIFIER

         :             organizationalUnitName (2 5 4 11)

58 13 4: PrintableString 'NIST'

         :           }
         :         }
         :       }

64 17 13: UTCTime '970807000000Z' 79 17 13: UTCTime '970907000000Z' 94 30 34: SEQUENCE { 96 30 32: SEQUENCE { 98 02 1: INTEGER 18 101 17 13: UTCTime '970731000000Z' 116 30 12: SEQUENCE { 118 30 10: SEQUENCE { 120 06 3: OBJECT IDENTIFIER cRLReason (2 5 29 21) 125 04 3: OCTET STRING, encapsulates { 127 0A 1: ENUMERATED 1

         :                 }
         :             }
         :           }
         :         }
         :       }

130 A0 14: [0] { 132 30 12: SEQUENCE { 134 30 10: SEQUENCE { 136 06 3: OBJECT IDENTIFIER cRLNumber (2 5 29 20) 141 04 3: OCTET STRING, encapsulates { 143 02 1: INTEGER 12

         :               }
         :           }
         :         }
         :       }
         :     }

146 30 9: SEQUENCE { 148 06 7: OBJECT IDENTIFIER dsaWithSha1 (1 2 840 10040 4 3)

         :     }

157 03 47: BIT STRING 0 unused bits, encapsulates { 160 30 44: SEQUENCE { 162 02 20: INTEGER

         :           22 4E 9F 43 BA 95 06 34 F2 BB 5E 65 DB A6
         :           80 05 C0 3A 29 47

184 02 20: INTEGER

         :           59 1A 57 C9 82 D7 02 21 14 C3 D4 0B 32 1B
         :           96 16 B1 1F 46 5A
         :         }
         :       }
         :   }

Housley, et. al. Standards Track [Page 127] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

Author Addresses

 Russell Housley
 RSA Laboratories
 918 Spring Knoll Drive
 Herndon, VA 20170
 USA
 EMail:  rhousley@rsasecurity.com
 Warwick Ford
 VeriSign, Inc.
 401 Edgewater Place
 Wakefield, MA 01880
 USA
 EMail:  wford@verisign.com
 Tim Polk
 NIST
 Building 820, Room 426
 Gaithersburg, MD 20899
 USA
 EMail:  wpolk@nist.gov
 David Solo
 Citigroup
 909 Third Ave, 16th Floor
 New York, NY 10043
 USA
 EMail:  dsolo@alum.mit.edu

Housley, et. al. Standards Track [Page 128] RFC 3280 Internet X.509 Public Key Infrastructure April 2002

Full Copyright Statement

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 the copyright notice or references to the Internet Society or other
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 The limited permissions granted above are perpetual and will not be
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
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Housley, et. al. Standards Track [Page 129]

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