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rfc:rfc3157

Network Working Group A. Arsenault Request for Comments: 3157 Diversinet Category: Informational S. Farrell

                                                Baltimore Technologies
                                                           August 2001
           Securely Available Credentials - Requirements

Status of this Memo

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

Copyright Notice

 Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

 This document describes requirements to be placed on Securely
 Available Credentials (SACRED) protocols.

Table Of Contents

 1. Introduction.................................................1
 2. Framework Requirements.......................................4
 3. Protocol Requirements........................................7
 4. Security Considerations.....................................10
 References.....................................................12
 Acknowledgements...............................................12
 Authors' Addresses.............................................13
 Appendix A: A note on SACRED vs. hardware support..............14
 Appendix B: Additional Use Cases...............................14
 Full Copyright Statement.......................................20

1. Introduction

 "Credentials" are information that can be used to establish the
 identity of an entity, or help that entity communicate securely.
 Credentials include such things as private keys, trusted roots,
 tickets, or the private part of a Personal Security Environment (PSE)
 [RFC2510] - that is, information used in secure communication on the
 Internet.  Credentials are used to support various Internet
 protocols, e.g., S/MIME, IPSec and TLS.

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 In simple models, users and other entities (e.g., computers like
 routers) are provided with credentials, and these credentials stay in
 one place.  However, the number, and more importantly the number of
 different types, of devices that can be used to access the Internet
 is increasing.  It is now possible to access Internet services and
 accounts using desktop computers, laptop computers, wireless phones,
 pagers, personal digital assistants (PDAs) and other types of
 devices.  Further, many users want to access private information and
 secure services from a number of different devices, and want access
 to the same information from any device.  Similarly credentials may
 have to be moved between routers when they are upgraded.
 This document identifies a set of requirements for credential
 mobility.  The Working Group will also produce companion documents,
 which describe a framework for secure credential mobility, and a set
 of protocols for accomplishing this goal.
 The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"
 in this document are to be interpreted as described in [RFC2119].

1.1 Background and Motivation

 In simple models of Internet use, users and other entities are
 provided with credentials, and these credentials stay in one place.
 For example, Mimi generates a public and private key on her desktop
 computer, provides the public key to a Certification Authority (CA)
 to be included in a certificate, and keeps the private key on her
 computer.  It never has to be moved.
 However, Mimi may want to able to send signed e-mail messages from
 her desktop computer when she is in the office, and from her laptop
 computer when she is on the road, and she does not want message
 recipients to know the difference.  In order to do this, she must
 somehow make her private key available on both devices - that is,
 that credential must be moved.
 Similarly, Will may want to retrieve and read encrypted e-mail from
 either his wireless phone or from his two-way pager.  He wants to use
 whichever device he has with him at the moment, and does not want to
 be denied access to his mail or to be unable to decrypt important
 messages simply because he has the wrong device.  Thus, he must be
 able to have the same private key available on both devices.
 The following scenario relating to routers has also been offered:
 "Once upon a time, a router generated a keypair.  The administrators
 transferred the public key of that router to a lot of other (peer)
 routers and used that router to encrypt traffic to the other routers.
 And this was good for many years.  Then one day, the network

Arsenault & Farrell Informational [Page 2] RFC 3157 SACRED - Requirements August 2001

 administrators found that this particular little router couldn't
 handle an OC-192.  So they trashed it and replaced it with a really
 big router.  While they were there, the craft workers inserted a
 smart card into the router and logged into the router.  They gave the
 appropriate commands and entered the correct answers and so the
 credentials (keypair) were transferred to the new, big router.
 Alternatively, the craft people could have logged into the router,
 given it a minimal configuration and transferred the credentials from
 a credential server to the router.  They had to perform the correct
 incantations and authentications for the transfer to be successful.
 In this way, the identity of the router was moved from an old router
 to a new one.  The administrators were glad that they didn't have to
 edit the configurations of all of the peer routers as well."
 It is generally accepted that the private key in these examples must
 be transferred securely.  In the first example, the private key
 should not be exposed to anyone other than Mimi herself (and ideally,
 it would not be directly exposed to her).  Furthermore, it must be
 transferred correctly.  It must be transferred to the proper device,
 and it must not be corrupted - improperly modified - during transfer.
 Making credentials securely available (in an interoperable fashion)
 will provide substantial value to network owners, administrators, and
 end users.  The intent is that this value be provided largely
 independent of the hardware device used to access the secure
 credential and the type of storage medium to which the secure
 credential is written.  Different credential storage devices, (e.g.,
 desktop or laptop PC computer memory, a 3.5 inch flexible diskette, a
 hard disk file, a cell phone, a smart card, etc.) will have very
 different security characteristics and, often very different protocol
 handling capabilities.  Using SACRED protocols, users will be able to
 securely move their credentials between different locations,
 different Internet devices, and different storage media as needed.
 In the remainder of this document we present a set of requirements
 for the secure transfer of software-based credentials.

1.2 Working Group Organization and Documents

 The SACRED Working Group is working on the standardization of a set
 of protocols for securely transferring credentials among devices.  A
 general framework is being developed that will give an abstract
 definition of protocols which can meet the credential-transfer
 requirements.  This framework will allow for the development of a set
 of protocols, which may vary from one another in some respects.
 Specific protocols that conform to the framework can then be
 developed.

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 Work is being done on a number of documents.  This document
 identifies the requirements for the general framework, as well as the
 requirements for specific protocols.  Another document will describe
 the protocol framework.  Still others will define the protocols
 themselves.

1.3 Structure of This Document

 Section 1 of this document provides an introduction to the problem
 being solved by this working group.  Section 2 describes requirements
 on the framework.  Section 3 identifies the overall requirements for
 secure credential-transfer protocols, and separate requirements for
 two different classes of solutions.  Section 4 identifies Security
 Considerations.  Appendix A describes the relationship of the SACRED
 solutions and credential-mobility solutions involving hardware
 components such as smart cards.  Appendix B contains some additional
 scenarios which were considered when developing the requirements.

2. Framework Requirements

 This section describes requirements that the SACRED framework has to
 meet, as opposed to requirements that are to be met by a specific
 protocol that uses the framework.

2.1 Credential Server and Direct solutions

 There are at least two different ways to solve the problem of secure
 credential transfer between devices.  One class of solutions uses a
 "credential server" as an intermediate node, and the other class
 provides direct transfer between devices.
 A "credential server" can be likened to a server that sits in front
 of a repository where credentials can be securely stored for later
 retrieval.  The credential server is active in the protocol, that is,
 it implements security enforcing functionality.
 To transfer credentials securely from one end device to another is a
 straightforward two-step process.  Users can have their credentials
 securely "uploaded" from one device, e.g., a wireless phone, to the
 credential server.  They can be stored on the credential server, and
 "downloaded" when needed using another device; e.g., a two-way pager.
 Some advantages of a credential server approach compared to
 credential transfer are:

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 1. It provides a conceptually clean and straightforward approach.
    For all end devices, there is one protocol, with a set of actions
    defined to transfer credentials from the device to the server, and
    another set of actions defined to transfer credentials from the
    server to the device.  Furthermore, this protocol involves clients
    (the devices) and a server (the credential server), like many
    other Internet protocols; thus, the design of this protocol is
    likely to be familiar to most people familiar with most other
    Internet protocols.
 2. It provides for a place where credentials can be securely stored
    for arbitrary lengths of time.  Given a reasonable-quality server
    operating under generally accepted practices, it is unlikely the
    credentials will be permanently lost due to a hardware failure.
    This contrasts with systems where credentials are only stored on
    end devices, in which a failure of or the loss of the device could
    mean that the credentials are lost forever.
 3. The credential server may be able to enforce a uniform security
    policy regarding credential handling.  This is particularly the
    case where credentials are issued by an organization for its own
    purposes, and are not "created" by the end user, and so must be
    governed by the policies of the issuer, not the user.
 However, the credential server approach has some potential
 disadvantages, too:
 1. It might be somewhat expensive to maintain and run the credential
    server, particularly if there are stringent requirements on
    availability and reliability of the server.  This is particularly
    true for servers which are used for a large community of users.
    When the credential server is intended for a small community, the
    complexity and cost would be much less.
 2. The credential server may have to be "trusted" in some sense and
    also introduces a point of potential vulnerability.  (See the
    Security Considerations section for some of the issues.)  Good
    protocol and system design will limit the vulnerability that
    exists at the credential server, but at a minimum, someone with
    access to the credential server will be able to delete credentials
    and thus deny the SACRED service to system users.
 Thus, some users may prefer a different class of solution, in which
 credentials are transferred directly from one device to another
 (i.e., having no intermediary element that processes or has any
 understanding of the credentials).

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 For example, consider the case where Mimi sends a message from her
 wireless phone containing the credentials in question, and retrieves
 it using her two-way pager.  In getting from one place to another,
 the bits of the message cross the wireless phone network to a base
 station.  These bits are likely transferred over the wired phone
 network to a message server run by the wireless phone operator, and
 are transferred from there over the Internet to a message server run
 by the paging operator.  From the paging operator they are
 transferred to a base station and then finally to Mimi's pager.
 Certainly, there are devices other than the original wireless phone
 and ultimate pager that are involved in the credential transfer, in
 the sense that they transmit bits from one place to another.
 However, to all devices except the pager and the wireless phone, what
 is being transferred is an un-interpreted and unprocessed set of
 bits.  No security-related decisions are made, and no actions are
 taken based on the fact that this message contains credentials, at
 any of the intermediate nodes.  They exist simply to forward bits.
 Thus, we consider this to be a "direct" transfer of credentials.
 Solutions involving the direct transfer of credentials from one
 device to another are potentially somewhat more complex than the
 credential-server approach, owing to the large number of different
 devices and formats that may have to be supported.  Complexity is
 also added due to the fact that each device may in turn have to
 exhibit the behavior of both a client and a server.
 We believe that both classes of solutions are useful in certain
 environments, and thus that the SACRED framework will have to define
 solutions for both.  The extent to which elements of the above
 solutions overlap remains to be determined.
 This all leads to our first set of requirements:
 F1.   The framework MUST support both "credential server" and
       "direct" solutions.
 F2.   The "credential server" and "direct" solutions SHOULD use the
       same technology as far as possible.

2.2 User authentication

 There is a wide range of deployment options for credential mobility
 solutions.  In many of these cases, it is useful to be able to re-use
 an existing user authentication scheme, for example where passwords
 have previously been established, it may be more secure to re-use
 these than try to manage a whole new set of passwords.  Different
 devices may also limit the types of user authentication scheme that
 are possible, e.g., not all mobile devices are practically capable of
 carrying out asymmetric cryptography.

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 F3.   The framework MUST allow for protocols which support different
       user authentication schemes

2.3 Credential Formats

       Today there is no single standard format for credentials and
       this is not likely to change in the near future.  There are a
       number of fairly widely deployed formats, e.g., [PGP],
       [PKCS#12] that have to be supported.  This means that the
       framework has to allow for protocols supporting any credential
       format.
 F4.   The details of the actual credential type or format MUST be
       opaque to the protocol, though not to processing within the
       protocol's peers.  The protocol MUST NOT depend on the internal
       structure of any credential type or format.

2.4 Transport Issues

 Different devices allow for different transport layer possibilities,
 e.g., current WAP 1.x devices do not support TCP.  For this reason
 the framework has to be transport "agnostic".
 F5.   The framework MUST allow use of different transports.

3. Protocol Requirements

 In this section, we identify the requirements for secure credential-
 transfer solutions.  We will begin by listing a set of relevant
 vulnerabilities and the requirements that must be met by all
 solutions.  Then we identify additional requirements that must be met
 by solutions involving a credential server, followed by additional
 requirements that must be met by solutions involving direct transfer
 of credentials.

3.1 Vulnerabilities

 This section lists the vulnerabilities against which a SACRED
 protocol SHOULD offer protection.  Any protocol claiming to meet the
 requirements listed in this document MUST explicitly indicate how (or
 whether) it offers protection for each of these vulnerabilities.
 V1.      A passive attacker can watch all packets on the network and
          later carry out a dictionary attack.
 V2.      An attacker can attempt to masquerade as a credential server
          in an attempt to get a client to reveal information on line
          that allows for a later dictionary attack.

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 V3.      An attacker can attempt to get a client to decrypt a chosen
          "ciphertext" and get the client to make use of the resulting
          plaintext - the attacker may then be able to carry out a
          dictionary attack (e.g., if the plaintext resulting from
          "decryption" of a random string is used as a DSA private
          key).
 V4.      An attacker could overwrite a repository entry so that when
          a user subsequently uses what they think is a good
          credential, they expose information about their password
          (and hence the "real" credential).
 V5.      An attacker can copy a credential server's repository and
          carry out a dictionary attack.
 V6.      An attacker can attempt to masquerade as a client in an
          attempt to get a server to reveal information that allows
          for a later dictionary attack.
 V7.      An attacker can persuade a server that a successful login
          has occurred, even if it hasn't.
 V8.      (Upload) An attacker can overwrite someone else's
          credentials on the server.
 V9.      (When using password-based authentication) An attacker can
          force a password change to a known (or "weak") password.
 V10.     An attacker can attempt a man-in-the-middle attack for lots
 V11.     User enters password instead of name.
 V12.     An attacker could attempt various denial-of-service attacks.

3.2 General Protocol Requirements

 Looking again at the examples described in Section 1.1, we can
 readily see that there are a number of requirements that must apply
 to the transfer of credentials if the ultimate goal of supporting the
 Internet security protocols (e.g., TLS, IPSec, S/MIME) is to be met.
 For example, the credentials must remain confidential at all times;
 it is unacceptable for nodes other than the end-user's device(s) to
 see the credentials in any readable, cleartext form.
 These, then, are the requirements that apply to all secure
 credential-transfer solutions:
 G1.      Credential transfer both to and from a device MUST be
          supported.
 G2.      Credentials MUST NOT be forced by the protocol to be present
          in cleartext at any device other than the end user's.
 G3.      The protocol SHOULD ensure that all transferred credentials
          be authenticated in some way (e.g., digitally signed or
          MAC-ed).
 G4.      The protocol MUST support a range of cryptographic
          algorithms, including symmetric and asymmetric algorithms,
          hash algorithms, and MAC algorithms.

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 G5.      The protocol MUST allow the use of various credential types
          and formats (e.g., X.509, PGP, PKCS12, ...).
 G6.      One mandatory to support credential format MUST be defined.
 G7.      One mandatory to support user authentication scheme MUST be
          defined.
 G8.      The protocol MAY allow credentials to be labeled with a text
          handle, (outside the credential), to allow the end user to
          select amongst a set of credentials or to name a particular
          credential.
 G9.      Full I18N support is REQUIRED (via UTF8 support) [RFC2277].
 G10.     It is desirable that the protocol be able to support
          privacy, that is, anonymity for the client.
 G11.     Transferred credentials MAY incorporate timing information,
          for example a "time to live" value determining the maximum
          time for which the credential is to be usable following
          transfer/download.

3.3 Requirements for Credential Server-based solutions

 The following requirements assume that there is a credential server
 from which credentials are downloaded to the end user device, and to
 which credentials are uploaded from an end user device.
 S1.      Credential downloads (to an end user) and upload (to the
          credential server) MUST be supported.
 S2.      Credentials MUST only be downloadable following user
          authentication or else only downloaded in a format that
          requires completion of user authentication for deciphering.
 S3.      It MUST be possible to ensure the authenticity of a
          credential during upload.
 S4.      Different end user devices MAY be used to
          download/upload/manage the same set of credentials.
 S5.      Credential servers SHOULD be authenticated to the user for
          all operations except download.  Note: This requirement can
          be ignored if the credential format itself is strongly
          protected, as there is no risk (other than user confusion)
          from an unauthenticated credential server.
 S6.      It SHOULD be possible to authenticate the credential server
          to the user as part of a download operation.
 S7.      The user SHOULD only have to enter a single secret value in
          order to download and use a credential.
 S8.      Sharing of secrets across multiple servers MAY be possible,
          so that penetration of some servers does not expose the
          private parts of a credential ("m-from-n" operation).
 S9.      The protocol MAY support "away-from-home" operation, where
          the user enters both a name and a domain (e.g.
          RoamingStephen@baltimore.ie) and the domain can be used in
          order to locate the user's credential server.

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 S10.     The protocol MUST provide operations allowing users to
          manage their credentials stored on the credential server,
          e.g., to retrieve a list of their credentials stored on a
          server; add credentials to the server; delete credentials
          from the server.
 S11.     Client-initiated authentication information (e.g., password)
          change MUST be supported.
 S12.     The user SHOULD be able to retrieve a list of
          accesses/changes to their credentials.
 S13.     The protocol MUST support user self-enrollment.  One
          scenario calling for this is where a previously unknown user
          uploads his credential without requiring manual operator
          intervention.
 S14.     The protocol MUST NOT prevent bulk initializing of a
          credential server's repository.
 S15.     The protocol SHOULD require minimal client configuration.

3.4 Requirements for Direct-Transfer Solutions

 The full set of requirements for this case has not been elucidated,
 and this list is therefore provisional.  An additional requirements
 document (or a modification of this one) will be required prior to
 progression of a direct-transfer protocol.
 The following requirements apply to solutions supporting the "direct"
 transfer of credentials from one device to another.  (See Section 2
 for the note on the meaning of "direct" in this case.)
 D1.   It SHOULD be possible for the receiving device to authenticate
       that the credential package indeed came from the purported
       sending device.
 D2.   In order for a sender to know that a credential has been
       received by a recipient, it SHOULD be possible for the
       receiving device to send an acknowledgment of credential
       receipt back to the sending device, and for the sending device
       to authenticate this acknowledgment.

4. Security Considerations

4.1 Hardware vs. Software

 Mobile credentials will never be as secure as a "pure" hardware-based
 solution, because of potential attacks through the operating system
 of the end-user device.  However, an acceptable level of security may
 be accomplished through some simple means.  In fact the level of
 security may be improved (compared to password encrypted files)
 through the use of SACRED protocols.

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 The platforms to which credentials are downloaded usually cannot be
 regarded as tamper-resistant, and it therefore is not too hard to
 analyze contents of their memories.  Further, storage of private
 keys, even if they are encrypted, on a credential server, will be
 unacceptable in some environments.  Lastly, replacement of installed
 or downloaded SACRED client software with a Trojan horse program will
 always be possible, such a program could email the username and
 password to the program's author.

4.2 Auditing

 Although out of scope of the SACRED protocol development work,
 implementations should carefully audit events that may be security
 relevant.  In particular credential server implementations should
 audit all operations and should include information about the time
 and source (e.g., IP address) of the operation, the claimed identity
 of the client (possibly masked - see below), the type and result of
 the operation and possibly other operation specific information.
 Implementations should also take care not to include security
 sensitive information in the audit trail, especially not sensitive
 authentication information.
 It may be sensible to mask the claimed identity in some way in order
 to ensure that even if a user enters her password in a "username"
 field, that that information is not in clear in the audit trail,
 regardless of whether or not it was received in clear.
 Similar mechanisms which should be supported, but which are out of
 scope of protocol development include alerts and account locking, in
 particular following repeated authentication failures.

4.3 Defense against attacks

 Credential servers are major targets.  Someone who can successfully
 attack a credential server might be able to gain access to the
 credentials of a number of users, unless those credentials are
 sufficiently protected (e.g., encrypted sufficiently that they cannot
 be read or used by someone who gains access to them).  Attackers
 might also be able to substitute credentials of users, to carry out
 other system attacks (e.g., an attacker could provide a user with a
 "trusted root" credential that the attacker controls, which would
 later allow the attacker to have some other certificate accepted by
 the user counter to policy).
 In addition, a credential server is a major target for denial of
 service attacks.  Ensuring that a credential server is unavailable to
 legitimate users can be of great assistance to attackers.  Users who
 were not able to retrieve needed credentials might be forced to

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 operate insecurely, or not operate at all.  Credential servers are
 especially vulnerable to denial of service attacks if they do lots of
 expensive cryptographic operations - it might not take very many
 operations for the attacker to bring service to an unacceptable
 level.
 Thus, great care should be taken in designing systems that use
 credential servers to protect against these attacks.

References

 [PGP]       Callas, J., Donnerhacke, L., Finney, H. and R. Thayer,
             "OpenPGP Message Format", RFC 2440, November 1998.
 [PKCS12]    "PKCS #12 v1.0: Personal Information Exchange Syntax
             Standard", RSA Laboratories, June 24, 1999.
 [CMS]       Housley, R., "Cryptographic Message Syntax", RFC 2630,
             June 1999.
 [PKCS15]    "PKCS #15 v1.1: Cryptographic Token Information Syntax
             Standard," RSA Laboratories, June 2000.
 [RFC2026]   Bradner, S., "The Internet Standards Process -- Revision
             3", BCP 9, RFC 2026, October 1996.
 [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2277]   Alvestrand, H., " IETF Policy on Character Sets and
             Languages", BCP 18, RFC 2277, January 1998.
 [RFC2510]   Adams, C. and S. Farrell, "Internet X.509 Public Key
             Infrastructure Certificate Management Protocols", RFC
             2510, March 1999.
 [RFC2616]   Fielding, R., Gettys, J., Mogul, J., Frysyk, H.,
             Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
             Transfer Protocol - HTTP/1.1", RFC 2616, June 1999.

Acknowledgements

 The authors gratefully acknowledge the text containing additional use
 cases in Appendix B that was supplied by Neal Mc Burnett
 (nealmcb@avaya.com).

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Authors' Addresses

 Alfred Arsenault
 Diversinet Corp.
 P.O. Box 6530
 Ellicott City, MD 21042
 USA
 Phone: +1 410-480-2052
 EMail: aarsenault@dvnet.com
 Stephen Farrell,
 Baltimore Technologies,
 39 Parkgate Street,
 Dublin 8,
 IRELAND
 Phone: +353-1-881-6000
 EMail: stephen.farrell@baltimore.ie

Arsenault & Farrell Informational [Page 13] RFC 3157 SACRED - Requirements August 2001

Appendix A: A note on SACRED vs. hardware support.

 One way of accomplishing many of the goals of the SACRED WG is to put
 the credentials on hardware tokens - e.g., smart cards, PCMCIA cards,
 or other devices.  There are a number of types of hardware tokens
 today that provide secure storage for sensitive information, some
 degree of authentication, and interfaces to a number of types of
 wireless and other devices.  Thus, in the second example from section
 1.1, Will could simply put his private key on a smart card, always
 take the smart card with him, and be assured that whichever device he
 uses to retrieve his e-mail, he will have all of the information
 necessary to decrypt and read messages.
 However, hardware tokens are not appropriate for every environment.
 They cost more than software-only solutions, and the additional
 security they provide may or may not be worth the incremental cost.
 Not all devices have interfaces for the same hardware tokens.  And
 hardware tokens are subject to different failure modes than typical
 computers - it is not at all unusual for a smart card to be lost or
 stolen; or for a PCMCIA card to physically break.
 Thus, it is appropriate to develop complementary software-based
 solution that allows credentials to be moved from one device to
 another, and provides a level of security sufficient for its
 environments.  While we recognize that the level of security provided
 by a software solution may not be as high as that provided by the
 hardware solutions discussed above, and some organizations may not
 consider it sufficient at all, we believe that a worthwhile solution
 can be developed.
 Finally, SACRED protocols can also complement hardware credential
 solutions by providing standard mechanisms for the update of
 credentials which are stored on the hardware device.  Today, this
 often requires returning (with) the device to an administrative
 centre, which is often inconvenient and may be costly.  SACRED
 protocols provide a way to update and manage credentials stored on
 hardware devices without requiring such physical presence.

Appendix B: Additional Use Cases

 This appendix describes some additional use cases for SACRED
 protocols.  SACRED protocols are NOT REQUIRED to support all these
 use cases, that is, this text is purely informative.

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B.1 Home/Work Desktop Computer

 Scenario Overview
 A university utilizing a PKI for various applications and services
 on-campus is likely to find that many of its users would like to make
 use of the same PKI-enabled services and applications on computers
 located in their residence.  These home computers may be owned either
 by the university or by the individual but are permanently located at
 the residence as opposed to laptop systems that may be taken home.
 The usage depicted in this scenario may be motivated by formal
 telecommuting arrangements or simply by the need to catch up on work
 from home in the evenings.  The basic scenario should apply equally
 well to the commercial, health care, and higher education
 environments.
 Assumptions
 This scenario assumes that the institution has not implemented a
 hardware token-based PKI mobility solution
 The home computer has a dial-up as opposed to a permanent network
 connection.
 The PKI applications, whenever practical, should be functional in
 both on-line and off-line modes.  For example, the home user signing
 an email message to be queued for later bulk sending and the reading
 of a received encrypted message may be supported off-line while
 composing and queuing of an encrypted message might not be supported
 in off-line mode.
 Applications using digital signatures may require "non-repudiation".
 The institution prefers that the user be identified via a single
 certificate / key-pair from all computers used by the individual.
 The home computer system can not be directly supported by the
 institution's IT staff.  Hardware, operating system versions, and
 operating system configurations will vary widely.  Significant
 software installation or specialized configurations will be difficult
 to implement.
 Uniqueness of Scenario
 vThe PKI mobility support needed for this scenario is, in general,
 similar to the other mobility scenarios.  However, it does have
 several unique aspects:

Arsenault & Farrell Informational [Page 15] RFC 3157 SACRED - Requirements August 2001

 1. The home-user scenario differs from the general public workstation
    case in that it provides the opportunity to permanently store the
    user's certificate and key-pair on the workstation.
 2. Likewise the appropriate CA certificates and even certificates for
    other users can be permanently stored or cached on the home
    workstation.
 3. Another key difference is the need to support off-line use of the
    PKI credentials given the assumed dial-up network connection.
 4. The level of hardware and software platform consistency (operating
    system versions and configurations) will vary widely.
 5. Finally, the level of available technical support is significantly
    less for home systems than for equivalent systems managed by the
    IT staff at the office location.

B.2 Public Lab / On-campus Shared Workstation

 Scenario Overview
 Many colleges and universities operate labs full of computer systems
 that are available for use by the general student population.  These
 computers are typically configured with identical hardware and an
 operating system build that is replicated to all of the systems in
 the lab.  Many typical configurations provide no permanent storage of
 any type while others may offer individual disk space for personal
 files on a central server.  Some scheme is generally used to ensure
 that the configuration of the operating system is preserved across
 users and that temporary files created by one user are removed before
 the next user logs in.  Students generally sit down at the next
 available workstation without any clear pattern of usage.
 The same basic technical solutions used to operate public labs are
 often also used in general environments where several people share a
 single workstation.  This is often found in locations with shift work
 such as medical facilities and service bureaus that provide services
 to multiple time zones.
 Assumptions
 1. This scenario assumes that the institution has not implemented a
    hardware token-based PKI mobility solution.
 2. The computer systems are permanently networked with LAN
    connections.

Arsenault & Farrell Informational [Page 16] RFC 3157 SACRED - Requirements August 2001

 3. The configuration of the computer system is centrally maintained
    and customizations are relatively easy to implement.  For example
    it would be easy to load enterprise root certificates, LDAP server
    configurations, specialized software, and any other needed
    components of the PKI on to the workstations.
 4. Applications using digital signatures may require "non-
    repudiation" in some of the anticipated environments.  Examples of
    this might include homework submission in a public lab environment
    or medical records in a health care environment.
 5. The institution prefers that the user be identified via a single
    certificate / key-pair from all computers used by the individual.
 6. Many anticipated implementations of this scenario will not
    implement any user authentication at the desktop operating system
    level.  Instead, user authentication will occur at during the
    startup of networked applications such as email, web-based
    services, etc.  Login at the desktop level may be with generic
    user names that are more targeted at matching printouts to
    machines than identifying users.
 7. Users, with almost ridiculous frequency, will walk away from a
    system forgetting to first logout from running authenticated
    applications.
 Uniqueness of Scenario
 The PKI mobility support needed for this scenario is, in general,
 similar to the other mobility scenarios.  However, it does have
 several unique aspects:
 1. Unlike situations with personal workstations, there is no
    permanent storage available to hold user key pairs and
    certificates.
 2. Appropriate CA certificates and custom software are easily added
    and maintained for these types of shared systems.
 3. The workstations are installed in public locations and users will
    frequently forget to close applications before permanently walking
    away from the workstation.

Arsenault & Farrell Informational [Page 17] RFC 3157 SACRED - Requirements August 2001

B.3 Public Kiosk Mobility

 Overview
 This scenario describes the needs of the traveler or the shopper.
 This person is traveling light (no computer) or is burdened with
 everything but a computer.  It recognizes the increasing availability
 of Internet access points in public spaces, such as libraries,
 airports, shopping malls, and "cyber cafes".
 The Need
 In our increasingly mobile society, the chances of needing
 information when away from the normal computing place are great.  One
 may need to look up a telephone number.  Have you tried to find a
 phone book at a public phone lately?  It may become necessary to use
 a data device to find the next place to rush to.  With the
 proliferation of wireless devices (electronic leashes), others have
 the ability to create a need for quick access to electronic
 information.  A pager can generate a need to check the email inbox or
 address book.  A cell phone can drive you to your database to answer
 a pressing question.
 The ability to quickly access sensitive or protected information or
 services from publicly available devices will only become more
 necessary as we become more and more "connected".
 The Device
 The access device is more a function of the best discount or
 marketing effort than of design.  Any number of hardware platforms
 will be encountered.
 Since these devices are open to the public I/O ports are not likely
 to be.  In order to protect the device and its immediate network
 environment, most devices will be in some sort of protective
 container.  Access to serial, parallel, USB, firewire, SCSI, or
 PCMCIA connections will not be possible.  Likewise floppy, zip, or CD
 drives.  Therefore, any software "token" must be obtained from the
 network itself.
 The Concerns
 1. Getting the "token".  Since it will be necessary to obtain the
    token (key, certificate, credential) from across the network.  How
    can it be protected during transit?

Arsenault & Farrell Informational [Page 18] RFC 3157 SACRED - Requirements August 2001

 2. Where did you get it?  One of the primary controls in PKI is
    protection of the private key.  Placing the key on a host that is
    accessible from a public network means that there is an inherent
    exposure from that network.  The access controls and other
    security measures on the host machine are an area of concern.
 3. How did you get it?  When you obtained the token from the server,
    how did it know that you are you?  Authentication becomes
    critical.
 4. What happens to the token when you leave?  You've checked your
    mail, downloaded a recipe from that super-secure recipe server,
    found out how to get to the adult beverage store for the... uh...
    accessories... for the meal, and you're off!  Is your token?  Or
    is it still sitting there on the public kiosk waiting for those
    youngsters coming out of the music store to notice and cruise the
    information highway on your ticket?

Arsenault & Farrell Informational [Page 19] RFC 3157 SACRED - Requirements August 2001

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Acknowledgement

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Arsenault & Farrell Informational [Page 20]

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