





Network Working Group                                      R. Zuccherato
Request for Comments: 3163                          Entrust Technologies
Category: Experimental                                        M. Nystrom
                                                            RSA Security
                                                             August 2001


              ISO/IEC 9798-3 Authentication SASL Mechanism

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

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

IESG Note

   It is the opinion of the Security Area Directors that this document
   defines a mechanism to use a complex system (namely PKI certificates)
   for authentication, but then intentionally discards the key benefits
   (namely integrity on each transmission).  Put another way, it has all
   of the pain of implementing a PKI and none of the benefits.  We
   should not support it in use in Internet protocols.

   The same effect, with the benefits of PKI, can be had by using
   TLS/SSL, an existing already standards track protocol.

Abstract

   This document defines a SASL (Simple Authentication and Security
   Layer) authentication mechanism based on ISO/IEC 9798-3 and FIPS PUB
   196 entity authentication.














Zuccherato & Nystrom          Experimental                      [Page 1]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


1. Introduction

1.1. Overview

   This document defines a SASL [RFC2222] authentication mechanism based
   on ISO/IEC 9798-3 [ISO3] and FIPS PUB 196 [FIPS] entity
   authentication.

   This mechanism only provides authentication using X.509 certificates
   [X509].  It has no effect on the protocol encodings and does not
   provide integrity or confidentiality services.

   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 [RFC2119].

   The key benefit of asymmetric (public key) security, is that the
   secret (private key) only needs to be placed with the entity that is
   being authenticated.  Thus, a private key can be issued to a client,
   which can then be authenticated by ANY server based on a token
   generated by the client and the generally available public key.
   Symmetric authentication mechanisms (password mechanisms such as
   CRAM-MD5 [RFC2195]) require a shared secret, and the need to maintain
   it at both endpoints.  This means that a secret key for the client
   needs to be maintained at every server that may need to authenticate
   the client.

   The service described in this memo provides authentication only.
   There are a number of places where an authentication only service is
   useful, e.g., where confidentiality and integrity are provided by
   lower layers, or where confidentiality or integrity services are
   provided by the application.

1.2. Relationship to TLS

   The functionality defined here can be provided by TLS, and it is
   important to consider why it is useful to have it in both places.
   There are several reasons for this, e.g.:

      -  Simplicity.  This mechanism is simpler than TLS.  If there is
         only a requirement for this functionality (as distinct from all
         of TLS), this simplicity will facilitate deployment.

      -  Layering.  The SASL mechanism to establish authentication works
         cleanly with most protocols.  This mechanism can fit more
         cleanly than TLS for some protocols.





Zuccherato & Nystrom          Experimental                      [Page 2]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


      -  Proxies.  In some architectures the endpoint of the TLS session
         may not be the application endpoint.  In these situations, this
         mechanism can be used to obtain end-to-end authentication.

      -  Upgrade of authentication.  In some applications it may not be
         clear at the time of TLS session negotiation what type of
         authentication may be required (e.g., anonymous, server,
         client-server).  This mechanism allows the negotiation of an
         anonymous or server authenticated TLS session which can, at a
         later time, be upgraded to provide the desired level of
         authentication.

2.  Description of Mechanism

2.1. Scope

   The mechanism described in this memo provides either mutual or
   unilateral entity authentication as defined in ISO/IEC 9798-1 [ISO1]
   using an asymmetric (public-key) digital signature mechanism.

2.2. Authentication modes

   This SASL mechanism contains two authentication modes:

      -  Unilateral client authentication: The client digitally signs a
         challenge from the server, thus authenticating itself to the
         server.

      -  Mutual authentication: The client digitally signs a challenge
         from the server and the server digitally signs a challenge from
         the client.  Thus both the client and server authenticate each
         other.

2.3. SASL key

   This mechanism has two SASL keys corresponding to the two different
   modes:

      -  "9798-U-<algorithm>" for unilateral client authentication.

      -  "9798-M-<algorithm>" for mutual authentication.

   Each SASL key may be used with a list of algorithms.  A list of
   supported algorithms is given in Section 4.







Zuccherato & Nystrom          Experimental                      [Page 3]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


2.4. Unilateral Client Authentication

   This section gives a brief description of the steps that are
   performed for unilateral client authentication.  The actual data
   structures are described fully in Section 3.

      a) The server generates a random challenge value R_B and sends it
         to the client.

      b) The client generates a random value R_A and creates a token
         TokenAB.  The token contains R_A, the client's certificate and
         also a digital signature created by the client over both R_A
         and R_B.  Optionally, it also contains an identifier for the
         server.

      c) The client sends the token to the server.

      d) The server verifies the token by:

         -  verifying the client's signature in TokenAB (this includes
            full certificate path processing as described in [RFC2459]),

         -  verifying that the random number R_B, sent to the client in
            Step 1, agrees with the random number contained in the
            signed data of TokenAB, and

         -  verifying that the identifier for the server, if present,
            matches the server's distinguishing identifier.

2.5. Mutual Authentication

   This section gives a brief description of the steps that are
   performed for mutual authentication.  The actual data structures are
   described fully in Section 3.

      a) The server generates a random challenge value R_B and sends it
         to the client.

      b) The client generates a random value R_A and creates a token
         TokenAB.  The token contains R_A, the client's certificate and
         also a digital signature created by the client over both R_A
         and R_B.  Optionally, it also contains an identifier for the
         server.

      c) The client sends the token to the server.

      d) The server verifies the token by:




Zuccherato & Nystrom          Experimental                      [Page 4]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


         -  verifying the client's signature in TokenAB (this includes
            full certificate path processing as described in [RFC2459]),

         -  verifying that the random number R_B, sent to the client in
            Step 1, agrees with the random number contained in the
            signed data of TokenAB, and

         -  verifying that the identifier for the server, if present,
            matches the server's distinguishing identifier.

      e) The server creates a token TokenBA.  The token contains a third
         random value R_C, the server's certificate and a digital
         signature created by the server over R_A, R_B and R_C.
         Optionally, it also contains an identifier for the client.

      f) The server sends the token to the client.

      g) The client verifies the token by:

         -  verifying the server's signature in TokenBA (this includes
            full certificate path processing as described in [RFC2459]),

         -  verifying that the random number R_B, received by the client
            in Step 1, agrees with the random number contained in the
            signed data of TokenBA,

         -  verifying that the random number R_A, sent to the server in
            Step 2, agrees with the random number contained in the
            signed data of Token BA and

         -  verifying that the identifier for the client, if present,
            matches the client's distinguishing identifier.

3.  Token and Message Definition

   Note -   Protocol data units (PDUs) SHALL be DER-encoded [X690]
            before transmitted.

3.1. The "TokenBA1" PDU

   TokenBA1 is used in both the unilateral client authentication and
   mutual authentication modes and is sent by the server to the client.

   TokenBA1 contains a random value, and, optionally, the servers name
   and certificate information.






Zuccherato & Nystrom          Experimental                      [Page 5]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   TokenBA1 ::= SEQUENCE {
        randomB   RandomNumber,
        entityB   [0] GeneralNames OPTIONAL,
        certPref  [1] SEQUENCE SIZE (1..MAX) OF TrustedAuth OPTIONAL
   }

3.2. The "TokenAB" PDU

   TokenAB is used in the unilateral client authentication and mutual
   authentication modes and is sent by the client to the server.
   TokenAB contains a random number, entity B's name (optionally),
   entity certification information, an (optional) authorization
   identity, and a signature of a DER-encoded value of type TBSDataAB.
   The certA field is used to send the client's X.509 certificate (or a
   URL to it) and a related certificate chain to the server.

   The authID field is to be used when the identity to be used for
   access control is different than the identity contained in the
   certificate of the signer.  If this field is not present, then the
   identity from the client's X.509 certificate shall be used.

   TokenAB ::= SEQUENCE {
        randomA   RandomNumber,
        entityB   [0] GeneralNames OPTIONAL,
        certA     [1] CertData,
        authID    [2] GeneralNames OPTIONAL,
        signature SIGNATURE { TBSDataAB }

   }(CONSTRAINED BY {-- The entityB and authID fields shall be included
     -- in TokenAB if and only if they are also included in TBSDataAB.
     -- The entityB field SHOULD be present in TokenAB whenever the
     -- client believes it knows the identity of the server.--})

   TBSDataAB ::= SEQUENCE {
        randomA RandomNumber,
        randomB RandomNumber,
        entityB [0] GeneralNames OPTIONAL,
        authID  [1] GeneralNames OPTIONAL
   }

3.3. The "TokenBA2" PDU

   TokenBA2 is used in the mutual authentication mode and is sent by the
   server to the client.  TokenBA2 contains a random number, entity A's
   name (optionally), certification information, and a signature of a
   DER-encoded value of type TBSDataBA.  The certB field is to be used
   to send the server's X.509 certificate and a related certificate
   chain to the client.



Zuccherato & Nystrom          Experimental                      [Page 6]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   TokenBA2 ::= SEQUENCE {
        randomC   RandomNumber,
        entityA   [0] GeneralNames OPTIONAL,
        certB     [1] CertData,
        signature SIGNATURE { TBSDataBA }
   }(CONSTRAINED BY {-- The entityA field shall be included in TokenBA2
     -- if and only if it is also included in TBSDataBA.  The entityA
     -- field SHOULD be present and MUST contain the client's name
     -- from their X.509 certificate.--})

   TBSDataBA ::= SEQUENCE {
        randomB RandomNumber,
        randomA RandomNumber,
        randomC RandomNumber,
        entityA GeneralNames OPTIONAL
   }

3.4. The "TrustedAuth" type

   TrustedAuth ::= CHOICE {
        authorityName         [0] Name,
             -- SubjectName from CA certificate
        issuerNameHash        [1] OCTET STRING,
             -- SHA-1 hash of Authority's DN
        issuerKeyHash         [2] OCTET STRING,
             -- SHA-1 hash of Authority's public key
        authorityCertificate  [3] Certificate,
             -- CA certificate
        pkcs15KeyHash         [4] OCTET STRING
             -- PKCS #15 key hash
   }

   The TrustedAuth type can be used by a server in its initial message
   ("TokenBA1") to indicate to a client preferred certificates/public
   key pairs to use in the authentication.

   A trusted authority is identified by its name, hash of its name, hash
   of its public key, its certificate, or PKCS #15 key hash.  If
   identified by its name, then the authorityName field in TrustedAuth
   contains the SubjectName of its CA certificate.  If it is identified
   by the hash of its name then the issuerNameHash field contains the
   SHA-1 hash of the DER encoding of SubjectName from its CA
   certificate.  If it is identified by the hash of its public key then
   the issuerKeyHash field contains the SHA-1 hash of the authority's
   public key.  The hash shall be calculated over the value (excluding
   tag and length) of the subject public key field in the issuer's
   certificate.  If it is identified by its certificate then the
   authorityCertificate field contains its CA certificate.  If it is



Zuccherato & Nystrom          Experimental                      [Page 7]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   identified by the PKCS #15 key hash then the pkcs15KeyHash field
   contains the hash of the CA's public key as defined in PKCS #15
   [PKCS15] Section 6.1.4.

3.5. The "CertData" type

   The certification data is a choice between a set of certificates and
   a certificate URL.

   The certificate set alternative is as in [RFC2630], meaning it is
   intended that the set be sufficient to contain chains from a
   recognized "root" or "top-level certification authority" to all of
   the sender certificates with which the set is associated.  However,
   there may be more certificates than necessary, or there may be fewer
   than necessary.

   Note -   The precise meaning of a "chain" is outside the scope of
            this document.  Some applications may impose upper limits on
            the length of a chain; others may enforce certain
            relationships between the subjects and issuers of
            certificates within a chain.

   When the certURL type is used to specify the location at which the
   user's certificate can be found, it MUST be a non-relative URL, and
   MUST follow the URL syntax and encoding rules specified in [RFC1738].
   The URL must include both a scheme (e.g., "http" or "ldap") and a
   scheme-specific part.  The scheme-specific part must include a fully
   qualified domain name or IP address as the host.

   CertData ::= CHOICE {
        certificateSet     SET SIZE (1..MAX) OF Certificate,
        certURL            IA5String,
        ... -- For future extensions
   }

3.6. The "RandomNumber" type

   A random number is simply defined as an octet string, at least 8
   bytes long.

   RandomNumber ::= OCTET STRING (SIZE(8..MAX))

3.7. The "SIGNATURE" type

   This is similar to the "SIGNED" parameterized type defined in
   [RFC2459], the difference being that the "SIGNATURE" type does not
   include the data to be signed.




Zuccherato & Nystrom          Experimental                      [Page 8]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   SIGNATURE { ToBeSigned } ::= SEQUENCE {
        algorithm AlgorithmIdentifier,
        signature BIT STRING
   }(CONSTRAINED BY {-- Must be the result of applying the signing
     -- operation indicated in "algorithm" to the DER-encoded octets of
     -- a value of type -- ToBeSigned })

3.8. Other types

   The "GeneralNames" type is defined in [RFC2459].

4.  Supported Algorithms

   The following signature algorithms are recognized for use with this
   mechanism, and identified by a key.  Each key would be combined to
   make two possible SASL mechanisms.  For example the DSA-SHA1
   algorithm would give 9798-U-DSA-SHA1, and 9798-M-DSA-SHA1.  All
   algorithm names are constrained to 13 characters, to keep within the
   total SASL limit of 20 characters.

   The following table gives a list of algorithm keys, noting the object
   identifier and the body that assigned the identifier.

      Key              Object Id           Body
      RSA-SHA1-ENC   1.2.840.113549.1.1.5  RSA
      DSA-SHA1       1.2.840.10040.4.3     ANSI
      ECDSA-SHA1     1.2.840.10045.4.1     ANSI

   Support of the RSA-SHA1-ENC algorithm is RECOMMENDED for use with
   this mechanism.

5.  Examples

5.1. IMAP4 example

   The following example shows the use of the ISO/IEC 9798-3
   Authentication SASL mechanism with IMAP4 [RFC2060].

   The base64 encoding of challenges and responses, as well as the "+ "
   preceding the responses are part of the IMAP4 profile, not part of
   this specification itself (note that the line breaks in the sample
   authenticators are for editorial clarity and are not in real
   authenticators).








Zuccherato & Nystrom          Experimental                      [Page 9]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   S: * OK IMAP4 server ready
   C: A001 AUTHENTICATE 9798-U-RSA-SHA1
   S: + MAoECBI4l1h5h0eY
   C: MIIBAgQIIxh5I0h5RYegD4INc2FzbC1yLXVzLmNvbaFPFk1odHRwOi8vY2VydHMt
      ci11cy5jb20vY2VydD9paD1odmNOQVFFRkJRQURnWUVBZ2hBR2hZVFJna0ZqJnNu
      PUVQOXVFbFkzS0RlZ2pscjCBkzANBgkqhkiG9w0BAQUFAAOBgQCkuC2GgtYcxGG1
      NEzLA4bh5lqJGOZySACMmc+mDrV7A7KAgbpO2OuZpMCl7zvNt/L3OjQZatiX8d1X
      buQ40l+g2TJzJt06o7ogomxdDwqlA/3zp2WMohlI0MotHmfDSWEDZmEYDEA3/eGg
      kWyi1v1lEVdFuYmrTr8E4wE9hxdQrA==
   S: A001 OK Welcome, 9798-U-RSA-SHA1 authenticated user: Magnus

6. IANA Considerations

   By registering the 9798-<U/M>-<algorithm> protocols as SASL
   mechanisms, implementers will have a well-defined way of adding this
   authentication mechanism to their product.  Here is the registration
   template for the SASL mechanisms defined in this memo:

        SASL mechanism names:     9798-U-RSA-SHA1-ENC
                                  9798-M-RSA-SHA1-ENC
                                  9798-U-DSA-SHA1
                                  9798-M-DSA-SHA1
                                  9798-U-ECDSA-SHA1
                                  9798-M-ECDSA-SHA1
                                  ; For a definition of the algorithms
                                  see Section 4 of this memo.

        Security Considerations:  See Section 7 of this memo
        Published specification:  This memo
        Person & email address to
        contact for further
        information:              See Section 9 of this memo.
        Intended usage:           COMMON
        Author/Change controller: See Section 9 of this memo.

7.  Security Considerations

   The mechanisms described in this memo only provides protection
   against passive eavesdropping attacks.  They do not provide session
   privacy or protection from active attacks.  In particular, man-in-
   the-middle attacks aimed at session "hi-jacking" are possible.

   The random numbers used in this protocol MUST be generated by a
   cryptographically strong random number generator.  If the number is
   chosen from a small set or is otherwise predictable by a third party,
   then this mechanism can be attacked.





Zuccherato & Nystrom          Experimental                     [Page 10]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   The inclusion of the random number R_A in the signed part of TokenAB
   prevents the server from obtaining the signature of the client on
   data chosen by the server prior to the start of the authentication
   mechanism.  This measure may be required, for example, when the same
   key is used by the client for purposes other than entity
   authentication.  However, the inclusion of R_B in TokenBA2, whilst
   necessary for security reasons which dictate that the client should
   check that it is the same as the value sent in the first message, may
   not offer the same protection to the server, since R_B is known to
   the client before R_A is chosen.  For this reason a third random
   number, R_C, is included in the TokenBA2 PDU.

8.  Bibliography

   [FIPS]      FIPS 196, "Entity authentication using public key
               cryptography," Federal Information Processing Standards
               Publication 196, U.S. Department of Commerce/N.I.S.T.,
               National Technical Information Service, Springfield,
               Virginia, 1997.

   [ISO1]      ISO/IEC 9798-1:  1997, Information technology - Security
               techniques - Entity authentication - Part 1: General.

   [ISO3]      ISO/IEC 9798-3:  1997, Information technology - Security
               techniques - Entity authentication - Part 3: Mechanisms
               using digital signature techniques.

   [PKCS15]    RSA Laboratories, "The Public-Key Cryptography Standards
               - PKCS #15 v1.1:  Cryptographic token information syntax
               standard", June 6, 2000.

   [RFC1738]   Berners-Lee, T., Masinter L. and M. McCahill "Uniform
               Resource Locators (URL)", RFC 1738, December 1994.

   [RFC2026]   Bradner, S., "The Internet Standards Process -- Revision
               3", BCP 9, RFC 2026, October 1996.

   [RFC2060]   Crispin, M., "Internet Message Access Protocol - Version
               4rev1", RFC 2060, December 1996.

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2195]   Klensin, J., Catoe, R. and P. Krumviede "IMAP/POP
               AUTHorize Extension for Simple Challenge/Response", RFC
               2195, September 1997.





Zuccherato & Nystrom          Experimental                     [Page 11]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   [RFC2222]   J. Meyers, "Simple Authentication and Security Layer",
               RFC 2222, October 1997.

   [RFC2459]   Housley, R., Ford, W., Polk, W. and D. Solo "Internet
               X.509 Public Key Infrastructure: X.509 Certificate and
               CRL Profile", RFC 2459, January 1999.

   [RFC2630]   R. Housley, "Cryptographic Message Syntax", RFC 2630,
               June 1999.

   [X509]      ITU-T Recommendation X.509 (1997) | ISO/IEC 9594-8:1998,
               Information Technology - Open Systems Interconnection -
               The Directory: Authentication Framework.

   [X690]      ITU-T Recommendation X.690 (1997) | ISO/IEC 8825-1:1998,
               Information Technology - ASN.1 Encoding Rules:
               Specification of Basic Encoding Rules (BER), Canonical
               Encoding Rules (CER) and Distinguished Encoding Rules
               (DER).

9. Authors' Addresses

   Robert Zuccherato
   Entrust Technologies
   1000 Innovation Drive
   Ottawa, Ontario
   Canada K2K 3E7

   Phone: +1 613 247 2598
   EMail: robert.zuccherato@entrust.com


   Magnus Nystrom
   RSA Security
   Box 10704
   121 29 Stockholm
   Sweden

   Phone: +46 8 725 0900
   EMail: magnus@rsasecurity.com











Zuccherato & Nystrom          Experimental                     [Page 12]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


APPENDICES

A. ASN.1 modules

A.1. 1988 ASN.1 module

   SASL-9798-3-1988

   DEFINITIONS IMPLICIT TAGS ::=

   BEGIN

   -- EXPORTS ALL --

   IMPORTS

   Name, AlgorithmIdentifier, Certificate
        FROM PKIX1Explicit88 {iso(1) identified-organization(3) dod(6)
        internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
        id-pkix1-explicit-88(1)}

   GeneralNames
        FROM PKIX1Implicit88 {iso(1) identified-organization(3) dod(6)
        internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
        id-pkix1-implicit-88(2)};

   TokenBA1 ::= SEQUENCE {
        randomB   RandomNumber,
        entityB   [0] GeneralNames OPTIONAL,
        certPref  [1] SEQUENCE SIZE (1..MAX) OF TrustedAuth OPTIONAL
   }

   TokenAB ::= SEQUENCE {
        randomA   RandomNumber,
        entityB   [0] GeneralNames OPTIONAL,
        certA     [1] CertData,
        authID    [2] GeneralNames OPTIONAL,
        signature SEQUENCE {
             algorithm AlgorithmIdentifier,
             signature BIT STRING
       }
   } -- The entityB and authID fields shall be included in TokenAB
     -- if and only if they are also included in TBSDataAB.  The entityB
     -- field SHOULD be present in TokenAB whenever the client
     -- believes it knows the identity of the server.
     -- The signature operation shall be done on a
     -- DER-encoded value of type TBSDataAB.




Zuccherato & Nystrom          Experimental                     [Page 13]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   TBSDataAB ::= SEQUENCE {
        randomA RandomNumber,
        randomB RandomNumber,
        entityB [0] GeneralNames OPTIONAL,
        authID  [1] GeneralNames OPTIONAL
   }

   TokenBA2 ::= SEQUENCE {
        randomC   RandomNumber,
        entityA   [0] GeneralNames OPTIONAL,
        certB     [1] CertData,
        signature SEQUENCE {
             algorithm AlgorithmIdentifier,
             signature BIT STRING
        }
   } -- The entityA field shall be included in TokenBA2
     -- if and only if it is also included in TBSDataBA.  The entityA
     -- field SHOULD be present and MUST contain the client's name
     -- from their X.509 certificate.  The signature shall be done
     -- on a DER-encoded value of type TBSDataBA.

   TBSDataBA ::= SEQUENCE {
        randomB RandomNumber,
        randomA RandomNumber,
        randomC RandomNumber,
        entityA GeneralNames OPTIONAL
   }

   TrustedAuth ::= CHOICE {
        authorityName         [0] Name,
             -- SubjectName from CA certificate
        issuerNameHash        [1] OCTET STRING,
             -- SHA-1 hash of Authority's DN
        issuerKeyHash         [2] OCTET STRING,
             -- SHA-1 hash of Authority's public key
        authorityCertificate  [3] Certificate,
             -- CA certificate
        pkcs15KeyHash         [4] OCTET STRING
             -- PKCS #15 key hash
   }

   CertData ::= CHOICE {
        certificateSet     SET SIZE (1..MAX) OF Certificate,
        certURL            IA5String
   }

   RandomNumber ::= OCTET STRING (SIZE(8..MAX))




Zuccherato & Nystrom          Experimental                     [Page 14]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   END

A.2. 1997 ASN.1 module

   SASL-9798-3-1997

   DEFINITIONS IMPLICIT TAGS ::=

   BEGIN

   -- EXPORTS ALL --

   IMPORTS

   AlgorithmIdentifier, Name, Certificate
        FROM PKIX1Explicit93 {iso(1) identified-organization(3) dod(6)
        internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
        id-pkix1-explicit-93(3)}

   GeneralNames
        FROM PKIX1Implicit93 {iso(1) identified-organization(3) dod(6)
        internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
        id-pkix1-implicit-93(4)};

   TokenBA1 ::= SEQUENCE {
        randomB   RandomNumber,
        entityB   [0] GeneralNames OPTIONAL,
        certPref  [1] SEQUENCE SIZE (1..MAX) OF TrustedAuth OPTIONAL
   }

   TokenAB ::= SEQUENCE {
        randomA   RandomNumber,
        entityB   [0] GeneralNames OPTIONAL,
        certA     [1] CertData,
        authID    [2] GeneralNames OPTIONAL,
        signature SIGNATURE { TBSDataAB }
   }(CONSTRAINED BY {-- The entityB and authID fields shall be included
     -- in TokenAB if and only if they are also included in TBSDataAB.
     -- The entityB field SHOULD be present in TokenAB whenever the
     -- client believes it knows the identity of the server.--})

   TBSDataAB ::= SEQUENCE {
        randomA RandomNumber,
        randomB RandomNumber,
        entityB [0] GeneralNames OPTIONAL,
        authID  [1] GeneralNames OPTIONAL
   }




Zuccherato & Nystrom          Experimental                     [Page 15]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


   TokenBA2 ::= SEQUENCE {
        randomC   RandomNumber,
        entityA   [0] GeneralNames OPTIONAL,
        certB     [1] CertData,
        signature SIGNATURE { TBSDataBA }
   }(CONSTRAINED BY {-- The entityA field shall be included in TokenBA2
     -- if and only if it is also included in TBSDataBA.  The entityA
     -- field SHOULD be present and MUST contain the client's name
     -- from their X.509 certificate.--})

   TBSDataBA ::= SEQUENCE {
        randomB RandomNumber,
        randomA RandomNumber,
        randomC RandomNumber,
        entityA GeneralNames OPTIONAL
   }

   TrustedAuth ::= CHOICE {
        authorityName         [0] Name,
             -- SubjectName from CA certificate
        issuerNameHash        [1] OCTET STRING,
             -- SHA-1 hash of Authority's DN
        issuerKeyHash         [2] OCTET STRING,
             -- SHA-1 hash of Authority's public key
        authorityCertificate  [3] Certificate,
             -- CA certificate
        pkcs15KeyHash         [4] OCTET STRING
             -- PKCS #15 key hash
   }

   CertData ::= CHOICE {
        certificateSet     SET SIZE (1..MAX) OF Certificate,
        certURL            IA5String,
        ... -- For future extensions
   }

   RandomNumber ::= OCTET STRING (SIZE(8..MAX))

   SIGNATURE { ToBeSigned } ::= SEQUENCE {
        algorithm AlgorithmIdentifier,
        signature BIT STRING
   }(CONSTRAINED BY {-- Must be the result of applying the signing
     -- operation indicated in "algorithm" to the DER-encoded octets of
     -- a value of type -- ToBeSigned })

   END





Zuccherato & Nystrom          Experimental                     [Page 16]

RFC 3163      ISO/IEC 9798-3 Authentication SASL Mechanism   August 2001


Full Copyright Statement

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

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















Zuccherato & Nystrom          Experimental                     [Page 17]

