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Versions: 00 01 02 rfc2528                                 Informational
PKIX Working Group                                   R. Housley (SPYRUS)
Internet Draft                                            W. Polk (NIST)
expires in six months                                     August 5, 1998


                Internet X.509 Public Key Infrastructure

         Representation of Key Exchange Algorithm (KEA) Keys in
         Internet X.509 Public Key Infrastructure Certificates

                   <draft-ietf-pkix-ipki-kea-02.txt>


Status of this Memo

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
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   Copyright (C) The Internet Society (1998). All Rights Reserved.



















Housley & Polk                                                  [Page 1]


INTERNET DRAFT                                             August 5 1998


         Representation of Key Exchange Algorithm (KEA) Keys in
         Internet X.509 Public Key Infrastructure Certificates




                           Table of Contents



Abstract ..........................................................    3
1.  Executive Summary .............................................    3
2.  Requirements and Assumptions ..................................    3
2.1.  Communication and Topology ..................................    3
2.2.  Acceptability Criteria ......................................    4
2.3.  User Expectations ...........................................    4
2.4.  Administrator Expectations ..................................    4
3.  KEA Algorithm Support .........................................    5
3.1.  Subject Public Key Info .....................................    5
3.1.1.  Algorithm Identifier and Parameters .......................    5
3.1.2.  Encoding of KEA Public Keys ...............................    6
3.2.  Key Usage Extension in KEA certificates .....................    6
4. ASN.1 Modules ..................................................    7
4.1 1988 Syntax ...................................................    7
4.2 1993 Syntax ...................................................    7
5. References .....................................................    8
6. Patent Statements ..............................................    8
7. Security Considerations ........................................    8
8. Author Addresses ...............................................    9






















Housley & Polk                                                  [Page 2]


INTERNET DRAFT                                             August 5 1998


Abstract

   This is the third draft of a profile for specification of Key
   Exchange Algorithm (KEA) keys in Internet Public Key Infrastructure
   X.509 certificates.  There are only minor changes in content from the
   second draft. Several modifications are required now that KEA has
   been declassified.  A patent statement is required, and a published
   reference for the KEA algorithm is required.  After these modifica-
   tions, the document will be complete.  Please send comments on this
   document to the ietf-pkix@imc.org mail list.



1.  Executive Summary


   This specification contains guidance on the use of the Internet Pub-
   lic Key Infrastructure certificates to convey Key Exchange Algorithm
   (KEA) keys. This specification is an addendum to RFC xxxx, "Internet
   X.509 Public Key Infrastructure:  Certificate and CRL Profile".
   Implementations of this specification must also conform to RFC xxxx.
   Implementations of this specification are not required to conform to
   other parts from that series.

   The Key Exchange Algorithm (KEA) is a classified algorithm for
   exchanging keys.  This specification profiles the format and seman-
   tics of fields in X.509 V3 certificates containing KEA keys. The
   specification addresses the subjectPublicKeyInfo field and the
   keyUsage extension.


2.  Requirements and Assumptions

   The goal is to augment the X.509 certificate profile presented in
   Part 1 to facilitate the management of KEA keys for those communities
   which use this algorithm.


2.1.  Communication and Topology


   This profile, as presented in Part 1 and augmented by this specifica-
   tion, supports users without high bandwidth, real-time IP connec-
   tivity, or high connection availablity.  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.  The profile does not prohibit the use of an X.500 Directory,



Housley & Polk                                                  [Page 3]


INTERNET DRAFT                                             August 5 1998


   but other means of distributing certificates and certificate revoca-
   tion lists (CRLs) are supported.


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 ser-
   vices determines the attributes contained in the certificate as well
   as the ancillary control information in the certificate such as pol-
   icy data and certification path constraints.

   The goal of this document is to profile KEA certificates, specifying
   the contants and semantics of attributes which were not fully speci-
   fied by Part 1.  If not specifically addressed by this document, the
   contents and semantics of the fields and extensions must be as
   described in Part 1.


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 sophistication/attentiveness of the users themselves.
   This manifests itself in minimal user configuration responsibility
   (e.g., root 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 users, the Internet PKI profile is structured to support the
   individuals who generally operate Certification Authorities (CAs).
   Providing administrators with unbounded choices increases the chances
   that a subtle CA administrator mistake will result in broad comprom-
   ise or unnecessarily limit interoperability.  This profile defines
   the object identifiers and data formats that must be supported to
   intepret KEA public keys.




Housley & Polk                                                  [Page 4]


INTERNET DRAFT                                             August 5 1998


3.  KEA Algorithm Support


   This section describes object identifiers and data formats which may
   be used with PKIX certicate profile to describe X.509 certificates
   containing a KEA public key.  Conforming CAs are required to use the
   object identifiers and data formats when issuing KEA certificates.
   Conforming applications shall recognize the object identifiers and
   process the data formats when processing such certificates.


3.1.  Subject Public Key Info


   The certificate identifies the KEA algorithm, conveys optional param-
   eters, and specifies the KEA public key in the subjectPublicKeyInfo
   field. The subjectPublicKeyInfo field is a SEQUENCE of an algorithm
   identifier and the subjectPublicKey field.

   The certificate indicates the algorithm through an algorithm identif-
   ier.  This algorithm identifier consists of an object identifier
   (OID) and optional associated parameters.  Section 3.1.1 identifies
   the preferred OID and parameters for the KEA algorithm.  Conforming
   CAs shall use the identified OID when issuing certificates containing
   public keys for the KEA algorithm. Conforming applications supporting
   the KEA algorithm shall, at a minimum, recognize the OID identified
   in section 3.1.1.

   The certificate conveys the KEA public key through the subjectPub-
   licKey field.  This subjectPublicKey field is a BIT STRING.  Section
   3.1.2 specifies the method for encoding a KEA public key as a BIT
   STRING.  Conforming CAs shall encode the KEA public key as described
   in Section 3.1.2 when issuing certificates containing public keys for
   the KEA algorithm. Conforming applications supporting the KEA algo-
   rithm shall decode the subjectPublicKey as described in section 3.1.2
   when the algorithm identifier is the one presented in 3.1.1.


3.1.1.  Algorithm Identifier and Parameters


   The Key Exchange Algorithm (KEA) is a classified algorithm for
   exchanging keys.  A KEA "pairwise key" may be generated between two
   users if their KEA public keys were generated with the same KEA
   parameters.  The KEA parameters are not included in a certificate;
   instead a "domain identifier" is supplied in the parameters field.

   When the subjectPublicKeyInfo field contains a KEA key, the algorithm



Housley & Polk                                                  [Page 5]


INTERNET DRAFT                                             August 5 1998


   identifier and parameters shall be as defined in [sdn.701r]:

      id-keyExchangeAlgorithm  OBJECT IDENTIFIER   ::=
             { 2 16 840 1 101 2 1 1 22 }

      KEA-Parms-Id     ::= OCTET STRING


   CAs shall populate the parameters field of the AlgorithmIdentifier
   within the subjectPublicKeyInfo field of each certificate containing
   a KEA public key with an 80-bit parameter identifier (OCTET STRING),
   also known as the domain identifier. The domain identifier will be
   computed in three steps: (1) the KEA parameters are DER encoded using
   the Dss-Parms structure; (2) a 160-bit SHA-1 hash is generated from
   the parameters; and (3) the 160-bit hash is reduced to 80-bits by
   performing an "exclusive or" of the 80 high order bits with the 80
   low order bits.  The resulting value is encoded such that the most
   significant byte of the 80-bit value is the first octet in the octet
   string.

   The Dss-Parms is provided in [RFC xxx] and reproduced below for com-
   pleteness.

        Dss-Parms  ::=  SEQUENCE  {
            p             INTEGER,
            q             INTEGER,
            g             INTEGER  }


3.1.2.  Encoding of KEA Public Keys


   A KEA public key, y, is conveyed in the subjectPublicKey BIT STRING
   such that the most significant bit (MSB) of y becomes the MSB of the
   BIT STRING value field and the least significant bit (LSB) of y
   becomes the LSB of the BIT STRING value field.  This results in the
   following encoding: BIT STRING tag, BIT STRING length, 0 (indicating
   that there are zero unused bits in the final octet of y), BIT STRING
   value field including y.


3.2.  Key Usage Extension in KEA certificates


The key usage extension may optionally appear in a KEA certificate.  If
a KEA certificate includes the keyUsage extension, only the following
values may be asserted:




Housley & Polk                                                  [Page 6]


INTERNET DRAFT                                             August 5 1998


      keyAgreement;
      encipherOnly; and
      decipherOnly.

   The encipherOnly and decipherOnly values may only be asserted if the
   keyAgreement value is also asserted.  At most one of encipherOnly and
   decipherOnly shall be asserted in keyUsage extension.

   4. ASN.1 Modules

   4.1 1988 Syntax

   PKIXkea88 {iso(1) identified-organization(3)         dod(6) inter-
   net(1) security(5) mechanisms(5) pkix(7)         id-mod(0) to be
   assigned(?) } BEGIN ::=

   -- EXPORTS ALL --

   -- IMPORTS NONE --

      id-keyExchangeAlgorithm  OBJECT IDENTIFIER   ::=
             { 2 16 840 1 101 2 1 1 22 }

      KEA-Parms-Id     ::= OCTET STRING

   END

   4.2 1993 Syntax

   PKIXkea93 {iso(1) identified-organization(3)         dod(6) inter-
   net(1) security(5) mechanisms(5) pkix(7)         id-mod(0) to be
   assigned(?) }

   BEGIN ::=

   -- EXPORTS ALL --

   IMPORTS         ALGORITHM-ID
           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) }

     KeaPublicKey ALGORTHM-ID ::=  { OID id-keyExchangeAlgorithm
                                     PARMS KEA-Parms-Id }

      id-keyExchangeAlgorithm  OBJECT IDENTIFIER   ::=
             { 2 16 840 1 101 2 1 1 22 }




Housley & Polk                                                  [Page 7]


INTERNET DRAFT                                             August 5 1998


      KEA-Parms-Id     ::= OCTET STRING

   END

   5. References


   [KEA]      "Skipjack and KEA Algorithm Specification", Version 2.0,
              29 May 1998. available from
   http://csrc.nist.gov/encryption/skipjack-kea.htm

   [SDN.701R] SDN.701, "Message Security Protocol", Revision 4.0
              1996-06-07 with "Corrections to Message Security Protocol,
              SDN.701, Rev 4.0, 96-06-07." August 30, 1996.

   [RFC xxxx] R. Housley, W. Ford, W. Polk and D. Solo "Internet X.509
              Public Key Infrastructure: X.509 Certificate and CRL
              Profile", July 28, 1998.

6. Patent Statements

   To be added.

7. Security Considerations

   This specification is devoted to the format and encoding of KEA keys
   in X.509 certificates.  Since certificates are digitally signed, no
   additional integrity service is necessary. Certificates need not 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 sec-
   tion highlights critical issues that should be considered by imple-
   mentors, administrators, and users.

   The procedures performed by CAs and RAs to validate the binding of
   the subject's identity of their public key greatly affect the
   assurance that should be placed in the certificate.  Relying parties
   may wish to review the CA's certificate practice statement.

   The protection afforded private keys is a critical factor in main-
   taining security.  Failure of users to protect their KEA private keys
   will permit an attacker to masquerade as them, or decrypt their per-
   sonal information.

   The availability and freshness of revocation information will affect
   the degree of assurance that should be placed in a certificate.



Housley & Polk                                                  [Page 8]


INTERNET DRAFT                                             August 5 1998


   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.  Simi-
   larly, implementations of the Path Validation mechanism described in
   section 6 that omit revocation checking provide less assurance than
   those that support it.

   The path validation algorithm specified in [RFC xxxx] 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 certifi-
   cate. The authenticated distribution of trusted CA public keys (usu-
   ally in the form of a "self-signed" certificate) is a security criti-
   cal out of band process that is beyond the scope of this specifica-
   tion.

   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 will
   make the trusted CA information difficult to maintain.  On the other
   hand, selection of only one trusted CA may limit users to a closed
   community of users until a global PKI emerges.

   The quality of implementations that process certificates may also
   affect the degree of assurance provided.  The path validation algo-
   rithm described in section 6 relies upon the integrity of the trusted
   CA information, and especially the integrity of the public keys asso-
   ciated 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.

8. Author Addresses:

   Russell Housley
   SPYRUS
   PO Box 1198
   Herndon, VA 20172
   USA
   housley@spyrus.com

   Tim Polk
   NIST
   Building 820, Room 426



Housley & Polk                                                  [Page 9]


INTERNET DRAFT                                             August 5 1998


   Gaithersburg, MD 20899
   USA
   wpolk@nist.gov
















































Housley & Polk                                                 [Page 10]