Network Working Group                                        R. HousleyRequest for Comments: 2528                                       SPYRUSCategory: Informational                                         W. Polk                                                                   NIST                                                             March 1999                Internet X.509 Public Key Infrastructure         Representation of Key Exchange Algorithm (KEA) Keys in         Internet X.509 Public Key Infrastructure CertificatesStatus 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 (1999).  All Rights Reserved.Table of Contents   Abstract ........................................................ 2   1.  Executive Summary ........................................... 2   2.  Requirements and Assumptions ................................ 2   2.1.  Communication and Topology ................................ 2   2.2.  Acceptability Criteria .................................... 2   2.3.  User Expectations ......................................... 3   2.4.  Administrator Expectations ................................ 3   3.  KEA Algorithm Support ....................................... 3   3.1.  Subject Public Key Info ................................... 3   3.1.1.  Algorithm Identifier and Parameters ..................... 4   3.1.2.  Encoding of KEA Public Keys ............................. 5   3.2.  Key Usage Extension in KEA certificates ................... 5   4. ASN.1 Modules ................................................ 5   4.1 1988 Syntax ................................................. 5   4.2 1993 Syntax ................................................. 6   5. References ................................................... 6   6. Security Considerations ...................................... 7   7. Authors' Addresses ........................................... 8   8. Full Copyright Statement ..................................... 9Housley & Polk               Informational                      [Page 1]RFC 2528                        PKIX KEA                      March 1999Abstract   The Key Exchange Algorithm (KEA) is a classified algorithm for   exchanging keys.  This specification profiles the format and   semantics of fields in X.509 V3 certificates containing KEA keys. The   specification addresses the subjectPublicKeyInfo field and the   keyUsage extension.1.  Executive Summary   This specification contains guidance on the use of the Internet   Public Key Infrastructure certificates to convey Key Exchange   Algorithm (KEA) keys. This specification is an addendum to RFC 2459,   "Internet X.509 Public Key Infrastructure: Certificate and CRL   Profile".  Implementations of this specification must also conform to   RFC 2459.  Implementations of this specification are not required to   conform to other parts from that series.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 [RFC 2459] and augmented by this   specification, 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.  The profile does not prohibit the use of an X.500 Directory,   but other means of distributing certificates and certificate   revocation 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   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 & Polk               Informational                      [Page 2]RFC 2528                        PKIX KEA                      March 1999   The goal of this document is to profile KEA certificates, specifying   the contents and semantics of attributes which were not fully   specified by [RFC 2459].  If not specifically addressed by this   document, the contents and semantics of the fields and extensions   must be as described in [RFC 2459].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   compromise or unnecessarily limit interoperability.  This profile   defines the object identifiers and data formats that must be   supported to interpret KEA public keys.3.  KEA Algorithm Support   This section describes object identifiers and data formats which may   be used with [RFC 2459] 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   parameters, and specifies the KEA public key in the   subjectPublicKeyInfo field. The subjectPublicKeyInfo field is a   SEQUENCE of an algorithm identifier and the subjectPublicKey field.Housley & Polk               Informational                      [Page 3]RFC 2528                        PKIX KEA                      March 1999   The certificate indicates the algorithm through an algorithm   identifier.  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   subjectPublicKey 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 algorithm 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 an 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   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.Housley & Polk               Informational                      [Page 4]RFC 2528                        PKIX KEA                      March 1999   The Dss-Parms is provided in [RFC 2459] and reproduced below for   completeness.        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: