PKIX Working Group R. Housley (SPYRUS) Internet Draft W. Polk (NIST) expires in six months October 14, 1997 Internet Public Key Infrastructure Representation of Key Exchange Algorithm (KEA) Keys in Internet Public Key Infrastructure Certificates 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 working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract This is the second draft of a profile for specification of Key Exchange Algorithm (KEA) keys in Internet Public Key Infrastructure X.509 certificates. Please send comments on this document to the ietf-pkix@tandem.com mail list. 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 xxxx, "Internet 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 Housley & Polk [Page 1] INTERNET DRAFT July 30 1997 other parts from that series. 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. 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 specification, supports users without high bandwidth, real-time IP connectivity, 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, 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. The goal of this document is to profile KEA certificates, specifying the contants and semantics of attributes which were not fully specified 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. Housley & Polk [Page 2] INTERNET DRAFT July 30 1997 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 intepret KEA public keys. 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 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. 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 Housley & Polk [Page 3] INTERNET DRAFT July 30 1997 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 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 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 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 Housley & Polk [Page 4] INTERNET DRAFT July 30 1997 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: 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. References [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 Public Key Infrastructure: X.509 Certificate and CRL Profile", October 14, 1997. Patent Statements This specification references classified public key encryption technology for provisioning key exchange services. Security Considerations This entire memo is about security mechanisms. Author Addresses: Russell Housley SPYRUS PO Box 1198 Herndon, VA 20172 USA housley@spyrus.com Tim Polk Housley & Polk [Page 5] INTERNET DRAFT July 30 1997 NIST Building 820, Room 426 Gaithersburg, MD 20899 USA wpolk@nist.gov Housley & Polk [Page 6]