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
<draft-ietf-pkix-ipki-kea-01.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
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]
