Additional Methods for Generating Key Identifiers and Key Identifier Semantic Extension
draft-turner-additional-methods-4kis-05

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Network Working Group                                          S. Turner
Internet-Draft                                                      IECA
Intended Status: Informational                                   S. Kent
Expires: December 1, 2012                                            BBN
                                                            May 30, 2012

           Additional Methods for Generating Key Identifiers
                 and Key Identifier Semantic Extension
              draft-turner-additional-methods-4kis-05.txt

Abstract

   This document specifies additional methods for generating key
   identifiers from a public key.  This document also specifies an
   extension to identify the algorithms used to generate the key
   identifiers.

Status of this Memo

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Turner & Kent           Expires December 1, 2012                [Page 1]
Internet-Draft   Additional Methods For Key Identifiers     May 30, 2012

1.  Introduction

   [RFC5280] defines the AKI (Authority Key Identifier) and SKI (Subject
   Key Identifier) certificate extensions.  These extensions allow one
   certificate to refer to another certificate via the matching of these
   corresponding values.  These identifiers enable a relying party to
   disambiguate between two CA (Certification Authority) certificates
   with the same Subject name, located in the same directory entry. 
   These identifiers are used during certification path construction in
   support of heuristics to reduce relying party workload.  These
   identifiers are not used during certificate path validation.  These
   key identifiers are used by PKI-enabled security protocols, such as
   CMP (Certificate Management Protocol) [RFC4210] and CMS
   (Cryptographic Message Syntax) [RFC5652], to identify the certificate
   used to protect a message, a session, etc.

   [RFC5280] describes two example mechanisms for generating AKI/SKI
   values: a 160-bit SHA-1 (Secure Hash Algorithm) hash of the public
   key and a four-bit type field with the value 0100 followed by the
   least significant 60 bits of the SHA-1 hash.  Both of these
   mechanisms were designed to be non-security critical.  That is, the
   use of a hash algorithm was intended to provide a high probability
   (but not a guarantee) of uniqueness.  [RFC5280] allows for additional
   mechanisms.  (This is consistent with the fact that the SKI and AKI
   extensions are always marked non-critical.)  In addition, some
   secruity protocols (e.g., SMIME [RFC5751]) as a shorthand way to
   refer to a cert.

   This document defines two additional mechanisms for generating key
   identifier values, using SHA-256 and SHA-512 [SHS]. Sample code for
   SHA-256 and SHA-512 can be found in [RFC6234]. The motivation for
   defining these additional means of generating AKI/SKI values is to
   accommodate use of additional, standard one-way hash functions that
   are becoming more widely used in PKI contexts.  Note that these
   example methods like the examples methods from [RFC5280] are designed
   to be non-security critical.  

   With these additional mechanisms, CAs can omit code for algorithms
   that are otherwise unwanted or unused.  For example, a CA that issues
   certificates hashed with SHA-256 and signed with ECDSA on the P-256
   curve [RFC5480] might no longer need to implement SHA-1 as part of
   their CA application.

   This document also specifies an extension to identify the algorithm
   used to generate the SKI.  The extension also identifies the hash
   algorithm input used to generate to the key identifier. 
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