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Independent Submission S. Turner Request for Comments: 7093 IECA Category: Informational S. Kent ISSN: 2070-1721 BBN

                                                             J. Manger
                                                               Telstra
                                                         December 2013

      Additional Methods for Generating Key Identifiers Values

Abstract

 This document specifies additional example methods for generating Key
 Identifier values for use in the AKI (Authority Key Identifier) and
 SKI (Subject Key Identifier) certificate extensions.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.

 This is a contribution to the RFC Series, independently of any other
 RFC stream.  The RFC Editor has chosen to publish this document at
 its discretion and makes no statement about its value for
 implementation or deployment.  Documents approved for publication by
 the RFC Editor are not a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.

 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7093.

Copyright Notice

 Copyright (c) 2013 IETF Trust and the persons identified as the
 document authors.  All rights reserved.

 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.

Turner, et al. Informational [Page 1] RFC 7093 Additional Examples For KIs December 2013

1. Introduction

 [RFC5280] defines the AKI (Authority Key Identifier) and SKI (Subject
 Key Identifier) certificate extensions.  [RFC5280] describes two
 example mechanisms for generating AKI and 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 not be
 critical to security.  This document defines three additional
 mechanisms for generating Key Identifier values using SHA-256,
 SHA-384, and SHA-512 [SHS] that are similar to those examples defined
 in [RFC5280] as well as one based on hashing the certificate's
 Subject Public Key Info field.

2. Additional Methods for Generating Key Identifiers

 [RFC5280] specifies two examples for generating key identifiers from
 public keys.  Four additional mechanisms are as follows:

 1) The keyIdentifier is composed of the leftmost 160-bits of the
    SHA-256 hash of the value of the BIT STRING subjectPublicKey
    (excluding the tag, length, and number of unused bits).

 2) The keyIdentifier is composed of the leftmost 160-bits of the
    SHA-384 hash of the value of the BIT STRING subjectPublicKey
    (excluding the tag, length, and number of unused bits).

 3) The keyIdentifier is composed of the leftmost 160-bits of the
    SHA-512 hash of the value of the BIT STRING subjectPublicKey
    (excluding the tag, length, and number of unused bits).

 4) The keyIdentifier is composed of the hash of the DER encoding of
    the SubjectPublicKeyInfo value.

Turner, et al. Informational [Page 2] RFC 7093 Additional Examples For KIs December 2013

3. Examples

 This section provides some examples.  The keys and SKIs are presented
 in hexadecimal (two hex digits per byte).

 Given the following DER-encoded SubjectPublicKeyInfo value holding an
 P-256 ECDSA (Elliptic Curve Digital Signature Algorithm) key:

   30 59
      30 13
         06 07 2A8648CE3D0201    -- id-ecPublicKey
         06 08 2A8648CE3D030107  -- secp256r1
      03 42 00
            04 7F7F35A79794C950060B8029FC8F363A
               28F11159692D9D34E6AC948190434735
               F833B1A66652DC514337AFF7F5C9C75D
               670C019D95A5D639B72744C64A9128BB

 The SHA-256 hash of the 65 bytes 047F7F...BB is:
   BF37B3E5808FD46D54B28E846311BCCE1CAD2E1A62AA9092EF3EFB3F11451F44

 The SHA-1 hash of these 65 bytes is:
   6FEF9162C0A3F2E7608956D41C37DA0C8E87F0AE

 The SHA-256 hash of the 91 bytes 305930...BB is:
   6D20896AB8BD833B6B66554BD59B20225D8A75A296088148399D7BF763D57405

 Using method 1 from Section 2, the subjectKeyIdentifier would be:

   30 1D
      06 03 551D0E -- id-ce-subjectKeyIdentifier
      04 16
         04 14 BF37B3E5808FD46D54B28E846311BCCE1CAD2E1A

 Using method 4 from Section 2 with SHA-256 and no truncation, the
 subjectKeyIdentifier extensions would be:

   30 29
      06 03 551D0E -- id-ce-subjectKeyIdentifier
      04 22
         04 20 6D20896AB8BD833B6B66554BD59B2022
               5D8A75A296088148399D7BF763D57405

Turner, et al. Informational [Page 3] RFC 7093 Additional Examples For KIs December 2013

4. Security Considerations

 The security considerations of [RFC5280] apply to certificates.  The
 security considerations of [RFC5758] apply to the hash algorithms.

 While hash algorithms provide preimage resistance, second-preimage
 resistance, and collision resistance, none of these properties are
 needed for key identifiers.

5. Acknowledgements

 The authors wish to thank Santosh Chokhani, Stephen Farrell, Tom
 Gindin, Peter Gutmann, Henry Holtz, David Kemp, Timothy Miller,
 Michael StJohns, Stefan Santesson, Jim Schaad, Rene Struik, Koichi
 Sugimoto, and Carl Wallace for taking the time to participate in the
 discussions about this document.  The discussions resulted in
 numerous editorial and technical changes to the document.

6. Normative References

 [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
            Housley, R., and W. Polk, "Internet X.509 Public Key
            Infrastructure Certificate and Certificate Revocation List
            (CRL) Profile", RFC 5280, May 2008.

 [RFC5758]  Dang, Q., Santesson, S., Moriarty, K., Brown, D., and T.
            Polk, "Internet X.509 Public Key Infrastructure:
            Additional Algorithms and Identifiers for DSA and ECDSA",
            RFC 5758, January 2010.

 [SHS]      National Institute of Standards and Technology (NIST),
            FIPS Publication 180-3: Secure Hash Standard, October
            2008.

Turner, et al. Informational [Page 4] RFC 7093 Additional Examples For KIs December 2013

Authors' Addresses

 Sean Turner
 IECA, Inc.
 3057 Nutley Street, Suite 106
 Fairfax, VA 22031
 USA

 EMail: turners@ieca.com

 Stephen Kent
 BBN Technologies
 10 Moulton St.
 Cambridge, MA 02138
 USA

 EMail: kent@bbn.com

 James Manger
 Telstra
 6 / 150 Lonsdale Street
 Melbourne, Victoria 3000
 Australia

 EMail: james.h.manger@team.telstra.com

Turner, et al. Informational [Page 5]