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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 7093

Network Working Group                                          S. Turner
Internet-Draft                                                      IECA
Intended Status: Informational                                   S. Kent
Expires: April 22, 2014                                              BBN
                                                               J. Manger
                                                                 Telstra
                                                        October 19, 2013


       Additional Methods for Generating Subject Key Identifiers
              draft-turner-additional-methods-4kis-11.txt

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).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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Copyright Notice

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

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   described in the Simplified BSD License.




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1.  Introduction

   [RFC5280] defines the AKI (Authority Key Identifier) and SKI (Subject
   Key Identifier) certificate extensions.  [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.  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.


















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4.  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 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

5.  Security Considerations

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




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

6.  IANA Considerations

   None.

7.  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.

8.  References

8.1.  Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

8.2.  Informative References

   None











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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

   EMail: kent@bbn.com

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

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



























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