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Independent Submission                                         S. TurnerRequest for Comments: 7093                                          IECACategory: Informational                                          S. KentISSN: 2070-1721                                                      BBN                                                               J. Manger                                                                 Telstra                                                           December 2013Additional Methods for Generating Key Identifiers ValuesAbstract   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; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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 20131.  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 20133.  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 fromSection 2, the subjectKeyIdentifier would be:     30 1D        06 03 551D0E -- id-ce-subjectKeyIdentifier        04 16           04 14 BF37B3E5808FD46D54B28E846311BCCE1CAD2E1A   Using method 4 fromSection 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                 5D8A75A296088148399D7BF763D57405Turner, et al.                Informational                     [Page 3]

RFC 7093               Additional Examples For KIs         December 20134.  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 2013Authors' 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.comTurner, et al.                Informational                     [Page 5]