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 Subject 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). 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
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to this document.
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.
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
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.
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