draft-ietf-dnsext-tsig-sha-04.txt

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INTERNET-DRAFT                                 HMAC-SHA TSIG Identifiers


   SHA-1 truncated to 96 bits (12 octets) SHOULD be implemented.



















































D. Eastlake 3rd                                                 [Page 6]


INTERNET-DRAFT                                 HMAC-SHA TSIG Identifiers


4. TSIG Policy Provisions and Truncation Error

   Use of TSIG is by mutual agreement between a resolver and server.
   Implicit in such "agreement" are policies as to acceptable keys and
   algorithms and, with the extensions in this doucment, truncations. In
   particular note the following:

      Such policies MAY require the rejection of TSIGs even though they
   use an algorithm for which implementation is mandatory.

      When a policy calls for the acceptance of a TSIG with a particular
   algorithm and a particular non-zero amount of trunction it SHOULD
   also permit the use of that algorithm with lesser truncation (a
   longer MAC) up to the full HMAC output.

      Regardless of a lower acceptable truncated MAC length specified by
   policy, a reply SHOULD be sent with a MAC at least as long as that in
   the corresponding request unless the request specified a MAC length
   longer than the HMAC output.

      Implementations permitting policies with multiple acceptable
   algorithms and/or truncations SHOULD permit this list to be ordered
   by presumed strength and SHOULD allow different truncations for the
   same algorithm to be treatred as spearate entities in this list. When
   so implemented, policies SHOULD accept a presumed stronger algorithm
   and truncation than the minimum strength required by the policy.

      If a TSIG is received with truncation which is permitted under
   Section 3 above but the MAC is too short for the policy in force, an
   RCODE of TBA [22 suggested](BADTRUNC) MUST be returned.






















D. Eastlake 3rd                                                 [Page 7]


INTERNET-DRAFT                                 HMAC-SHA TSIG Identifiers


5. IANA Considerations

   This document, on approval for publication as a standards track RFC,
   (1) registers the new TSIG algorithm identifiers listed in Section 2
   with IANA and (2) Section 4 allocates the BADTRUNC RCODE TBA [22
   suggested].




6. Security Considerations

   For all of the message authentication code algorithms listed herein,
   those producing longer values are believed to be stronger; however,
   while there have been some arguments that mild truncation can
   strengthen a MAC by reducing the information available to an
   attacker, excessive truncation clearly weakens authentication by
   reducing the number of bits an attacker has to try to brute force
   [RFC 2104].

   Significant progress has been made recently in cryptanalysis of hash
   function of the type used herein, all of which ultimately derive from
   the design of MD4. While the results so far should not effect HMAC,
   the stronger SHA-1 and SHA-256 algorithms are being made mandatory
   due to caution.

   See the Security Considerations section of [RFC 2845].  See also the
   Security Considerations section of [RFC 2104] from which the limits
   on truncation in this RFC were taken.



6. Copyright and Disclaimer

   Copyright (C) The Internet Society (2005).  This document is subject to
   the rights, licenses and restrictions contained in BCP 78, and except
   as set forth therein, the authors retain all their rights.


   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.






D. Eastlake 3rd                                                 [Page 8]


INTERNET-DRAFT                                 HMAC-SHA TSIG Identifiers


7. Normative References

   [FIPS 180-2] - "Secure Hash Standard", (SHA-1/224/256/384/512) US
   Federal Information Processing Standard, with Change Notice 1,
   February 2004.

   [RFC 1321] - Rivest, R., "The MD5 Message-Digest Algorithm ", RFC
   1321, April 1992.

   [RFC 2104] - Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
   Hashing for Message Authentication", RFC 2104, February 1997.

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

   [RFC 2845] - Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
   Wellington, "Secret Key Transaction Authentication for DNS (TSIG)",
   RFC 2845, May 2000.



8. Informative References.

   [RFC 2931] - Eastlake 3rd, D., "DNS Request and Transaction
   Signatures ( SIG(0)s )", RFC 2931, September 2000.

   [RFC 3174] - Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm
   1 (SHA1)", RFC 3174, September 2001.

   [RFC 3645] - Kwan, S., Garg, P., Gilroy, J., Esibov, L., Westhead,
   J., and R. Hall, "Generic Security Service Algorithm for Secret Key
   Transaction Authentication for DNS (GSS-TSIG)", RFC 3645, October
   2003.

   [RFC 3874] - R. Housely, "A 224-bit One-way Hash Function: SHA-224",
   September 2004,

   [SHA2draft] - Eastlake, D., T. Hansen, "US Secure Hash Algorithms
   (SHA)", work in progress.













D. Eastlake 3rd                                                 [Page 9]


INTERNET-DRAFT                                 HMAC-SHA TSIG Identifiers


Author's Address

   Donald E. Eastlake 3rd
   Motorola Laboratories
   155 Beaver Street
   Milford, MA 01757 USA

   Telephone:   [phone] (w)

   EMail:       [e-mail]



Expiration and File Name

   This draft expires in December 2005.

   Its file name is draft-ietf-dnsext-tsig-sha-04.txt


































D. Eastlake 3rd                                                [Page 10]