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Versions: (draft-dupont-dnsext-tsig-md5-deprecated) 00 01 02 03

DNSext Working Group                                           F. Dupont
Internet-Draft                                                       ISC
Updates: 2845,2930,4635                                   April 27, 2009
(if approved)
Intended status: Standards Track
Expires: October 29, 2009

     Deprecation of HMAC-MD5 in DNS TSIG and TKEY Resource Records

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Internet-Draft        Deprecating HMAC-MD5 in TSIG            April 2009

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
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   Please review these documents carefully, as they describe your rights
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   The main goal of this document is to deprecate the use of HMAC-MD5 as
   an algorithm for the TSIG (secret key transaction authentication)
   resource record in the DNS (domain name system).

1.  Introduction

   The secret key transaction authentication for DNS (TSIG, [RFC2845])
   was defined with the HMAC-MD5 [RFC2104] cryptographic algorithm.  As
   the MD5 [RFC1321] security was recognized to be lower than expected,
   [RFC4635] standardized new TSIG algorithms based on SHA
   [RFC3174][RFC3874][RFC4634] digests.

   But [RFC4635] did not deprecate the HMAC-MD5 algorithm.  This
   document is targeted to complete the process, in details:
   1.  Mark HMAC-MD5.SIG-ALG.REG.INT as optional in the TSIG algorithm
       name registry managed by the IANA under the IETF Review Policy
   2.  Make HMAC-MD5.SIG-ALG.REG.INT support "not Mandatory" for
   3.  Provide a keying material derivation for the secret key
       establishment for DNS (TKEY, [RFC2930]) using a Diffie-Hellman
       exchange with SHA256 [RFC4634] in place of MD5 [RFC1321]
   4.  Finally recommend the use of HMAC-SHA256.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Implementation Requirements

   The table of section 3 of [RFC4635] is replaced by:

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Internet-Draft        Deprecating HMAC-MD5 in TSIG            April 2009

             | Requirement Level | Algorithm Name           |
             | Optional          | HMAC-MD5.SIG-ALG.REG.INT |
             | Optional          | gss-tsig                 |
             | Mandatory         | hmac-sha1                |
             | Optional          | hmac-sha224              |
             | Mandatory         | hmac-sha256              |
             | Optional          | hmac-sha384              |
             | Optional          | hmac-sha512              |

   Implementations that support TSIG MUST also implement HMAC-SHA1 and
   HMAC-SHA256 (i.e., algorithms at the "Mandatory" requirement level)
   and MAY implement GSS-TSIG and the other algorithms listed above
   (i.e., algorithms at a "not Mandatory" requirement level).

3.  TKEY keying material derivation

   When the TKEY [RFC2930] uses a Diffie-Hellman exchange, the keying
   material is derived from the shared secret and TKEY resource record
   data using MD5 [RFC1321] at the end of section 4.1 page 9.

   This is amended into:

         keying material =
              XOR ( DH value, SHA256 ( query data | DH value ) |
                              SHA256 ( server data | DH value ) )

   using the same conventions.

4.  IANA Consideration

   This document extends the "TSIG Algorithm Names - per [] and
   [RFC2845]" located at
   http://www.iana.org/assignments/tsig-algorithm-names by adding a new
   column to the registry "Compliance Requirement".

   The registry should contain the following:

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    | Algorithm Name           | Compliance Requirement | Reference   |
    | gss-tsig                 | Optional               | [RFC3645]   |
    | HMAC-MD5.SIG-ALG.REG.INT | Optional               | [][RFC2845] |
    | hmac-sha1                | Mandatory              | [RFC4635]   |
    | hmac-sha224              | Optional               | [RFC4635]   |
    | hmac-sha256              | Mandatory              | [RFC4635]   |
    | hmac-sha384              | Optional               | [RFC4635]   |
    | hmac-sha512              | Optional               | [RFC4635]   |

   where [] is this document.

5.  Availability Considerations

   MD5 is no more universally available and its use should lead to
   increasing operation issues.  SHA1 is likely to suffer from the same
   kind of problem.  To summary MD5 has reached end-of-life and SHA1
   follows few years behind.

   According to [RFC4635], implementations which support TSIG are
   REQUIRED to implement HMAC-SHA256.

6.  Security Considerations

   This document does not assume anything about the cryptographic
   security of different hash algorithms.  It is a routine maintenance,
   its goal is better availability of some security mechanisms in a
   predictable future.

   Requirement levels are adjusted for TSIG and related specifications
   (i.e., TKEY):
      The use of MD5 and HMAC-MD5 is NOT RECOMMENDED.
      The use of HMAC-SHA256 is RECOMMENDED.

7.  Acknowledgments

   Olafur Gudmundsson kindly helped in the procedure to deprecate the
   MD5 use in TSIG, i.e., the procedure which led to this memo.  Alfred
   Hoenes, Peter Koch and Paul Hoffman proposed some improvements.

8.  References

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8.1.  Normative References

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

   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake, D., and B.
              Wellington, "Secret Key Transaction Authentication for DNS
              (TSIG)", RFC 2845, May 2000.

   [RFC2930]  Eastlake, D., "Secret Key Establishment for DNS (TKEY
              RR)", RFC 2930, September 2000.

   [RFC4635]  Eastlake, D., "HMAC SHA TSIG Algorithm Identifiers",
              RFC 4635, August 2006.

8.2.  Informative References

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              February 1997.

   [RFC3174]  Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
              (SHA1)", RFC 3174, September 2001.

   [RFC3645]  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.

   [RFC3874]  Housley, R., "A 224-bit One-way Hash Function: SHA-224",
              RFC 3874, September 2004.

   [RFC4634]  Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and HMAC-SHA)", RFC 4634, July 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226, BCP 26,
              May 2008.

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Author's Address

   Francis Dupont

   Email: Francis.Dupont@fdupont.fr

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