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Versions: 00 draft-ietf-dnsext-tsig-md5-deprecated

Network Working Group                                          F. Dupont
Internet-Draft                                                       ISC
Intended status: Standards Track                            May 11, 2008
Expires: November 12, 2008


                      Deprecated HMAC MD5 in TSIG
             draft-dupont-dnsext-tsig-md5-deprecated-00.txt

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Abstract

   The goal of this document is to deprecate the usage 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 security is today recognized to be lower than expected, the
   [RFC4635] standardized new TSIG algorithms based on SHA
   [RFC3174][RFC3874] [RFC4634] digests.



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   But it failed to deprecate the HMAC MD5 algorithm.  This document is
   targeted to correct this point, in details:
   1.  Mark HMAC-MD5.SIG-ALG.REG.INT as deprecated and replaced by hmac-
       sha256 in the TSIG algorithm name registry managed by the IANA
       under the IETF Consensus Policy [RFC2434]
   2.  Make HMAC-MD5.SIG-ALG.REG.INT support Optional for
       implementations
   3.  Provide a keying material derivation for the secret key
       establishment for DNS (TKEY, [RFC2930]) using a Diffie-Hellman
       exchange
   4.  Finally recommend the use of at least hmac-sha256.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2.  IANA Considerations

   In the registry of TSIG algorithm names, add this comment
   "(deprecated, see hmac-sha256)" in the HMAC-MD5.SIG-ALG.REG.INT
   entry.

   This is copied from the registry of DNSSEC algorithm numbers which
   was updated by [RFC3110].


3.  Implementation Requirements

   The table of section 3 of [RFC4635] is updated into:

             +-------------------+--------------------------+
             | 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 and MAY implement gss-tsig and the other algorithms
   listed above.





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4.  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 8.

   This is amended into:

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

   using the same conventions.


5.  Security Considerations

   The use of MD5 and HMAC MD5 is NOT RECOMMENDED in TSIG and related
   specifications (i.e., TKEY).

   But SHA-1 seems to be vulnerable too, so the use of at least SHA256
   is RECOMMENDED.  As implementations which support TSIG are REQUIRED
   to implement HMAC SHA256, in particular the hmac-sha256 algorithm is
   RECOMMENDED for default use in TSIG.


6.  Acknowledgments

   Cryptographic module validation programs made MD5 not approved so not
   available.  They provide a good incentive to deprecate MD5 at a place
   it is still mandatory to support and likely heavily used.

   Olafur Gudmundsson kindly helped in the procedure to deprecate the
   MD5 usage in TSIG, i.e., the procedure which gave this memo.


7.  References

7.1.  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



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              RR)", RFC 2930, September 2000.

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

7.2.  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.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 2434, BCP 26,
              October 1998.

   [RFC3110]  Eastlake, D., "RSA/SHA-1 SIGs and RSA KEYs in the Domain
              Name System (DNS)", RFC 3110, May 2001.

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

   [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.


Author's Address

   Francis Dupont
   ISC

   Email: Francis.Dupont@fdupont.fr














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