DNSext Working Group                                           F. Dupont
Internet-Draft                                                       ISC
Updates: 2845,2930,4635                                November 19, 2008                                   April 27, 2009
(if approved)
Intended status: Standards Track
Expires: May 23, October 29, 2009

     Deprecation of HMAC-MD5 in DNS TSIG and TKEY Resource Records
              draft-ietf-dnsext-tsig-md5-deprecated-01.txt
              draft-ietf-dnsext-tsig-md5-deprecated-02.txt

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Abstract

   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
       [RFC5226]
   2.  Make HMAC-MD5.SIG-ALG.REG.INT support "not Mandatory" for
       implementations
   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",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Implementation Requirements

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

             +-------------------+--------------------------+
             | 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 colum
   column to the registry "Compliance Requirement".

   The registry should contain the following:

    +--------------------------+------------------------+-------------+
    | Algorithm Name           | Compliance Requirement | Reference   |
    +--------------------------+------------------------+-------------+
    | gss-tsig                 | Optional               | [RFC3645]   |
    | HMAC-MD5.SIG-ALG.REG.INT | Optional               | [RFC2845][] [][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.  Security  Availability Considerations

   MD5 was proven is no more universally available and its use should lead to be less secure than expected in some uses, but
   HMAC-MD5
   increasing operation issues.  SHA1 is not one of these uses, i.e., today HMAC-MD5 was not
   proved insecure [Bellovin].

   But for many reasons like likely to avoid insecure uses of MD5, or
   certification suffer from the same
   kind of cryptographic modules (e.g., [FIPS140-2], one cannot
   assume problem.  To summary MD5 will be provided by all cryptographic modules, so even
   HMAC-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 lead today to assume anything about the cryptographic
   security issues, it can lead to
   operational issues.

   The use of MD5 and HMAC-MD5 different hash algorithms.  It is NOT RECOMMENDED 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).

   But SHA1 seems to be vulnerable too, so the TKEY):
      The use of at least SHA256 MD5 and HMAC-MD5 is NOT RECOMMENDED.  Implementations which support TSIG are REQUIRED to
   implement HMAC-SHA256, the
      The use of HMAC-SHA256 algorithm is RECOMMENDED for
   default use in TSIG.

6. RECOMMENDED.

7.  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 use in TSIG, i.e., the procedure which led to this memo.  Alfred
   Hoenes, Peter Koch and paul Paul Hoffman proposed some improvements.

7.

8.  References

7.1.

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.

7.2.

8.2.  Informative References

   [Bellovin]
              Bellovin, S., "[Cfrg] HMAC-MD5", March 2006, <http://
              www.ietf.org/mail-archive/web/cfrg/current/msg01197.html>.

   [FIPS140-2]
              National Institute of Standards and Technology (NIST),
              "FIPS PUB 140-2: Security Requirements for Cryptographic
              Modules", May 2001, <http://csrc.nist.gov/publications/
              fips/fips140-2/fips1402.pdf>.

   [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.

Author's Address

   Francis Dupont
   ISC

   Email: Francis.Dupont@fdupont.fr

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