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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Internet-Draft Deprecated HMAC MD5 in TSIG May 2008
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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