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DNSext Working Group F. Dupont
Internet-Draft ISC
Updates: 2845,2930,4635 May 8, 2009
(if approved)
Intended status: Standards Track
Expires: November 9, 2009
Deprecation of HMAC-MD5 in DNS TSIG and TKEY Resource Records
draft-ietf-dnsext-tsig-md5-deprecated-03.txt
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Dupont Expires November 9, 2009 [Page 1]
Internet-Draft Deprecating HMAC-MD5 in TSIG May 2009
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Abstract
The main purpose 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), and the use of MD5
in TKEY (secret key establishment for DNS).
1. Introduction
The secret key transaction authentication for DNS (TSIG, [RFC2845])
was defined with the HMAC-MD5 [RFC2104] cryptographic algorithm.
When the MD5 [RFC1321] security came to be considered 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 detail:
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 replaced by:
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Internet-Draft Deprecating HMAC-MD5 in TSIG May 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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Internet-Draft Deprecating HMAC-MD5 in TSIG May 2009
+--------------------------+------------------------+-------------+
| 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 longer universally available and its use may lead to
increasing operation issues. SHA1 is likely to suffer from the same
kind of problem. In summary MD5 has reached end-of-life and SHA1
will likely follow in the near term.
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. Its purpose is a better
availability of some security mechanisms in a predictable time frame.
Requirement levels are adjusted for TSIG and related specifications
(i.e., TKEY):
The support of HMAC-MD5 is changed from mandatory to optional.
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, Paul Hoffman and Edward Lewis proposed some
improvements.
8. References
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Internet-Draft Deprecating HMAC-MD5 in TSIG May 2009
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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Internet-Draft Deprecating HMAC-MD5 in TSIG May 2009
Author's Address
Francis Dupont
ISC
Email: Francis.Dupont@fdupont.fr
Dupont Expires November 9, 2009 [Page 6]
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