DNSext Working Group F. Dupont Internet-Draft ISC Updates: 2845,2930,4635
June 30,November 19, 2008 (if approved) Intended status: Standards Track Expires: January 1,May 23, 2009 Deprecation of HMAC-MD5 in DNS TSIG and TKEY Resource Records draft-ietf-dnsext-tsig-md5-deprecated-00.txtdraft-ietf-dnsext-tsig-md5-deprecated-01.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 1,May 23, 2009. 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 deprecated and replaced by HMAC- SHA256optional 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. TSIG Algorithm Name Registry In the registry of TSIG algorithm names, add this comment "(deprecated, see hmac-sha256)" in the HMAC-MD5.SIG-ALG.REG.INT entry. This follows the style of 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 | +-------------------+--------------------------+ | DeprecatedOptional | 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). 4.3. 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. 5.4. IANA Consideration The section Section 2 should be applied according to the current IANA preferences, i.e.,This document extends the update is in"TSIG Algorithm Names - per [RFC2845]" located at http://www.iana.org/assignments/tsig-algorithm-names by adding a [RFC3110] style and can be adaptednew colum to the style chosen by IANA for TSIG algorithm names. 6.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] | | 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 Considerations MD5 was proven to be less secure than expected in some uses, but HMAC-MD5 is not one of these uses, i.e., today HMAC-MD5 was not proved insecure [Bellovin]. But for many reasons like to avoid insecure uses of MD5, or certification of cryptographic modules (e.g., [FIPS140-2], one cannot assume MD5 will be provided by all cryptographic modules, so even HMAC-MD5 does not lead today to security issues, it can lead to operational issues. The use of MD5 and HMAC-MD5 is NOT RECOMMENDED in TSIG and related specifications (i.e., TKEY). But SHA1 seems to be vulnerable too, so the use of at least SHA256 is RECOMMENDED. Implementations which support TSIG are REQUIRED to implement HMAC-SHA256, the HMAC-SHA256 algorithm is RECOMMENDED for default use in TSIG. 7.6. 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 use in TSIG, i.e., the procedure which led to this memo. Alfred Hoenes andHoenes, Peter Koch and paul Hoffman proposed some improvements. 8.7. References 126.96.36.199. 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. 188.8.131.52. 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. [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. [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 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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