MD2 to Historic Status
The information below is for an old version of the document that is already published as an RFC.
This is an older version of an Internet-Draft that was ultimately published as RFC 6149.
|Last updated||2020-07-29 (Latest revision 2010-12-29)|
|RFC stream||Internet Engineering Task Force (IETF)|
|IESG||IESG state||RFC 6149 (Informational)|
|Responsible AD||Robert Sparks|
|Send notices to||(None)|
Network Working Group S. Turner Internet-Draft IECA Obsoletes: 1319 (once approved) L. Chen Intended Status: Informational NIST Expires: June 28, 2011 December 29, 2010 MD2 to Historic Status draft-turner-md2-to-historic-10.txt Abstract This document recommends the retirement of MD2 and discusses the reasons for doing so. This document recommends RFC 1319 be moved to Historic status. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on June 28, 2011. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Turner & Chen Expires 2011-06-28 [Page 1] Internet-Draft MD2 to Historic 2010-12-29 1. Introduction MD2 [MD2] is a message digest algorithm that takes as input a message of arbitrary length and produces as output a 128-bit "fingerprint" or "message digest" of the input. This document recommends that MD2 be retired. Specifically, this document recommends RFC 1319 [MD2] be moved to Historic status. The reasons for taking this action are discussed. [HASH-Attack] summarizes the use of hashes in many protocols and discusses how attacks against a message digest algorithm's one-way and collision-free properties affect and do not affect Internet protocols. Familiarity with [HASH-Attack] is assumed. 2. Rationale MD2 was published in 1992 as an Informational RFC. Since its publication, MD2 has been shown to not be collision-free [ROCH1995] [KNMA2005] [ROCH1997], albeit successful collision attacks for properly implemented MD2 are not that damaging. MD2 has also been shown to have successful pre-image and second-preimage attacks [KNMA2005] [MULL2004] [KMM2010]. 3. Documents that Reference RFC 1319 Use of MD2 has been specified in the following RFCs: Proposed Standard (PS): o [RFC3279] Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile. o [RFC4572] Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP). Informational: o [RFC1983] Internet Users' Glossary. o [RFC2315] PKCS #7: Cryptographic Message Syntax Version 1.5. o [RFC2898] PKCS #5: Password-Based Cryptography Specification Version 2.0. o [RFC3447] Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1. Turner & Chen Expires 2011-06-28 [Page 2] Internet-Draft MD2 to Historic 2010-12-29 Experimental: o [RFC2660] The Secure HyperText Transfer Protocol. There are other RFCs that refer to MD2, but their status is either Historic or Obsoleted. References and discussions about these RFCs are omitted. The exceptions are: o [RFC2313] PKCS #1: RSA Encryption Version 1.5. o [RFC2437] PKCS #1: RSA Cryptography Specifications Version 2.0. 4. Impact on Moving MD2 to Historic The impact of moving MD2 to Historic on the RFCs specified in Section 3 is minimal, as described below. Regarding PS RFCs: o MD2 support in TLS was dropped in TLS 1.1. o MD2 support is optional in [RFC4572], and SHA-1 is specified as the preferred algorithm. o MD2 is included in the original PKIX certificate profile and the PKIX algorithm document [RFC3279] for compatibility with older applications, but its use is discouraged. SHA-1 is identified as the preferred algorithm for the Internet PKI. Regarding Informational RFCs: o The Internet Users' Guide [RFC1983] provided a definition for Message Digest and listed MD2 as one example. o PKCS#1 v1.5 [RFC2313] stated that there are no known attacks against MD2. PKCS#1 v2.0 [RFC2437] updated this stance to indicate that MD2 should only be supported for backward compatibility and to mention the attacks in [ROCH1995]. PKCS#1 [RFC3447] indicates that support MD2 is only retained for compatibility with existing applications. o PKCS#5 [RFC2898] recommends that the Password Based Encryption Scheme (PBES) that uses MD2 not be used for new applications. Turner & Chen Expires 2011-06-28 [Page 3] Internet-Draft MD2 to Historic 2010-12-29 o PKCS#7 [RFC2315] was replaced by a series of standards track publications, "Cryptographic Message Syntax" [RFC2630] [RFC3369] [RFC5652] and "Cryptographic Message Syntax (CMS) Algorithms" [RFC3370]. Support for MD2 was dropped in [RFC3370]. RFC 2818 "HTTP Over TLS", which does not reference MD2, largely supplanted implementation of [RFC2660]. [RFC2660] specified MD2 for use both as a digest algorithm as a MAC algorithm [RFC2104]. Note that this is the only reference to HMAC-MD2 found in the RFC repository. 5. Other Considerations MD2 has also fallen out of favor because it is slower than both MD4 [MD4] and MD5 [MD5]. This is because MD2 was optimized for 8-bit machines while MD4 and MD5 were optimized for 32-bit machines. MD2 is also slower than the Secure Hash Standard (SHS) [SHS] algorithms: SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512. 6. Security Considerations MD2 is different from MD4 and MD5 in that is not a straight Merkle- Damgaard design. For a padded message with t blocks, it generates a nonlinear checksum as its t+1 block. The checksum is considered as the final block input of MD2. As confirmed in 1997 by Rogier et. al. [ROCH1997], the collision resistance property of MD2 highly depends on the nonlinear checksum. Without the checksum, a collision can be found in 2^12 MD2 operations according, while with the checksum, the best collision attack takes 2^63.3 operations with 2^50 memory complexity [MULL2004], which is not significantly better than the birthday attack. Even though collision attacks on MD2 are not significantly more powerful than the birthday attack, MD2 was found not to be one-way. In [KMM2010], a pre-image can be found with 2^104 MD2 operations. In an improved attack described in [KMM2010], a pre-image can be found in 2^73 MD2 operations. Because of this "invertible" property of MD2, when using MD2 in HMAC, it may leak information of the keys. Obviously, the pre-image attack can be used to find a second pre- image. The second pre-image attack is even more severe than a collision attack to digital signatures. Therefore, MD2 must not be used for digital signatures. Some may find the guidance for key lengths and algorithm strengths in [SP800-57] and [SP800-131] useful. Turner & Chen Expires 2011-06-28 [Page 4] Internet-Draft MD2 to Historic 2010-12-29 7. Recommendation Despite MD2 seeing some deployment on the Internet, this specification recommends obsoleting MD2. MD2 is not a reasonable candidate for further standardization and should be deprecated in favor of one or more existing hash algorithms (e.g., SHA-256 [SHS]). RSA Security considers it appropriate to move the MD2 algorithm to Historic status. It takes a number of years to deploy crypto and it also takes a number of years to withdraw it. Algorithms need to be withdrawn before a catastrophic break is discovered. MD2 is clearly showing signs of weakness and implementations should strongly consider removing support and migrating to another hash algorithm. 8. IANA Considerations None. 9. Acknowledgements We'd like to thank RSA for publishing MD2. We'd also like to thank all the cryptographers who studied the algorithm. For his contribution to this draft we'd like to thank Ran Atkinson, Alfred Hoenes, John Linn, and Martin Rex. 10. Informative References [HASH-Attack] Hoffman, P., and B. Schneier, "Attacks on Cryptographic Hashes in Internet Protocols", RFC 4270, November 2005. [KNMA2005] Knudsen, L., and J. Mathiassen, "Preimage and Collision Attacks on MD2," FSE 2005. [KMM2010] Knudsen, L., Mathiassen, J., Muller, F., and Thomsen, S., "Cryptanalysis of MD2", Journal of Cryptology, 23(1):72-90, 2010. [MD2] Kaliski, B., "The MD2 Message-Digest Algorithm", RFC 1319, April 1992. [MULL2004] Muller, F., "The MD2 Hash Function Is Not One-Way", ASIACRYPT, LNCS 3329, pp. 214-229, Springer, 2004. [MD4] Rivest, R., "The MD4 Message-Digest Algorithm", RFC 1320, April 1992. [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. Turner & Chen Expires 2011-06-28 [Page 5] Internet-Draft MD2 to Historic 2010-12-29 [RFC1983] Malkin, G., "Internet Users' Glossary", RFC 1983, August 1996. [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, February 1997. [RFC2313] Kaliski, B., "PKCS #1: RSA Encryption Version 1.5", RFC 2313, March 1998. [RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message Syntax Version 1.5," RFC 2315, March 1998. [RFC2437] Kaliski, B., and J. Staddon, "PKCS #1: RSA Cryptography Specifications Version 2.0", RFC 2437, October 1998. [RFC2630] Housley, R., "Cryptographic Message Syntax", RFC 2630, June 1999. [RFC2660] Rescorla, E., and A. Schiffman, "The Secure HyperText Transfer Protocol", RFC 2660, August 1999. [RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography Specification Version 2.0", RFC 2898, September 2000. [RFC3279] Polk, W., Housley, R., and L. Bassham, "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3279, April 2002. [RFC3369] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3369, August 2002. [RFC3370] Housley, R., "Cryptographic Message Syntax (CMS) Algorithms", RFC 3370, August 2002. [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1" RFC 3447, February 2003. [RFC4572] Lennox, J., "Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)", RFC 4572, July 2006. [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, August 2002. [ROCH1995] Rogier, N., and P. Chauvaud, "The compression function of Turner & Chen Expires 2011-06-28 [Page 6] Internet-Draft MD2 to Historic 2010-12-29 MD2 is not collision free", Presented at Selected Areas in Cryptography '95, Carleton University, Ottawa, Canada. May 18-19, 1995. [ROCH1997] Rogier, N. and P. Chauvaud, "MD2 is not secure without the checksum byte", Des. Codes Cryptogr. 12(3), 245-251 (1997). [SP800-57] National Institute of Standards and Technology (NIST), Special Publication 800-57: Recommendation for Key Management - Part 1 (Revised), March 2007. [SP800-131] National Institute of Standards and Technology (NIST), Special Publication 800-131: DRAFT Recommendation for the Transitioning of Cryptographic Algorithms and Key Sizes, June 2010. [SHS] National Institute of Standards and Technology (NIST), FIPS Publication 180-3: Secure Hash Standard, October 2008. Authors' Addresses Sean Turner IECA, Inc. 3057 Nutley Street, Suite 106 Fairfax, VA 22031 USA EMail: firstname.lastname@example.org Lily Chen National Institute of Standards and Technology 100 Bureau Drive, Mail Stop 8930 Gaithersburg, MD 20899-8930 USA EMail: email@example.com Turner & Chen Expires 2011-06-28 [Page 7]