< draft-turner-md5-seccon-update-00.txt   draft-turner-md5-seccon-update-01.txt >
Network Working Group S. Turner Network Working Group S. Turner
Internet Draft IECA Internet Draft IECA
Updates: 1321 (once approved) L. Chen Updates: 1321, 2202 (once approved) L. Chen
Intended Status: Informational NIST Intended Status: Informational NIST
Expires: January 5, 2011 July 5, 2010 Expires: January 8, 2011 July 8, 2010
Updated Security Considerations for the MD5 Message-Digest Algorithm Updated Security Considerations for the
draft-turner-md5-seccon-update-00.txt MD5 Message-Digest Algorithm and HMAC-MD5
draft-turner-md5-seccon-update-01.txt
Abstract Abstract
This document updates the security considerations for the MD5 message This document updates the security considerations for the MD5 message
digest algorithm. digest algorithm. It also updates the security considerations for
HMAC-MD5.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. This document may contain material provisions of BCP 78 and BCP 79. This document may contain material
from IETF Documents or IETF Contributions published or made publicly from IETF Documents or IETF Contributions published or made publicly
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This Internet-Draft will expire on January 5, 2011. This Internet-Draft will expire on January 8, 2011.
Copyright Notice Copyright Notice
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1. Introduction 1. Introduction
MD5 [MD5] is a message digest algorithm that takes as input a message MD5 [MD5] is a message digest algorithm that takes as input a message
of arbitrary length and produces as output a 128-bit "fingerprint" or of arbitrary length and produces as output a 128-bit "fingerprint" or
"message digest" of the input. The published attacks against MD5 "message digest" of the input. The published attacks against MD5
show and that it is not prudent to use MD5 when collision resistance show and that it is not prudent to use MD5 when collision resistance
is required. This document replaces the security considerations in is required. This document replaces the security considerations in
RFC 1321 [MD5]. RFC 1321 [MD5].
[HMAC] defined a mechanism for message authentication using
cryptographic hash functions. Any message digest algorithm can be
used, but the cryptographic strength of HMAC depends on the
properties of the underlying hash function. [HMAC-MD5] defined test
cases for HMAC-MD5. This document updates the security
considerations in [HMAC-MD5].
[HASH-Attack] summarizes the use of hashes in many protocols and [HASH-Attack] summarizes the use of hashes in many protocols and
discusses how attacks against a message digest algorithm's one-way discusses how attacks against a message digest algorithm's one-way
and collision-free properties affect and do not affect Internet and collision-free properties affect and do not affect Internet
protocols. protocols.
2. Security Considerations 2. Security Considerations
MD5 was published in 1992 as an Informational RFC. Since that time, MD5 was published in 1992 as an Informational RFC. Since that time,
MD5 has been studied extensively. What follows are recent attacks MD5 has been studied extensively. What follows are recent attacks
against MD5's collisions, pre-image, and second pre-image resistance. against MD5's collisions, pre-image, and second pre-image resistance.
Additionally, attacks against MD5 used in message authentication with Additionally, attacks against MD5 used in message authentication with
a shared secret (i.e., HMAC-MD5) are discussed. a shared secret (i.e., HMAC-MD5) are discussed.
Some may find the guidance for key lengths and algorithm strengths in Some may find the guidance for key lengths and algorithm strengths in
[SP800-57] and [SP800-131] useful. [SP800-57] and [SP800-131] useful.
2.1. Collision Resistance 2.1. Collision Resistance
The first paper that demonstrates actual collisions of MD5 was The first paper that demonstrates actual collisions of MD5 was
published in 2004 [MD5-Analysis1]. The detailed attack techniques for published in 2004 [WFLY2004]. The detailed attack techniques for MD5
MD5 were published at EUROCRYPT 2005 [MD5-Analysis2]. Since then, a were published at EUROCRYPT 2005 [WAYU2005]. Since then, a lot of
lot of research results have been published to improve collision research results have been published to improve collision attacks on
attacks on MD5. The attacks presented in [MD5-Analysis3] can find MD5 MD5. The attacks presented in [KLIM2006] can find MD5 collision in
collision in about one minute on a standard notebook PC (Intel about one minute on a standard notebook PC (Intel Pentium, 1.6 GHz.).
Pentium, 1.6 GHz.). In [MD5-Analysis4], the collision attack on MD5 In [STEV2007], he claim that it takes 10 seconds or less on a 2.6Ghz
was successfully applied to X.509 certificates. Pentium4 to find collisions. In
[STEV2007][SLdeW2007][SSALMOdeW2009][SLdeW2009], the collision
attacks on MD5 were successfully applied to X.509 certificates.
Notice that the collision attack on MD5 can also be applied to Notice that the collision attack on MD5 can also be applied to
password based challenge-and-response authentication protocols such password based challenge-and-response authentication protocols such
as APOP protocol used in post office authentication as presented in as APOP protocol used in post office authentication as presented in
[MD5-Analysis5]. [LEUR2007].
In fact, more delicate attacks on MD5 to improve the speed of finding In fact, more delicate attacks on MD5 to improve the speed of finding
collisions have published recently. However, the aforementioned collisions have published recently. However, the aforementioned
results have provided sufficient reason to eliminate MD5 usage in results have provided sufficient reason to eliminate MD5 usage in
applications where collision resistance is required such as digital applications where collision resistance is required such as digital
signatures. signatures.
2.2. Pre-image and Second Pre-image Resistance 2.2. Pre-image and Second Pre-image Resistance
Even though the best result can find a pre-image attack of MD5 faster Even though the best result can find a pre-image attack of MD5 faster
than exhaustive search as presented in [MD5-Analysis6], the than exhaustive search as presented in [SAAO2009], the complexity
complexity 2^123.4 is still pretty high. 2^123.4 is still pretty high.
2.3. HMAC 2.3. HMAC
The cryptanalysis of HMAC-MD5 usually conducted together with NMAC The cryptanalysis of HMAC-MD5 usually conducted together with NMAC
(Nested MAC) since they are closely related. NMAC uses two (Nested MAC) since they are closely related. NMAC uses two
independent keys K1 and K2 such that NMAC(K1, K2, M) = H(K1, H(K2, independent keys K1 and K2 such that NMAC(K1, K2, M) = H(K1, H(K2,
M), where K1 and K2 are used as secret IVs for hash functions M), where K1 and K2 are used as secret IVs for hash functions
H(IV,M). If we re-write HMAC equation using two secret IVs such that H(IV,M). If we re-write HMAC equation using two secret IVs such that
IV2 = H(K Xor ipad) and IV1 = H(K Xor opad), then HMAC(K, M) = IV2 = H(K Xor ipad) and IV1 = H(K Xor opad), then HMAC(K, M) =
NMAC(IV1, IV2, M). Here it is very important to notice that IV1 and NMAC(IV1, IV2, M). Here it is very important to notice that IV1 and
IV2 are not independently selected. IV2 are not independently selected.
The first analysis was explored on NMAC-MD5 using related keys in The first analysis was explored on NMAC-MD5 using related keys in
[HMAC-Analysis1]. The partial key recovery attack cannot be extended [COYI2006]. The partial key recovery attack cannot be extended to
to HMAC-MD5, since for HMAC, recovering partial secret IVs can hardly HMAC-MD5, since for HMAC, recovering partial secret IVs can hardly
lead to recovering (partial) key K. Another paper presented at Crypto lead to recovering (partial) key K. Another paper presented at Crypto
2007 [HMAC-Analysis2] extended results of [HMAC-Analysis1] to a full 2007 [FLN2007] extended results of [COYI2006] to a full key recovery
key recovery attack on NMAC-MD5. Since it also uses related key attack on NMAC-MD5. Since it also uses related key attack, it does
attack, it does not seem applicable to HMAC-MD5. not seem applicable to HMAC-MD5.
A EUROCRYPT 2009 paper presented a distinguishing attack on HMAC-MD5 A EUROCRYPT 2009 paper presented a distinguishing attack on HMAC-MD5
[HMAC-Analysis3] without using related keys. It can distinguish an [WYWZZ2009] without using related keys. It can distinguish an
instantiation of HMAC with MD5 from an instantiation with a random instantiation of HMAC with MD5 from an instantiation with a random
function with 2^97 queries with probability 0.87. This is called function with 2^97 queries with probability 0.87. This is called
distinguishing-H. Using the distinguishing attack, it can recover distinguishing-H. Using the distinguishing attack, it can recover
some bits of the intermediate status of the second block. However, as some bits of the intermediate status of the second block. However, as
it is pointed in [HMAC-Analysis3], it cannot be used to recover the it is pointed in [WYWZZ2009], it cannot be used to recover the
(partial) inner key H(K Xor ipad). It is not obvious how the attack (partial) inner key H(K Xor ipad). It is not obvious how the attack
can be used to form a forgery attack either. can be used to form a forgery attack either.
The attacks on HMAC-MD5 do not seem to indicate a practical The attacks on HMAC-MD5 do not seem to indicate a practical
vulnerability when used as a message authentication code. Considering vulnerability when used as a message authentication code. Considering
that the distinguishing-H attack is different from distinguishing-R that the distinguishing-H attack is different from distinguishing-R
attack, which distinguishes an HMAC from a random function, the attack, which distinguishes an HMAC from a random function, the
practical impact on HMAC usage as a PRF such as in a key derivation practical impact on HMAC usage as a PRF such as in a key derivation
function is not well understood. function is not well understood.
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protocols. However, since MD5 must not be used for digital protocols. However, since MD5 must not be used for digital
signatures, for a new protocol design, a ciphersuite with HMAC-MD5 signatures, for a new protocol design, a ciphersuite with HMAC-MD5
should not be included. should not be included.
3. IANA Considerations 3. IANA Considerations
None. None.
4. Normative References 4. Normative References
[HASH-Attack] Hoffman, P., and B. Schneier, "Attacks on [COYI2006] S. Contini, Y.L. Yin. Forgery and partial key-
Cryptographic Hashes in Internet Protocols", RFC
4270, November 2005.
[HMAC-Analysis1] S. Contini, Y.L. Yin. Forgery and partial key-
recovery attacks on HMAC and NMAC using hash recovery attacks on HMAC and NMAC using hash
collisions. ASIACRYPT 2006. LNCS 4284, Springer, collisions. ASIACRYPT 2006. LNCS 4284, Springer,
2006. 2006.
[HMAC-Analysis2] Fouque, P.-A., Leurent, G., Nguyen, P.Q.: Full key- [FLN2007] Fouque, P.-A., Leurent, G., Nguyen, P.Q.: Full key-
recovery attacks on HMAC/NMAC-MD4 and NMAC-MD5. recovery attacks on HMAC/NMAC-MD4 and NMAC-MD5.
CRYPTO 2007. LNCS, 4622, Springer, 2007. CRYPTO 2007. LNCS, 4622, Springer, 2007.
[HMAC-Analysis3] X. Wang, H. Yu, W. Wang, H. Zhang, and T. Zhan. [HASH-Attack] Hoffman, P., and B. Schneier, "Attacks on
Cryptanalysis of HMAC/NMAC-MD5 and MD5-MAC. LNCS Cryptographic Hashes in Internet Protocols", RFC
5479. Advances in Cryptology - EUROCRYPT2009, 4270, November 2005.
Springer 2009.
[MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC
1321, April 1992.
[MD5-Analysis1] X. Wang, D. Feng, X. Lai, H. Yu, Collisions for [HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC:
Hash Functions MD4, MD5, HAVAL-128 and RIPEMD, Keyed-Hashing for Message Authentication", RFC
2004, http://eprint.iacr.org/2004/199.pdf 2104, February 1997.
[MD5-Analysis2] X. Wang and H. Yu. How to Break MD5 and other Hash [HMAC-MD5] Cheng, P., and R. Glenn, "Test Cases for HMAC-MD5
Functions. LNCS 3494. Advances in Cryptology - and HMAC-SHA-1", RC 2201, September 1997.
EUROCRYPT2005, Springer 2005.
[MD5-Analysis3] V. Klima. Tunnels in Hash Functions: MD5 Collisions [KLIM2006] V. Klima. Tunnels in Hash Functions: MD5 Collisions
within a Minute. Cryptology ePrint Archive, Report within a Minute. Cryptology ePrint Archive, Report
2006/105 (2006), http://eprint.iacr.org/2006/105. 2006/105 (2006), http://eprint.iacr.org/2006/105.
[MD5-Analysis4] Stevens, M., Lenstra, A., de Weger, B., Target [LEUR2007] G. Leurent, Message freedom in MD4 and MD5
Collisions for MD5 and Colliding X.509
Certificates for Different Identities. Cryptology
ePrint Archive, Report 2006/360 (2006),
http://eprint.iacr.org/2006/360.
[MD5-Analysis5] G. Leurent, Message freedom in MD4 and MD5
collisions: Application to APOP. Proceedings of collisions: Application to APOP. Proceedings of
FSE 2007. Lecture Notes in Computer Science 4715. FSE 2007. Lecture Notes in Computer Science 4715.
Springer 2007. Springer 2007.
[MD5-Analysis6] Y. Sasaki and K. Aoki. Finding preimages in full [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC
1321, April 1992.
[SAAO2009] Y. Sasaki and K. Aoki. Finding preimages in full
MD5 faster than exhaustive search. Advances in MD5 faster than exhaustive search. Advances in
Cryptology - EUROCRYPT 2009, LNCS 5479 of Lecture Cryptology - EUROCRYPT 2009, LNCS 5479 of Lecture
Notes in Computer Science, Springer, 2009. Notes in Computer Science, Springer, 2009.
[SLdeW2007] Stevens, M., Lenstra, A., de Weger, B., Chosen-
prefix Collisions for MD5 and Colliding X.509
Certificates for Different Identities. EuroCrypt
2007.
[SLdeW2009] Stevens, M., Lenstra, A., de Weger, B., "Chosen-
prefix Collisions for MD5 and Applications",
Journal of Cryptology, 2009.
http://deweger.xs4all.nl/papers/%5B42%5DStLedW-
MD5-JCryp%5B2009%5D.pdf.
[SSALMOdeW2009] Stevens, M., Sotirov, A., Appelbaum, J., Lenstra,
A., Molnar, D., Osvik, D., and B. de Weger. Short
chosen-prefix collisions for MD5 and the creation
of a rogue CA certificate, Crypto 2009.
[SP800-57] National Institute of Standards and Technology [SP800-57] National Institute of Standards and Technology
(NIST), Special Publication 800-57: Recommendation (NIST), Special Publication 800-57: Recommendation
for Key Management - Part 1 (Revised), March 2007. for Key Management - Part 1 (Revised), March 2007.
[SP800-131] National Institute of Standards and Technology [SP800-131] National Institute of Standards and Technology
(NIST), Special Publication 800-131: DRAFT (NIST), Special Publication 800-131: DRAFT
Recommendation for the Transitioning of Recommendation for the Transitioning of
Cryptographic Algorithms and Key Sizes, June 2010. Cryptographic Algorithms and Key Sizes, June 2010.
[STEV2007] Stevens, M., On Collisions for MD5.
http://www.win.tue.nl/hashclash/On%20Collisions%20
for%20MD5%20-%20M.M.J.%20Stevens.pdf.
[WAYU2005] X. Wang and H. Yu. How to Break MD5 and other Hash
Functions. LNCS 3494. Advances in Cryptology -
EUROCRYPT2005, Springer 2005.
[WFLY2004] X. Wang, D. Feng, X. Lai, H. Yu, Collisions for
Hash Functions MD4, MD5, HAVAL-128 and RIPEMD,
2004, http://eprint.iacr.org/2004/199.pdf
[WYWZZ2009] X. Wang, H. Yu, W. Wang, H. Zhang, and T. Zhan.
Cryptanalysis of HMAC/NMAC-MD5 and MD5-MAC. LNCS
5479. Advances in Cryptology - EUROCRYPT2009,
Springer 2009.
Authors' Addresses Authors' Addresses
Sean Turner Sean Turner
IECA, Inc. IECA, Inc.
3057 Nutley Street, Suite 106 3057 Nutley Street, Suite 106
Fairfax, VA 22031 Fairfax, VA 22031
USA USA
EMail: turners@ieca.com EMail: turners@ieca.com
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