International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Collision-Resistant usage of MD5 and SHA-1 via Message Preprocessing

Michael Szydlo
Yiqun Lisa Yin
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Abstract: A series of recent papers have demonstrated collision attacks on popularly used hash functions, including the widely deployed MD5 and SHA-1 algorithm. To assess this threat, the natural response has been to evaluate the extent to which various protocols actually depend on collision resistance for their security, and potentially schedule an upgrade to a stronger hash function. Other options involve altering the protocol in some way. This work suggests a different option. We present several simple message pre-processing techniques and show how the techniques can be combined with MD5 or SHA-1 so that applications are no longer vulnerable to the known collision attacks. For some applications, this may a viable alternative to upgrading the hash function.
  title={Collision-Resistant usage of MD5 and SHA-1 via Message Preprocessing},
  booktitle={IACR Eprint archive},
  keywords={SHA-1, MD5, padding, hash collision, signature},
  note={RSA Conference 2006 13074 received 29 Jul 2005, last revised 18 Oct 2005},
  author={Michael Szydlo and Yiqun Lisa Yin},