Collision-Resistant usage of MD5 and SHA-1 via message preprocessing

  • Authors:
  • Michael Szydlo;Yiqun Lisa Yin

  • Affiliations:
  • RSA Laboratories, Bedford, MA;Independent Security Consultant

  • Venue:
  • CT-RSA'06 Proceedings of the 2006 The Cryptographers' Track at the RSA conference on Topics in Cryptology
  • Year:
  • 2006

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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.