Paper 2005/248

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

Michael Szydlo and Yiqun Lisa Yin


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.

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Publication info
Published elsewhere. RSA Conference 2006
SHA-1MD5paddinghash collisionsignature
Contact author(s)
mszydlo @ rsasecurity com
2005-10-18: revised
2005-07-30: received
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Creative Commons Attribution


      author = {Michael Szydlo and Yiqun Lisa Yin},
      title = {Collision-Resistant usage of {MD5} and {SHA}-1 via Message Preprocessing},
      howpublished = {Cryptology ePrint Archive, Paper 2005/248},
      year = {2005},
      note = {\url{}},
      url = {}
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