Collision-Resistant Usage of MD5 and SHA-1 Via Message Preprocessing

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. Key words: SHA-1, MD5, padding, hash collision, signature

• Type: Conference
• Year: 2006
• Where: CTRSA
• Authors: Michael Szydlo, Yiqun Lisa Yin
• Keywords: Collision Attacks, Cryptology, CTRSA 2006, Hash Function, Stronger Hash Function