New Local Collisions for the SHA-2 Hash Family

The starting point for collision attacks on practical hash functions is a local collision. In this paper, we make a systematic study of local collisions for the SHA-2 family. The possible linear approximations of the constituent Boolean functions are considered and certain impossible conditions for such approximations are identified. Based on appropriate approximations, we describe a general method for finding local collisions. Applying this method, we obtain several local collisions and compute the probabilities of the various differential paths. Previously, only one local collision due to GilbertHandschuh was known. We point out two impossible conditions in the GH local collision and provide an example of an impossible differential path for linearized SHA-2 using this local collision. Sixteen new local collisions are obtained none of which have any impossible conditions. The probabilities of these local collisions are a little less than the GH local collision. On the other hand, ...

• Type: Conference
• Year: 2007
• Where: ICISC
• Authors: Somitra Kumar Sanadhya, Palash Sarkar
• Keywords: Cryptology, GH Local Collision, ICISC 2007, Impossible Conditions, Local Collision