Paper 2004/146

Near-Collisions of SHA-0

Eli Biham, Rafi Chen

Abstract

In this paper we find two near-collisions of the full compression function of SHA-0, in which up to 142 of the 160 bits of the output are equal. We also find many full collisions of 65-round reduced SHA-0, which is a large improvement to the best previous result of 35 rounds. We use the very surprising fact that the messages have many neutral bits, some of which do not affect the differences for about 15--20 rounds. We also show that 82-round SHA-0 is much weaker than the (80-round) SHA-0, although it has more rounds. This fact demonstrates that the strength of SHA-0 is not monotonous in the number of rounds.