Some thoughts on Collision Attacks in the Hash Functions MD5, SHA-0 and SHA-1 ⋆

Abstract. The design principle of Merkle-Damg˚ard construction is collision resistance of the compression function implies collision resistance of the hash function. Recently multi-block collisions have been found on the hash functions MD5, SHA-0 and SHA-1 using differential cryptanalysis. These multi-block collisions raise several questions on some definitions and properties used in the hash function literature. In this report, we take a closer look at some of the literature in cryptographic hash functions and give our insights on them. We bring out some important differences between the 1989’s Damg˚ard’s hash function and the hash functions that followed it. We conclude that these hash functions did not consider the pseudo-collision attack in their design criteria. We also doubt whether these hash functions achieve the design principle of Merkle-Damg˚ard’s construction. We formalise some definitions on the properties of hash functions in the literature. Keywords: Hash function, collision attacks, MD5, SHA-0 and SHA-1