Improved Collision Attack on the Hash Function Proposed at PKC'98

In this article, we present an improved collision attack on the hash function proposed by Shin et al. at PKC’98. The attack has a complexity of about 2 hash computations, while the previous attack of Chang et al. presented at SAC 2002 has a complexity of about 2 hash computations. In the analysis of the hash function we combined existing approaches with recent results in cryptanalysis of hash functions. We show that message-dependent rotations can be exploited to construct collisions. The weak design of the step function facilitates high-probability multi-block collisions.