Colliding message pair for 53-step HAS-160

HAS-160 is an iterated cryptographic hash function that is widely used in Korea. In this article, we present a collision attack on the hash function HAS-160 reduced to 53-steps. The attack has a complexity of about 235 hash computations. It is based on the work of Cho et al. presented at ICISC 2006. We improve the attack complexity of Cho et al. by a factor of about 2 20 using a slightly different strategy for message modification in the first 20 steps of the hash function and present the first actual colliding message pair for 53-step HAS-160. Furthermore, we show how the attack can be extended to 59-step HAS-160 by using a characteristic spanning over two message blocks. © Springer-Verlag Berlin Heidelberg 2007.status: publishe