International Association for Cryptologic Research (IACR)
Abstract
In this article, we describe a novel collision attack for up to 5 rounds of the Grøstl hash function. This significantly improves upon the best previously published results on 3 rounds. By using a new type of differential trail spanning over more than one message block we are able to construct collisions for Grøstl on 4 and 5 rounds with complexity of 267 and 2120, respectively. Both attacks need 264 memory. Due to the generic nature of our attack we can even construct meaningful collisions in the chosen-prefix setting with the same attack complexity