Rotational Rebound Attacks on Reduced Skein

In this paper the authors combine the recent rotational cryptanalysis with the rebound attack, which results in the best cryptanalysis of Skein, a candidate for the SHA-3 competition. The rebound attack approach was so far only applied to AES-like constructions. For the first time, they show that this approach can also be applied to very different constructions. In more detail, they develop a number of techniques that extend the reach of both the inbound and the outbound phase, leading to rotational collisions for about 53/57 out of the 72 rounds of the Skein-256/512 compression function and the Threefish cipher.