International Association
for Cryptologic Research

On October 2-nd 2012 NIST announced its selection of the Keccak scheme as the new SHA-3 hash standard. In this paper

we present the first published collision finding attacks on reduced-round versions of Keccak-384 and Keccak-512,

providing actual collisions for 3-round versions, and describing attacks which are much faster than birthday

attacks for 4-round Keccak-384. For Keccak-256, we increase the number of rounds which can be attacked to 5.

All these results are based on a new type of {\\it self-differential} attack, which makes it possible to map

a large number of Keccak inputs into a relatively small subset of possible outputs with a surprisingly large probability, which

makes it easier to find random collisions in this subset.