Katholieke Universiteit Leuven
The hash function skein is the submission of the researcher to the NIST hash competition, and is arguably a serious candidate for selection as SHA-3. This paper presents the first third-party analysis of skein, with an extensive study of its main component: the block cipher threefish. The authors notably investigate near collisions, distinguishers, impossible differentials, key recovery using related-key differential and boomerang attacks. In particular, they present near collisions on up to 17 rounds, an impossible differential on 21 rounds, a related-key boomerang distinguisher on 34 rounds, a known-related-key boomerang distinguisher on 35 rounds, and key recovery attacks on up to 32 rounds, out of 72 in total for threefish-512.