The Boomerang Attacks on the Round-Reduced Skein-512
Cryptographic hash functions, which provide integrity, authentication and etc., are very important in modern cryptology. In 2005, as the most widely used hash functions MD5 and SHA-1 were broken by Wang et al., NIST started a hash competition for a new hash standard (SHA-3) in 2007. Skein, which is one of the finalists, is a ARX-type hash function (based on modular addition, rotation and exclusive-OR). The core of the compression function of Skein is a tweakable block cipher called Threefish, which is proposed with 256-, 512-, 1024-bit block sizes and 72, 72, 80 rounds, respectively. The hash function Skein is one of the five finalists of the NIST SHA-3 competition; it is based on the block cipher Threefish which only uses three primitive operations: modular addition, rotation and bitwise XOR (ARX). This paper studies the boomerang attacks on Skein-512.