Linear Cryptanalysis for the Compression Function of Hamsi-256

Hamsi is one of 14 remaining candidates in NIST´s Hash Competition for the future hash standard SHA-3 and Hamsi-256 is one of four kinds of Hamsi. In this paper we make linear cryptanalysis for the compression function of Hamsi-256. We first discuss how to get linear approximations for the key steps of the compression function and present a algorithm to get linear approximations for the compression function. Then, we get the average linear biases characteristic and good linear approximations for the different round compression function. Finally, we give the complexity analysis about the corresponding success probability of linear cryptanalysis and obtain a conclusion of that if the round number of the compression function is no less than 4, the compression function is secure against linear cryptanalysis.