Attacks on StreamHash 2

Abstract

StreamHash 2 is a hash function proposed by Michał Trojnara at the Cryptography and Security Systems in 2011 Conference. This algorithm is a member of StreamHash family which was first introduced in 2008 during the SHA-3 Competition. In this paper we will show collision attacks on the internal state of the StreamHash 2 hash function with complexity about 2^8n for the 32n-bit version of the algorithm and its reduced version with complexity 2^8n. We will also show its application to attacking the full StreamHash 2 function (finding a collision on all output bits) with complexity about 2^88 . We will try to show that any changes made to the construction (for instance the ones proposed for StreamHash 3) will have no effect on the security of the family due to critical fault build into the compression function.