Integral Distinguishers for Reduced-round Stribog.

In January 2013, the Stribog hash function officially replaced GOST R 34.11-94 as the new Russian cryptographic hash standard GOST R 34.11-2012. In this paper we investigate the structural integral properties of reduced-round versions of the Stribog compression function and its internal permutation. Specifically, we present forward and backward higher order integrals that can be used to distinguish 4 and 3.5 rounds, respectively. Using the start from the middle approach, we combine the two proposed integrals to get 6.5-round and 7.5-round distinguishers for the internal permutation and 6-round and 7-round distinguishers for the compression function.