Fixed Points of Special Type and Cryptanalysis of Full GOST

Abstract

GOST, the Russian encryption standard, is a block cipher of 64-bit block and 256-bit key size and consists of 32 rounds. In this work, we show that the probability that the GOST permutations produced through random keys have at least one fixed point and exactly two fixed points of special type are twice and five times more than those of random permutations respectively. We utilize this property of GOST to mount a new reflection attack on full GOST.