Practical distinguishers against 6-round Keccak-f exploiting self-symmetry

Abstract

This paper presents new distinguishers against Keccak-f[1600] permutation reaching up to 6-rounds. The main intuition is to exploit the self-symmetry of the internal state of Keccak. Formal analysis reveals that the proposed distinguisher can penetrate up to 3 rounds and the penetration depends only on the hamming weight of the round-constant of the initial round. New strategies developed in this work, when combined, are shown to distinguish up to 5-rounds with a probability of 1 using a single query. Finally, the extension to 6-rounds with a complexity of 211 gives us the most efficient 6-round distinguisher reported in literature. All claims and formal arguments conform to the results obtained by extensive experimentation. © 2014 Springer International Publishing.