Improved Analysis of ECHO-256

ECHO-256 is a second-round candidate of the SHA-3 competition. It is an AESbased hash function that has attracted a lot of interest and analysis. Up to now, the best known attacks were a distinguisher on the full internal permutation and a collision on four rounds of its compression function. The latter was the best known analysis on the compression function as well as the one on the largest number of rounds so far. In this paper, we extend the compression function results to get a distinguisher on 7 out of 8 rounds using rebound techniques. We also present the rst 5-round collision attack on the ECHO-256 hash function.