No abstract

Whirlpool is a hash function based on a block cipher that can be seen as a scaled up variant of the AES. The main difference is the (compared to AES) extremely conservative key schedule. In this work, we present a distinguishing attack on the full compression function of Whirlpool. We obtain this result by improving the rebound attack on reduced Whirlpool with two new techniques. First, the inbound phase of the rebound attack is extended by up to two rounds using the available degrees of freedom of the key schedule. This results in a near-collision attack on 9.5 rounds of the compression function of Whirlpool with a complexity of 2 176 and negligible memory requirements. Second, we show how to turn this near-collision attack into a distinguishing attack for the full 10 round compression function of Whirlpool. This is the first result on the full Whirlpool compression function.

Abstract. In this work, we introduce a new non-random property for hash/compression functions using the theory of higher order differentials. Based on this, we show a second-order differential collision for the compression function of SHA-256 reduced to 47 out of 64 steps with practical complexity. We have implemented the attack and provide an example. Our results suggest that the security margin of SHA-256 is much lower than the security margin of most of the SHA-3 finalists in this setting. The techniques employed in this attack are based on a rectangle/boomerang approach and cover advanced search algorithms for good characteristics and message modification techniques. Our analysis also exposes flaws in all of the previously published related-key rectangle attacks on the SHACAL-2 block cipher, which is based on SHA-256. We provide valid rectangles for 48 steps of SHACAL-2.

We introduce the rebound attack as a variant of differential cryptanalysis on hash functions and apply it to the hash function Whirlpool, standardized by ISO/IEC. We give attacks on reduced variants of the Whirlpool hash function and the Whirlpool compression function. Next, we introduce the subspace problems as generalizations of near-collision resistance. Finally, we present distinguishers based on the rebound attack, that apply to the full compression function of Whirlpool and the underlying block cipher W .

We investigate generic methods to find near-collisions in cryptographic hash functions. We introduce a new generic approach based on methods to find cycles in the space of codewords of a code with low covering radius. We give an analysis of our approach and demonstrate it on the SHA-3 candidate TIB3.