Paper 2012/672 Original: eprint.iacr.org/2012/672 ↗

Collision Attacks on Up to 5 Rounds of SHA-3 Using Generalized Internal Differentials

Abstract

On October 2-nd 2012 NIST announced its selection of the Keccak scheme as the new SHA-3 hash standard. In this paper we present the first published collision finding attacks on reduced-round versions of Keccak-384 and Keccak-512, providing actual collisions for 3-round versions, and describing an attack which is $2^{45}$ times faster than birthday attacks for 4-round Keccak-384. For Keccak-256, we increase the number of rounds which can be attacked to 5. All these results are based on a generalized {\it internal differential attack} (introduced by Peyrin at Crypto 2010), and use it to map a large number of Keccak inputs into a relatively small subset of possible outputs with a surprisingly large probability. In such a \textit{squeeze attack} it is easier to find random collisions in the reduced target subset by a standard birthday argument.