Grøstl – a SHA-3 candidate

Grostl is a SHA-3 candidate proposal. Grostl is an iterated hash function with a compression function built from two fixed, large, distinct permutations. The design of Grostl is transparent and based on principles very different from those used in the SHA-family. The two permutations are constructed using the wide trail design strategy, which makes it possible to give strong statements about the resistance of Grostl against large classes of cryptanalytic attacks. Moreover, if these permutations are assumed to be ideal, there is a proof for the security of the hash function. Grostl is a byte-oriented SP-network which borrows components from the AES. The S-box used is identical to the one used in the block cipher AES and the diffusion layers are constructed in a similar manner to those of the AES. As a consequence there is a very strong confusion and diffusion in Grostl. Grostl is a so-called wide-pipe construction where the size of the internal state is significantly larger than the size of the output. This has the effect that all known, generic attacks on the hash function are made much more difficult. Grostl has good performance on a wide range of platforms and counter-measures against side-channel attacks are well-understood from similar work on the AES.