Cryptanalysis of reduced variants of the FORK-256 hash function

Authors:
Florian Mendel;Joseph Lano;Bart Preneel
Affiliations:
Institute for Applied Information Processing and Communications, Graz University of Technology, Graz, Austria;Dept. ESAT/SCD-COSIC, Katholieke Universiteit Leuven, Heverlee, Belgium;Dept. ESAT/SCD-COSIC, Katholieke Universiteit Leuven, Heverlee, Belgium
Venue:
CT-RSA'07 Proceedings of the 7th Cryptographers' track at the RSA conference on Topics in Cryptology
Year:
2007

Citing 4
Cited 3

A new dedicated 256-bit hash function: FORK-256

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EUROCRYPT'05 Proceedings of the 24th annual international conference on Theory and Applications of Cryptographic Techniques
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IMA'05 Proceedings of the 10th international conference on Cryptography and Coding

A meet-in-the-middle collision attack against the new FORK-256

INDOCRYPT'07 Proceedings of the cryptology 8th international conference on Progress in cryptology
Extending FORK-256 attack to the full hash function

ICICS'07 Proceedings of the 9th international conference on Information and communications security
Cryptanalysis of FORK-256

FSE'07 Proceedings of the 14th international conference on Fast Software Encryption

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Abstract

FORK-256 is a hash function presented at FSE 2006. Whereas SHA-like designs process messages in one stream, FORK-256 uses four parallel streams for hashing. In this article, we present the first cryptanalytic results on this design strategy. First, we study a linearized variant of FORK-256, and show several unusual properties of this linearized variant. We also explain why the linearized model can not be used to mount attacks similar to the recent attacks by Wang et al. on SHA-like hash functions. Second, we show how collision attacks, exploiting the non-bijectiveness of the nonlinear functions of FORK-256, can be mounted on reduced variants of FORK-256. We show an efficient attack on FORK-256 reduced to 2 streams and present actual colliding pairs. We expect that our attack can also be extended to FORK-256 reduced to 3 streams. For the moment our approach does not appear to be applicable to the full FORK-256 hash function.