A New Approach to Χ2 Cryptanalysis of Block Ciphers

Authors:
Jorge Nakahara, Jr.;Gautham Sekar;Daniel Santana Freitas;Chang Chiann;Ramon Hugo Souza;Bart Preneel
Affiliations:
EPFL, Lausanne, Switzerland;Interdisciplinary Institute for BroadBand Technology (IBBT), Belgium and Katholieke Universiteit Leuven, Belgium;Federal University of Santa Catarina, Brazil;University of São Paulo, Brazil;Federal University of Santa Catarina, Brazil;Interdisciplinary Institute for BroadBand Technology (IBBT), Belgium and Katholieke Universiteit Leuven, Belgium
Venue:
ISC '09 Proceedings of the 12th International Conference on Information Security
Year:
2009

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Abstract

The main contribution of this paper is a new approach to Χ 2 analyses of block ciphers in which plaintexts are chosen in a manner similar to that in a square/saturation attack. The consequence is a faster detection of Χ 2 correlation when compared to conventional Χ 2 cryptanalysis. Using this technique we (i) improve the previously best-known Χ 2 attacks on 2- and 4-round RC6, and (ii) mount the first attacks on the MRC6 and ERC6 block ciphers. The analyses of these fast primitives were also motivated by their low diffusion power and, in the case of MRC6 and ERC6, their large block sizes, that favour their use in the construction of compression functions. Our analyses indicate that up to 98 rounds of MRC6 and 44 rounds of ERC6 could be attacked.