Cryptology ePrint Archive: Report 2013/089

Filtered nonlinear cryptanalysis of reduced-round Serpent, and the Wrong-Key Randomization Hypothesis.

James McLaughlin and John A. Clark

Abstract: We present a deterministic algorithm to find nonlinear S-box approximations, and a new nonlinear cryptanalytic technique; the “filtered” nonlinear attack, which achieves the lowest data complexity of any known-plaintext attack on reduced-round Serpent so far. We demonstrate that the Wrong-Key Randomization Hypothesis is not entirely valid for attacks on reduced-round Serpent which rely on linear cryptanalysis or a variant thereof, and survey the effects of this on existing attacks (including existing nonlinear attacks) on 11 and 12-round Serpent.

Category / Keywords: secret-key cryptography / Nonlinear cryptanalysis, generalized linear cryptanalysis, multidimensional linear cryptanalysis, WKRH, Wrong-Key Randomization Hypothesis, Serpent

Publication Info: Updated and expanded version of a paper submitted to ACISP 2013. Graphs of attack performance, and truncated differential bias tables for Serpent S2/S4^{-1} were not in the ACISP version; furthermore a memory optimisation and a more thorough analysis of the Nguyen/Wu/Wang multidimensional attack were added after the ACISP submission. Some of the material in this paper includes revisions of results from 2013/022 in light of the new work on the WKRH.

Date: received 20 Feb 2013

Contact author: jmclaugh at cs york ac uk

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Version: 20130220:172725 (All versions of this report)

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