Nonlinear Cryptanalysis of Reduced-Round Serpent and Metaheuristic Search for S-Box Approximations

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Provided by: International Association for Cryptologic Research
Topic: Security
Format: PDF
The authors utilize a simulated annealing algorithm to find several nonlinear approximations to various S-boxes which can be used to replace the linear approximations in the outer rounds of existing attacks. They propose three variants of a new nonlinear cryptanalytic algorithm which overcomes the main issues that prevented the use of nonlinear approximations in previous paper, and they present the statistical frameworks for calculating the complexity of each version. They present new attacks on 11-round serpent with better data complexity than any other known-plaintext or chosen-plaintext attack, and with the best overall time complexity for a 256-bit key.
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