Cryptology ePrint Archive: Report 2004/110

Designing Against the `Overdefined System of Equations' Attack

Carlisle Adams

Abstract: Recently, Courtois and Pieprzyk proposed an attack on symmetric ciphers that takes advantage of a previously-unexploited property of substitution boxes, or s-boxes, in the round function. This paper gives a brief overview of this ``overdefined system of equations'' attack and shows how the attack may be avoided through the use of round functions that contain a variety of protection mechanisms, including combinations of operators from different algebraic groups, a circular rotation step, and substitution boxes (s-boxes) of large dimension.

Category / Keywords: secret-key cryptography / symmetric cipher design, cryptanalysis, substitution box, round function

Date: received 10 May 2004, last revised 11 May 2004

Contact author: cadams at site uottawa ca

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Version: 20040511:155311 (All versions of this report)

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