Cryptology ePrint Archive: Report 2015/1043

The Index j in RC4 is not Pseudo-random due to Non-existence of Finney Cycle

Subhamoy Maitra

Abstract: In this very short note we prove that the pseudo-random index j of RC4 is indeed not pseudo-random. This is a simple result that missed our attention for quite a long time. We show that in long term Pr(j = i+1) = 1/N - 1/N^2, instead of the random association 1/N and this happens for the non-existence of the condition S[i] = 1 and j = i+1 that is mandatory for the non-existence of the Finney cycle.

Category / Keywords: secret-key cryptography / RC4, Non-randomness. Pseudo-random Index.

Date: received 27 Oct 2015

Contact author: subho at isical ac in

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Version: 20151028:210928 (All versions of this report)

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