## Cryptology ePrint Archive: Report 2020/068

Further Clarification on Mantin's Digraph Repetition Bias in RC4

Pranab Chakraborty and Subhamoy Maitra

Abstract: In this paper we provide a theoretical argument towards an unsolved question related to Mantin's Digraph Repetition Bias" (Eurocrypt 2005) that is observed in the key-stream of RC4. The open question, that depends on the observation that arrival of four consecutive same bytes (of the form $AAAA$) in RC4 key-stream is slightly negatively biased, was posed by Bricout et al [Des. Codes Cryptogr. (2018) 86:743-770] in 2016. Moreover, for the first time, we consider the Reverse Digraph Repetition Bias" and show that there is significant negative bias in arrival of $ABBA$ ($A, B$ two distinct bytes) in RC4 key-stream.

Category / Keywords: secret-key cryptography / RC4, Non-randomness, Sequence, Stream Cipher

Date: received 23 Jan 2020, last revised 2 Feb 2020

Contact author: subho at isical ac in

Available format(s): PDF | BibTeX Citation

Note: Added a new section on Reverse Digraph Repetition Bias.

Short URL: ia.cr/2020/068

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