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Generalization of Roos bias in RC4 and some results on key-keystream relations
Dey Sabyasachi,
Published in Walter de Gruyter GmbH
Volume: 12
Issue: 1
Pages: 43 - 56

RC4 has attracted many cryptologists due to its simple structure. In [9], Paterson, Poettering and Schuldt reported the results of a large scale computation of RC4 biases. Among the biases reported by them, we try to theoretically analyze a few which show very interesting visual patterns. We first study the bias which relates the key stream byte zi with i−k[0], where k[0] is the first byte of the secret key. We then present a generalization of the Roos bias. In 1995, Roos observed the bias of initial bytes S[i] of the permutation after KSA towards fi=∑ir=1r+∑ir=0K[r]. Here we study the probability of S[i] equaling fy=∑yr=1r+∑yr=0K[r] for i≠y. Our generalization provides a complete correlation between zi and i−fy. We also analyze the key-keystream relation zi=fi−1 which was studied by Maitra and Paul [6] in FSE 2008. We provide more accurate formulas for the probability of both zi=i−fi and zi=fi−1 for different i’s than the existing works.

About the journal
JournalData powered by TypesetJournal of Mathematical Cryptology
PublisherData powered by TypesetWalter de Gruyter GmbH
Open AccessNo