Recovering RC4 Permutation from 2048 Keystream Bytes if jIs Stuck

In this paper, we study the behaviour of RC4 when the index jis stuck at a certain value not known to the attacker. Though it seems quite natural that RC4 would be weak if jdoes not change, it has never been studied earlier in a disciplined manner. This work presents the nontrivial issues involved in the analysis, identifying how the information regarding Sstarts leaking with as low as 258 keystream output bytes. The leakage of information increases as more bytes are available and finally the complete Sis recovered with 211bytes in around 225time complexity. The attack considers that "the deterministic index iat the point when jgot stuck" and "the value at which jremains stuck" are unknown. Further, the study presents a nice combinatorial structure that is relevant to the fault analysis of RC4.