Algebraic Analysis of LEX

Reza Z'aba, M., Raddum, H., Simpson, L., Dawson, E., Henricksen, M. and Wong, K.

LEX is a stream cipher that progressed to Phase 3 of the eSTREAM stream cipher project. In this paper, we show that the security of LEX against algebraic attacks relies on a small equation system not being solvable faster than exhaustive search. We use the byte leakage in LEX to construct a system of 21 equations in 17 variables. This is very close to the requirement for an efficient attack, i.e. a system containing 16 variables. The system requires only 36 bytes of keystream, which is very low.

Cite as: Reza Z'aba, M., Raddum, H., Simpson, L., Dawson, E., Henricksen, M. and Wong, K. (2009). Algebraic Analysis of LEX. In Proc. Seventh Australasian Information Security Conference (AISC 2009), Wellington, New Zealand. CRPIT, 98. Brankovic, L. and Susilo, W., Eds. ACS. 33-45.

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