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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