|Authors||M. R. Z'aba, H. Raddum, L. Simpson, E. Dawson, M. Henricksen and K. Wong|
|Title||Algebraic Analysis of LEX|
|Afilliation||, Communication Systems|
|Publication Type||Proceedings, refereed|
|Year of Publication||2009|
|Conference Name||Australasian Information Security Conference, AISC2009|
|Keywords||Advanced Encryption Standard, LEX, Stream Cipher|
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 require- ment for an efficient attack, i.e. a system containing 16 variables. The system requires only 36 bytes of keystream, which is very low.