Trivium is a stream cipher and has successfully been chosen as one of seven finalists by European eSTREAM project.In this paper

a differential cryptanalysis of Trivium based on automatic deduction is presented.This new technique enables the attacker to obtain differential characteristics on arbitrary-round Trivium.The technique is applied to 288-round Trivium

which results in an efficient distinguishing attack.Our attack only requires 2

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chosen IVs with a distinguishing advantage of 0.999665.The result is much better than the existing single linear cryptanalysis and Linear Cryptanalysis with Multiple Approximations on 288-round Trivium.We also apply the technique to more-round

Trivium and the modified Trivium proposed by Turan and Kara.The results show that Trivium reduced to no more than 359(out of 1152)initialization rounds is weak against differential cryptanalysis

and the modified Trivium is better against differential cryptanalysis than the original Trivium.