Abstract: A slide attack on modified Trivium stream cipher presented by Sonmez et.al.based on solving nonlinear equations was present. The result shows that there exist more than 2⁸⁵ slide pairs in the modified Trivium, which is much more than 2³⁹ slide pairs in the original Trivium. If a slide pair is obtained, the attacker can recover the 80-bit initial key of modified Trivium with a computational complexity of O(2³⁵)

Key words: cryptanalysis, slide attack, Trivium, initialization algorithm