Abstract:Based on the back tracking method and the correlation between input and output of the feedforward function, a new inversion attack is proposed to the feedforward stream cipher model with a linear feedback shift register based on a multiplication circuit by improving Golic’s inversion attack. The average computational complexity of back tracking method, and the average computational complexity of the new inversion attack are given. In comparison with Golic’s algorithm, both the space complexity and the average computational complexity of the new algorithm are less than that of Golic’s.