Security performance analysis of a chaotic stream cipher

In this paper, the security performance analysis for a self-synchronization and closed-loop feedback-based chaotic stream cipher is given. According to the chosen-ciphertext attack method, it is found that under the condition of selecting the ciphertext as fixed value, the original chaotic iterative equation is degenerated into an asymptotically stable iterative one, so that the explicit function of state variables and key parameters can be obtained. Based on this idea, and according to the chosen-ciphertext attack method, a single key decipher algorithm is further investigated. Firstly, multiple pairs of plaintext–ciphertext are obtained by choosing the corresponding multiple frames of ciphertext as fixed values. Secondly, a set of possible estimated values for this single key is acquired by utilizing among one pair of plaintext–ciphertext. Finally, the only estimated value that satisfies all the conditions of multiple pairs of plaintext–ciphertext is determined, as an estimated value from the set of all possible estimated values. Security performance analysis results have shown that, under the condition that only one unknown key needs to be deciphered while the remaining keys are all known, the proposed algorithm can, respectively, decipher each individual key accurately. In addition, the attack complexity of the proposed method is lower than that of the exhaustive attack.