Cryptanalysis of a Class of Chaotic Stream Ciphers (一类混沌流密码的分析)

This paper points out that a class of chaotic stream ciphers proposed recently is not secure enough, which is based on digital piecewise linear chaotic maps (PLCM). It has been known that digital PLCMs' statistical properties have essential degradation when PLCMs are realized in finite computing precision, and that such degradation is determined by the resolution of the control parameter (i.e., determined by which digital subset the control parameter is in). Hence, for the proposed chaotic stream ciphers, the whole key space can be divided into n−1 sub-spaces with incremental weakness degree, and the weakness of any fixed key cannot be improved by using higher precision. Based on the above fact, a kind of multi-resolution cryptoanalysis is presented to attack the chaotic ciphers. When secure key is selected randomly, the key entropy will decrease by 2 bits as a whole. Experiments show that this cryptanalysis is feasible and efficient