Weak key analysis for chaotic cipher based on randomness properties

Weak key analysis is a key issue in the design of chaotic ciphers.While most of the existing research focusing on the degradation of the chaotic sequences which causes weak keys,we point out that the parameters for which the chaotic sequences do not degrade are still possible to be weak keys.In this paper,we propose a new approach based on the rigorous statistical test to improve the weak key analysis.The weak keys of a specific chaotic cipher are investigated by using our method and a large number of new weak keys are detected.These results verify that our method is more effective.On the other hand,although statistical tests are now widely adopted to test the chaos-based bit sequences,there are few reports of analysis results on the weak keys or weak sequences of chaotic cipher.Thus our work may be helpful for current research on statistical tests of chaotic cipher.