Stream Cipher System Based on Chaotic Binary Sequences

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Stream ciphers provide probably the most important method of modern encipherment. The central problem in stream cipher cryptography is the difficulty of efficiently generating long unpredictable sequencers of binary signals form a short and random key. Although such an unpredictable sequence can be generated in various ways, linear feedback shift register (LFSR) sequences are employed in nearly all the methods. In this study, not using such sequences, we give a simple method to obtain a running key sequence of stream cipher system in which chaotic orbits of nonlinear maps are used. Two type of sequences of balanced I. I. D. (dependent and identically distributed) binary random variables have been defined, referred to as a chaotic binary sequence and a chaotic bit sequence, each of which is obtained from chaotic real-valued orbits generated by nonlinear maps. The stream cipher system proposed in this study has the following characteristics : 1) There are several parameters as short secret key : 2) The linear complexity of the running-key sequence of period N is nearly equal to N/2 : 3) The correlation property of ciphertexts is as good as those of the DES and FEAL.