| With the rapid development and extensive applications of computer technology, network technology, communication technology, and Internet in particular, the security of network information is becoming increasingly a key problem that must be solved urgently.That applying chaos theory to secure communication and information encryption has already become one of the hot research projects on the combination of nonlinear science and information science, and it is a novel branch of high-tech research fields. The main contents of this paper include the research on chaos synchronization theory and chaotic sequences application in information security.The main research contents and originality of this paper can be summarized as following:1．The author has summarized the current situation of application research on privacy communication and information encryption by using chaos, and pointed out that several existing problems should be solved at present.2．Several main chaotic synchronization techniques are introduced in this paper, and synchronization of a coupled time-delay chaotic neural system is studied, then the general synchronization condition in analytic is obtained by using Lyapunov functional method, consequently the complexity for calculating of the condition Lyapunov exponents is avoided. The computer stimulation result of private communication has illustrated that the theoretical analysis is correct. As the time-delay dynamics have infinite high-dimensional synchronal attractors, and the chaotic signals cannot be cracked easily due to their complexity, thus it is especially expected that the encryption system employing the time-delay dynamic possesses higher security performance.3．The author has discussed that the correlation performance of traditional linear shift feedback register (LSFR) sequences, such as m-sequence is not very ideal. The performances of Logistic-map and Chebyshev-map chaotic sequences are analyzed theoretically, and a lot of analyses and comparison experimentations have been done, including several properties such as randomicity, balance, run length, correlation function, odd/even correlation function, correlation side lobe normal error and linear complexity. The relationships of these properties versus initial value, system parameter and sequence length are studied in detailed.4．The author studied how to utilize chaotic signals to realize secure communication, and two feasible image secure communication schemes proposed based on chebyshev map chaotic sequences. In the first scheme, the chaotic self-synchronization is realized, i.e. the chaotic carrier can be retrieved directly from received signals. Furthermore, the synchronization error cannot be propagated. Hence, the first scheme is very suitable to an ideal channel or a high-SNR (signal to noise ratio) channel. The second scheme makes best use of excellent correlation features of chaotic sequences to realize a direct-sequence spread-spectrum (DS/SS) communication system. The approximate relationship function of BER (bits error ratio) versus spread-spectrum factor is also obtained. The stimulation results demonstrate that both schemes have higher security performances even under the situation of a noisy channel.5．The author has done some meaningful research in the aspect of the application of integrating chaos theory and traditional cryptography. The cryptography properties, such as confusion and diffusion, that chaotic systems possess are analyzed based on understanding of traditional cryptography principle. In order to cope with some shortages that belong to one type of chaotic encryption system, an improved multistage chaotic encryption system is proposed, the encryption/decryption algorithm is given in detail, and makes in-depth analysis of the security performances of the system, such as properties of confusion and diffusion, key space, weak key and capability against cryptanalysis, etc. Because the encryption system exploits two-stage chaotic system, and uses a permutator, it makes cryptanalysis more...
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