Studies On The Design And Implementation Of Chaotic Stream Ciphers

With the rapid development and wide application of communication technology and network technology, more and more information has been transmitted through the network. Therefore, the security of information is getting more and more important. The cryptography, which aims at the security of information, has become of the important research fields in information science and technology. Several new branches in this field such as chaotic cryptography and quanta cryptography have also attracted many research's interests. The main purpose of this dissertation is to investigate the theory and application of chaotic cryptography, especially the design and implementation of chaotic stream ciphers.The preliminaries including the theory of modern cryptography and chaos dynamics are presented at first. Then the author has discussed the chaotic sequences generated via logistic map with chaos and has claimed that this type chaotic sequences are not suitable for key stream. Based on the discussion above, a class of mixed chaotic sequences, which are produced by combining logistic chaotic sequences and m-sequences in form of exclusive-OR, has been proposed in this paper. The cryptographic properties, such as long period, randomicity, balance, run length, correlation function and linear complexity, of mixed chaotic sequences have been analyzed in detail. The results show that the new approach allows us to improve the complexity and the period of the chaotic system under the finite-precision circumstances. By using the Shrinking Generator, the author has designed and implemented the mixed chaotic system, and made 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, and so on.This type mixed chaotic sequences has been also employed to image encryption, futhermore a multistage image encryption algorithm has been presented in this paper. The computer simulation demonstrates that this image encryption scheme have low computational complexity, high security and no distortion.Finally, the summarization has been obtained and the future research directions have been also given.