The Designs And Researches Of Chaos-based Secure Communications

Chaos is a common phenomenon in the complex nature and the social activities of human beings. In the past 50 years, chaotic dynamics has been well explored both theoretically and experimentally. Therefore, we have well understood chaos occurred in all scientific fields. The output signal of chaotic system has the continuous broadband frequency spectrum and random-like behavior. Because chaotic system sensitively depends on initial condition, it can provide the effective error diffusion. Therefore, the chaotic system becomes a promising competitor in secure communication.The chaotic dynamics is described by non-linear dynamical equations after all. The messages hided in low-dimensional chaotic signals can be unmasked by means of nonlinear dynamics predicting and reconstructing technology even if the dynamical system is unknown. How to develop a chaos-based secure communication system with high secrecy, fast encryption speed and more noise-resistant capacity has been attracted much attention of scientists in the field of information science. This thesis applies the theories and methods of modern cryptography to the chaos-based secure communication system. We try to study and solve the problems mentioned above by adding complexity in chaotic code and choosing suitable chaotic model.The first chapter briefly introduces the basic chaotic phenomenon, some knowledge of cryptology, research survey of chaotic cryptology and some unmasking technology of chaos-based secure system.The second chapter studies the digital chaotic secure communication based on the synchronization of multi-scroll chaotic systems. More and more chaotic multi-scroll systems have been put forward these years. Due to the unique character of the multi-scroll chaotic system, we apply the chaotic system to construct chaotic keys in the scheme of communication while the expanded key technology is used to improve its secrecy. Numerical results show that the secure communication system is highly secure against the error function attack, and there is some ability against noise when the synchronization signal is disturbed by noise.In the third chapter, we present a scheme of digital secure communication based on the stream cipher produced by real-time synchronization due to some shortcomings in secure communication based on cellular automata. The shortcomings include the low encryption speed, the slow speed of error diffusion, undirectivity of the error diffusion, the small key space, and so on. A modified cellular automaton is proposed for encryption while the expanded key technology and confusion technology are adopted. Numerical results show that the secure communication scheme can produce good pseudo-randomness key stream while it has very fast speed of encryption and decryption and high anti-attack ability.The forth chapter goes on to study the design of chaotic code based on a modified cellular automata model. A secure communication scheme, in which spatiotemporal chaos produced by a modified couple-map is adopted to produce the expanded keys and to diffuse error, is proposed. Numerical results show that the secure communication scheme can produce good pseudo-randomness key stream while it has very fast speeds of encryption and decryption and high anti-attack ability...