The Designs And Researches Of Chaos-based Secure Communications

Over the past decades, there has been tremendous interest in studying the behavior of chaotic system. Chaotic systems are characterized by a number of features, such as sensitive dependence on initial conditions; aperiodicity, random-like behavior, continuous broadband power spectrum, and so on. These properties coincide with the requirements for signals applied in secure communication systems. A large variety of encryption algorithms have been proposed for realizing chaotic communication since Pecora and Carroll proposed synchronization of chaotic systems. However, the recent researches show that even with chaotic dynamics completely hidden most of known models of chaotic communication are insecure. They are insecure against some very weak attacks, including nonlinear dynamics forecasting and reconstructing. Apart from this, slow encryption speed and weakness in resistance to channel noise are also the serious inherent drawbacks of chaotic cryptosystems, which reduced the interest of scientist in studying chaos-based communication.Research about self-synchronizing stream ciphers is still difficult topic in the conventional cryptography. Up to now, currently accepted standard of stream ciphers is still empty. Chaos-based cryptosystems, in particular, spatiotemporal-chaos-based cryptosystems may contribute to develop new and successful stream cipher approaches if the above drawbacks of chaotic cryptosystems be solved. In this paper we propose two secure communication systems based on one-way-coupled chaotic map lattice and Lorenz system. The technology of son cryptographic key and operation of binary digit are applied in our secure communication systems. The numerical results show that these new cryptosystems can avoid the attack of error function. The paper is organized as follows:The first chapter mainly reviews the developed history of chaos theory and basic characteristic of chaos. The methods of calculating Lyapunov exponent have been briefly introduced. In the second chapter, the definition of chaotic synchronization and chaos-based secure communication are introduced.In the third chapter, a secure communication system based on one-dimensional one-way coupled map lattice is introduced. The security of the cryptosystem is analyzed. It is found that the cryptosystem is not enough security under the attack of error function and the fixed point of the map. An improved encryption algorithm is proposed. The technology of son cryptographic key and operation of binary digit are applied. The numerical results show that the new cryptosystem can avoid the attack of error function and the fixed point of the map.In the fourth chapter, a Lorenz chaotic cryptosystem based chaotic modulation is introduced. The security of the cryptosystem is analyzed. It is found that the cryptosystem is not security under the attack of error function. A new digital communication system based Lorenz chaotic system is proposed. The technology of son cryptographic key and operation of binary digit are applied. The numerical investigations show that the new cryptosystem can avoid the attack of error function.