Study On Secure Methods Of Network Communication Based On Chaos System

At present, there puts forward more and more high requests to the communication security with the development of computer technology and the popularization of the network, in particular the rapid increasement of the application and the service based on the network. The traditional communication secrecy method is cannot meet the requirement of communication security. The network digital information security problem is not merely the sensitive problem in the international competition, also the important problem related with the national sovereignty and security. It carves out the new interspaces and direction for secrecy communication research that the emergency of chaos technology and the development in decades. Therefore it is very significant and practical to research the network information security. This thesis mainly investigates chaos theory′s application in network information security.This has decided to have the fairly good application prospect in secret communication for the characters of the chaotic signal such as the randomness of the chaotic signal, the sensibility to the initialconditions and the unpredictably. These characters show good foreground in the field of secret communication. Nonlinear chaotic signal include continuous chaotic signal, discrete chaotic signal, digital chaotic signal, super chaotic signal, and space-time chaotic signal etc. When they are used in secret communications, they require some characters of chaotic signal, such as complexity, avoid-track and indeterminism. On the other side, the complicated chaotic signal enhance the levity in the transmission course through some methods such as adjusting the chaotic circuit and the parameters of the model frequently or transmitting multi-chaotic signal. The more complicated, the more randomicity of the signal transmitted, the more complexity of the dynamic control and adjustment of the signal transmitted, we can get more secrecy.The thesis analyses the model of the classical chaos system, for example Chua's circuit, Lorenz system, Rossler system, Chen's circuit, Duffing system and so on, in which Duffing system is chosen to be the model of the chaotic system and the main study object. The study of Duffing system is done on the base of Melnikov method to the elliptic integrals, which is the main method. Based on the discussion about those methods, we know exactly how Duffing system generates chaos and the temperament that Duffing system shows in chaos state. And then we particular discuss and analyze Duffing system when there is noise from in or out the system, prove that Duffing system has strong immunity to noise. We even design the electronic circuit of Duffing system, and do lots of experience and simulation with the circuit. We get the five typestate space forms in simulations.It is the key to realize the chaotic communication is chaotic synchronization. The chaotic communication will be possible if we realize the chaotic synchronization.We analyze the conception of synchronization of chaos, and then compare the existing chaotic control methods such as drive-answer synchronization, active-passive synchronization, error-feedback synchronization, couple synchronization, adaptive synchronization, impulsive synchronization variable feedback infinitesimal disturbance synchronization and beat synchronization.Our work mentioned above and combined with the current study of chaotic secrecy communication methods, such as chaotic spreading spectrum, chaotic keying, chaotic modulation, Chaos Masking and chaotic cryptosystem. The thesis brings forward to three methods of digital secure communication based on Duffing system.The first method studies the crisis condition for Duffing system to generate chaos. And then analyze the convergence property of parameters matching between sending model and accepting model. For the first time, we bring forward to carry out digital communication with chaotic masking using continuous chaotic sequence. We show the base principle of how the Duffing system be used in digital communication with chaotic masking technology. We carry some simulation experience with computer. So we slide to use chaotic system in digital secure communication.Other two methods are both based on to make use of the state signalof single chaotic system in the secrecy communication. The combinations of state signals of a chaotic system are still chaotic signal. So we can use those combinations in the communications. This can improve the performance of the system,make more sufficiency of resource of system, without any more difficulty in synchronization and the complexity of the system.The second method is to use the state signal in complex chaos cover method. The method doesn't increase the complexity of the system, but it is more difficult to find the encrypted signal.The third method is to utilize the specialty and characteristics of chaotic signal. We generate a false random chaotic signal by a base chaotic signal generator, using single chaotic circuit in different state space, we use the multiple combination of state signal in the chaos shift keying method. We transfer different chaotic signal representing different digital signal in the wide area channel. So the complexity, randomicity and dynamic controllablity and agility of the sent signal are strengthen. And so we improve the difficulty to decrypt the code and improve the secrecy in digital communication environment. There are huge potential to spread the available spectrum. We prove the credibility of the method thought theoretic analysis and simulation with Duffing chaotic system. The method makes it to be very difficult for those try to decrypt to follow chaotic signal. And further improve secrecy level.The main works and innovations are as follows,1. We deduce in theory and analog simulation that Duffing system alsohas the immunological competence in the noise environment and interference of the same frequency to innate drive signal.2. We do the computer simulation of Duffing system and get the different form of chaotic signal.3. We design the electronic circuit of Duffing system, and do some experience with the circuit.4. We bring forward the digital communication with chaotic masking technology using continuous chaotic sequence. We introduce the chaotic masking method used in digital communication. And give out the principle of digital communication with chaotic masking using Duffing chaotic system. We simulate the technology, get satisfactive result.5. We bring forward the method of using the state signal in security communication and analyze the viability.6. We design the method of using state signal in complex chaos cover method, and do the principle analysis and the emulation analysis .The method make more sufficient use of the system resource, and increase the difficulty to trace and decrypt the signal.7. We designed the method for the state signal of single chaotic system to use in chaotic shift keying method. Transferring that kind of signal in wide area channel, The complexity ,randomicity and dynamic controllability and agility of the sent signal are strengthen. There are huge potential to spread the available spectrum. We prove the credibility of the method thought theoretic analysis and simulation with Duffing chaotic system.There will be a good application prospect for chaos encrypt technology with the development of the digital integrate circuit which made the chaos signal digitizing and jointed with the modern digital spread spectrum communication. We believe that chaos encrypt method will be used widely in network secrecy communication through tireless efforts.