Research On Chaotic Stream Ciphers Design And Its Application

The rapid development of computer technology,Internet technology and information technology has changed the way we live and work,providing us with convenience and problems.Information security has been severely challenged,and it has also received more and more attention.Information security relies on the development of cryptography,which undoubtedly puts higher demands on modern cryptography.Chaos is a kind of phenomenon widely existed in nature.The characteristics of chaotic initial value sensitivity,stochastic behavior,long-term unstable orbit,etc.are very consistent with the requirements of cryptography,so chaotic cryptography has become a new branch in a field of cryptography.Chaos cryptography began in the early 1990 s and has been developed for more than 20 years.We have gradually discovered many advantages of chaotic ciphers for encryption,but there are some problems that are difficult to overcome.The purpose of this thesis is to design a chaotic sequence cipher scheme that can overcome the finite precision effect,and design a corresponding chaotic quantification method,which can achieve good results in image encryption.The main work and innovations of this thesis have the following aspects:(1)In this thesis,the development of chaos and the basic concepts of chaos are introduced in detail.The chaotic dynamics are analyzed and the knowledge system of cryptography is introduced.On this basis,the problem of degradation of dynamic characteristics caused by the finite precision effect of digital chaotic systems and the common remedies for solving the effects of finite precision are analyzed.(2)In this thesis,the in-depth research and analysis are made on the degradation of dynamic characteristics caused by the finite precision effect of digital chaotic systems.Based on the generalized Lorenz system,the fourth-order Runge-Kutta method is used,three perturbation schemes based on generalized Lorenz system,cascaded generalized Lorenz system and switched generalized Lorenz system are proposed.(3)This thesis also focuses on the quantization scheme of chaotic sequence preprocessing.After analyzing the commonly used chaotic quantization method,a new quantization scheme based on multi-bit quantization extraction is proposed.The chaotic system scheme is used to test and analyze the randomness and statistical characteristics of the obtained chaotic binary sequence.The results show that the design of the chaotic system scheme and the design of the quantization scheme are effective.(4)Finally,the application of chaotic stream ciphers in image encryption direction is introduced.Compared with the advantages and disadvantages of traditional encryption algorithm and chaotic encryption algorithm in image encryption,this thesis uses wavelet transform to obtain frequency domain information,encrypts the frequency domain,and combines chaotic stream ciphers to propose a chaotic image encryption scheme based on wavelet transform.Finally,the simulation analysis is carried out.The simulation results show that the encryption scheme has the advantages of large key space,strong key sensitivity and good statistical characteristics.Ability to resist exhaustive attacks,statistical attacks,alien entropy attacks,and differential attacks.