Research On Theory And Implementation Technology Of Non-stationary Chaotic Stream Cipher

The nonlinear random resource is the key of stream cipher. The consistence between the characteristics of chaos and the design criteria of stream cipher makes chaos be widely used in the design of nonlinear random source that stream cipher required. However, the dynamical degradation of chaotic systems realized on computer and other digital devices with finite computing precision (often called digital chaotic system), will pose a huge security threat on the digital chaos-based cryptosystem, and then becomes a big barrier problem stopping chaos from practical applications. Therefore, it is very crucial to resort some new methods to deal with the dynamical degradation and construct rigorous chaos in finite state space for chaotic cryptography.The existing countermeasures for the dynamical degradation of digital chaotic systems mainly focus on the improvement of some statistical characteristics, and cannot produce chaotic outputs with desirable dynamical performance for cryptography. Besides, the existing chaos models on the finite state space do not consider the implementation in practical chaos secure applications. In addition, the output of chaotic systems often carries system characteristics, which enables attackers to effectively analyze the system by using the obtained orbit information, and induces a threat to the corresponding chaotic cryptosystem. Consequently, it is of great scientific significance and has practical value to study the theory and method of solving these problems for chaotic cryptography.To solve the problems of existing chaos model in finite state space, this paper learns from the idea of external feedback anti-control of chaos, first establishes a two-way hybrid chaotic systems model by utilizing the impulsive synchronization control mechanism and the compensation control mechanism in the sliding window, then expands the phase space of digital system in the hybrid model to infinite dimensional metric space in the sense of topological equivalence and prove that the controlled digital system is a Devaney’s chaos. Finally, we complete the front end of the simulation, design and verification of the hybrid model.Given the safe hidden trouble in the cryptosystems based on chaotic systems with fixed parameters, this paper designs a chaotic system with variable parameters in the sense of Wiggins, where the transformation of control parameter can be regarded as a random walk in proper finite group. The output sequence of the chaotic system with variable parameter has been verified to be non-stationary, which makes the cryptosystem based on the time-varying chaotic system own higher security.In respond to the problems of the existing countermeasures for the dynamical degradation of digital chaotic systems, this paper first learns from the idea of chaotification to solve the dynamical degradation of digital chaotic systems:a novel variable parameter control method is proposed based on the differential mean value theorem and the state feedback control technique, which can not only realize the chaotification of given digital chaotic systems but also make the systems produce chaotic outputs with desirable performance for cryptography. Hereby, a new pseudo-random number generator with good randomness is proposed; a hybrid control method is proposed by borrowing the idea of external chaotification, which can not only realize the chaotification of given digital chaotic systems but also produce chaotic outputs with desirable performance for cryptography.Based on the above research and the complementarities between digital chaotic systems and continuous chaotic systems, this paper first constructs a hybrid chaotic system with variable parameters, and then analyzes the synchronization robustness under noisy environment and the chaotic feature of the hybrid model theoretically. Finally, a novel non-stationary chaotic stream cipher model--hybrid chaotic stream cipher with variable parameters is designed, and its front-end hybrid simulation is completed on the Cadence and FPGA platform. The non-stationary characteristics that the hybrid chaotic system with variable parameters owns along with the higher nonlinear complexity and the good randomness of the generated key sequence, makes the chaotic stream cipher model own high security. In conclusion, the above researches have important scientific significance and application value for the research of chaotic stream cipher.