| Summary: | 碩士 === 國立成功大學 === 工程科學系 === 88 === This thesis is concerned primarily with the chaotic synchronization and cryptograph as a systematic scheme to design secure communications for a class of chaotic systems. In general, chaotic synchronization can be considered that using only one available scalar output of chaotic systems in the transmitter, the receiver is then designed via a nonlinear observer technique to achieve the states synchronization. In this thesis, an adaptive observer-based driven system with a scalar transmitted signal is designed so that not only chaos synchronization but also secure communications of chaotic systems in the presence of system’s disturbances and unknown parameters are attained. All results can be guaranteed by the Lyapunov stability theorem.
On the other hand, to enhance the security of communication systems, this thesis presents a secure communication approach based on cryptograph and chaotic synchronization. Given the observability of a class of chaotic systems, the main transmitter and an observer-based main receiver, with an appropriate observer gain, are constructed to synchronize with each other. Two slave systems, driven by the transmitted signal, are designed to synchronize and generate secret keys. Secret keys have encrypted the plaintext so that an intruder can’t attack the hidden message. The convergence of the overall system can be guaranteed without the computations of Lyapunov exponent. Moreover, numerical results are given to demonstrate the effectiveness of the proposed scheme.
Furthermore, a cryptography technique for enhancing the security of communication networks using a dead-beat chaotic system as a transmitter and Haar wavelets for multiplexing and demultiplexing is also proposed. In this way, digital messages can be securely encrypted, and transmission messages can be easily recovered in finite time. In addition, the discrete-time Henon-based secure communication system has been successfully applied to an image processing. Finally, as a first step for implementing the chaotic synchronization-based communication systems by IC modules, the implementation of the Henon chaos using Xilinx FPGA technique is derived. Digital and MATLAB simulations are given to confirm the validity of the FPGA IC design.
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