Research Of New Data Encryption Algorithm And Effective Continuous Phase Modulation

The information in secrecy systems could not only be artificially stealed, but be interfered by noise in transmission. This paper focuses on the research of secrecy communication system based on the above issues. On the one hand, in order to guarantee the security of the system, block encryption algorithm is adopted to design the secrecy part, and linear cryptanalysis is used to verify its security. On the other hand, channel coding can be used in the system to enhance the ability to resist noise interference. But at the same time, channel coding adds the information redundancy which would decrease the spectrum efficiency of the system. In this paper, the continuous phase modulation(CPM) is put forward to be serially concatenated with channel coding using iterative decoding, which can not only improve the spectrum efficiency of the system, but also can closely achieve the BER(Bit Error Rate) performance of Turbo codes. The main contents of this thesis are as follows:First, a cipher using block cipher algorithm with several rounds of iterations is designed. Its security is analyzed based on the linear approximation of nonlinear S box, which is the core of the encryption structure. For the problem of the fixed original key with short length and weak resistance for attack, Logistic chaotic map is used to solve it. And then the key space is expanded effectively and the security is improved because of the generation of dynamic original key.Second, the inner coding characteristic of CPM is studied. Replacing traditional phase of CPM with tilted phase can make the Rimoldi decomposition model and the time- invariant phase trellis diagram be derived. The Viterbi algorithm based on trellis is used to implement maximum likelihood detection(MLD) of MSK signals. Meanwhile, the delay caused by path selection in the algorithm is analyzed and improved. The simulation results verify the effectiveness of the Rimoldi decomposition and prove that CPM has coding gain and can be studied as an encoder.Third, considering the noise interference in secrecy communication system, CPM is put forward to be applicated in serially concatenated codes. The maximum a posteriori probability(MAP) iterative decoding algorithm suitable for CPM detector is derived. And by means of analyzing and modifying the phase branch metric, the complexity of computation is reduced. Simulations show that serially concatenated CPM can obviously improve the reliability of system with iterative decoding using pseudo random interleaver.