Reasearch On Key Stream Generator And Its Application

Stream cipher is widely used in the fields of politics, military and diplomacy at early time. Now it has been extended to civilian area, such as telemetry data encryption and transmission, etc. The main task of stream cipher is to construct and design a key stream generator. How to find pseudo random sequences with good properties, having large amount of codes and being easy to produce is the most important subjects. In this thesis, we focus on the construction of key stream generator, properties and testing methods of pseudo-random sequences, the application of stream cipher in the PCM/FM telemetry system and other issues. The main works and conclusions are described in the following aspects.1. By using a combing method, a random generator is designed. It is composed of multiple LFSRs, among them one LFSR controlling the others. The relationships between key stream sequence and the LFSRs'spans are as follows. The sequence {s } is generated by the generator. The period of {s } isp s = p s1 p s2 L psn, where 2 1and p siindicates the period of m sequence{s i } which generated by LFSRi, ni is the span of LFSRi. At the same time, the linear complexity of {s } is Ls , whereLs i = ni,Ls iindicates the linear complexity of m sequence {s i }generated by LFSRi. The autocorrelation of {s } iswherecs iindicates the autocorrelation of each m sequence {s i }. Upper and lower bounds of the linear complexity of the generator are also derived.2. A mutual clock-controlled generator based on principle of clock-controlled is designed.This generator is consist of three LFSRs which mutual control each others. The period, complexity and other properties of the generator are discussed. The linear complexity of proposed generator is proved based on principle of minimal polynomial. The results show that the properties of the clock-controlled generator are better than the Gunter generator and stop-and-go generator.3. For the telemetry system, a synchronizing cipher encryption and self-synchronizing stream cipher encryption are proposed. The key stream is generated by mutual clock-controlled generator, in which the initial key is chaotic sequences generated with chebyshev map. Synchronization performance and encryption strength are also analyzed. The results show that it is more difficult to break the initial key and more secure than chaotic encryption and generator encryption separately.Finally, the two encryption modes are simulated in Gauss and Rice channels.The results show that the BER of self-synchronizing encryption is lower than synchronous encryption when they have the same code rate and at the small SNR.