Reasearch On Key Stream Generating Algorithm And Its Application

As the encryption and decryption method of stream cipher is simple, it is very suitable for the high real-time streaming data transmission requirements of confidentiality. The one of key issues of stream cipher is to design the key stream generation algorithm. How to construct key stream sequences with large period, high linear complexity and good pseudo-randomness is an important issue of great concern to cryptographers. In this thesis, the main works focus on the design of key stream generation algorithm, properties and statistical test methods of pseudo-random sequences, the application of stream cipher in the PCM/FM telemetry system and other issues. The main contributions and conclusions are described as follows.1. To improve the weakness that the same plaintext strings have the same ciphertext strings in character encryption and decryption scheme, two improved algorithms of character encryption and decryption are proposed. One is based on two shift registers disturbance mode, and the other is based on chaotic sequence. The first algorithm is to take turns working of two shift registers through increasing the number of shift register, the second algorithm is to change the shift register's initial state through the introduction of chaotic sequence. Practical analysis results of these two algorithms show that two improved algorithms solve the problem that the same plaintext strings have the same ciphertext strings, enlarge the ciphertext space and improve the crack difficulty of the ciphertext.2. Due to chaos degeneration question caused by computer limited precision in one chaos system, an algorithm of pseudo-random sequence generation with alternating parameter of multistage chaos mapping is proposed. Based on one-dimensional Logistic mapping and two-dimensional Henon map, the system output is one of the two-dimensional Henon chaotic iterative values, which is controlled by the Hamming weight of Logistic chaotic iteration value with alternating parameter. Analysis results of balance, run-length properties, correlation and local random statistical properties, show that the sequences generated by the chaos system with good pseudo-randomness are difficult to predict. Compared with the single chaotic map, this system has higher complexity and stronger confidentiality.3. Based on linear congruence theory, a linear congruence comparator constructed by two independent linear congruence generators and a simple comparator is designed. As a disturbance signal, the output sequence of the linear congruence comparator is superimposed to the chaotic orbit to improve its pseudo-randomness. Analysis results of the computational complexity that the attacker crack the seed key by intercepting the output sequence of the linear congruence comparator, the balance, correlation and sensitivity to initial conditions of chaotic sequence after adding random perturbations, show that the computational complexity is power exponential growth, and the output sequence has forward and backward unpredictability. The key stream generator with a larger key space can generate good pseudo-randomness sequences, and effectively overcome the short period problem of chaotic sequence in the case of finite precision.4. For the telemetry system, the encryption and decryption and key synchronization scheme of telemetry data are designed. The PCM telemetry data is encrypted frame by frame, and the sub-master key in the previous frame is used for data encryption in the next one, in order to ensure key synchronization between sender and receiver. Analysis results of key synchronization reliability and bit error rate, show that this scheme can improve the success rate of key synchronization in the case of relatively large bit error rate.