Stream Cipher Design And Implementation

In information times, with the rapid development and wide applications of integrated circuit technology, computing technology and network technology, more and more information has been transmitted through the network. Therefore, the security of information is getting more and more important. The Cryptography, which aims at the security of information, has become one of the important research fields in information science and technology. The main purpose of this dissertation is on the design and implementation of stream ciphers. The theory of modem cryptography is discussed and presented at first, which includes the mathematical model, the secure measure and the classification of the cryptography systems. On the basis of modem stream cipher, the theory of the shift register, a systematic design approach of nonlinear combination shift register is proposed and the critic techniques are expressed in detail. Then the complete design flow is given, and the design environment developed. According to the practical requirement, a nonlinear combined cipher system is designed in this environment and implemented by FPGA. At last it is applied in computer communication. A new stream cipher approach based on shift register is proposed. After presenting the detailed encipher rule and decipher rule, its characteristics is analyzed. Moreover, two optimized methods are provided, which are multi-encoding method and method disturbing the state of shift register. The hardware implementation architectures are also presented. Combining the two methods or iterating these methods can improve the anti-broken capability. After studying the chaotic stream cipher, a method by changing the chaotic parameter randomly is provided, which can increase the period of the chaotic stream cipher when implemented in finite precision. The results of study in theoretical analysis and experiment simulation show that this method can enlarge the period of chaotic key stream and strengthen the anti-broken capability. Moreover, the hardware architecture of this method is also presented. At last, a method on creation and calculation of a kind of irrational number is researched. The digit number of the extension of this irrational number is random on certain basis. Therefore, a stream cipher is designed, which uses the extension digit of the irrational number as the key stream.