The Study And Design Of Stream Ciphers Based On The Linear Feedback Shift Register

With the rapid development and wide application of communication and network, more and more information has been transmitted through the network. Therefore, the information security and protection are getting more and more important. The cryptography, which aims at the information security, has become the important research fields in information science and technology. The stream cipher is one of the important branches of modern cryptography. Together with the effectively mathematical tools, the development of shift register theory has brought quite great progress of stream cipher theory. The main purpose of this dissertation is to analyze and design stream ciphers based on linear feedback shiftregister. The main study from several following respects:Firstly, the author has emphasized on discussing the linear feedback shift register. Especially, the m-sequence which is widely used at present has been discussed. The author pointed out that m-sequence has favorably random statistical characteristic, also proved that m-sequence is pseudo-random sequence in fact.Secondly, several stream cipher algorithms based on the linear feedback shift register have been analyzed. The author has discussed several problems which should be pay attention to in design stream cipher algorithms, and has newly annotated RC4. In particular, two kinds of new encryption algorithms have been discussed from a secure standpoint, they are stream ciphers of block encryption and linear shift register which has information to feedback. The author pointed out that even if the trapdoor parameter t is known, the former is also secure, however, the latter is insecure.Thirdly, a class of sequences encryption method, which based on the linearfeedback shift register, has been proposed in this paper with the form of instance. This encryption method is described as that ciphertext c(pj) of pi is the differencebetween pi's encoding s'} and pt.i's encoding s]^, which s\ and s]^ are allappeared in the state space of shift register. This method has innate shortcoming, in the same character combination, the latter character's ciphertext has dependent relation with the former. Aiming at this shortcoming, the author has presented a modified method: after one plaintext letter is encrypted, we can disturb the states of shift register, and then began to encrypt the next character. The results showed that this new approach can improve the statistical peculiarity of ciphertext and withstand the adversary's attack. In the end, we designed a hardware implement project of this improved method.