Research On Chaos Based Encryption Algorithm And Hash Function Construction

With the development and popularization of computer and network,information management system, E-commerce, E-government, E-mail and network games are being applied widely and act as a necessary part in the daily lives. Information security has become the common focus of both academia and enterprises. The research on information security has important academic meaning and practical value.Encryption algorithm and Hash function are two basic techniques in cryptography and play an important role in ensuring the security of information. With the widely use of digital products and the evolution of attacks, the research and development of more information security techniques with security, high efficiency and reliability are demanded. Currently, it is one of the hot promising projects on the combination of nonlinear science and information science to apply chaos theory to information security. In this dissertation, chaos-based encryption algorithm and Hash function have been carefully studied and applied to protect the security of information.The following tasks have been accomplished in this dissertation:①Chaos theory and modern cryptography are introduced. Detailed analysis of the state-of-the-art techniques in chaos-based cryptography is carried out. First, the relationship between chaos theory and cryptography is compared. Then, the detailed descriptions of different chaos-based ciphers are given in the order of the chaos-based stream cipher, the chaos-based block ciphers, the chaos-based public key cipher, other chaos-based cipher, the chaos-based image encryption and the chaos-based Hash functions.②The security of a cryptosystem based on iterating a chaotic map is analyzed. A loophole of this cryptosystem is pointed out and a remedial modification is suggested. Furthermore, some issues which should be considered are presented, while designing this kind of cryptosystem. Finally, an encryption algorithm based on multiple Logistic maps is proposed.③The difference of the piecewise linear chaotic map (PCLM) is analyzed. A method to generate S-box is proposed. Based on this method, a block cipher with dynamic S-boxes is presented. Theory analysis and computer simulation results show that this cryptosystem has good security and high speed.④A common used model in spatiotemporal chaotic systems, i.e. the coupled map lattice, is introduced. In order to apply this model in cryptography, two issues are analyzed, which are the periodicity in the finite computer precision and the stability of synchronization between the coupled map lattices.⑤Tow typical schemes of constructing Hash function based on spatiotemporal chaos are analyzed. Some defects of a Hash function scheme are pointed out and the corresponding improvement is proposed. The improved Hash function remedies the loophole of collision in the original one and has higher efficiency.⑥By combining the traditional iteration structure of Hash function with the two dimensional coupled map lattices, a novel Hash function construction is proposed. Theory analysis and computer test results show that it has high security and flexibility.⑦Finally, the research work of this dissertation is summarized, and the future developing direction is indicated.