Study On Block Cipher Algorithm Based On Chaos And Group

With development of information technology and increasing frequency of information exchange, the research on information security technology is becoming more and more important. As a novel technology in cryptography, digital chaotic cipher has attracted researcher dense interest and widely study. Chaos, as a kind of nonlinear phenomenon, has many remarkable characteristics: such as pseudo-random, unpredictability of evolution of its orbits, sensitivity to initial conditions and system parameters. These characteristics are in accordance with the requirements of cryptography. Since 1980s, the idea of using chaotic systems to design new ciphers has attracted more and more attention. Recently, much more contributions are made to get many promising achievements. At the same time, some systematic ways to design chaotic ciphers have been proposed with careful considerations on the security of algorithms.This dissertation focuses on the design and analysis for some new chaotic block cryptosystems, which are based on chaos system and group theory, and modify a symmetric image encryption scheme based on 3D chaotic cat map. The main achievements and originality contained in this dissertation are as follows:①The research status and advances of chaotic ciphers have been summarized, analyzed and overviewed. The analyzing method of chaotic block cipher has been expatiated in detail, and several existing key problems to be solved urgently have been pointed out. Finally, Group theory, which is used in the thesis, is introduced.②A new chaotic block cipher based on chaotic maps and group theory of abstract algebra is proposed. The new block cipher remedies partially some flaws of the known chaotic cryptosystem. A large key size, diffusion and confusion of three group operations and shuffles of permutation protect effectively the proposed cipher against statistical attack, chosen plaintext attack and some others attacks.③Based on the study of some existing chaotic encryption algorithms and AES, a new block cipher based on chaotic map and algebraic operations is proposed. A large key size, substitution and shift of bits and shuffles of permutation based on key have greatly protect the proposed cipher against many known attacks.④Security analysis of a symmetric image scheme based on 3D Cap map is carried out in detail and security hole is point out. Based on the analysis, a modified symmetric image scheme based on 3D Cap map is proposed. The modified scheme enhances the resistance of chosen plain-image attack and enlarges the key space. At the same time, the proposed scheme also preserves the excellent performance against other attacks.⑤A new permutation algorithm based on key is proposed, which provides some cryptographic shuffles of permutation.It is an exploration of constructing new block ciphers based on chaotic maps and algebraic operations. At the same time, by combining chaotic maps with algebraic operations, it is also an attempt to overcome the intrinsic flaws of the known chaotic cipher.Finally, the research work of this paper is summarized, and the future developing direction is indicated.