Research On Chaotic Cryptographic Hash Algorithms

With the fast development of computer and Internet communication technology, information globalization has become faster and faster and Internet information security has been one of the important factors of the development of a country, an enterprise, as well as a company. As an important branch of Cryptography, Hash function is a one-way function and a kind of encryption map. It is used for protecting sensitive message. Therefore, the main research of this dissertation is the novel Hash function. In recent years, as the merits of chaos are suitable for Hash function construction, Hash function based on chaotic maps is studied widely. So this dissertation focuses on analysis and construction of Hash function algorithms based on chaotic maps, under the condition that those approaches satisfy the security requirements. The following detailed tasks have been accomplished in this dissertation:(1) The basis of chaos theory is introduced explicitly. Firstly, the background of Hash function, the distinct definitions of chaos and the characteristics of some classic chaotic systems are presented. Secondly, the judgment and criterion of chaos including Lyapunov exponent, Poincare surface of section and power spectrum are presented. Finally, several kinds of typical discrete chaotic maps are described.(2) Hash theory basis is introduced in detail from different aspects. To start with, cryptography is introduced from encryption and decryption, symmetric secret key encryption, public key encryption and password analysis. Furthermore, the relationship between chaos and cryptography is presented briefly. Lastly, the definition and classification of Hash function, as well as the design theory and measurement method of Hash function are illustrated are described.(3)A novel hash function construction based on chaotic Logistic map and skew tent map is proposed. The proposed algorithm divides the message into groups and then changes groups into their corresponding ASCII codes which are used for the iteration times of Logistic map. The generated values of Logistic map are set as the initial values of the skew tent map, and finally hash value with length of 128-bit is generated according to the rules. The one-way hash function, diffusion and confusion and collision of the algorithm are studied by simulation. Theoretical analysis and computer simulation indicate that the proposed algorithm can satisfy the performance requirements of hash function. (4) Classic MD5 and Hash algorithm based on chaotic look-up table are introduced to compare with the presented algorithm in analysis of diffusion and confusion capability as well as collision resistance, thereby the presented algorithm showing a better performance.At last, the research tasks of the dissertation are summarized, and some difficult problems and further work are indicated.