Study On Some Key Problems Of Block Ciphers

With the development of the computer and communication technology, the users' requirements for the information's safety storage, safety process and safety transmission are getting more and more exigent. Because of the properties of the high-speed, easy-standardization, easy-implementation by the software or hardware, and so on, block cipher has become the core scheme of the data encryption, digital signature, authorization, key management in information and network safety. The research of the block cipher can be divided into 3 parts: the design theory, the safety analyzing, and the statistical performance test.In the first half part of the thesis, the available typical attack methods to block cipher such as differential cryptology analyzing, serial cryptology analyzing and the algebraic attack aiming at AES are introduced. The generic design theories of the block cipher are presented based on the available attack means. The structures, styles, advantages and disadvantages of some frequently used block ciphers are given in detail. The design rules and the structure methods for the Round-Function, S-Boxes, P-Permutation of the block cipher as well as several rules for the key-expansion algorithm are discussed in detail. The most two typical block ciphers, Rijindael Algorithm (Advanced Encryption Standard) and Camellia Algorithm (New European Schemes for Signatures, Integrity and Encryption) are introduced.Based on the above knowledge, the core components S-Boxes of the Rijndael Algorithm and the Camellia Algorithm, which are the only nonlinear components, are analyzed and compared in detail. Eight algebraic properties of S-boxes such as balanceness, strict avalanche criterion, differential uniformance, algebraic order, and so on are calculated and proved. The reason that the S-boxes which are constructed by the inverse operation on finite field has the specialty of 4-difference is analyzed. Two kinds of the algebraic structures of the both algorithms are also given. It is proven that the S-Boxes of the Rijindael Algorithm and Camellia Algorithm have favorable algebraic characteristics and complex algebraic structure, which provides academic guarantees for the applications of the two algorithms in many fields.