The Research On Key Technology Of AES And Short-Block Encryption Technology

Rijndael is finalized as Advanced Encryption Standard (AES) in 2000, and it has become the international standard in commerce field. There are more and more people attaching importance to the cryptanalysis and application study of AES. Pre-payment code meter is urgently needed for market in the view of shortcomings of electricity sale by IC card way. Short-block encryption is the key technique in that meter. The short-block encryption technology can achieve that the ciphertext contains the maximal information, this is other encryption algorithm cannot live up to. Some applications in country economy such as pre-payment code meter need cipher to meet the request, the cipher of purchase information is fixed size (12bit, 16bit, etc) decimal number, and it is transmitted and inputted by user. It is easy to convert data during different carry system, but the converted ciphertext can't contain the maximal information. So it is urgently necessary to study the key problems of short-block encryption technology in pre-payment code meter industry, so it is significant to develop country economy.In this thesis, the design principle and algebraic characteristics of AES are introduced in detail, status quo of cryptography and study is outlined firstly, the algebraic expression of S-box and InvS-box, the algebraic characteristics of boolean substitution and the characteristics of affine transformation are presented. And an improved S-box is constructed, the improved S-box has better characteristics in 10 algebraic characteristics, such as periods of affine transformed pair, periods of iterative-output, items of algebraic expression of S-box and InvS-box, balanceness, strict avalanche criterion, non-linear degree, resistance against the XSL attack etc.And then integral cryptanalysis and algebraic attack of AES are studied. Aim at that AES has the characteristics of square cipher structure, square-4 attack, square-5 attack and square-6 attack are studied, and the square-6 attack is applied to square-7. Based on square attack, 7-round related-key attacking Rijndael-128/192 and 9-round related-key attacking Rijndael-128/256 are studied, and the complexity of these attacks are analysed in detail. Multivariate quadratic (MQ) equations in GF(2) and GF(2~8) are studied, the XSL attack to the MQ equations is analysed, the BES attack is disproved and the other MQ expression of AES in GF(2~8) is presented.Finally the short-block encryption algorithm based on AES is introduced, and the S-box's improved method of short-block encryption algorithm is presented, the new S-box is applied to the short-block encryption simulation system and the security of system enhance obviously.