Differential-Algebraic Cryptanalysis On SMS4Cryptosystem

Using modern cryptography technology can effectively solve the problem of information security protection. Block cipher has the characteristic with encryption and decryption faster, good safety performance, so that it has developed rapidly and widely applied to many fields.The analysis methods, for instance:differential cryptanalysis, higher order differential cryptanalysis, integral cryptanalysis, side channel analysis, algebra attack, differential attacked. So far, the differential analysis is the most effective and common analysis method to be used, its effectiveness is to be able to find high-probability differential characteristics. The effectiveness of algebraic attacks is able to find an effective method for solving equations, its weakness is the number of rounds and the more the number of equations. Thus, it will be more and more difficult to solve the equations. At the same time, scholars advanced differential-algebraic attack thinking that combined differential analysis and algebraic attack thinking, used this new method of block cipher improve more efficacious.So far, the research of SMS4cryptosystems analysis method is mainly concentrated in the differential analysis method. The SMS4Differential-Algebraic attack method analysis the SMS4cryptosystems has a certain meaning and value.Based on SMS4cryptosystem encryption and decryption process, the basic principles and algorithm of differential cryptanalysis and algebraic attacks, this paper researched the differential analysis on SMS4algorithm to22rounds. This paper used Boolean functions of the S-box algorithm to establish and solve equations, detailed the differential-algebraic attack on SMS4algorithm to21rounds and proved the effectiveness and superiority.The mainly results are summarized as follows:1) We have obtained the SMS4Cryptosystem S-box Boolean function expression. Using the nature and method of Boolean function and resulted it with VC design.2) We have researched SMS4algorithm with the new idea. Using Boolean functions of the S-box algorithm, linear expression and expression of the round function to establish and solve equations, detailed the differential-algebraic attack on SMS4algorithm to21rounds. We summed up the attack on the SMS4algorithm can use a new method to study.3) SNR determined the effectiveness of an analysis on Block cipher, and calculated the SNR of differential-algebraic attacks on the SMS4algorithm to21rounds, we compared the validity to the other analysis method.