The Differential Attack Of Serpen

With the development of the information technique,the problem of information security has become more and more serious.And the modern cryptography theory and technique,as the key of the information security,has been concerned by the governments all of the world.In 1949, the paper "A Mathematical Theory of Communication"[10]å'Œ"The Communication Theory of Secrecy System"[9],tell that only "one time pad" could provide absolutely security.And the paper signed the birth of cryptography. In 1976, the innovative paper " New Direction in Cryptography"[1] from Differ and Hellman,and the Data Encryption Standard[11],which was presented by NBS in the second year,both mean the birth of modern cryptography.Well in 1997,the NIST start a project which collect block cipher algorithm publicly from the cryptographists all over the world,for the Advanced Encryption Standard[20],or AES for short.Since then,block cipher become the hot pot in cryptography. This project at last got fifteen algorithms,which are on behalf of the most high level of designing of the block cipher.Serpent[19] as one of them, is designed by Ross J. Anderson, Eli Biham and Lars R. Knudsen.The three designers are all world famous.While Rijndael was the last winner,Serpent got the second most tickets.The design of Serpent contain the most advance technique,including SPN and public S-box,so we can say that the analysis of this algorithm means the challenge for much classic designing experiments.Also it is a hard job.The differential analysis,invented by E.Biham and A.Shamir during they are analysing the DES,has been widely used in analysing the block cipher and Hash function.The differential attack the cipher by searching the probability between the input difference and the output difference.In the foundation of differential analysis, many new methods were invented, such as high order differentials[12,13], truncated differentials[12,14,15], impossible differentials[16], and the list goes on.Now the differential analysis and the linear attack both are the most important method to attack the block cipher and Hash function.In this paper,firstly we will introduce the modern cryptography and information technique.Secondly,we will search for that how the differential analysis work and a SPN example is used to show the differential attack.At last,after telling the Serpent algorithm,we will apply the differential attack on Serpent.In the end we get three five rounds differential path with the probability(?),(?) and(?). The first and the second one are both begin at the difference x28=4, go through S3,become x28=10,and then go ahead and back. The last one,with the good probability (?),begin at the difference x28=10, go through S3,become x28=2,and then go ahead and back.