Analysis Of Blockcipher CLEFIA

With the development of the computer technology and communication technology, requirements for security storage, safe handling and secure transport of information become more and more urgent for users. In the e-commerce and e-government era, people are facing a critical problem that information security problems, an effective means to solve this problem is the use of moden crytography. Block cipher is an important research branch of modern cryptogr- aphy, it has many features such as high rates, easy for standardization,and efficient for both software and hardware implementations. Block ciphers are usually core components in informat- ion and Internet security for data encryption,data signature,authentication and key management; it also be used to construct stream ciphers, pseudo-random number generator, MACs(Message Authentieation codes), Hash function, signature programs, it is widely used in computer commu- nications and information security field.CLEFIA[1,2] is a block cipher which is developed by SONY company recently, SONY intended to protect the company's music and video and other digital content distribution as well as the protection and authentication of "advanced" copyright. It had been released to the public in the 2007 Fast Software Encryption Conference (FSE2007). As CLEFIA is a relatively new encryption algorithms, executing safety analysis of CLEFIA is a challenging subject, it has great significance. Concentrating on security analysis of CLEFIA, some achievements have been obtained in this paper:1.Given the equivalent structure of CLEFIA, so that it has the traditional Feistel structure. As the current mature analysis methods of the block cipher are aimed at the traditional Feistel structure, so we constructed the equivalent structure of CLEFIA which has traditional Feistel structure, so we can apply the original analysis method to CLEFIA successfully;2.On the basis of the equivalent structure, by adopting Collision-Square attack we realized an attack on 6 round successfully. First, we constructed a 4 round differentiator, then used the differentiator to analyze the relations between bytes,used the idea of collision attack to recover some of the key, finally, we combined with Square attack to verify whether the results of byte combination to meet the balance, then verify that whether the guessed key correct or not;3.On the basis of the equivalent structure, we used impossible differential analysis to realize an attack on 14-round CLEFIA-128. we proposed a new 9-round impossible differential, then used the idea of solving equations in the finite field to prove that the differential is impossible, finally, we added 2 rounds before the impossible differential and 3 round after the impossible differential to analyze 14-rounds CLEFIA.