Searching Differential Characteristic Of Typical Block Cipher On Feistel-SP Structure

This paper focuses on analysising a series of typical block ciphers on the Feistel-SP structure. This series of block cipher are Camellia, MIBS, E2, etc.Different block ciphers of Feistel-SP structure establish a reasonable differential propagation system.Searching out multi-round iterative differential mode and multi-round differential path of typical block ciphers. The page main work is as follows:First, Matsui algorithm ideology is applied to block ciphers of Feistel-SP structure,then it is improved and optimized. Transforming the differential distribution table of S-box into intensive distribution table,then a strict pruning techniques based on vector is proposed, used to filter out differential path as soon as possible. Case in light weight block cipher MIBS,applying this automated search technology,the best differential probability of 4-round is searched out. Giving differential characteristics of R-round( 4 ?R ?11)and searching out two 12-round optimal Iterative differential paths, probability is 2-56,the result is the best so far.Secondly, a expressive method of new symbol differential is proposed,then a new automated search technology is proposed based on former.With the optimal iterative differential mode of typical block cipher on Feistel-SP, which not only greatly reduce the computational complexity,but also construct the multi-round differential mode by this iterative differential mode. Taking for instance light weight block cipher MIBS,this paper give 3-round,4-round optimal iterative differential mode, searching out all optimal iterative differential paths in this mode. the probability is 2-20,2-26 respectively,because paper presents a common search algorithm on Feistel-SP structure. Camellia is an example of the applicability analysis,establishing its Feistel-SP structural model and replacing S(Substitution) and P(Permutation) components.Searching out the iterative differential mode,further searching out the differential paths of high probablity.Finally, we proposed 3-round and 4-round optimal iterative differential mode and optimal iterative differential characteristics of Camellia in the end. The probablity is 2-52,2-71 respectively. the result is the best so far.Finally,two high propability differential paths of 12-round are presented using improved Matsui automated search algorithm in third chapter,then we use the chosen plaintext attack to restore 13-round and 14-round sub-key bits. Summarizing the normal thoughts and steps of restore sub-key bits, introducing SNR concept and using counter to count right and wrong sub-key pair. The main steps of SNR’s operation is sampling, de-noising and purification. 13-round and 14-round analysis of the data is presented in Table 5.1, the successful probability is 99.9%, and 14-round is 50.15%.