Impossible Differential Cryptanalysis Of Lightweight Block Ciphers

Along with the development of information technology in the society,and the rapid growth of the Internet.How to maintain the secure transmission of customer information and data information in the complex Internet,meanwhile ensure that the meaning will not be forged or deleted by network attack.This problem has become a hot topic in the scientific research of cryptographic algorithms.Compared with the traditional block cipher,the lightweight block cipher is relatively simple in the algorithm structure,the requirements for running environment are not very demand-ing.Lightweight block cipher algorithm could satisfy the security requirements on the resource-constrained devices.So the safety research of the lightweight block cipher algori-thm is particularly important,it is not only the optimization of the algorithm itself,ensure the security of the data in the running environment,but also conducive to the further deve-lopment of lightweight block cipher algorithm.This thesis firstly introduces the research status of block cipher and light-weight block cipher,and then illustrates some notions of block cipher,including its mathematical model,encryption structure,analysis methods and security indicators.Then,the impossible diffe-rential analysis method used in this paper is especially described in detail,and the analysis steps are given at last.Then,we use this method to analyze four lightweight block cipher algorithms.The specific research contents are as follows:(1)To improve the PFP algorithm impossible differential distinguisher,a new PFP algorithm 7 rounds impossible differential distinguisher,extend three rounds on the basis of distinguisher.The PFP algorithm carry out 10 rounds of impossible differential analy-sis.Compared with the 6-round of impossible differential analysis for PFP algorithm in the algorithm design literature[55],the number of attack rounds in this thesis is increased by 4rounds,and 10 rounds of attack are carried out on the algorithm,which only increases2^0.7 in time complexity.(2)Impossible differential analysis on LiCi algorithm.When verifying that the 16-round LiCi algorithm cannot resist the impossible differential analysis,literature[57]proposed a10-round impossible differential distinguisher for LiCi algorithm,and based on this carried out a 16-round impossible differential analysis.By analyzing the algorithm structure and combining the differential characteristics of S-box,we construct a 11-round impossible differential distinguisher of LiCi algorithm,and extend to the 17-round impossible differen tial analysis of LiCi algorithm.It is worth noting that the time complexity of our analysis is only2^-6that of the literature[57],and the efficiency of the attack has been significantly improved.(3)The structure analysis of GRANULE algorithm and the study of the encryption and decryption direction,as well as the S-box difference distribution table research,using com-puter programming method searched the differential path in the direction of encryption and decryption automatically.Based on the searched differential path of encryption and decryp-tion direction with probability of 1,we define the contradiction detection function.And then traverse the differential path of encryption and decryption direction,look for the differen-tial path with contradictory bit,and while we carry out the impossible differential path.Fi-nally,we obtain multiple 7-round impossible differential distinguishesr.On the basis of the distinguisher,it is extended for 3 rounds forward and 3 rounds back,and the impossible differential analysis for GRANULE algorithm is performed for 13 rounds.This analysis requires2^50.7chosen plaintexts,and time complexity is2^52.30 13-round encryption.Com-pared with the existing analysis results,the data complexity and time complexity have been significantly reduced.(4)The PICO algorithm of SPN structure and the search of impossible differential distinguisher.Based on the study of S-box differential characteristics and the propagation characteristics of permutation layer,we found an impossible differential distinguisher with7 rounds.This is the longest distinguisher up to now.