New Analysis And Design Method Of Block Ciphers

Block cipher algorithms play a vital role in the field of data encryption due to their high security,simple design,easy standardization,fast encryption and decryption speed,and suitable for software and hardware implementation.This dissertation studies the security of block ciphers from the aspects of the cryptographic properties of block cipher components and the analysis theory of block ciphers.Specifically,this dissertation studies the mathematical properties of rotationally symmetric functions,the number of differential branches of nonlinear transformations,the quantum analysis method of SMS4 and MARS Feistel structure,the quantum analysis method of NBC algorithm,automatic search of the number of active S boxes,etc.Based on the theoretical security research of the block cipher mentioned above,this dissertation designs a block cipher algorithm suitable for lightweight communication.Research on the block cipher components The basic components of block ciphers include nonlinear confusion layer design and linear diffusion layer design.Non-linear layer design usually adopts S-box substitute table,and the design of S-box generally adopts high-order Boolean function design.Studying the mathematical characteristics of this type of function is an important basis for S-box selection and safety assessment.In this part,we analyze the number of differential branches of nonlinear permutation and find a general upper bound.Moreover we show that the upper bound is good by comparing this upper bound with Griesmer bound and Sarkar bound.At the same time,a specific discussion is carried out on the commonly used scene of n=8.The famous Nordstrom Robinson code explains that the number of differential branches of the 8-bit S-box can reach to 6.And then we give the cryptographic properties of this type of S-boxs.Analysis theory of block ciphers In the era of post quantum,the quantum analysis of block ciphers is a hot area in the field of cryptography.In this dissertation,we give the safety assessment of two types of generalized Feistel structures and NBC which is a representative algorithm based on the second Feistel structures.Specifically,this article presents(2d-2)rounds of quantum discrimination attacks for the SMS type block cipher of the d branch,6 rounds of quantum discrimination attacks and 11 rounds of quantum key recovery attacks of NBC-128-like,10 rounds of quantum discrimination attacks and 16 rounds of quantum key recovery attacks of NBC-256-like,d Rounds of quantum discrimination attack and 2d Rounds of quantum key recovery attacks of the MARS type block cipher of the d branch under quantum choose plaintext attack and(d+1)Rounds of quantum discrimination attack and(2d+1)Rounds of quantum key recovery attacks of the MARS type block cipher of the d branch under quantum choose ciphertext attack.In terms of block cipher security assessment,we take the cryptographic algorithm Simpira as an example,and present its automatic search technology for differential and linear truncated trails based on the mixed integer linear programming MILP,thereby improving the security evaluation given by Simpira in the original text.A block cipher algorithm suitable for lightweight communication We have designed a block cipher algorithm suitable for lightweight communication-SimptSPN.The algorithm adopts a balanced Feistel structure design while he round function adopts a substitute permutation structure.The nonlinear layer adopts a lightweight 4-bit S-box design while the linear layer adopts a half-byte cyclic shift and a maximum distance separable code(MDS code)structure.The algorithm has no key arrangement algorithm.The 128bit key is divided into two 64-bit keys and used alternately in rounds.The algorithm has a total of 20 rounds.The algorithm reaches to the upper bound of the number of rounds of the differential and linear differentiator in 10 rounds,which is suitable for applications in resource-constrained environments and meets the application requirements of lightweight communication.