Security Analysis Of CFE Based On Chaotic Two-module Feistel Block Cipher Algorithm

High security and high speed block cipher algorithm of two-module Feistel struc-ture based on chaos is one of the 29 block cipher algorithms in the national cipher al-gorithm Design Competition held by Chinese Association for Cryptologic Research.CFE block cipher algorithm mainly adopts Feistel structure,and its plaintext grouping supports 128 bits and 256 bits,and the number of encryption rounds is 5 bits.The key K used in the algorithm is a vector of 8 length generated by the spatio-temporal chaotic system,and its input can be selected from 5 modes.The design features of the algorithm are that the chaotic sequence is used to generate the sub-key and the nonlinear S box,and the plaintext is used to participate in the selection of the nonlinear parts,so that the analysts can not take the coding link as a known factor when carrying out the cipher attack,and construct the difference and linear analysis based on the known S box.Because S box of the algorithm is controlled by 1 bit input factor,it is dynamic and variable,which makes the attacker cannot carry out password attack based on the traditional fixed coding link analysis method.Linear transformation is combined with forward diffusion and reverse diffusion to realize information diffusion.The innovation of the algorithm is that the chaotic sequence generated by the chaotic iterative algorithm is used as the round key in the key expansion scheme.When encrypting each packet of plaintext,the S-box is selected according to the plaintext of each round.In this paper,the following main analysis results are obtained for CFE block cipher algorithm.The analysis of cipher components includes S box,P permutation,wheel function and key expansion algorithm.For a fixed S box,it is found that it satisfies the bijective and strict avalanche criteria,and the difference distribution table of the S box is calculated,to obtain difference uniformity and maximum differ-ence characteristic probability.In terms of the security of cryptographic algorithms,because of the structural characteristics of dynamic S box,it is not suitable to ana-lyze the security of cryptographic algorithms by using integral attack,sliding attack,algebraic attack,cubic attack,interpolation attack and cyclic shift attack.It can resist differential attack,linear attack,difference-linear attack,meet-in-the-middle attack and invariant subspace attack.The main conclusions are as follows(1)There are 5 rounds of iteration in this algorithm,and the 5 rounds of im-possible difference feature chain with probability of 1 can be constructed.And the impossibility difference feature is used to differentiate the attack.(2)We present the number of active difference S box in the 5 rounds of the algorithm,and the probability is about 2-21.(3)There are 4 rounds boomerang attack in the algorithm.(4)The algorithm has the linear characteristics of 5 rounds zero correlation.