Minimal Analysis Of Linear Activity Wheel Function Of SMS4 Structure Block Cipher

The SMS4 block cipher algorithm is the first official commercial block cipher standard proposed in 2006 by our country,the safety of which is closely related to the minimum number of linear activity round function and the round number, but, up to now, there are no any research results about the relations between the minimum number of linear activity round function and the round number. In this paper, for the first time, through analyzing the structures and relations between any two rounds of SMS4, we get the general expression of r-round linear spread locus of SMS4. Then based on the analysis of r-round linear spread locus activity round function, we deduce finally the relations between the minimum number of linear activity round function and the round number of SMS4 block cipher.