Software-modeling complex cryptographic AES-like primitives nonlinear substitutions

Abstract

Any iterative block cipher should contain one non-linear primitive at least. Lack of a nonlinear transformations

significantly reduces the cryptographic cipher strength because of any combination of linear primitives could be reduced to the equivalent one, so as a consequence leads to the cipher compromise. In this paper method of non­linear substitution primitives synthesis is proposed, grounded on S-box construction accordingly to Rijndael algorithm. Three different classes of primitives have eval­uated with regard to cryptograms entropy. First class con­sists of primitives for which an encrypted data is repre­sented by one-dimensional binary vector(bytes), for the second one — data represented by square matrices with an order of eight, for the third one- by three-dimensional matrices (binary fourth-order cubes). Provided possibili­ties of optimizing the S-box parameters in order to achieve both a minimum correlation coefficient between input and output variables of a primitives and the maxi­mum block response dissipation entropy