On the Design of Secure Block Ciphers

Abstract — In this paper, we examine a class of block ciphers referred to as substitutionpermutation networks or SPNs. We assert that the basic SPN architecture can be used to provide an efficient implementation of a secure block cipher if the system S-boxes are carefully selected and connected with an appropriate linear transformation. Specifically, it is shown that ¡£¢¤ ¡ S-boxes which possess good diffusion and nonlinearity properties may be effectively used as components of a secure block cipher. As well, it is demonstrated that the cipher may be strengthened by replacing the permutation of bits between S-box rounds with a diffusive linear transformation