Dynamic Cellular Automata-Based S-Boxes

Abstract

The most important elements of many block ciphers are nonlinear functions known as substitution boxes (S-boxes). Classical S-boxes are usually represented by numerical tables, which are used today in current cryptographic standards, such as Data Encryption Standard (DES) or Advanced Encryption Standard (AES), but in the result of developing methods of cryptanalysis they do not ensure enough safety of ciphers. Therefore, the open research issue now is to design new more sophisticated classes of S-boxes, in particular dynamic ones. In this paper we propose a methodology to design dynamic cellular automata (CA)-based S-boxes, which can be considered as a generator of CA-based S-boxes. We provide an exhaustive experimental analysis of the proposed CA-based S-boxes in terms of non-linearity, autocorrelation, balance and strict avalanche criterion. We show that the proposed S-boxes have high quality cryptographic properties (high non-linearity and balance, also low autocorrelation and distance to fulfill strict avalanche criterion). The interesting feature of the proposed S-boxes is a dynamic flexible structure, fully functionally realized by CA, while the classical S-boxes are represented by predefined unchangeable table structures.