GENERATION OF CRYPTOGRAPHICALLY STRONG KEY-DEPENDENT 8-BIT S-BOXES

Abstract

A widely used strategy in the design of block ciphers is the generation of key-dependent substitution boxes (S-Boxes), i.e., secret S-Boxes that depend randomly on the cipher key, guaranteeing security due to the uncertainty provided by the randomness of the S-Box during the encryption process and not due to its cryptographic properties. On the other hand, in the specialized literature there are several methods to construct cryptographically strong S-Boxes to be used in block ciphers, however, the S-Boxes built by such methods are fixed and need to be generated beforehand. Inspired by finding key-dependent S-Boxes with good cryptographic properties, we present in this paper a new strategy to generate key-dependent and cryptographically strong 8-bit S-Boxes from 4-bit permutations and heuristic search.