Affine-Power S-Boxes over Galois Fields with Area-Optimized Logic Implementations

Abstract. Cryptographic S-boxes are fundamental in key-iterated sub-stitution permutation network (SPN) designs for block ciphers. As a natural way for realizing Shannon’s confusion and diffusion properties in cryptographic primitives through nonlinear and linear behavior, re-spectively, SPN designs served as the basis for the Advanced Encryption Standard and a variety of other block ciphers. In this work we present a methodology for minimizing the logic resources for n-bit affine-power S-boxes over Galois fields based on measurable security properties and find-ing corresponding area-efficient combinational implementations in hard-ware. Motivated by the potential need for new and larger S-boxes, we use our methodology to find area-optimized circuits for 8- and 16-bit S-boxes. Our methodology is capable of finding good upper bounds on the number of XOR and AND gate equivalents needed for these circuits, which can be further optimized using modern CAD tools.