S-BOX Architecture

Abstract

Substitution-Box (S-BOX) is the most critical block in the Advanced Encryption Standard (AES) algorithm, consumes 75% of total power during encryption. The primary idea to implement S-BOX is to have a unique byte substitution. In this paper 4 different architecture of SBOX discussed; (a) look-up table or ROM based S-BOX contains a pre-computed value stored at defined address (b) modified look-up table based approach which uses decoders and multiplexer makes overall substitution faster (c) computational method has composite field architecture to compute the substitution byte (d) blend of computational method and look up table method where pre-computed multiplicative inverse values are stored in lookup table to reduce power consumption. Look up table based method requires a fetching circuit from a certain location, suffers from area overhead; to overcome that to be substituted values are divided into groups and using decoders and multiplexer that values will be fetched. The computational method requires complex computation result in high power consumption. To overcome that one particular module is pre-computed and stored in a look-up table in the last method. The overall objective of this paper is to implement S-box using different methods and to come up with method which is optimum as far as the area, power, delay parameters are concerned and security wise robust. In this work a comparative study of all these methods has been explored with CMOS 180 nm, 90 nm, and 45 nm technology node.