Bridging the gap between symbolic and efficient AES implementations

The Advanced Encryption Standard (AES) is a symmetric block cipher used to encrypt data within many applications. As a result of its standardisation, and subsequent widespread use, a vast range of published techniques exist for efficient software implementations on diverse platforms. The most efficient of these implementations are written using very low-level approaches; platform dependent assembly language is used to schedule instructions, and most of the cipher is pre-computed into constant look-up tables. The need to resort to such a low-level approach can be interpreted as a failure to provide suitable high-level languages to the cryptographic community. This paper investigates the language features necessary to express AES more naturally (i.e., in a form closer to the original specification) as a source program, and the transformations necessary to produce efficient target programs in an automatic and portable manner.