Compact Implementations of LEA Block Cipher for Low-End Microprocessors

In WISA’13, a novel lightweight block cipher named LEA was released. This algorithm has certain useful features for hardware and software implementations, i.e., simple ARX operations, non-S-box architecture, and 32-bit word size. These features are realized in several platforms for practical usage with high performance and low overheads. In this paper, we further improve 128-, 192and 256-bit LEA encryption for low-end embedded processors. Firstly we present speed optimization methods. The methods split a 32-bit word operation into four byte-wise operations and avoid several rotation operations by taking advantages of efficient byte-wise rotations. Secondly we reduce the code size to ensure minimum code size. We find the minimum inner loops and optimize them in an instruction set level. After then we construct the whole algorithm in a partly unrolled fashion with reasonable speed. Finally, we achieved the fastest LEA implementations, which improves performance by 10.9% than previous best known results. For size optimization, our implementation only occupies the 280B to conduct LEA encryption. After scaling, our implementation achieved the smallest ARX implementations so far, compared with other state-of-art ARX block ciphers such as SPECK and SIMON.