Efficient Implementation of SPEEDY Block Cipher on Cortex-M3 and RISC-V Microcontrollers

Abstract

The SPEEDY block cipher family announced at the CHES 2021 shows excellent performance on hardware architectures. Due to the nature of the hardware-friendly design of SPEEDY, the algorithm has low performance for software implementations. In particular, 6-bit S-box and bit permutation operations of SPEEDY are inefficient in software implementations, where it performs word-wise computations. We implemented the SPEEDY block cipher on a 32-bit microcontroller for the first time by applying the bit-slicing techniques. The optimized encryption performance results on ARM Cortex-M3 for SPEEDY-5-192, SPEEDY-6-192, and SPEEDY-7-192 are 65.7, 75.25, and 85.16 clock cycles per byte (i.e., cpb), respectively. It showed better performance than AES-128 constant-time implementation and GIFT constant-time implementation in the same platform. In RISC-V, the performance showed 81.9, 95.5, and 109.2 clock cycles per byte, which outperformed the previous works. Finally, we conclude that SPEEDY can show efficient software implementation on low-end embedded environments.