Energy Evaluation of Software Implementations of Block Ciphers under Memory Constraints

Software implementations of modern block ciphers often require large lookup tables along with code size increasing optimizations like loop unrolling to reach peak performance on general-purpose processors. Therefore, block ciphers are difficult to implement efficiently on embedded devices like cell phones or sensor nodes where run-time memory and program ROM are scarce resources. In this paper, the performance, energy consumption, runtime memory requirements, and code size of the five block ciphers RC6, Rijndael, Serpent, Twofish, and XTEA on the StrongARM SA-1100 processor was analyzed and compared. Most previous evaluations of block ciphers considered performance as the sole metric of interest and did not care about memory requirements or code size. In contrast to previous work, this study of the performance and energy characteristics of block ciphers has been conducted with "lightweight" implementations which restrict the size of lookup tables to 1 kB and also impose constraints on the code size. The author found that Rijndael and RC6 can be well optimized for high performance and energy efficiency, while at the same time meeting the demand for low memory (RAM and ROM) footprint. In addition, the impact of key expansion and modes of operation on the overall performance and energy consumption of each block cipher was discussed. Simulation results show that RC6 is the most energy-efficient block cipher under memory constraints and thus the best choice for resource-restricted devices