Techniques to Reduce Switching and Leakage Energy in Unrolled Block Ciphers

Energy consumption of block ciphers is critical in resource constrained devices. Unrolling has been explored in literature as a technique to increase efficiency by eliminating energy spent in loop control elements such as registers and multiplexers. However these savings are minimal and are offset by the increase in glitching power that comes with unrolling. We propose an efficient latch-based glitch filter for unrolled designs that reduces energy per encryption by an order of magnitude over a straightforward implementation, and by 28-45 percent over the best existing glitch filtering schemes. We explore the optimal number of glitch filters that should be used in order to minimize total energy, and provide estimates of the area cost. Partially unrolled designs also benefit from using our scheme with energies competitive to fully serialized implementations. Power gating to reduce leakage power and reuse of computed key enable unrolled designs to be more efficient than serialized ones without compromising latency advantages. We demonstrate our approach on the SIMON-128 and AES-128 block ciphers.

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