Pulse latch based FSRs for low-overhead hardware implementation of cryptographic algorithms

In this paper, we address the problem of low-overhead implementation of Feedback Shift Registers (FSRs). We present a dynamic pulse latch which is based on transistors with two different channel lengths. The channel lengths are selected to make the latch suitable for replacing flip-flops in FSRs. The presented latch is 1.92 times smaller and 3.94 times less power consuming compared to the smallest standard flip-flop in the same technology. By re-implementing FSRs of Grain-80 stream cipher with the presented latch, we achieve 32.24% reduction in area, 36.77% reduction in total power, and 10.81% increase in the maximum clock frequency compared to the original, flip-flop based version of Grain-80. If, in addition, the static time borrowing technique is applied, we achieve an additional 25.5% increase in the maximum clock frequency at the expense of 4.68% smaller gain in area and 2.67% smaller gain in total power.