DSPs, BRAMs and a Pinch of Logic: New Recipes for AES on FPGAs

Abstract

We present an AES cipher implementation that is based on the BlockRAM and DSP units embedded within Xilinx's Virtex-5 FPGAs. An iterative "basic" module outputs a 32 bit column of an AES round each clock cycle, with a throughput of 1.76 Gbit/s when processing two 128 bit inputs. This construct is replicated four times for a 128 bit datapath for a full AES round with 6.21 Gbit/s throughput when processing eight inputs. Finally, the "round" module is replicated ten times for a fully unrolled design that yields over 55 Gbit/s of throughput. The combination and arrangement of the specialized embedded functions available in the FPGA allows us to implement our designs using very few traditional user logic elements such as flip-flops and lookup tables, yet still achieve these high throughputs. The complete source code for these designs is made publicly available for use in further research and for replicating our results. Our contribution ends with a discussion of comparing cipher implementations in the literature, and why these comparisons can be meaningless without a common reporting style, platform, or within the context of a specific constrained application.