Performance evaluation of the Advanced Encryption Standard candidates has led to intensive study of both hardware and software implementations. However, although plentiful papers present various implementation results, it seems that efficiency could still be greatly improved by applying good design rules adapted to devices and algorithms. This paper addresses various approaches for efficient FPGA implementations of the Advanced Encryption Standard algorithm. As different applications of the AES algorithm may require different speed/area tradeoffs, we propose a rigorous study of the possible implementation schemes, but also discuss design methodology and algorithmic optimization in order to improve previously reported results. We propose heuristics to evaluate hardware efficiency at different steps of the design process. We also define an optimal pipeline that takes the place and route constraints into account. Resulting circuits significantly improve previously reported results: throughput is up to 18.5 Gbits/sec and area requirements can be limited to 542 slices and 10 RAM blocks with a ratio throughput/area improved by at least 25% of the best-known designs in the Xilinx Virtex-E technology.
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