Compact Implementation of Threefish and Skein on FPGA

The SHA-3 finalist Skein is built from the tweak able Threefish block cipher. In order to have a better understanding of the computational efficiency of Skein (resource sharing, memory access scheme, scheduling, etc.), we design a low-area processor for Threefish and describe how to implement Skein on our architecture. We harness the intrinsic parallelism of Threefish to design a pipelined ALU and interleave several tasks in order to achieve a tight scheduling. From our point of view, the main advantage of Skein over other SHA-3 finalists is that the same coprocessor allows one to encrypt or hash a message.