Grøstl Implementation Guide

The Grostl hash function is a finalist in the SHA-3 competition organized by NIST. In this paper, we describe a number of implementation techniques and tricks for Grostl. They allow us to develop a range of efficient implementations for various platforms, from 8-bit microcontrollers to modern desktop processors using 256-bit AVX instructions. These results demonstrate the implementation flexibility of the algorithm and we hope will inspire further optimizations and ports to other platforms. The information in this paper will also be useful for developers planning to implement Grostl efficiently on the platform of their choice. Furthermore, we believe also hardware implementations may benefit from the optimization techniques presented in this paper.