The Grøstl 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 Grøstl. 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 Grøstl efficiently on
the platform of their choice. Furthermore, we believe also hardware implementations may benefit from
the optimization techniques presented in this paper.