Hash functions are one of the most important cryptographic primitives. Some of the currently employed hash functions like SHA-1 or MD5 are considered broken today. Therefore, in 2007 the US National Institute of Standards and Technology announced a competition for a new family of hash functions. Keccak is one of the five final candidates to be chosen as SHA-3 hash function standard. In this paper, we present an implementation of the Keccak hash function family on graphics cards, using NVIDIA’s CUDA framework. Our implementation allows to choose one function out of the hash function family and hash arbitrary documents. In addition we present the first ready-to-use implementation of the tree mode of Keccak which is even more suitable for parallelization.