First, we are happy to announce that Dan Bernstein is the winner of the fourth Keccak cryptanalysis prize for his attack posted on NIST's hash forum Second preimages for 6 (7? (8??)) rounds of Keccak?. The attack exploits the low degree of Keccak-f's round function into a (second) preimage attack at the sponge function level and has been recently extended to 8 rounds, as suggested in the initial posting. We are currently arranging practical details with the winner to give him the awarded Belgian chocolates.

Second, we are also happy to announce that (in alphabetical order) Gerhard Hoffmann and Guillaume Sevestre are the ex aequo winners of the Hex-Hot-Ticks prize for the most interesting implementation of Keccak on exotic platforms. They will each receive a Himitsu-Bako secret box.

• Gerhard Hoffmann wrote an implementation of Keccak[] on a NVIDIA graphics processing unit using the Compute Unified Device Architecture (CUDA). His source code comprises a batch execution of Keccak[] and an experimental implementation of the tree hashing mode using leaf interleaving defined in Section 4.4 of the main document v2.1.
• Guillaume Sevestre implemented a tree hashing mode on top of Keccak[r=256,c=544] on a NVIDIA graphics processing unit, also using CUDA. His source code contains two variants of his tree hashing mode and a parallel stream cipher.

Congratulations to all of them!