The Skein Hash Function Family

Jörg Walter has created a new implementation of Threefish-256 and Skein-256 for the Atmel AVR 8-bit microcontrollers. His implementation is very fast:

• Threefish in 8800 cycles
• Skein in 18500 cycles for short messages
• 290 cycles per byte for long messages
• PRNG in 1250 cycles per byte

His implementation is called Fhreefish, available at this link.

At the Fast Software Encryption (FSE 2010) conference, Dmitry Khovratovich and Ivica Nikolic are presenting a paper on the cryptanalysis of ARX cryptosystems. ARX stands for Addition, Rotation, and Xor (eXclusive or). Combining these three operations is a general way to construct efficient cryptographic primitives, and we actually followed this way when designing Skein. The paper actually analyzes Threefish, the block cipher inside Skein.

This is the first time we've gotten everyone together at the same time.

Left to right, Mihir, Jesse, Jon, Doug, Stefan, Niels, Bruce, Yoshi.

We were down for a few days and are now back. Thanks for your patience.

The links links on the tweak story are now fixed. My apologies to those who tried to get to them and couldn't.

Jon

We're releasing a tweak of Skein in accordance with the allowed tweaks for Round 2 of the competition. The tweak is simple, it's just revised rotation constants.

A paper with the changes is available here. The fully revised Skein paper, with all the accordant changes made is available here. And the fully-revised NIST submission CD is available here.

Keep them coming!

Alberto Fajardo has an implementation in .NET that is tuned for speed. Take a look at http://code.google.com/p/skeinfish/.

Sriram Krishnan has done a managed implementation of Skein in .NET, which is available on his blog at http://www.sriramkrishnan.com/blog/2009/08/nskein-skein-implementation-net.html.

The Botan C++ crypto library now includes Skein-512. http://botan.randombit.net/news/releases/1_8_3.html

Martin Kausche has done a Skein implementation in Ada, too.