The Skein Hash Function Family

AN EFFICIENT PARALLEL ALGORITHM FOR SKEIN HASH FUNCTIONS
K. Atighehchi and A. Enache and T. Muntean and G. Risterucci

Altran Praxis and AdaCore have released SPARKSkein - a new reference implementation of Skein-512 written and verified using the SPARK language and toolset. In particular, this release includes a complete proof of type-safety for the implementation, test cases for structural coverage, performance, and the reference test vectors from the Skein specification.

Download is available from the downloads page or here directly.

Hagen Fürstenau has updated his pyskein implementation of Skein in Python. The new implementation includes the one-pass MAC generation, nonce and personalization inputs, and the Skein-PRNG. All the extra features are done for all three state sizes, Skein-256, Skein-512, and Skein-1024.

The package is available at http://packages.python.org/pyskein/.

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.