Skein and Threefish Software Suite

This software suite brings you Skein and Threefish functions for Java, C, and go. Some notable features of this software suite are:

• All three state sizes of Skein and Threefish: 256, 512, and 1024 bits
• Support of Skein MAC
• Variable length of hash and MAC - even in numbers of bits
• Support of the full message length as defined in the Skein paper (2^96 -1 bytes, not just a meager 4 GiB :-) )
• Tested with the official test vectors that are part of the NIST CD (except Tree hashes)
• The Java interface uses the well known Bouncy Castle lightweight mechanisms, thus easy to use for Java programmers.
• The C API follows in general the lower level openSSL model

I used some open source and public domain sources to implement and compile this suite. Most notably are the Skein C reference and Skein C optimized implementations of the Skein team and a very well written C# implementation from Alberto Fajardo.

The Java implementation

The Skein and Threefish functions for Java a fairly complete and tested and could be used in productive environments. The ant build file produces a small jar file that contains the Skein, Threefish, and some other useful and often needed algorithms.

The Java implementation is a derivation (in parts a large derivation) of Alberto Fajardo's C# implementation for .Net. Some Java specific programming tricks to deal with unsigned data types were necessary (Java does not support unsigned data types). Also Java misses ref parameters in function calls.

Because I'm familiar with the Bouncy Castle crypto library I decided to design the Java interface along the lines of BouncyCastle's lightweight crypto API.

The C implementation

The C implementation provides a similar functionality as the Java implementation.

Currently the Skein implementation uses the Threefish reference implementation not the full unrolled version. It is planned to switch to the full unrolled version to simplify maintenace and to have a better software module structure.

A Skein API and its functions.

This API and the functions that implement this API simplify the usage of Skein. The design and the way to use the functions follow the openSSL design but at the same time take care of some Skein specific behaviour and possibilities.

The functions enable applications to create a normal Skein hashes and message authentication codes (MAC).

Threefish cipher API and its functions.

This API and the functions that implement this API simplify the usage of the Threefish cipher. The design and the way to use the functions follow the openSSL design but at the same time take care of some Threefish specific behaviour and possibilities.

These are the low level functions that deal with Threefisch blocks only. Implementations for cipher modes such as ECB, CFB, or CBC may use these functions.

The Go implementation

This implementation also provides the full feature set, thus you may use it to produce Skein hashes or Skein MAC. The API is similar to Java and uses the same function names as much as possible.

Download and installation instructions for the Go package

Because this is a multi-language implementation it would be tricky to use the standard way to get and install the Go Skein packages. Nevertheless, it's quite simple to get and install the Skein package.

I assume that you have already setup your Go environment and know how to use the go command.

1. Clone the complete Git repository
2. change in the go subdirectory inside the repository directory
3. Set the GOPATH environment variable to include the current path, for example: export GOPATH=`pwd`
4. run the Go commands:
   • go install crypto/threefish
   • go install crypto/skein
   • go test crypto/threefish
   • go test crypto/skein

The test commands should run without problems and should not report any error.

The Threefish cipher implementation

Alberto did a wonderfull job here. In his implementation he unrolled all three Threefish algorithms (256, 512, 1024).The Java implementatiom also has unrolled Threefish algorithms that are even faster than Alberto's C# implementation. This happens because Java has all the code really unrolled. The C# implementation uses a lot of function calls with ref parameters. This unrolled code gives the Java JIT compiler good input for optimization.

The standalone Threefish cipher for C has the same code basis as the Java implementation. Therefore also full unrolled code without loop constructs.

Credits

Credits go to

• the Skein team for their design of Skein and Threefish and their reference and optimized C implementations
• Alberto Fajardo for his well structured C# implementation and his work to unroll the Threefish algorithms.