Thursday, December 18, 2008

32-bit Skein is possible

Looking over the Skein paper, I saw this little gem:
5.4 The Word Size as a Tunable Parameter

All versions of Skein are specified with 64-bit words. The word size can be seen as a tunable parameter; we can define a Skein variant with 32-bit words. This variant would run much faster on 32-bit CPUs, but significantly slower on 64-bit CPUs.

At this point, we have not searched for rotation or permutation constants for a 32-bit variant, nor have we analyzed it to determine how many rounds would be required for security. However, given the knowledge obtained from the 64-bit variants, this would not be complicated.
So, yeah, it would be possible to make a 32-bit version of Skein, but it hasn't been done yet.