New cipher used by iTunes

[Charles M. Hannum]

I took a look at the new cipher used in iTunes 4.7, and spent some time 
reducing it.  The algorithm appears to have a similar structure to a 10-round 
Twofish variant with fixed S-boxes, optimized via precomputed tables.  I have 
not fully analyzed what the permutation matrix and polynomial are, though.

There are a couple of strange changes.  E.g., they had put the IV mixing 
between the pre-whitening and post-whitening, but this turned out to 
effectively cancel out and be equivalent to an altered version with a more 
traditional CBC structure.

I'm including the current working implementation, along with some test 
vectors, if anyone else wants to take a look at it.

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