RE: 2 interesting projects...

[Gene_Gaunt/ReviewWorks@xxxxxxxxxxxxxxx]

You can download Twofish "C" source from:

http://www.counterpane.com/twofish.html

Set a compile-time flag to create big-endian byte swaps for AS/400.
However, that "C" version is slow and pedagogical.  It's fundamentally
different from the faster MI implementation from News/400 because:

The design of the Twofish round function and key schedule permits
a wide variety of tradeoffs between speed, software size, key setup
time, gate count, and memory.  That's an important advantage in the
AES competition.  Twofish uses a Maximum Distance Separable
(MDS) matrix multiplication from key material and from fixed S-boxes.
The "C" version calculates all of the multiplicands on-the-fly, while the
News/400 version pre-calculates the outer layer of multiplicands from
fixed S-boxes using REXX do-loops, and stores them in a 4096-byte
MI variable initialization.  (You can see this monster hex variable in the
QPRCRTPG API spooled file output after the REXX runs.)

Even faster implementations of Twofish can be achieved by pre-
computing the inner layer of MDS matrix multiplicands for specific keys,
and then storing them in OS/400 objects. I choose not to follow that route
because it would require a secure key management system for Twofish
on AS/400, and that's a different issue that doesn't interest me now.

By the way, if you order the Twofish book (John Wiley & Sons) through
the Twofish web site you can get a 20% discount off the Border's price.
(I bought my copy from Border's.)

As for PGP on AS/400, I'd love to see the code that cooks up huge prime
numbers for the Rivest-Shamir-Adleman public keys.  No matter if it's "C"
or MI, I'll bet the prime number cook-up is slow.


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