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24 June 1998

To: cryptography@c2.net
Subject: Matt Blaze: difference distribution table for Skipjack
Date: Wed, 24 Jun 1998 20:18:17 -0400
From: "Perry E. Metzger" <perry@piermont.com>

I thought this would be of interest to those examining the algorithm.

To: coderpunks@toad.com
Subject: difference distribution table for Skipjack
Date: Wed, 24 Jun 1998 19:54:23 -0400
From: Matt Blaze <mab@research.att.com>

I've generated the 256x256 difference distribution table for
the Skipjack F function.  This table gives the number of
times each possible output XOR differential occurs for each possible
input differential.  It is in the format of Appendix B of
Biham and Shamir's DES book, and is a simple ASCII table.

The table is BIG (65536 entries - 200K bytes).  You can ftp it from:

  <ftp://ftp.research.att.com/dist/mab/sj.dist>

There are a few surprising spikes in the table, but they probably
disappear after a few rounds.  I haven't done anything beyond
generating the table yet.

(If you don't know what a difference distribution table is
good for, you won't be able to make much use of this one
until you understand differential cryptanalysis at the
level of Biham and Shamir's book).

-matt