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The quick proof of why the initial and final permutations add nothing to the security of DES is presented in an informal and quite obvious sidebar.

Actually, I found the proof not completely convincing. It's really a proof that it doesn't strengthen the DES against a *known plaintext* attack, but there are other weaker attacks it may make marginally more difficult (or easier..); for instance, partially-known plaintext or some forms of verifiable plaintext.

I'm afraid I'm not quite following you here, could you expound a bit? Ah:) Isn't it great to be talking about encryptions again?:) Patrick _______________________________________________________________________ / These opinions are mine, and not Verity's (except by coincidence;). \ | (\ | | Patrick J. Horgan Verity Inc. \\ Have | | patrick@verity.com 1550 Plymouth Street \\ _ Sword | | Phone : (415)960-7600 Mountain View \\/ Will | | FAX : (415)960-7750 California 94303 _/\\ Travel | \___________________________________________________________\)__________/