[104132] in Cypherpunks
Re: DESX
daemon@ATHENA.MIT.EDU (Dave Emery)
Sat Oct 10 22:05:19 1998
Date: Sat, 10 Oct 1998 21:51:51 -0400
From: Dave Emery <die@die.com>
To: Anonymous <nobody@replay.com>
Cc: cypherpunks@cyberpass.net
Mail-Followup-To: Anonymous <nobody@replay.com>, cypherpunks@cyberpass.net
In-Reply-To: <199810102206.AAA06060@replay.com>; from Anonymous on Sun, Oct 11, 1998 at 12:06:14AM +0200
Reply-To: Dave Emery <die@die.com>
On Sun, Oct 11, 1998 at 12:06:14AM +0200, Anonymous wrote:
> | So what's DESX?
>
> DESX is a modification of DES which uses a 64+56+64 bit key, with
> what is called "pre- and post-whitening". Specifically, break the key
> into three pieces, 64 bit K1, 56 bit K2, 64 bit K3. Then DESX is
> defined by:
>
> C = K1 xor DES (K2, K3 xor P)
>
> where P is plaintext, C is ciphertext, and DES (K, P) is the DES
> encryption of P under key K.
>
> The encryption then has three steps:
>
> - XOR the input with K3
> - DES encrypt that with K2
> - XOR the result with K1
>
> The first and last steps are called "whitening" because by xoring with
> a random value, any structure is destroyed. White light is a uniform
> and unstructured mixture of all colors.
>
Anybody have any estimate as to how much actual strength this
adds to DES ? How would one break it in a practical cracker machine ?
--
Dave Emery N1PRE, die@die.com DIE Consulting, Weston, Mass.
PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2 5D 27 BD B0 24 88 C3 18
