[202] in Cypherpunks
tripple des
daemon@ATHENA.MIT.EDU (Timothy Newsham)
Tue May 4 16:55:36 1993
From: Timothy Newsham <newsham@wiliki.eng.hawaii.edu>
To: cypherpunks@toad.com
Date: Tue, 4 May 1993 10:14:30 -1000 (HST)
Crypto question:
why was the following chosen for tripple DES :
EN(DE(EN(data,k1),k2),k3);
The encryption would involve passing data through IP,
then doing 16 rounds forward with k1,
(factoring out the IP-1 and IP)
then doing 16 rounds backwards with k2
(factoring out the next IP-1 and IP)
then doing 16 rounds forward with k3
then going through IP-1
How would this compare with
EN(EN(EN(data,k1),k2),k3);
which goes through IP, does 16 rounds each with k1, k2 then
k3, then IP-1 ?
The only difference is that the key scheduler rotates backwards
(or another interpretation keys used in reverse order) for the
second stage.
Does anyone know the rationale behind this?
