[66994] in Cypherpunks
Re: the key of DES
daemon@ATHENA.MIT.EDU (I~nigo Gonzalez)
Tue Oct 1 18:28:04 1996
Date: Tue, 01 Oct 1996 23:35:37 +0200
From: "I~nigo Gonzalez" <nexus@adv.es>
To: Kim Yoonjeong <yjkim@ssrnet.snu.ac.kr>
Cc: cypherpunks@toad.com
Kim Yoonjeong wrote:
>=20
> Hello, all !
> With given a unknown DES system with 64 bits plaintext p, ciphertext c,
> can there be MORE THAN ONE keys ?
I don't think so:
I you look closely to 1-Round DES, you can have this case:
Let p=3DLR (plaintext) and K=3Dkey (without parity check)
When computing f(R,k) in 1-Round DES I can have the same
input (and output) in the S-Boxes with:=20
=20
p=3DLR, with k ; and p=3DL(R'), with k'
(k' denotes 1-complement of k)
You have _two_ different (plaintext,key) pairs with
the same input using f(R,k) and f(R',k').
>From this, you can prove that:
if y=3DDES(p,k) then y'=3DDES(p',k')
wich is what everyone really wants: a beautiful chance of using
a trapdoor in DES.
Did you like it? - Don't use DES: It's not reliable.
--
I=F1igo Gonz=E1lez - ADV Internet Technical Advisor <nexus@adv.es>
"Never say anything online that you wouldn't want to see on the
front page of The New York Times." - alt.2600.moderated Posting
