Re: Some questions on DES Encryption...
From: Jack Lloyd (firstname.lastname@example.org)
Date: Mon, 10 Mar 2003 13:53:29 -0500 (EST) From: Jack Lloyd <email@example.com> To: Kryptik Logik <firstname.lastname@example.org>
On 8 Mar 2003, Kryptik Logik wrote:
> 1. In DES algorithm, given an encrypted text and the corresponding plain
> text for that is it possible to retrieve the key. Essentially, how secure
> is DES to known-plain text attack.
1 plaintext + 1 matching ciphertext + 2^55 work -> key
> I read some where that it is quite resistant requiring 2^55 plain texts
> to get the key but why is this so? What particular feature of the
> algorithm makes it this way?
I think you're thinking of linear or differential cryptanalysis here. These
are attacks which make use of a lot of data to analyze patterns in the
text. They are not particularly practical, as 2^55 blocks = 256 petabytes.
I think it's highly unlikely that you'll be encrypting that much data with
DES anytime soon.
In any case, I don't think secprog@ is the right place for questions like
this. Try email@example.com, the general sanity level is much
higher there than in cypherpunks or sci.crypt.