Re: Some questions on DES Encryption...

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 cryptography@wasabisystems.com, the general sanity level is much higher there than in cypherpunks or sci.crypt.

-Jack Received on Mon Mar 10 14:40:15 2003