Re: Some questions on DES Encryption...

From: Jack Lloyd (lloyd@acm.jhu.edu)
Date: 03/10/03

  • Next message: DeMello, Christopher: "FW: Some questions on DES Encryption..."
    Date: Mon, 10 Mar 2003 13:53:29 -0500 (EST)
    From: Jack Lloyd <lloyd@acm.jhu.edu>
    To: Kryptik Logik <kryptiklogik@hushmail.com>
    
    

    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


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