Re: Matrix-Multiplication: Security?

From: Peter Pearson (ppearson_at_nowhere.invalid)
Date: 05/27/05

  • Next message: Unruh: "Re: CIA Sculpture Draws Code Breakers" 
    Date: Fri, 27 May 2005 14:49:46 -0700

    Anton wrote:

    >> Sorry Anton! Matrix operations are linear algebra. "Linear" means "weak"
    >> in cryptography. Good crypto must always be non-linear.
    >
    > Ok, may you give me some further information about how "secure" my
    > programm is compared with non-linear systems?
    > How can I calculate the security of an algorithm?

    The security of an encryption algorithm is typically described
    in terms of
     - the "ground rules" of the attack; e.g.,
         - ciphertext only (not assumed in serious work)
         - known plaintext
         - chosen plaintext
     - the amount of data (e.g., plaintext-ciphertext pairs)
       required for the attack, and
     - the number of computational steps (yeah, vague) required
       to perform the attack.
    The "number of bits of security" typically refers to the
    base-2 log of the number of computational steps required
    to break the cipher, since a convenient reference point
    is the number of guesses that it would take to search
    exhaustively for the key, and the key is typically a
    string of binary bits of known length. Thus, if exhaustive
    search of the keyspace is the best known attack, the length
    of the key equals the "number of bits of security." Since
    you're never sure there isn't a better attack that you just
    haven't thought of, this security measure is typically only
    a guess.

    In the case of a linear algorithm, one expects that an amount
    of known plaintext equal to the key length, and the corresponding
    ciphertext, would suffice to break the cipher, and that the
    computation would consist primarily of inverting some matrix. 

    -- 
Peter Pearson
To get my email address, substitute:
nowhere -> spamcop, invalid -> net
  • Next message: Unruh: "Re: CIA Sculpture Draws Code Breakers"

    Relevant Pages

    • Re: Enigma machine strenght using a computer
      ... cipher with rotors that spin backwards, forwards, stop and start based ... Is this a good way to get security on modern ... encryption less error-prone and they were a cost effective way to get ... case) than not since a wider base uses the same algorithm. ...
      (sci.crypt)
    • Re: Enigma machine strenght using a computer
      ... cipher with rotors that spin backwards, forwards, stop and start based ... Is this a good way to get security on modern ... encryption less error-prone and they were a cost effective way to get ... case) than not since a wider base uses the same algorithm. ...
      (sci.crypt)
    • Re: Enigma machine strenght using a computer
      ... cipher with rotors that spin backwards, forwards, stop and start based ... Is this a good way to get security on modern ... encryption less error-prone and they were a cost effective way to get ... I personally think this is a silly requirement, no one algorithm can be ...
      (sci.crypt)
    • Re: Enigma machine strenght using a computer
      ... cipher with rotors that spin backwards, forwards, stop and start based ... on other rotors, change their values according to the phase of the moon ... Is this a good way to get security on modern ... I personally think this is a silly requirement, no one algorithm can be ...
      (sci.crypt)
    • Re: My little something...
      ... encryption time is not a negligible cost. ... most unlikely attack is not a good use of your time, and may, as always, give ... a false sense of security. ... MITM attack would only be possible if I used SAME CIPHER twice. ...
      (sci.crypt)