Re: Cracking decrypted file when knowing partial contents

briggs_at_encompasserve.org
Date: 04/20/04 

Date: 20 Apr 2004 14:55:44 -0600

In article <40856D3D.9040605@end.universe>, Ford Prefect <restaurant@end.universe> writes:
> Adfa wrote:
>> Would it be easier to crack an encrypted file if the cracker knew some of
>> the contents of the file?
>>
>> For example, an encrypted MS Word file where the cracker knew word-for-word
>> a few paragraphs of the document, but not necessarily the exact byte
>> postions of those paragraphs in the file.
>
> Well, DUH! Of course it would make it easier to crack if you know
> part of the clear text...
>
> ...how clueless does one have to be to even ask such as question?

More clueful than you, apparently. You got the answer wrong.

Modern ciphers are designed to be strong not only against known
ciphertext and known plaintext attacks but against chosen plaintext
and adaptive chosen plaintext as well.

If you're going to fall to a known plaintext attack, you don't even
belong in the game.

What you could say is that it _might_ be easier to crack an encrypted
message if one knows some plaintext and if the encryption is weak.

        John Briggs

Relevant Pages

  • Re: Cracking decrypted file when knowing partial contents
    ... Of course it would make it easier to crack if you know ... ciphertext and known plaintext attacks but against chosen plaintext ... message if one knows some plaintext and if the encryption is weak. ...
    (sci.crypt)
  • Re: Chosen attacks
    ... >ciphertext attack. ... Clearly if you know the plaintext then you know if you have the right key. ... Note that a stream cypher reused is totally open to chosen plaintext ... you know the encryption and if that same ...
    (sci.crypt)
  • Indistinguishability and integrity in symmetric encryption
    ... "The 'right' security property for general-purpose symmetric encryption". ... >symmetric encryption scheme (for which the empty plaintext is not ... A has interfaces to an encryption oracle ... It is assumed that the ciphertext returned by A is different to all those ...
    (sci.crypt)
  • Re: NEWBIE QUESTION: Key space exhaustion - How do I know when Im there?
    ... key exhaustion is the only option, ... looking at the result of a block decryption, then by all means you have ... found a big fat weakness in the encryption system. ... E.g. the resulting plaintext "makes sense" ...
    (sci.crypt)
  • RE: Encrypted Communications and Predictable Communications?
    ... There are more sophisticated attacks which might use known plaintext ... consider a database system, with a client application on one machine and a database server on another. ... How much does the predictability of such message exchanges ... Should the encryption system take steps to ensure that the encrypted data contains random information to pad out messages to at least the minimum ...
    (SecProg)