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Re: What can an attacker see in an encrypted message?

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On 2015-10-05, Anonymous Remailer (austria) <mixmaster@remailer.privacy.at> wrote:
>
> After seeing all of the cryptanalysis on the ng recently it occurs 
> to me to ask, just how much can an attacker figure out from a 
> ciphertext? What if he or she has some of the passphrase? Here I'm 
> talking about a ciphertext created using one of the algorithms 
> available in gpg.

AFAIK the answer is no. Ie, knowedge of part of the key does not
decrypt part of the answer (The "sequential cracking" one sees in movies
does not work). Otherwise cracking would be really easy. It would scale
essentially like the length of the key rather than like exponential in
the length of the key.

>
> Let's say, purely for example, that the passphrase is the ever 
> powerful "qwertyuiop" that's been brought up here.
>
> If the attacker has figured out that "qwer" is a part of the 
> passphrase can that attacker read any of the ciphertext? If so, how 
> much? Does that knowledge of some of the passphrase allow the 
> attacker to figure out the rest of it?

It makes bute force that much easier. Firstly they would try the ture
passphrase, since it would seem be part of the pattern. But even if they
had to try every letter of the rest of the phrase, it would shorten the
search from 26^10 to 26^6 assuming they knew the phrase was only lower
case letters from a-z. Of not, it is 256^10 to 256^8

>
> And, pretty much on this same subject, could an attacker tell what 
> kind of data is encrypted in a file? Can they tell if it's a binary 
> or a plaintext file that's encrypted?
>
> Can they tell much about the contents of the ciphertext at all 
> without having part of the passphrase, or a part of the session key?
>
> Could the attacker figure out a frequency of characters, or tell 
> that some particular characters are used in a ciphertext without 
> having the passphrase or session key?
>
> Would a nation state attacker be able to figure out much from a 
> ciphertext created using one of the algorithms available in gpg?
>
> Paranoid in Palookaville
>

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Thread

What can an attacker see in an encrypted message? "Anonymous Remailer (austria)" <mixmaster@remailer.privacy.at> - 2015-10-05 14:02 +0200
  Re: What can an attacker see in an encrypted message? Richard Heathfield <rjh@cpax.org.uk> - 2015-10-05 13:39 +0100
  Re: What can an attacker see in an encrypted message? Paulo Marques <pmarques@grupopie.com> - 2015-10-05 14:19 +0100
  Re: What can an attacker see in an encrypted message? William Unruh <unruh@invalid.ca> - 2015-10-05 20:46 +0000
  Re: What can an attacker see in an encrypted message? Robert Wessel <robertwessel2@yahoo.com> - 2015-10-05 22:39 -0500
    Re: What can an attacker see in an encrypted message? Jakob Bohm <jb-usenet@wisemo.com> - 2015-10-06 08:01 +0200
      Re: What can an attacker see in an encrypted message? PA7PTL <PA7PTL@panteltje.com> - 2015-10-06 07:07 +0000
        Re: What can an attacker see in an encrypted message? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-06 11:22 +0100
          Re: What can an attacker see in an encrypted message? eugene.styer@gmail.com - 2015-10-06 08:48 -0700
    Re: What can an attacker see in an encrypted message? Richard Heathfield <rjh@cpax.org.uk> - 2015-10-06 10:15 +0100
  Re: What can an attacker see in an encrypted message? Jeffrey Goldberg <nobody@goldmark.org> - 2015-10-06 11:22 -0500
    Re: What can an attacker see in an encrypted message? Jakob Bohm <jb-usenet@wisemo.com> - 2015-10-06 20:12 +0200
      Re: What can an attacker see in an encrypted message? Jeffrey Goldberg <nobody@goldmark.org> - 2015-10-07 19:21 -0500
        Re: What can an attacker see in an encrypted message? Richard Heathfield <rjh@cpax.org.uk> - 2015-10-08 06:33 +0100
          Re: What can an attacker see in an encrypted message? Jeffrey Goldberg <nobody@goldmark.org> - 2015-10-08 22:21 -0500
            Re: What can an attacker see in an encrypted message? Richard Heathfield <rjh@cpax.org.uk> - 2015-10-09 07:34 +0100
  Re: What can an attacker see in an encrypted message? Anonymous <anonymous@foto.nl1.torservers.net> - 2015-10-07 09:20 -0400

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