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The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:16:52 ADT
Jim Gillogly (jim@mentat.com)
Mon, 6 Apr 98 11:35:55 PDT
Peter Wayner asks:
> ... The
> whole process works by the kid staring intently at a block of
> text that, for the sake of argument, is as impenetrable as a hex
> dump. ...
The phenomenon of "cipher brains" is well-documented, although of
course it doesn't work on serious ciphers. Top cryppies can see
patterns in stuff that looks random to the hoi polloi.
> Here's my question: For what crypto systems is this impossible
> to do without a copy of the key? We know that a one-time pad can
> yield any message given the right key. So the kid couldn't pull
> the right message out of thin air. But how likely is it that two
> plausible messages will be emerge from the same DES encrypted
> message.
Depends on the plaintext and the length of the message. For English
and a message of more than 30 characters or so, it's very unlikely
that it can be done with any DES-like cipher. If the plaintext
looks random, then of course any decryption becomes plausible.
To get a feeling for the difficulty, try to construct a sensible
sentence that can be transformed into an equally sensible one using
simple substitution on the letters. Getting a long one is hard.
Jim Gillogly
The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:16:52 ADT