From: fc@all.net (Dr. Frederick B. Cohen)
Date: Wed, 11 Oct 95 11:12:45 PDT
To: jim@acm.org
Subject: Re: Elementrix POTP
In-Reply-To: <199510111708.KAA09582@mycroft.rand.org>
Message-ID: <9510111810.AA21080@all.net>
MIME-Version: 1.0
Content-Type: text


> > Sorry to continue "beating a dead horse" here, but I forwarded a few
> > C-punks' messages regarding the Elementrix "Power One-Time Pad" to
> > this person, and I thought you might be interested in her (somewhat
> > cryptic <g>) response.
...

> Except for one thing, i.e. this line from the last blather:
> 
> >The encryption is not done by using an encryption algorithm.
> 
> 'Nuff said for now, I think.

Not quite enough for my taste.  If this system can be uniquely initiated
by a finite sequence of bits transferred between the two parties and can
be used to encrypt more than that many bits, it is not a one-time-pad -
period - full stop.

By definition, the information content of a one-time-pad is one bit per
bit of transmitted information.  If a finite number of bits is enough to
initialize this system, then by definition, it ceases to be a
one-time-pad as soon as one more than that many bits have been
transmitted using those bits as the initialization key.  This is a
direct result of information theory, and cannot be circumvented by any
amount of wizardry or genius.

Even if you found that information theory is palpably inconsistent, the
definition of a one-time-pad (as defined by Shannon in his second most
famous 1949 paper) is in terms of information theory, and therefore, the
end of the theory is also the end of the definition of a one-time-pad.

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