From: futplex@pseudonym.com (Futplex)
Date: Wed, 13 Dec 1995 05:54:07 +0800
To: cypherpunks@toad.com (Cypherpunks Mailing List)
Subject: Re: The Elevator Problem
In-Reply-To: <9512111557.AA09207@envirolink.org>
Message-ID: <199512112229.RAA27787@thor.cs.umass.edu>
MIME-Version: 1.0
Content-Type: text/plain


Munster writes:
> Ok, here was the method of key generation i was talking about.  With the light 
> communications, the idea was to use photons whose waves pulsed in certain 
> directions (up/down, left/right, and diagonally) to create a way toommunicate 
> much like morse code.  

Right, this is the main quantum crypto idea of Brassard et al. (See for
example _Applied Crypto_ v.1 pp.408-410)

[...]
> but since the contents of the key were never 
> touched on DIRECTLY, no eavesdfropper could determine the key, 

No, the integrity of the system really depends upon the quantum properties
of light. Among other things, Heisenberg's Uncertainty Principle makes it
impossible for Eve to "eavesdrop" on the photons without affecting them
measurably.

[...]
> however, if one wwas to use the orientation symbols in ones 
> messages, as if they were being beamed, but in an email message instead, one 
> could make use of the simple key, and the simple game of '20 questions' to 
> generate a totally secure key 
[...]

In this situation Eve can read the email traffic without modifying it, so the
game is up.

-Futplex <futplex@pseudonym.com>