From: frantz@netcom.com (Bill Frantz)
Date: Mon, 19 Feb 1996 12:49:59 +0800
To: acg@mandrake.cen.ufl.edu (Alexandra Griffin)
Subject: Re:
Message-ID: <199602190417.UAA23975@netcom7.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain


At  8:13 PM 2/18/96 -0500, Dave Emery wrote:
>> 
>> Bob writes:
>> 
>> > Does anyone know if the new in-line optical amplifiers (not switches!) have
>> > any effect on quantum crypto messages?
>
>  Optical
>> repeaters have to pass your signal through an intermediate electronic
>> stage anyway, since we have no purely optical valve/transistor
>> equivalents (bosons don't interact with each other at all).
>
>        This is not true.   There is now a whole technology of optical
>amplifiers for fiber communications systems that used Ettrium doped
>fibers pumped with strong light from a laser at a slightly shorter
>wavelength. These fiber optical amplifiers have gains in the order of
>10-12 db in a section of special doped fiber only about 10 feet long.

I don't think that it matters whether you convert to electronics or amplify
with laser techniques.  The cryptographic secret is kept in the quantum
uncertainity of the state of the (single) photon.  Anything that collapses
that quantum uncertainity acts as a man-in-the-middle and stops the key/OTP
generation.


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