From: Matthew J Ghio <mg5n+@andrew.cmu.edu>
Date: Thu, 14 Oct 93 10:06:57 PDT
To: doug@netcom.com (Doug Merritt)
Subject: Re: Spread-spectrum net (vulnerability of)
In-Reply-To: <9310140244.AA04580@netcom2.netcom.com>
Message-ID: <AgjMNry00awLA=V1Vw@andrew.cmu.edu>
MIME-Version: 1.0
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Matthew J Ghio <mg5n+@andrew.cmu.edu> said:
>Switching frequencies rapidly to prevent triangulation is still the best
>defense.

Doug Merritt <doug@netcom.com> wrote in reply:
>Think from the point of view of the spotters. They can look at a
>broad-spectrum scan, gradually eliminate known sources, and end up
>homing in on the remaining high power signals.

This is similar to the discussion of breaking advanced cryptographic
techniques, comparing possibility to practicality.  Sure anything is
possible, given enuff resources.  But the question is weather or not its
feasible for them to try to track it down.  If it takes them a month and
costs them $10000 in equipment and salaries to track down one
transmitter, then they haven't really accomplished much.

I would say frequency switching would be better than a continuous signal
spread across many frequencies.  Here's why: Once you've locked onto a
signal and try to triangulate, it's gone.  After one transmitter has
swithced off a certain frequency, another transmitter can use it. 
Multiple broadcast sources on a frequency give confusing readings which
makes locating them difficult.  Finally, why would the FCC or equivilent
be trying to shut down such a network?  Someone would have to complain
first.  And why would someone complain?  They would only complain if the
broadcast was interfering with their transmissions.  This can be solved
easily.  While data was not being received, have the receivers monitor
noise levels on various frequencies, and select only those not being
used for transmission.  This could be implemented without additional
hardware, as we will already have an onboard computer for routing data,
this would simly make use of idle time.  (BTW many cordless phones
already do this.)