From: wcs@anchor.ho.att.com
Date: Thu, 3 Jun 93 08:57:59 PDT
To: cypherpunks@toad.com
Subject: Re:  Crypto anarchy in a VW? (not the bug)
Message-ID: <9306031432.AA23113@anchor.ho.att.com>
MIME-Version: 1.0
Content-Type: text


> >There are a lot of ways to get a signal around the world without using a 
> >satellite, ask any amateur radio enthusiast.  
I thought the motivation for satellite at the beginning of this discussion
was that it's extremely hard to find out WHO sent a transmission
to a satellite - everybody's got a dish pointed UP at the same destination,
the FCC isn't likely to go flying helicopters around to locate transmissions
that could have come from anywhere in the country, and there's really
nothing to direction-find on, and the receivers can similarly be anywhere,
since it's a broadcast network.  If the satellite uses some kind of protocol
such as AlohaNet, you get reasonable shared utilization.
(Of course, the alternatives to direction-finding are to go after the bird's
owners, or to jam the transmission channel.)  Moon-bounce offers similar
advantages, and there aren't any owners to trace :-), though jamming is
still possible.

Another technique that's pretty obscure, and relatively low data rate,
but pretty hard to trace, is meteor-burst, which reflects signals of the
ionization trails left by micrometeors.  Typical systems a few years ago
transmitted at 4800 baud, getting effective throughput of maybe 300 bps,
since the channel isn't constant.  It was used for applications like
sending snow depth reports back from mountains, since it needs very little
power and isn't particularly bothered by weather conditions.

Are networks like amateur packet radio hard to trace, assuming enough
repeaters are around?

> One of the really great techniques I've hear about recently is a data
> channel that runs at 90% T1 speed over the ~900 MHz spread spectrum

NCR WaveLAN, which is now also being OEMed by DEC, runs spread spectrum
at (I think) 2 Mbps, and can use an optional DES chip for encryption.
The PC cards are compatible with some vanilla Ethernet card,
so it uses standard Ethernet protocols.  In broadcast mode, range is only
a few hundred meters, depending on building configurations, but
it can also be used with a directional antenna to get 5-6 mile range.

			Bill Stewart