From: willis@iris.rand.org (Willis H. Ware)
Newsgroups: comp.society.privacy
Subject: Re: Computer Privacy Digest V1#065
Date: 24 Jul 92 23:48:16 GMT
Organization: Computer Privacy Digest
X-Submissions-To: comp-privacy@pica.army.mil
X-Administrivia-To: comp-privacy-request@pica.army.mil
X-Computer-Privacy-Digest: Volume 1, Issue 066, Message 4 of 6

--

RE cellular phones and interception thereof.

Leonard Erickson <leonard@qiclab.scn.rain.com> indeed had it right.  There
is a special law covering only cellular phones that makes the mere act of
intercepting them illegal; these phones are treated separately than
interception of other radio signals under the Communications Act of 1934.
Thus if one had a cellular in his car connected to a cordless which he
used outside his car to link to it, the cordless link from handset to car
comes under the Communications Act of 1934 but the cellular link from car
to system comes under the special law.  One could scanner-intercept the
cordless link but not the cellular link!!

Moreover, I believe I'm correct in saying that it is also illegal to
market a product [e.g., scanner] that can intercept the cellular
frequencies.  That reduces the number of people who can do it, if one
choses to ignore the law, from our 250M population to the subset of 25-40M
who are electronically astute enough of doing it on their own with parts
from radio shops.  I guess that's what's called risk reduction?

Hope is coming but slowly.  A new generation of cellular phones is being
proposed that will use other forms of modulation.  One proposes spread
spectrum modulation; the transmitted signal, instead of staying on one
frequency and being modulated to convey intelligence, hopes at a high rate
from frequency to frequency, staying on any one only for microseconds or
perhaps milliseconds at a time.  The transmitter and receiver must
synchronize with each other, and then step around together.  The receiver
can then reassemble the signal.

The intelligence is not in the rate or sequence of hopping but still in a
modulated signal that moves around, or in digitized voice that is moved
around on a carrier.  That will make interception much more difficult
because conventional receivers will not handle such signals.  Since the
signal energy is splattered all over a wide band, conventional receivers
usually won't even detect the presence of a spread-spectrum signal.
It takes very special ones that would not normally be a consumer
electronics item, but of course is well within the capability of the
electronic engineer.

My understanding is that at least two proposals exist, and differ on
the details of how the signal is jumped around.  There is also a
proposal to digitize the signal and use so-called time-division
multiplexing which is the scheme used on teleco T-1 and faster lines.
Again a special receiver which can synchronize to the transmitter or to a
stable clock is necessary.

I'm told that Motorola is talking about, may already have introduced
encrypted cellular fones using some proprietary encryption algorithm.
Cellulars and regular handsets with the Federal DES algorithm in them
already exist but restrictions on use and export of Federally approved
encryption makes them less attractive.

And of course, all parties that wish to talk securely must have secure
phones; it is not a system-level service but rather a subscriber-provided
end-to-end individual service.  The signal stays encrypted from your
handset to mine.

						Willis Ware
						Santa Monica, CA