Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site hydra.UUCP
Path: utzoo!linus!philabs!cmcl2!harvard!think!mit-eddie!cybvax0!frog!hydra!die
From: die@hydra.UUCP (Dave Emery)
Newsgroups: net.ham-radio
Subject: Re: Eavesdropping revisited [How's that again?]
Message-ID: <138@hydra.UUCP>
Date: Thu, 31-Oct-85 01:05:11 EST
Article-I.D.: hydra.138
Posted: Thu Oct 31 01:05:11 1985
Date-Received: Sun, 3-Nov-85 08:01:20 EST
References: <154@pyuxv.UUCP>
Reply-To: die@hydra.UUCP (David I. Emery)
Followup-To: !decvax!frog!die
Distribution: net
Organization: Charles River Data Systems, Framingham MA
Lines: 69
Keywords: encryption shortsightedness
Summary:  Why wasn't encryption used in cellular standard  

In article <154@pyuxv.UUCP> craig@pyuxv.UUCP writes:
>  Congress has a measure under consideration that would
>strengthen such privacy law requirements extending protection to
>cellular and cordless telephones.  Markup is expected, for both the
>House and Senate versions of the bill, by early next year.  There is a
>possibility of enactment by the end of 1986.

	I have always wondered why the cellular radio standard didn't
include digital transmission under (optional?) encryption.  Digital
transmission would make cellular signals difficult to intercept with
scanners or even TV sets, and the hardware required - much like a descrambler
for a broadcast tv signal - would be specialized enough so random members
of the general public couldn't legally acquire it on the pretext of
using it for some legitmate purpose (unlike TVRO's and SSB receivers !!).
For a few dollars more the system could supply DES with reasonable
key security that would make the cellular link at least as private
as the rest of the telephone system.

	The current transmission method for cellular phones is FM, and
the channel spacing is such that there would be plenty of room for
a 16 or 32 khz QPSK (or even diphase) adaptive slope (ADPCM) or
CSVD transmission of high quality voice. As for performance, I have read some
claims that clever demodulators can do as well demodulating digital voice
signals near threshold as nbFM.  

	It seems a shame that the designers of a system as sophisticated
as the cellular phone system chose not to consider the security issue
seriously.  I beleive that most of the design work was done in the
late 70's when DES chips and LSI PCM chips were at least beginning to
appear on the market, certainly any far sighted system architect could
have confidently predicted that the required digital hardware would
soon be available and eventually be quite cheap.   My guess is that low
cost in the short term and reduced technological risk dominated their
thinking.  Perhaps someone on the net can shed some light on why the
current fm based system was chosen.

	The real tragedy is that the proliferation of the current generation
of FM based hardware will make it very difficult to convert the whole system
over to digital.  Perhaps the present transmission sites can be equiped with
dual mode radios that would allow subscribers to use digital transmission
as an option and thus allow those who understand the risk and want to
protect their privacy to enjoy the conveniance and flexibility of roaming
cellular phones with a modicum of privacy too. I should think that there might
be quite a market for such a higher privacy (and price no doubt) service
as people begin to discover that 900 mhz scanners (and some tv sets as Bob
Parnass points out) can pick up their fm conversations clearly.

	Unfortunately, though the NSA has been very active in trying
to raise consciousness about security, the more political FCC has yet
to authorize secure digital transmission over the current 900 mhz cellular
phone frequencies.   One would think that the government would get
its act together and lead on the issue for once  by requiring
that all cellular systems be equiped with dual mode capability by some
future date.

	The cost of digital base station transcievers at cell sites and of the
required microprocessor systems for key management would be a reasonably
small addition to the cost of all the required hardware at cell sites.
I suspect that by charging more for a secure service the costs could be
recovered (I might add that the systems in the Boston area use microwave
links to tie the cells together and those ought to be secured too...). And
the digital hardware for mobiles could be implemented in a small number of
VLSI chips that ought not to add excessive cost, power consumption or weight
to these high tech transceivers.

          David I. Emery    Charles River Data Systems   617-626-1102
          983 Concord St., Framingham, MA 01701.
	  uucp: decvax!frog!die