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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: net.ham-radio
Subject: Re: Re: Re: Eavesdropping revisited [How's that again?]
Message-ID: <599@kitty.UUCP>
Date: Sun, 24-Nov-85 09:17:49 EST
Article-I.D.: kitty.599
Posted: Sun Nov 24 09:17:49 1985
Date-Received: Thu, 28-Nov-85 07:51:08 EST
References: <154@pyuxv.UUCP> <138@hydra.UUCP> <579@kitty.UUCP>
Distribution: net
Organization: Recognition Research Corp., Clarence, NY
Lines: 72

> >  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
> ...

	Digital speech encoding was not used in the cellular telephone concept
for reasons of practicability including, but not limited to:

1.	The cellular telephone design concept was considered to provide
	sufficient security to deter the casual listener using consumer-grade
	`scanners', antennas, etc.  No attempt was even considered to deter
	a `serious' listener who could spend many thousands of dollars for
	antenna towers, sophisticated receiving equipment, etc.  

2.	The cellular telephone concept was intended to be LOW cost and be
	capable of independent multi-vendor support.  Therefore, hardware had
	to be as simple as possible without employing any one vendor's
	proprietary technology.  While Motorola pretty much developed the
	cellular concept, they never did it from the standpoint of monopolizing
	the cellular market - such a monopoly never getting cellular telephones
	off the ground.  While Motorola has also pioneered digital speech
	encryption using CVSD modulation in their DVP radio systems, this was
	mostly proprietary technology which Motorola was hardly going to share
	with the world.

3.	Had a digital encryption circuit been used as part of the cellular
	concept, there is NO practicable way for such a circuit to be kept out
	of the public's hands.  There are at present at least 10 active vendors
	who manufacture cellular telephone apparatus, and no doubt there will
	be more.  Any `potential' vendor would have to be given encryption
	circuit details and be sold any integrated circuits designed for this
	purpose.

4.	Had a digital encryption scheme been used so that each cellular
	telephone had individual encryption keys, EACH receiving and trans-
	mitting site would have had to have a full database containing a
	unique cellular telephone identifier number and an encryption key.
	This same database would have to exist for hundreds and even thousands
	of sites - and be UPDATED.  THIS is probably the single most important
	reason why encryption is not practicable at this time using the present
	cellular concept.  (It would rather defeat the purpose of encryption
	if, say, the encryption key were transmitted in the clear prior to
	start of voice transmission, in case anyone thinks this is would
	eliminate a database requirement.)
	 
5.	Radio transmission is full-duplex, so that a monitor receiver would be
	able to hear only one side of the transmission. (Yes, I know one could
	use TWO monitor receivers, but how many people have that?)

6.	Mobile/portable transmit power is LOW, and the ~900 Mhz frequencies
	are extremely line-of-sight in their propagation, thereby limiting
	the receiving range of a casual eavesdropper to only a few miles under
	most circumstances.

7.	There are no identifier transmissions made between cellular telephones
	and base stations which would enable the casual listener - even if he
	could decode them - to learn the actual identity of the calling
	telephone.

8.	Cellular channel assignment for working communications is random.

===  Larry Lippman @ Recognition Research Corp., Clarence, New York        ===
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