From:	Robert Watkins <bob@**.NTU.EDU.AU>
Subject:	Re: Easy Unbreakable Encryption!
Date:	Thu, 22 Jun 1995 01:16:18 +0930

Stainless Steel Rat wrote:
> Robert> Except that there are probably about 10 million other phones in
> Robert> the city ALL on similar frequencies. More like a beacon in a
> Robert> floodlit area.
>
> Well, if it's impossible to single out your cellphone, then it must be
> impossible for you to make or receive calls, right? Wrong. The phone
> companies can receive your signals and distinguish it from the 9,999,999
> other cellphones out there just fine, thankyouverymuch. And if they can
> do it, so can I.
>
> All I need to find you is the frequency shift pattern used on your
> particular phone (takes a trivial run against the phone company's
> database to get that), two receivers keyed to that, and I'm on your
> tail.

Except for a couple of things... phones use several frequencies, changing
them as they move through cells, and they're only for the duration of the
call, even if you DON'T move into another cell. Every so often, they'll
broadcast a location if they're on, but they don't do that when they are in
use for talking. And finally, there'll be someone else, a few cells over,
who will be using the same frequency as you are...

So... move around (a typical cell is only a few blocks in size, in a city),
and only have the batteries in the phone when you are expecting a call.

Not to mention the range of the radio is sweet FA. Max range is only about
30 km, and in a city, they use a LOT less power (digital phones use just
enough for the receiver at the local cell to be able to hear it). So yeah,
go and track in on me like that... (The limit of 30km is due to the type
of frequency they use...)

If your game lets you hack codes out of the phone system, why not just
get it to relay the conversation to you, as well as the cell location? A
lot bloody simpler. (However, taking on Ma Bell in my game is NOT a good
thing to do...)

--
Robert Watkins bob@**.ntu.edu.au
Real Programmers never work 9 to 5. If any real programmers
are around at 9 am, it's because they were up all night.
*** Finger me for my geek code ***