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From: ee5391aa@hydra.unm.edu (Duke McMullan n5gax)
Newsgroups: misc.consumers,misc.misc,sci.misc,sci.electronics
Subject: Re: Telephone privacy gadgets
Summary: A fool and his money....
Keywords: Telephone, wiretap, bug, countermeasures, etc.
Message-ID: <776@ariel.unm.edu>
Date: 17 Oct 89 11:53:06 GMT
References: <799@mccall.uucp>
Sender: news@ariel.unm.edu
Reply-To: ee5391aa@hydra.unm.edu.UUCP (Duke McMullan n5gax)
Organization: University of New Mexico, Albuquerque, NM
Lines: 93

In article <799@mccall.uucp> tp@mccall.uucp (Terry Poot) writes:
>There are gadgets one can put on a telephone that purport to tell you if
>the conversation is being recorded. Does anyone know if they work?

The answer is an absolutely definite maybe, with an appended probably not.

First, "being recorded": There are ways -- of varying reliability -- to tell
if your line has been tapped, but it'll require something on the order of
deitic omniscience to tell you what's being done with that signal. Still, it's
very likely that if you're tapped, you're being recorded.

ECM -- governmentese for "electronic countermeasures" -- that apply to a tele-
phone system fall into three categories: Prevention, detection and correction.

Prevention (as usual) is the best, but what you asked about is detection. You
can buy from various sources instruments purported to tell you if your line has
an unauthorized tap on it. Do they work?

Usually not.

The methods vary. You can measure line impedance, which will detect low budget/
unsophisticated taps, you can listen for noise on the line, which is useless,
or you can use TDM.

That's technicalese for Time Domain Reflectometry. The idea is that you send a
sharp pulse signal down the line, and watch carefully (i.e., with an expensive
instrument) for reflections of the pulse which occur at every sufficiently
abrupt impedance change in the line (i.e., at a tap). The TDM system also
detects other telephones, connections to the service block, extension line
connections, staples which penetrate the insulation, sharp kinks in the wire,
etc. The TDM "signature" of the line is a pretty complex signal. This means
that you must have the signature of a "clean" line, and compare this with your
signatures as time goes on. When you spot a change, look into it.

Is that reliable? Well...sort of. I've heard that you can tell from the
location of a new blip in the signature where on the line the new impedance
lump is located (which squares with my [sketchy] knowledge of TDM), but two
other sources say that's a lot of bushwah in practice. It seems that you end
up doing a physical inspection of the entire line anyway, which can be done
without coughing up kilobucks for the TDM instrumentation and technician.

For an authorized tap (done by the TelCo), forget detection. It's done at the
central office (entirely in software, I'm told) and there exists no reasonable
detection method from your end of the line.

We should note that TDM methods usually involve breaking the line connection
at the service entrance and terminating the block with the line's
characteristic impedance, so you're not connected to TelCo when you do that
test. That means that it isn't likely to tell you anything useful about a tap
that's farther down the line than the telephone pole. Getting the signature of
the connected line 1) may cause trouble with the TelCo circuitry and 2) changes
anytime the TelCo techs do some line service, anythime the wind blows hard,
and usually changes a bit when it rains.

This applies to most detection methods: A simple bug is fairly easy to detect;
a sophisticated one very difficult. The measures have a way of staying a step
or two ahead of the countermeasures.

Additionally, there's the cost factor. As expensive as GOOD bugging equipment
is, the corresponding ECM stuff is a lot more expensive. Additionally, if I
decided to tap your line, I don't waste money picking out lines at random: I
just install the tap, sit back, listen, record, and prepare my blackmail
info.

On the other hand, you are in a worse position. Have I in fact bugged your
line? You do a fairly simple (inexpensive) check. Nothing. Was your line
bugged, or was it done in a way that you failed to detect? You spend more
money and time. Still nothing, but you're still worried. Lotsa money later,
you discover a fairly sophisticated radio transmitter, which you remove.
There are no fingerprints, or anything else conclusive with which you can
nail me. Still, everything's OK now, right?

Right? Well...was that the only bug there? Was it placed for you to find, with
another bug (which you haven't detected) backing it up? Did I place another
bug after you found this one? Am I, in fact, the one who put it there?

As you see, this sort of thing can lead directly to recursive paranoia. The
bugger has advantage; the buggee the disadvantage.

The only real safety is the preventative one: don't say anything on the
telephone that you wish to remain private!

Here's the best advice I've heard: If you're going to spend money on 'phone
security, you're better off buying expertise than equipment.

					Pay your 'phone bill,
						    d



          "In all levels of life, the sheep are only safe
                  when the wolves are not hungry." -- F.J. Lovret
     Duke McMullan n5gax nss13429r phon505-255-4642 ee5391aa@hydra.unm.edu