Electronic Espionage Detection and Prevention
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Electronic Espionage Detection and Prevention |
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Telephone Testing Equipment
Detection of telephone taps, too, is a complex process, perhaps even more so than the radio transmitter detection activities described on the radio transmitter detection equipment page. Telephone testing can be broken into two regions or areas:
TSCM Technical Services uses a variety of testing devices to assure that telephones are free of wiretaps and other eavesdropping modifications.
The ETA-3A is also used as an interface for other types of test equipment the can be connected to the telephone line.
Telephone wiring can also carry low frequency radio signals, not unlike those transmitted on AC power lines as carrier current transmissions. We use RF detection equipment to test each phone line for this kind of bug.
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First is called POTS testing. POTS
stands for Plain Old Telephone Service. It includes single line telephones, fax
machines, modems, and relatively obsolete 1A2 key system telephones. Also included
in POTS type testing are certain types of phones used in Centrex business telephone
systems.
The
second type of testing is that of modern business telephone systems and instruments,
defined as electronic telephones. The majority of these
systems use one of two categories of telephones. Digital telephones where
all of the telephone's functions including the transmission and reception of conversation
takes place as a digital bit stream transmitted on one or two pair of wires between the
phone and the PBX make up the first group. The second group is hybrid
telephones. These phones use digital control for all functions except voice.
Voice is an analog signal sent on a pair of wires separate from those carrying the
data.
For general testing, we use an ISA ETA-3A
telephone analyzer. This test device measures voltage and current on any wire pair
in the telephone cable, does a unitone and multitone tone sweep, has a high voltage
pulse, and a built-in high gain audio amplifier. It will detect a number of wire tap
techniques including series radio transmitters, drop-out type tape recorder interfaces,
hookswitch bypasses, infinity transmitters, and active microphones installed in the phone
or connected to its wiring. It is used on both POTS and electronic instruments.
One of the most difficult attacks to
detect on digital phones is one where the phone has been modified to continue to transmit
audio after the handset has been placed back on hook. The audio is converted into
data in the telephone for transmission to the PBX. It is hard to detect because only
data is detected on the telephone wiring. There is no actual analog room audio.
We use a high bandwidth laboratory oscilloscope to analyze the bitstream for
indications of room audio.
Wiretaps can be installed outside of the facility being tested.
Some types of wiretaps are designed to have no measurable electrical affect so they are
nearly impossible to locate with analyzers like the ETA-3A and other voltage and current
measuring testers. We use a line analyzer called a Time Domain Reflectometer in
instances where the access to the cabling for visual inspection is limited. TDRs are
like radar: they indicate what is connected to a line and how far away it is.