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Every electronic, electro-optical or
electromechanical device
gives off some type of electromagnetic signals,
whether or not the device
was designed to be a transmitter. This is why the
use of cellular phones is not permitted on airplanes
or in many areas in hospitals -- their unintentional
signals can interfere with equipment sensitive to
picking up electromagnetic radiation (EMR). Since
World War II, scientists have known that the EMR
that "leaks" from devices
can be intercepted and, using the proper equipment,
reconstructed on a different device.
The EMR that is emitted by electric devices
contains the information that the device
is displaying, storing or transmitting. With
equipment designed to intercept and reconstruct the data,
it is possible to steal information from
unsuspecting users by capturing the EMR signals. For
example, in theory, someone sitting in a van outside
a person's house can read the EMR that is emanating
from the user's laptop
computer inside the house and reconstruct
the information from the user's monitor on a
different device.
Different devices
have different levels of susceptibility to Tempest
radiation. A handheld calculator gives off a signal
as much as a few feet away, and a computer's
electromagnetic field can give off emissions up to
half a mile away. The distance at which emanations
can be monitored depends on whether or not there are
conductive media
such as power lines, water pipes or even metal
cabinets in the area that will carry the signals
further away from the original source.
The U.S. government originally began
studying this phenomenon in order to prevent
breaches in military security. The government was
using the technology to their advantage during WWII
and realized that they needed to protect themselves
against others using the same tactics against them.
The name Tempest,
or Tempest
radiation, originated with the U.S.
military in the 1960s as the name of the classified
study of what was at the time called
"compromising emanations." Today the
phenomenon is more commonly referred to as van
Eck phreaking, named after William van
Eck, the Dutch computer
scientist who brought it to general
attention in 1985 when he published his paper
"Electromagnetic Radiation from Video Display
Units: An Eavesdropping Risk?," in which he
demonstrated that the screen
content of a video
display
unit could be reconstructed at a distance using
low-cost home-built equipment - a TV set with its
sync pulse generators replaced with manually
controlled oscillators.
Van
Eck phreaking is a major security concern
in an age of increasing pervasive
computing. High-security government
agencies are protecting themselves by constructing safe
rooms that through the use of metallic
shielding block the EMR from emanating out of the
room or by grounding the signals so that they cannot
be intercepted. It is possible, though costly, for
individual users to shield their home computer
systems from EMR leakage. However, more and more
manufacturers are creating products off-the-shelf
that are safe from van
Eck phreaking.
While the name Tempest
was the code name for the military operations in the
1960s, at a later stage the word became an acronym
for Telecommunications Electronics Material
Protected from Emanating Spurious Transmissions and
an abbreviation of Transient Electromagnetic Pulse
Emanation Standard.
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