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76 PHYSICALSECURITYpower should be coordinated with computers via software
to allow them to power down gracefully.Electromagnetic Shielding
Because of their inherent vulnerability to interception,
wireless transmissions should be encrypted (or scram-
bled, in the case of analog voice communication) if
confidentiality, integrity, or authentication is essential.
Electromagnetic shielding is in direct opposition to wire-
less communication. The purpose of shielding is to block
outbound compromising emissions and inbound radiated
interference. The key idea is aFaraday cage(i.e., a conduc-
tive enclosure). This can be accomplished at several levels.
Shielding entire rooms and buildings with metal, con-
ductive wall coverings, conductive windows, and so forth
to control outbound radiation has been primarily an en-
deavor of governments. (Building underground has been
an alternative approach.) A future technique at this scale
may be to use conductive concrete, originally developed
to melt snow. (Preparing the concrete is tricky, so only pre-
fabricated slabs are commercially available at present.)
Wider application of shielding at the level of compo-
nents and their connecting wires seeks to improve EMC
so that each component functions properly. All computers
emit RF radiation, and government regulations limit how
much radiation is acceptable and where computers may
be used. To achieve EMC in components, there are spe-
cially designed, conductive enclosures, gaskets, meshes,
pipes, tapes, and sprays. The simplest EMC measure is
to use shielded cables and keep them separated to pre-
vent crosstalk. Given what was said earlier about nonstop
emissions, RF emitters such as mobile phones should be
kept away from computers with sensitive data.
Attenuation(lessening) of emissions is measured in
decibels (dB). Each 10-dB drop cuts the strength of the
signal to one tenth of what it was, so a 20-dB drop means
only 1% of the energy is escaping.
A recent discovery, dubbedSoft Tempest, provides
an inexpensive, partial solution for video display emis-
sions (comparable to attenuation of 10–20 dB). Special
fonts, which appear “antialiased” but crisp on the user’s
screen, are illegible on monitoring equipment because
key information about vertical edges is not radiated. GIF
(graphic interchange format) versions of such fonts can
be downloaded from http://www.cl.cam.ac.uk/∼mgk25/
st-fonts.zip. See Anderson (2001) for discussions of this
and of a perfect software defense against monitoring of
keyboard emissions.Weather Preparedness
Many regions of the world are subject to seasons when
monsoons, hurricanes (typhoons), tornadoes, damaging
hail, ice storms, or blizzards are more likely to occur, but
weather is inherently chaotic. Even if an event arrives in
its proper season, that arrival may be unexpected. In gen-
eral, the larger the scale of the weather event, the farther
in advance it can be anticipated. Despite dramatic ad-
vances in the accuracy and detail of regional forecasting,
the granularity of current weather models does not allow
precise forecasting of highly localized phenomena beyond
saying, “Small, bad things may happen within this largerarea.” As the probability of any specific point in that area
being hit with severe weather is small, such generalized
warnings often go unheeded.
Fortunately, the formation of small, intense weather
events can be detected by modern radar, and warnings of
potential and imminent danger can be obtained through
a variety of means. There are radio receivers that re-
spond specifically to warnings transmitted by meteorolog-
ical agencies or civil authorities. The Internet itself can be
the messenger. One mode of notification is e-mail. Other
services run in the background on a client machine, check-
ing with a specific site for the latest information. Some of
these services are free (though accompanied by advertis-
ing banners). There are also commercial software prod-
ucts and services that give highly detailed predictions in
certain situations. For example, one suite of hurricane-
related products can predict peak winds, wind direction,
and the arrival time of damaging winds at specific loca-
tions.
Fitted covers for equipment can be quickly deployed to
protect against falling water from a damaged roof, over-
head pipe leaks, or sprinkler systems. They can also be
used as dust covers when equipment is moved or stored,
during construction work, or when the panels of a sus-
pended ceiling need to be lifted.
As noted earlier, lightning can be surprisingly invasive,
penetrating where rain and wind do not. Moreover, it does
not always hit the most “logical” target, and it can arrive
unexpectedly. A bolt was documented to have traveled hor-
izontally 16 km (10 miles) before landfall; it appeared to
come out of a blue sky when, in reality, it originated in
a cloud hidden behind a hill. In any case, few businesses
will be willing to disconnect from the electric grid every
time the potential for lightning exists. Consequently, it is
essential that a building have a lightning protection sys-
tem in place and that surge protection be provided for
equipment. As a secondary precaution, magnetic media
and sensitive equipment should be kept away from metal
objects, especially structural steel. On the other hand, stor-
agewithina metal container affords the same protection
that passengers enjoy within the metal body of an automo-
bile; this is called theskin effectbecause the current passes
only through the outer skin of the metal. (The rubber tires
would need to be a mile thick to provide equivalent pro-
tection.)
It is now possible to receive automated alerts regard-
ing impending adverse space weather. The service can be
tailored with regard to the means of notification (e-mail,
FAX, or pager), the type of event expected (radio burst,
geomagnetic impulse, and so forth), and the threshold at
which a warning should be reported. See Space Environ-
ment Center (2002).Earthquake Preparedness
Certain regions of the world have a well-known his-
tory of frequent earthquakes, and planning for the in-
evitable is second nature. Complacency prevails where
damaging earthquakes strike decades or centuries apart;
earthquake survivability features may not be required by
building codes (although some cities are waking up to the
importance of such measures) or may not be calculated