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Scientific American:
June 26, 2007
Newly Declassified Window Film Keeps Out Hackers, Phone Calls, EMPs
Like a tinfoil hat for your house, new technology promises to block
hackers' access to your wireless transmissions-and protect against EMP
attacks and explosions, to boot
By Christopher Mims
When a Boeing 757 struck the Pentagon on September 11, 2001, a blastproof
film on its windows prevented them from shattering into a swarm of flying
shards. Now, a version of that same film promises to block not only
projectiles but also the collective electromagnetic chatter generated by
our increasingly wireless society.
Once manufactured under an exclusive contract with the U.S. government,
this recently declassified window film is now available to the public. But
don't expect to see it on store shelves anytime soon. Currently, it's only
available directly from the manufacturer, and at prices that will likely
make it prohibitive for all but the wealthiest home owners.
The two-millimeter-thick coating can block Wi-Fi signals, cell phone
transmissions, even the near-infrared, yet is almost transparent, making it
no more intrusive than conventional window treatments. It can keep signals
in (preventing attempts to spy on electronic communications) or out,
minimizing radio interference and even the fabled electronics-destroying
electromagnetic pulse (EMP) generated by a nuclear blast.
The film has already been plastered across the windows of more than 200
government buildings, including structures operated by the departments of
Defense and the Treasury, as well as in the homes of high-level members of
the current administration.
"We are limited by confidentiality agreements to say exactly which
buildings [the window film] is on," says Kent Davies, president of CPFilms,
Inc., in Martinsville, Va., which manufacturers the protective covering
dubbed LLumar Signal Defense Security Film. "But immediately after 9/11 one
of the senior military officials talked about a window film that seriously
protected against the damage from the plane crash. You can put two and two
together and assume it was also protecting against wireless signals."
But Is It for You?
Unlike the built-in security measures present in nearly all wireless
routers, Signal Defense Film doesn't come cheap. CPFilms declined to give
details of their pricing structure, in part because their technology is
only sold as part of an all-inclusive package (of which the film is one
component).
In addition, some experts are skeptical whether there is-or should be-a
market for the film outside of the government and large corporations.
"If you're military, sure, it's useful. But if you're a normal person, it's
kind of dumb," says Bruce Schneier, a consultant and authority in the
fields of cryptography and computer security. "The way you secure wireless
is [by securing your computer]-this is the wrong point to apply the
solution." Without means of encryption and software-based security, he
asserts, "you're out in the open anyway." Schneier himself is so confident
in his ability to secure his computers that he runs a completely open
wireless network in his home.
On the other hand, despite the widespread availability of wireless security
features, many organizations and individuals have failed to secure their
networks. In 2005, for instance, hackers broke into the wireless network of
a Marshalls department store by using an antenna to remotely intercept its
transmissions. Using this access as a starting point they managed to steal
more than 200 million credit card numbers from a central database of
customer information. The wireless network they breached was protected by
Wireless Encryption Protocol (WEP), an older standard whose weak encryption
can be cracked in under two minutes.
An internal audit revealed that the chain did not move quickly enough to
convert its networks to the stronger Wireless Protected Access (WPA)
standard. When the plot was finally uncovered, TJX, Marshalls's parent
company, hired dozens of investigators and offered to pay for fraud
monitoring for customers whose data was stolen.
Lisa Winckler, global director of research and technology at CPFilms,
argues that the film has applications beyond simply blocking Wi-Fi signals,
which are transmitted in the same unregulated 2.4-gigahertz band that is
used by many cordless handsets. By shielding against signals across a wide
swath of the electromagnetic spectrum, from 10 hertz to just shy of visible
light, Signal Defense film can also thwart eavesdropping technology that
depends on transmissions in the near-infrared, or terahertz range.
"With the advent of laser microphones," explains Winckler, "you can pick up
voice data [through a window]. It's done every day in government."
Born of the Cold War
Many of these more exotic applications-including blocking the stray
transmissions of keyboards, old-style televisions and computer monitors,
and even LCD flat-panel displays-originated in the military's so-called
TEMPEST program. TEMPEST was a code name for an initially classified effort
to determine whether foreign governments could extract useful information
from recordings of the stray electromagnetic noise generated by electronic
devices. (In the first unclassified paper on the subject, published in
1985, Wim van Eck, then a researcher at Neher Laboratories in the
Netherlands, demonstrated that it was possible to use a wireless antenna to
reproduce the image on a television screen even when they were separated by
a wall.)
"There was a huge movement in the government several years ago for TEMPEST
protection," says Arthur Money, who was an assistant secretary of defense
from 1999 to 2001 and has since become a consultant for defense
contractors, including CPFilms. As a result, according to computer security
expert Schneier, the government covered the windows of the National
Security Agency's headquarters with a fine metallic mesh, and sandwiched
metallic shielding between its wallboards.
In contrast to these early efforts, Signal Defense Film has the advantage
of being inconspicuous. It is transparent to over 50 percent of the light
that shines on it, "which is a lot," says Winckler, CPFilms's chief of
research and development. "Sunglasses are always less than 5 percent
transmission
. You could put this on the glass in an office building and
most people would come in on Monday morning and not know it was there."
CPFilms's Davies sees applications for Signal Defense Film in everything
from hospitals, which now have obligations under the federal Health
Insurance Portability and Accountability Act (HIPAA) to keep patients'
records private, to the financial sector, where interior conference rooms
might benefit from being shielded from electronic eavesdropping.
"Retailers are trying to make their environments more appealing by letting
in more light," says Davies, "but in doing so they're also allowing more
information to flow through the glass."
As Networks Proliferate, So Does Noise
As the number of wireless networks and devices multiplies, even individuals
who aren't worried about security stand to benefit from increased
electromagnetic shielding.
"We have had conversations with buildings, especially high-rise buildings
where there is a lot of signal going on at the upper floors of those
buildings," Winckler says. When the ambient signal from transmission
towers, other networks and even microwave ovens becomes overwhelming,
shielding a building can improve the performance of any wireless networks
within its walls.
Starting in 2009 even some cars will have their own wireless networks.
"Over time, you can imagine," former defense official Money speculates, "if
you had cars stacked up at a stoplight, the amount of interference is
potentially horrific. This film will probably be in every car window just
to keep interference down, let alone for privacy reasons."
Winkler also notes that in the unlikely event of a nuclear terrorist
attack, Signal Defense Security Film would help safeguard its users'
electronics from the potentially devastating effects of an electromagnetic
pulse, or EMP. Although the sensitivity of such information prevents her
from providing specifics on this feature of the film, she did note that it
attenuates electromagnetic signals by 35 decibels, which translates into a
greater than 99 percent decrease in signal strength.
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R. A. Hettinga