By Dan Goodin in Vancouver for The Register. This story has
been reproduced with permission.
Exploiting vibrational patterns and electromagnetic pulses that
emanate with every character entered, the Italian researchers are
able to remotely sniff keystrokes from significant distances. The
techniques use inexpensive equipment and can be hard for targets to
detect, making them ideal for snooping on unsuspecting people in
the office or building next door.
"The data is there," Andrea Barisani, of security firm Inverse
Path, told those attending the CanSecWest security conference in
Vancouver, British Columbia. "That's the important thing you need
to know: whenever you type your data goes somewhere else. Not many
people think about that."
The first method involves the use of laser microphones, which
have long been the stuff of thrillers with spies who eavesdrop on
conversations spoken from afar. By pointing the devices at windows,
snoops can read the sound waves and then reconstruct the words that
are being spoken.
Barisani, who was joined on stage by fellow Inverse Path
colleague Daniele Bianco, said laser microphones can be trained on
a laptop computer or desktop keyboard to similarly read the
characters being entered. Because each keystroke has a distinctly
different sound vibration, it is possible to remotely discern the
characters by capturing the sound and then subjecting it to
analysis.
The process is akin to the way secret codes are often cracked.
An eavesdropper first figures out which sound represents the space
bar. From there, he compares the input against words in a
dictionary for likely matches. The more input the device picks up,
the more accurate it becomes. Because keystrokes sound different
for different people, a snoop would need to learn the distinctive
sounds of each person being spied on.
Of course, the technique requires the eavesdropper to have a
clean line of sight to the target PC, but it remains suitable for
snooping on people typing in public places or next to windows. An
attacker can also use one line of sight to point the laser on the
victim and a separate straight line to receive the signal that's
bounced back for analysis. What's more, infrared lasers can be used
to escape detection.
There is another way
The second spying method uses electro-magnetic pulses to discern
which key has been tapped. By tapping into the local grid that's
powering the target PC, an attacker can measure leaked electrical
currents that change with every keystroke. The patterns are
captured using an oscilloscope and then subjected to filtering,
which can isolate each individual keystroke. The technique works at
distances of 15 meters, but the researchers said with more
expensive equipment it could work as far away as 100 meters.
The technique does come with one significant limitation: It
works only for keyboards using a PS/2 connector. USB keyboards and
keyboards for laptops are immune, and Barisani said it will be hard
to overcome the limitation.
The techniques outlined Thursday contribute to research
first disclosed in October by scientists in Switzerland. They
showed it was possible to use a variety of methods to capture
keystrokes of PS/2, universal serial bus or laptop keyboards. The
researchers, from the Security and Cryptography Laboratory at Ecole
Polytechnique Federale de Lausanne, are expected to formally
release their research paper soon.
Despite their limitations, the more recent techniques remain
impressive because they use off-the-shelf components that can be
put together at little expense and without much expertise. The
method involving the laser microphone costs only about $80. The
other comes to less than $200.
It's also worth noting that Barisani and Bianco developed the
techniques in their spare time over the course of some five
weeks.
"We're part-time hackers working on weekends," Barisani said.
"Imagine what a determined government agency can do."
© The Register
2009
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