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Attackers point a cheap laser, slightly better than what is used in laser pointers, at a shiny part of a laptop or even an object on the table with the laptop. A receiver is aligned to capture the reflected light beam and the modulations that are caused by the vibrations resulting from striking the keys.
This modulation is converted to an electrical signal that is fed into a computer soundcard. “The vibration patterns received by the device clearly show the separate keystrokes,” the researchers’ paper says. Each key has a unique vibration pattern that distinguishes it from the rest. The spacebar creates a significantly different set of vibrations, so the breaks between words are readily apparent.
Analyzing the sequences of individual keys that are struck and the spacing between words, the attacker can figure out what message has been typed. Knowing what language is being typed is a big help, they say.
Laptop lids, especially shiny logos and areas close to the hinges, provide the most easily read vibrations.
Anyone worried about this type of attack can make sure there is no line of sight to the laptop, move position frequently while typing and polluting the signal by striking random keys and later deleting them with the backspace key.
While they admit their hacking tools are rudimentary, they believe they could be improved upon with a little time, effort and backing.
“If our small research was able to accomplish acceptable results in a brief development time (approximately a week of work) and with cheap hardware,” they say. “Consider what a dedicated team or government agency can accomplish with more expensive equipment and effort,”
Read more about security in Network World's Security section.