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Researchers pluck keystrokes out of thin air

By Stuart Turton

Posted on 20 Mar 2009 at 11:24

Researchers have demonstrated two novel new ways of plucking keystrokes out of thin air, using basic equipment.

In a stand at the CanSecWest security conference, researchers from Inverse Path showed how they could point a laser pen at the reflective surface of a laptop and determine which letters were typed.

The pen was part of a homemade laser microphone device capable of measuring the vibrations caused by the keystrokes. These vibrations are unique to the key being pressed, meaning that once detected software need only feed them into a dictionary program to guess the word being typed.

Though the laser pen requires a direct line-of-sight, researchers say it will work at any distance between 50-100 feet and through windows. Because keystrokes sound different for different people, the laser pen has to be trained on the laptop for some time to become 100% accurate.

In the second method, the researchers plugged a digital oscilloscope and analog-digital converter into a plug socket 50 feet away from the machine they were monitoring.

They then used this technology to pluck out the electro-magnetic pulses caused by each keystroke from the surrounding electrical noise.

Coupled with filtering technology, the researchers were able to pick up keystrokes, though not full words and sentences. However, they claim this will be possible with better equipment.

This technique only works on PS/2 keyboards, however, somewhat diluting its usefulness.

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