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." ®