How to execute these attacks will be demonstrated at the Black Hat USA 2009 security conference in Las Vegas later this month by Andrea Barisani and Daniele Bianco, a pair of researchers for network security consultancy Inverse Path.

“The only thing you need for successful attacks are either the electrical grid or a distant line of sight, no expensive piece of equipment is required,” Barisani and Bianco say in a paper describing the hacks.

The equipment to carry out the power-line attack could cost as little as $500, and the laser attack gear costs about $100 if the attacker already owns a laptop with a sound card, says Barisani. Carrying out the attacks took about a week, he says.“We think it is important to raise the awareness about these unconventional attacks and we hope to see more work on this topic in the future,” Barisani and Bianco say in their paper. Others with more time and money could doubtless create better spying tools using the same concepts, they say.

In the power-line exploit, the attacker grabs the keyboard signals that are generated by hitting keys. Because the data wire within the keyboard cable is unshielded, the signals leak into the ground wire in the cable, and from there into the ground wire of the electrical system feeding the computer. Bit streams generated by the keyboards that indicate what keys have been struck create voltage fluctuations in the grounds, they say.

Attackers extend the ground of a nearby power socket and attach to it two probes separated by a resistor. The voltage difference and the fluctuations in that difference – the keyboard signals – are captured from both ends of the resistor and converted to letters (see diagram).

To pull the signal out of the ground noise, a reference ground is needed, they say. “A “reference” ground is any piece of metal with a direct physical connection to the Earth, a sink or toilet pipe is perfect for this purpose (while albeit not very classy) and easily reachable (especially if you are performing the attack from [a] hotel room,” they say in their paper.Since keyboards and mice signals are in the 1 to 20 kHz range, a filter can isolate that range for listening, they say.