Boffins sniff keystrokes with lasers, oscilloscopes
I know what you typed last summer
CanSecWest Researchers have devised two novel ways to eavesdrop on people as they enter passwords, emails, and other sensitive information into computers, even when they're not connected to the internet or other networks.
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." ®