It has been long known that it is possible to steal information from computers in a number of ways, including in ways that are quite simple to use.
A criminal can illegally obtain information by remote access to a computer (and download anything they want), or install on the computer monitoring software or hardware keyloggers, infect the computer with a virus, capture data using a sniffer or simply steal the computer itself.
However, technology does not stand still: information is regularly published on new methods of data capture.
For example, last year technology was successfully tested (margin of error was less than 5%) for recovering text entered by the user on their keyboard from a recording of noise issued by the keyboard. This means that data can be captured by a simple dictaphone, radio bug or directional microphone.
Another leakage channel comes from emanation issued by parts of the computer, including the keyboard (wired, wireless and on laptops). By taking and studying this emanation it is possible to recover all the text entered by the user.
These emanations have been studied for a long time. This is usually called “compomising emanation” or TEMPEST.
Several ways of capturing TEMPEST have been developed and successfully tested (and apparantly used by someone).
The most obvious method is radio capture on a determined frequency. By using special equipment capture distance is 20 metres and can even work through walls. While for capturing data in the same building all that is needed is an FM receiver with manual settings and a computer with a good sound card.
An experiment conducted in the institute Ecole Polytechnique Federale de Lausanne showed that this method has been put into practice, all of the 11 different studied keyboards were vulnerable to TEMPEST capture.
At the Black Hat USA 2009 security conference another capture method was shown using the electricity network. The keyboard cable is unshielded and therefore emits an impulse to the ground wire, and from there into the ground wire of the power supply system, which makes it possible to use this method, which is called “power line exploit“.
If the user’s laptop is not connected to the power supply (or too many are connected), then another capture method can be used: a laser is directed at the laptop’s body, a receiver captures the reflected beam and records its modulations caused by vibrations from pressings keys.
Recently, there have been more and more rumours concerning technology allowing for remote capture of not only data coming from the keyboard but also data from the monitor.
It is quite difficult to protect oneself from such methods. As an active defence various noise generators can be used, and as a passive defence shielding computer parts or the building as a whole.