There is a fascinating article about a side channel attack to dot-matrix printers at The Register.
This so-called side-channel attack works by recording the “acoustic emanations” of a confidential document being printed, and then processing it with software that translates the sounds into words. The method recovers as much as 95 per cent of the printed words when an attacker has contextual knowledge about the text being printed, such as the words included in a medical prescription or a living-will declaration. Up to 72 per cent of the text can be recovered when no context is known.
The attack, which so far works only on English text, was carried out under what the researchers described as “realistic — and arguably even pessimistic —– circumstances,” in which there was no shielding from ambient noise such as that made by people chatting in a nearby waiting room. Despite the wide availability of inkjet and laser printers, about 60 per cent of doctors in Germany continue to use dot-matrix devices. About 30 per cent of banks in Germany do so as well, according to the researchers.
Read the full article here.