Have you ever seen a Dot-Matrix Printer? They are usually found in offices, banks, and are still in wide use today. It is most known for its economy of use and the loud sound it makes when it prints on paper. Researchers have actually found a way to decipher those sounds and recover the information it is printing out!

This method is called a “side-channel attack” which was first used in the first world war by the Germans to spy on the French phone lines. In this modern case however, it works by the attacker first recording the noise from the dot-matrix printer.

This noise are then fed into a computer program that attempts to turn this noise into words. This works because the pins of the printer make different sounds depending on what it is printing out. With above 90% accuracy in deciphering the proper English words when attackers use the proper context of the message and 72% when the attackers do not.

So far, this type of attack is limited to English text. The researchers argued that the system works even with the presence of ambient noise such as that of human chatter.

In Germany the researchers noted that doctors still favour the use of dot-matrix printers rather than laser or inkjet printers. Almost 30% of banks there also use dot-matrix printers. These kinds of printers are also used by doctors for printing prescriptions in Germany, Austria, and Switzerland.

The researchers will be attending the Usenix Security Symposium that will be held in Washington, DC to share their finding with them.

If this technique were perfected, this could be used to spy on a diverse number of dot-matrix printers. A variant of this kind of technique could also used for inkjet printers. Although the software would have to learn each printer to increase the accuracy of this method, according to the authors of this research.

One way to counteract this technique would be to use acoustic shielding. Their experiment showed that the efficiency of the system dropped drastically as the mike is moved further away from the printer.

Learn more about their research here. The authors of the study are Michael Backes, Markus Durmuth, Sebastian Gerling, Manfred Pinkal, and Caroline Sporleder, of Germany\'s Saarland University. They are part of computer science and linguistics department.

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