How an ancient printer can spill your most intimate secrets

How an ancient printer can spill your most intimate secrets
How an ancient printer can spill your most intimate secrets

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By Dan Goodin in San Francisco
The Register
10th August 2010 

Researchers have devised a novel way to recover confidential messages 
processed in doctors' offices and elsewhere by analyzing the sounds made 
when documents are reproduced on dot-matrix printers.

This so-called side-channel attack works by recording the =E2=80=9Cacoustic 
emanations=E2=80=9D 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 =E2=80=9Crealistic -- and arguably even 
pessimistic --- circumstances,=E2=80=9D 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 

Countries such as Germany, Switzerland, and Austria require 
carbon-copy-capable dot-matrix printers to be used for printing 
prescriptions for narcotics, they said.


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