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Tom.Reding (talk | contribs) m Rep typographic ligatures like "fi" with plain text; minimal ref cleanup; WP:GenFixes on, replaced: fi → fi (2) using AWB |
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==== Acoustic emanations ====
With acoustic emanations, an attack that recovers what a dot-matrix printer processing English text is printing is possible. It is based on a record of the sound the printer makes, if the microphone is close enough to it. This attack recovers up to 72% of printed words, and up to 95% if knowledge about the text are done, with a microphone at a distance of 10 cm from the printer.<ref name="[Back10]">[[#Back1|Backes, 2010, p.1]]</ref>
After an upfront training phase ("a" in the picture below), the attack ("b" in the picture below) is fully automated and uses a combination of machine learning, audio processing, and speech recognition techniques, including spectrum features, Hidden Markov Models and linear classification.<ref name="[Back1]"/> The fundamental reason why the reconstruction of the printed text works is that, the emitted sound becomes louder if more needles strike the paper at a given time.<ref name="[Back2]"/> There is a correlation between the number of needles and the intensity of the acoustic emanation.<ref name="[Back2]"/>
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