Optical Time-Domain Eavesdropping Risks of CRT Displays

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Optical Time-Domain Eavesdropping Risks of CRT Displays (2002)

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by Markus G. Kuhn

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48 - 2 self

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@MISC{Kuhn02opticaltime-domain,
    author = {Markus G. Kuhn},
    title = {Optical Time-Domain Eavesdropping Risks of CRT Displays},
    year = {2002}
}

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Abstract

A new eavesdropping technique can be used to read cathode-ray tube (CRT) displays at a distance. The intensity of the light emitted by a raster-scan screen as a function of time corresponds to the video signal convolved with the impulse response of the phosphors. Experiments with a typical personal computer color monitor show that enough high-frequency content remains in the emitted light to permit the reconstruction of readable text by deconvolving the signal received with a fast photosensor. These optical compromising emanations can be received even after diffuse reflection from a wall. Shot noise from background light is the critical performance factor. In a sufficiently dark environment and with a large enough sensor aperture, practically significant reception distances are possible. This information security risk should be considered in applications with high confidentiality requirements, especially in those that already require "TEMPEST"-shielded equipment designed to minimize radio-frequency emission-security concerns.

Keyphrases

eavesdropping risk crt display background light raster-scan screen readable text information security risk high confidentiality requirement optical compromising emanation cathode-ray tube dark environment video signal radio-frequency emission-security concern critical performance factor new eavesdropping technique fast photosensor sensor aperture impulse response diffuse reflection time corresponds significant reception distance shot noise emitted light enough high-frequency content

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