[10554] in cryptography@c2.net mail archive
Optical Time-Domain Eavesdropping Risks of CRT Displays
daemon@ATHENA.MIT.EDU (John Young)
Wed Mar 6 13:14:06 2002
Date: Tue, 05 Mar 2002 21:26:17 -0800
To: cryptography@wasabisystems.com
From: John Young <jya@pipeline.com>
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Markus Kuhn has released this after learning of
Joe Loughry's announcement.
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Announced 5 March 2002.
To be presented at IEEE Oakland conference, May 2002
http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf
Optical Time-Domain Eavesdropping Risks of CRT Displays
Markus G. Kuhn
University of Cambridge, Computer Laboratory
JJ Thomson Avenue, Cambridge CB3 0FD, UK
mgk25@cl.cam.ac.uk
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.
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