Optical Time-Domain Eavesdropping Risks of CRT Displays

[Markus Kuhn]

The following paper was accepted for the 2002 IEEE Symposium on Security
and Privacy, Oakland, California, May 12-15, 2002. Considering the
recently increased interest in research on optical emission security,
you might enjoy having an early peek at it already now:

Optical Time-Domain Eavesdropping Risks of CRT Displays

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.

http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf

Markus

-- 
Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at acm.org,  WWW: <http://www.cl.cam.ac.uk/~mgk25/>