Defeating Optical Tempest will be easy...
camera_lumina at hotmail.com
Sat Jul 19 07:18:27 PDT 2003
Well, from what I'm understanding of so-called optical tempest, I'm not sure
most of the usual thinking will apply.
First of all, anyone know what the most energetic wavelengths are in the
CRT's output? (I have no idea.) Is it in the visible range? It may not be.
Thus contrast in the visible range may not equal contrast in the freqency
range that 'OT' will be using.
Also, and I'm not sure what this implies yet, but the screen-emitted beam
has lowest energy after hitting a letter, which is black. Thus this tempest
device must be particularly sensitive to the "white" background in order to
makeout the letters as the sweep comes through (and is blocked by the
And now that I think of it, I'm still not convinced that this does not
amount to specular reflection, even though we are now talking about the
"ballistic" beam...remember in order to determine what a letter is detecting
a -decrease- in the beam's reflected energy will be the key in reading a
Oh wait...the answer to defeating optical tempest is simple: have white
letters on a black background.
And after they've caught up with that trick, alternate the background colors
at random intervals (white on black, black on white, etc...).
Optical Tempest will only work under VERY ideal circumstances. I wouldn't
worry about it.
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