Defeating Optical Tempest will be easy...

Tyler Durden camera_lumina at
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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