New 'Reflections' on Optical Emission Security

[WombatWoman]

Yet another high-tech assist to espionage is now poised to cross the boundary between spy-movie fantasy and real world application. Useful imagery can be gleaned by analyzing the flickers which a CRT casts onto a wall.

"Reflected and diffuse light from an obscured computer monitor can still be used to reconstruct what is on its screen, say UK researchers. The technique could be used to spy on computers through an office window, for example, even if the monitor was not facing the window.

Markus Kuhn and colleagues at Cambridge University used a highly sensitive light sensor - a photomultiplier - to detect the diffuse light emitted by a computer monitor facing a wall.

They then applied a computer algorithm to match the light they gathered to pixels on the target screen. This approach requires knowledge of the speed at which the electron beam inside the monitor sweeps across the screen, illuminating its phosphor dots."

Article in "New Scientist"

FAQ written by the researcher, with images

The researcher's paper, as presented to the 2002 IEEE Symposium on Security and Privacy

To me, this is a real jaw-dropper, and when I was told about it, I initially did not believe it to be true. As a scientist born in the 1940s, I am a chronic victim of "future shock," and I think this news has given me a relapse.

Sometimes there's not much to say but "gee whiz."

And "board up those windows."

 

[Armitage]

I wonder if an LCD monitor would suffer from this same issue? Does it do a raster scan similar to a CRT, or does everything refresh at once?

My impression of how this works is that thet synchronize on the horizontal & vertical scan rates of the monitor, and can therefore pick up the color & intensity of every pixel as it is illuminated, even from a "diffuse reflection.

I suppose you could paint the walls flat black maybe?

 

[Armitage]

And don't forget, they can use a LASER Microphone to listen in & pick out which MP3 you're listening to

A Faraday cage, no windows, it's the only safe way!

 

[WombatWoman]

I wonder if an LCD monitor would suffer from this same issue?

Apparently not. From page 15 of the paper presented to the IEEE:

"The need for special security CRTs is likely to be reduced significantly with the further proliferation of liquid crystal displays (LCDs). Their pixels react considerably slower than CRT phosphors and most types of flat-panel displays refresh all pixels in a line simultaneously. Both these factors suggest that this technology has a significantly reduced risk of leaking information about individual pixels in diffuse optical emanations."

I suppose you could paint the walls flat black maybe?

Or paint the windows black. (Do I hear Rolling Stones music?)

LOL@ the Faraday cage suggestion! Soon every work-cubicle will be a fortress! Getting out my aluminum foil hat now. That #$!@ Dogbert is sending his mind-control signals through the office intercom again.

 

[Armitage]

Originally posted by: WombatWoman
I wonder if an LCD monitor would suffer from this same issue?

Apparently not. From page 15 of the paper presented to the IEEE:

"The need for special security CRTs is likely to be reduced significantly with the further proliferation of liquid crystal displays (LCDs). Their pixels react considerably slower than CRT phosphors and most types of flat-panel displays refresh all pixels in a line simultaneously. Both these factors suggest that this technology has a significantly reduced risk of leaking information about individual pixels in diffuse optical emanations."

Interesting ... Most of the TEMPEST ("Van Eck Phreaking" for those who've read Cryptonomicon) concerns are with the CRT monitor also. I can see alot of organizations that deal with classified data moving toward LCD screens.

 

[WombatWoman]

Most of the TEMPEST ("Van Eck Phreaking" for those who've read Cryptonomicon) concerns are with the CRT monitor also.

I'm glad you mentioned "Cryptonomicon," which would probably be enjoyed by most of those who post in the Highly Technical forum. An extraordinary trip for the mind, and the most stimulating thing I've read since Hofstadter's "Metamagical Themas."

The Wim Van Eck paper which sounded the alarm about EMR phreaking is available here. Van Eck isn't as entertaining a read as Neal Stephenson, but this is fascinating stuff.

I suggest a name for the new eavesdropping technologies which analyze optical emissions:

"TEMPEST in a CRT-pot."

 

[Armitage]

Yes, one of the better books I've read in a long time!

The interesting thing about the Van Eck stuff in Cryptonomicon was that they claimed to be capturing the signal directly from the video card hardware, while most stuff I've heard of captures the emmisions from the CRT itself ... much higher voltage.

I suppose it was largely some artistic liberty needed because the ability to do it to a laptop was somewhat key to the storyline.

 

[WombatWoman]

Originally posted by: ergeorge
The interesting thing about the Van Eck stuff in Cryptonomicon was that they claimed to be capturing the signal directly from the video card hardware, while most stuff I've heard of captures the emmisions from the CRT itself ... much higher voltage.

I suppose it was largely some artistic liberty needed because the ability to do it to a laptop was somewhat key to the storyline.

Of course, it has been said (by Asimov? Clarke? Heinlein? Pournelle???) that today's science fiction is tomorrow's science.

But not all of it. Otherwise we would all be flying around in personal air-cars, fighting off invasions of evil extraterrestrials who want to abduct our women, and creating human life in giant vats of protoplasm, as in the SF of the Golden Age.