From: tcmay@got.net (Timothy C. May)
Date: Thu, 14 Mar 1996 06:50:55 +0800
To: cypherpunks@toad.com
Subject: Re: Beat Remote Monitor Snooping?
Message-ID: <ad6c6026030210047e25@[205.199.118.202]>
MIME-Version: 1.0
Content-Type: text/plain


At 12:31 AM 3/13/96, JonWienke@aol.com wrote:
>I know that monitors emit RF signals that can be detected and decoded for a
>considerable distance.  I have a question about this.  Obviously, the
>difference between black and white (white text on black background, or vice
>versa) would be the most detectable, because the difference in signal levels
>would be the greatest.  Would it be possible to reduce or prevent this kind
>of snooping by using color schemes that all use the same signal levels?  For
>example, the color purple uses the red and blue color guns, and yellow uses
>the red and green color guns.  Would purple text on a yellow background be
>able to be read by a remote snooper?  If not, then perhaps these color
>schemes could be used to echo pass phrases--assuming the user isn't worried
>about someone looking over their shoulder.  Any comments?

I encourage you or anyone else to do experiments on RF emissions (so-called
van Eck radiation).

I'm not being catty. If I had my old lab at Intel I'd surely answer this
question for myself by doing some experiments. (As it is, it may be
possible to do some reasonable experiments just with t.v.s tuned to pick up
the emissions, radios tuned in, etc.).

Some of you out there may actually have hands-on expertise, as opposed to
first principles academic views. If so, you aren't speaking up.

So, a good opportunity for one of you to become an actual expert in van Eck
emissions, and the real or imagined risks of keyboard/CRT snooping from
afar.

(Personally, I'm not too worried. Easier ways to crack my security. Echoing
a passphrase on a CRT is not really needed, and I'm not sure
reasonably-available van Eck monitoring equipment can pick up keyboard-only
signals. Again, some experiments would be useful.)

If this actually is a real threat (and bear in mind there's a limit to how
many vans can be positioned...), then of course some fixes are possible:
use LCDs (where the RF emissions are orders of magnitude lower), use
visual-metaphor passphrase selection (e.g., where one clicks on letters
displayed on a color raster...unlikely that a monitor van can distinguish
the region selected unless it can monitor the mouse signals), and so on.

For the academic/theoretical point of view, Alta Vista shows a bunch of
hits on "van Eck" (or "Van Eck"), including our own Cypherpunks archives.
Also, some Usenet articles in sci.electronics, etc.

But someone actually reporting to us what they've found with modern systems
would be more interesting than rehashes of the old papers.

--Tim May

Boycott "Big Brother Inside" software!
We got computers, we're tapping phone lines, we know that that ain't allowed.
---------:---------:---------:---------:---------:---------:---------:----
Timothy C. May              | Crypto Anarchy: encryption, digital money,
tcmay@got.net  408-728-0152 | anonymous networks, digital pseudonyms, zero
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