CDR: Re: Burglar Politics, Tempesting PC's that watch TV and DVD

[Bill Stewart]

Here's an empirical result, if we can ignore theory a minute :-)

A few years ago, I was using my laptop a few feet away from
my parents' TV set, and text from my laptop showed up on the screen.
It was shredded into a couple of pieces, because the sync was hosed,
but it was quite identifiable as my text, so a spook with good
equipment shouldn't have much trouble reading it.
If you want more details, dredge the cypherpunks archives.

One of the issues is that most laptops have video ports
on the back to allow you to plug in real monitors,
and if you don't have anything plugged in, they're sitting there
with raw pins pointing out.  I'm not sure if my PC was in
"use both displays" mode or "only use the LCD" mode -
most laptops don't have an indicator other than "the LCD is dark"...
Among other things, most laptops are designed so that the 
PC model of display card interface is maintained,
so it's transparent to software that's poking around where it shouldn't.

Palmtops probably behave differently, but I wouldn't trust them either.


At 11:31 AM 10/11/00 -0400, Ray Dillinger wrote:
>On Wed, 11 Oct 2000, jim bell wrote:
>
>>> A popular, but false, myth. The video cards radiate more than the CRT's.
>>> Laptops tend to be the worst offenders.
>>> --Lucky Green <shamrock at cypherpunks.to>
>>
>>As to the video cards...
>>Sorry, Lucky, but you're going to have to support this a little better.
>>Emissions are a function of  the signal voltage in a conductor, and the
>>extent that this conductor is free to emit.  
>
>Given that a laptop uses an LCD display, there's really no good 
>reason, electronically speaking, why its video hardware should 
>have to do the ((scan+horizontal_retrace)*+vertical_retrace) 
>sequence that the technology for getting a coherent signal 
>relies upon. 
>
>But the fact is, laptop hardware does write bits in a predefined 
>order, (in fact the same order as CRT-based machines) so it's a 
>worthwhile question whether anyone can figure the order and pick 
>up the emissions from the video hardware.  
>
>This looks like the sort of thing that can be resolved by experiment 
>though; Anybody got enough DSP smarts to put an induction coil next 
>to a laptop monitor and *see* whether they can read the darn thing? 
>
>Also, it looks like the sort of thing that could be designed around. 
>If someone were building a "secure laptop" they could make a video 
>system and drivers that wrote the bits in a different, randomized 
>order each time, and which only wrote the changed bits.  If anybody 
>is actually making a product like this, it would be a strong 
>indication that *somebody* with money to spend on R&D considers 
>it a valid threat model, because nobody makes products without a 
>market.
>
>				Bear
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				Thanks! 
					Bill
Bill Stewart, bill.stewart at pobox.com
PGP Fingerprint D454 E202 CBC8 40BF  3C85 B884 0ABE 4639