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

[Ray Dillinger]

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