From: jim bell <jimbell@pacifier.com>
Date: Sun, 28 Apr 1996 10:15:26 +0800
To: Snow <cypherpunks@toad.com
Subject: Re: trusting the processor chip
Message-ID: <m0uDEIm-00093vC@pacifier.com>
MIME-Version: 1.0
Content-Type: text/plain


At 12:25 AM 4/27/96 -0500, Snow wrote:
>On Thu, 25 Apr 1996, jim bell wrote:
>> 
>> This analysis seems to assume that the entire production run of a standard 
>> product is subverted.  More likely,I think, an organization like the NSA 
>> might build a pin-compatible version of an existing, commonly-used product 
>> like a keyboard encoder chip that is designed to transmit (by RFI signals) 
>> the contents of what is typed at the keyboard.  It's simple, it's hard to 
>> detect, and it gets what they want.
>
>	I thought that most (all?) chips already radiated on the 
>electromagnetic spectrum? Isn't that what tempest is about?

There's a difference between trying to find a needle in a haystack, and 
finding a day-glo, red-hot needle that plays music at 110 decibels in that 
same haystack.  Digital logic chips do radiate EMI, but some radiate very 
little (because their are few logic transitions or they occur relatively 
infrequently) or are buried within other circuitry and they don't have a 
particularly good antenna.  The Trojan horse chip I'm hypothesizing would be 
specifically designed to radiate a fairly loud, continuous signal, on wires 
that are long enough to make a good antenna.  Ideally, the chip would have a 
crystal to produce a very constant frequency, so that other noise not on 
that frequency could be ignored.

The best place to put such a chip would be a location outside the computer's 
case, or at least it would have access to the outside.  I think that a 
keyboard controller would be optimum, because I suspect that there are a 
relatively small number of different designs.

Jim Bell
jimbell@pacifier.com