[iwar] Historical posting


From: Fred Cohen
From: fc@all.net
To: iwar@onelist.com
Mon, Jan 1, 1999 

fc  Mon Jan 1, 1999
Received: (from fc@localhost) by all.net (8.9.3/8.7.3) id FAA15269 for iwar@onelist.com; Tue, 18 Apr 2000 05:21:43 -0700
To: iwar@onelist.com
MIME-Version: 1.0
Mailing-List: list iwar@egroups.com; contact iwar-owner@egroups.com
Delivered-To: mailing list iwar@egroups.com
Precedence: bulk
List-Unsubscribe: 
Date: Mon, Jan 1, 1999
From: Fred Cohen 
Reply-To: iwar@egroups.com
Subject: [iwar] Historical posting

          


            
 Thank you for that enlightenment.  In the business of Information Security I
find that applied knowledge and learning are my most valuable and effective
weapons.  I know very little about the technical aspects of TEMPEST, and I
appreciate the chance to gain some insight.


From: Eric Schneider eric@s...

Tony Bartoletti wrote:
> 
> That article mentioned a product that purports to significantly
> reduce TEMPEST emanations "through software alone", by replacing
> the video driver with a version that (for text alone?) would
> substitute "off white" for white background, and "dark text" for
> truely black text.  It claimed this small change was significant.
> 
> Anyone else hear of it?  Or believe it?  Sounds plausible, yet
> still a bit fishy...

I think you are refering to the Anderson and Kuhn "Soft TEMPEST" paper
(http://www.cl.cam.ac.uk/~mgk25/ih98-tempest.pdf).  It is an excellent
read.  And yes, I believe it.  The premise wasn't about color changes,
but modifying the frequency spectra of fonts.  Text is (technically) a
natural target for "TEMPEST" monitoring.  The high contrast of letters
provides sharp transitions between intensities, which provides for very
strong harmonics (which are easier to intercept than lower
frequencies).  By filtering out the high frequency components of the
fonts (sharp transitions), the harmonics are reduced as well, making
reception at higher frequencies more difficult.  

I wouldn't consider the technique fool proof though.  The lower
frequency components are still present and could be received.   In the
days of 100+ MHz pixel clocks, baseband reception of the video
components gets a little easier too.  I really liked the deception
tactics they introduced in the paper.  Very cool.

Eric

------------------
http://all.net/