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The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:16:03 ADT
mgraffam@mhv.net
Tue, 17 Mar 1998 20:25:05 -0500
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On Tue, 17 Mar 1998, Perry E. Metzger wrote:
> Pamela Grannum writes:
> > And how far does the standard PC monitor emit????
> >
> > I would be surprised if it is 120ft.
>
> Physics doesn't work that way, I'm afraid.
>
> An electromagnetic signal doesn't "stop". It becomes weaker with
> distance, but of course that can be fixed with better detection
> equipment, up to a point. The practical distance isn't easily stated
> as "N meters" -- it strongly depends on the ingenuity of those looking
> for the signal, too.
Indeed, and in practice 120 ft isn't a problem.
"If no preventive measures are taken, eavesdropping on a
video display unit is possible at several hundred metres
distance, using only a normal black and white TV reciever,
a directional antenna and an antenna amplifier."
- Wim van Eck "Electromagnetic Radiation
from Video Display Units: An Eavesdropping
Risk?" section 2.4 "Implications"
Wim goes on to describe that certain monitors could get snooped
at a kilometer with better equipment.
To get a good grip on EMR, try "Theory of Electromagnetic Wave
Propagation" by Dr. Charles Papas. It will require physics ability,
and math (but I figure you have that if you're messin' with crypto :)
a bit of electronics would be nice too, to see into some of the
applications. Good stuff.
Michael J. Graffam (mgraffam@mhv.net)
http://www.mhv.net/~mgraffam -- Philosophy, Religion, Computers, Crypto, etc
"Two things fill the mind with ever new and increasing admiration and awe
the more often and steadily we reflect upon them: the starry heavens
above and the moral law within me. I do not seek or conjecture either of
them as if they were veiled obscurities or extravagances beyond the horizon
of my vision; I see them before me and connect them immediately with the
consciousness of my existence." - Immanuel Kant "Critique of Practical Reason"
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The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:16:03 ADT