linux-l: [ash at Linux Fonts gegen Computer-Abhoererei (fwd)]

Wolfgang Jung woju at
Di Jun 9 10:17:02 CEST 1998

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Date: Tue, 9 Jun 1998 09:28:40 +0200 (MET DST)
From: Hauke Johannknecht <ash at>
To: LinuxGer Mailingliste <linux-ger at>, 
    " Mailingliste" < at>
Subject: Linux Fonts gegen Computer-Abhoererei (fwd)
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Hihi. :)

- - - - - s n i p - - - - - (Wired (June 1998, p98))

"Stealth Fonts

A little known fact: Just about any run-of-the-mill PC is also a radio
transmitter. Electromagnetic signals emitted by your monitor, known as
tempest radiation, can be picked up miles away, and with a suitable
receiver the Desktop image can be reconstructed. To prevent eavesdropping,
the US Department of Defense spends roughly US$1.5 Billion a year on
expensive metallic shielding equipment. So how can you protect yourself
without paying a fortune?
Ross Anderson, a professor at Englangs University of Cambridge Computer
Laboratory Security Group, and Student Markus Kuhn have discovered that
tempest radiation can be dramatically reduced with nothing more than a
fancy screen font. With normal fonts, the electron guns in your monitor
abruptly switch on and off when they encounter the edge of a character,
emitting a pulse of telltale tempest radiation. But by smoothing the
edges of the characters using a mathematical algorithm, the guns switch
more gently, thus avoiding compromising signals.
'This is going to completely change the tempest game,' says Anderson.
Soft Tempest screen drivers vor Linux may be freely available on the Net
this year. - Tom Standage."

(Daneben waren noch zwei Bildchen zu sehen, das obere mit scharfen Font
und das untere mit sanften Uebergaengen)
Zu den Bildern war folgender Text zu lesen:

"Top: The message is rendered in a normal font (magnified here)
Bottom: After Soft Tempest smoothing (an effect invisible to the user),
the same message is protected from eavedroppers."

- - - - - - s n a p - - - - - -

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