[8448] in cryptography@c2.net mail archive
Spark gap digitizers (was NONSTOP Crypto Query)
daemon@ATHENA.MIT.EDU (Arnold G. Reinhold)
Mon Jan 15 12:49:52 2001
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Date: Mon, 15 Jan 2001 12:22:30 -0500
To: "Trei, Peter" <ptrei@rsasecurity.com>, John Young <jya@pipeline.com>,
"'Ray Dillinger'" <bear@sonic.net>
From: "Arnold G. Reinhold" <reinhold@world.std.com>
Cc: cryptography@c2.net
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I remember those. They were made by Summagraphics. We purchased a=20
large format one (about 4 feet X 5 feet) to digitize apparel=20
patterns. They had linear microphones along the top and left sides of=20
the table. You had to be careful not to put your free hand between=20
the spark pen and the microphones. I recall reading about 3-D=20
versions.
The tablets were accurate to a few hundredths of an inch but were not=20
that reliable. I think they simply started two counters when the=20
spark went off and stopped each when the microphone registered a=20
sound. If I remember right the did around 5 points per second. We=20
eventually switched to mechanical technology.
The noise from a spark probably has a much faster rise time than a=20
keyboard click, but with modern signal processing it might well be=20
feasible to resolve key presses. Of course, if one can get access to=20
the room where the computer is used, it is probably easier to bug the=20
keyboard directly. Still it may be time to add mouse-based=20
passphrase input as an option to programs like PGP.
Arnold Reinhold
At 10:24 AM -0500 1/15/2001, Trei, Peter wrote:
>I've seen an existance proof which indicates that this is possible.
>Back when I was first getting involved with computers (circa 1972),
>some digitizer tablets worked by speed-of-sound measurements.
>The stylus tip contained a small spark gap which was energized
>when the stylus pressed on the tablet. This created a spark,
>and the spark a minuscule roll of thunder. Microphones situated
>along the edges of the tablet recorded the arrival times of the sound,
>and the location of the stylus calculated within a millimeter or two.
>
>This was a peripheral for a DEC PDP-8E.
>
>This was calculating a position over about 20 cm to a millimeter,
>in real time, in 1972. Doing so to a resolution of a centimeter or
>two, in 2001, ever several meters sounds feasible.
>
>Peter Trei=A0
>
>> ----------
>> From: Ray Dillinger[SMTP:bear@sonic.net]
>> Sent: Friday, January 12, 2001 4:37 PM
>> To: John Young
>> Cc: cryptography@c2.net
>> Subject: Re: NONSTOP Crypto Query
>>
>>
>>
>> On Fri, 12 Jan 2001, John Young wrote:
>>
>> >Wright also describes the use of supersensitive microphones
>> >to pick up the daily setting of rotors on cryptomachines of the
>> >time, in particular the Hagelins made by CryptoAG.
>>
>> Hmmm. That sounds like a trick that could be brought up to
>> date. If you get two sensitive microphones in a room, you
>> should be able to do interferometry to get the exact locations
>> on a keyboard of keystrokes from the sound of someone typing.=A0
>> I guess three would be better, but with some reasonable
>> assumptions about keys being coplanar or on a surface of known
>> curvature, two would do it. Interesting possibilities.
>>
>> Bear
>>
>> [A quick contemplation of the wavelength of the sounds in question
> > would put an end to that speculation I suspect. --Perry]
> >
