Ray Dillinger wrote:
> 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.
> 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]

Hmm. 6 kHz has a wavelength of 5 cm. I would guess you can easily get
resolution to 1/10 of a wavelength under ideal conditions. Which is .5
cm, which is half the size of a key, more or less.

Sounds pretty feasible to me.




"There is no limit to what a man can do or how far he can go if he
doesn't mind who gets the credit." - Robert Woodruff

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