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.
Cheers,
Ben.
--
http://www.apache-ssl.org/ben.html
"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
