Date: Fri, 12 Jan 2001 16:40:16 -0800
    From: David Honig <[EMAIL PROTECTED]>

    At 01:37 PM 1/12/01 -0800, Ray Dillinger wrote:
    >Hmmm.  That sounds like a trick that could be brought up to 
    >date.  If you get two sensitive microphones in a room, you 

    >[A quick contemplation of the wavelength of the sounds in question
    >would put an end to that speculation I suspect. --Perry]

    Maybe not, because you can use the click--- you look only at intensity
    envelope, summing all frequencies essentially.

    [Remember your basic science: you can't resolve something smaller than
    half a wavelength. (Well, you can, with certain techniques, but things
    get seriously hairy at that point, and in general the limit is half a
    wavelength.) Given this, it is unlikely that you're going to figure
    out whether the g or the h key was struck. If I'm wrong here, I'd like
    to hear a detailed counterargument or evidence. --Perry]

Even if you can't get it -exactly- right, knowing even a small patch
of keys for each keyclick can help a lot.  If you're hoping for a
password, this just cut your search space enormously (and I'll bet
that things like the space key or a shift key sound quite different
than a normal key anyway---and this doesn't even include subtle
squeaks, etc).  And if you're monitoring ordinary text, what strings
are words and what aren't also apply a very strong constraint.  You
may have to do a little statistics, but hey, that's not hard.

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