aural cryptography

[Peter Gutmann]

John Kelsey <kelsey.j at ix.netcom.com> writes:

>I was re-reading the original visual cryptography paper last night, and had
>an odd thought: Why couldn't we do something similar with sounds?  The human
>ear/brain is pretty good at pulling patterns out of noise; would it be
>possible to randomly embed half of a low-quality voice channel in each of two
>sound channels, so that they didn't sound obviously bad apart, but when played
>at the same time, would allow the listener to hear a spoken message pretty
>clearly?

There's an RFID technique that relies on having two fairly narrow RF beams and
you have to place the token at the intersection point of the two in order to
get anything out of it.  I don't know whether it uses interference of the
signals or the fact that you have to be receiving boths signals
simultaneously, it's been awhile since I read about it.  The technique goes
back to at least WWII and the German Knickebein target-location system,
although that one was definitely something based on processing two discrete
signals in a modification of the Lorentz landing aid system, and not any
property of interference between the two signals.

Peter.

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