[11720] in cryptography@c2.net mail archive
Re: unforgeable optical tokens?
daemon@ATHENA.MIT.EDU (Ian Clelland)
Sat Sep 21 10:05:44 2002
Date: Sat, 21 Sep 2002 01:22:50 -0700
From: Ian Clelland <ian@veryfresh.com>
To: Hadmut Danisch <hadmut@danisch.de>
Cc: cryptography@wasabisystems.com
Mail-Followup-To: Hadmut Danisch <hadmut@danisch.de>,
cryptography@wasabisystems.com
In-Reply-To: <20020920203802.GA5801@danisch.de>
> Not really. Illuminating the device at different locations and
> angles is certainly not as good as a cryptographical challenge.
> Since the location and angle is done by some mechanical device,
> the numers of locations and angles is certainly "small"
I think you're right here; in order for the challenges to be
reproducable, the locations / angles that the reader uses would
have to be discrete, probably by some sort of stepper motor.
However, if the readers are autonomous (and each one needs to
see the physical token once in order to identify it later,)
then every reader could be calibrated differently, and would
therefore use one relatively small subset of locations / angles
out of a large number of subsets.
> and once you are in posession of the token (e.g. as a clerk ini
> the shop), it might be possible to generate a complete table of
> all location/angle/response triples.
I wonder if an analysis of the diffraction patterns produced by
passing light though a token like this would provide enough
information to reconstruct the internal 3-D shape... it strikes
me as being a problem similar to X-ray crystallography.
Ian Clelland
<ian@veryfresh.com>
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