From: "Beavis B. Thoopit" <beavis@bioanalytical.com>
Date: Fri, 10 Nov 1995 00:23:00 +0800
To: shields@tembel.org (Michael Shields)
Subject: Re: Timed-release crypto and information economics
In-Reply-To: <47m82v$4p4@yage.tembel.org>
Message-ID: <199511091558.KAA00768@bioanalytical.com>
MIME-Version: 1.0
Content-Type: text/plain


I have not yet convinced myself that a time-release information device
is impossible....

Does there exist a storage device that, due to _dynamics_ (or other
factor), prevents the total contents being read in one instance?

Bubble memory device?  Torsion wire memory device?

Back at IBM, an old school customer engineer friend of mine used to
bring in relics of IBM's illustrious past.  One curious device was a
memory device for an old terminal.  This device consisted of about
10 feet of piano wire coiled into a spiral of about 6 inches diameter.
An acuator would "twist" torsion waves onto the end of the wire.
These waves would propagate down the wire and would be sensed falling
off the opposite end.  About 400+ bits could be stored on the wire by
twisting (cwise/0 or ccwise/1) them onto one end, sensing them as
they came off, and re-twisting them back on.  The bits chased each
other around this loop.

Assume that I can only read the bits as they fall off the end (one
bit at a time).
Assume a transformation function (with state) in the middle of the
"wire" which cryptographically transforms the bits.
Assume a device that holds 2^somewhatbig bits.
Assume a traversal delay around the device of 1 unit.
Assume disturbing the device ("grabbing the wire") destroys the information.
Assume the message sender loads the wire with an "encrypted" message.

Can I precompute a message that after N iterations around the "wire"
(and through the transform) will spill out plaintext (N time units
into the future)?
Does such a tranformation exist?  (rings of the technology in S/key...)