From: "Beavis B. Thoopit" <beavis@bioanalytical.com>
Date: Fri, 10 Nov 1995 12:40:50 +0800
To: tcmay@got.net (Timothy C. May)
Subject: Re: Timed-release crypto and information economics
In-Reply-To: <acc7a170020210041a84@[205.199.118.202]>
Message-ID: <199511100331.WAA02410@bioanalytical.com>
MIME-Version: 1.0
Content-Type: text/plain


Tim May responded:
> The tamper-proof (more correctly, "tamper-resistant" or
> "tamper-responding") hardware is so that attackers do not alter the clocks,
> as one example, to "speed up" the time release. Or grab the key, as another
> example.
>
> (Cranking up the clock speed may or may not be possible and still have the
> device work, but it's still an attack to consider.)
> 
> If the attacker can grab the internal state of the device, he can of course
> run the "transform" talked about above on his equipment.
> 
> >If the transform exists, it will ease/eliminate the reliance on the
> >"economics" of cryptography to build a tamper-proof physical device.
> 
> You'll need to more carefully argue your thesis. I cannot imagine a method,
> save perhaps for quantum computing techniques, which can avoid the need for
> "secure secrets," either via a person keeping a secret or a box keeping a
> secret.

Above, I said "ease/eliminate"... let me limit my claim to "ease".

I see 2 unique points in this scheme that I have not seen discussed
much:  1) Using _dynamics_ to _limit_ (maybe not prevent) penetration
of a system.  2) Using a feedback state machine in a heavily iterative
manner to hide the message.

The tamper-resistant circuits discussed (and some enjoying some
hopefully profitable sales) have been _static_.  There is no (of which
I am aware) continual change in the circuit/mechanism.  I propose a
device in some form of incessant motion (electrical or otherwise).
It seems a greater (thought I am sure not impossible) task to capture
the state of a moving target.  It seems that there may be a device
that inherently allows itself to be read serially (one bit after
another).

Add the feedback state machine to this (ephemeral) device, and you
may have a nice platform for time-released information.

The torsion-wire device described in a previous post is a nice example
of a device that allows access to only one bit at a time.  (Now, maybe
some sort of camera could be used to "see" all of the bits at once in
flight along the wire.  For argument, let's assume not.)  The problem
with the torsion wire device is that the math transform needs to live
somewhere between the two ends; access to the bits at the front and
back of the transform is not allowed.

I want something cheaper than a satellite, but beaming bits to a
satellite that performs the iterative, feedback transform and transmits
the transformed bits back home may
illustrate the type of platform needed.  It allows me to see only
one bit at a time.  The bits are munched each "round".  A delay is
inherent in the system and is not "acceleratable".

If this platform exists, how do I precompute a message to take
advantage of it?