From: "Perry E. Metzger" <perry@snark.imsi.com>
Date: Wed, 4 May 94 09:37:46 PDT
To: "Michael V. Caprio Jr." <mikecap@wpi.edu>
Subject: Re: Why Digital Cash is Not Being Used
In-Reply-To: <199405041620.MAA04197@coyote.WPI.EDU>
Message-ID: <9405041635.AA02723@snark.imsi.com>
MIME-Version: 1.0
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"Michael V. Caprio Jr." says:
> 
> > 2) In order to demonstrate that you have it you generally speaking
> >    have to have already given it away.
> 
> I would use the analogy of information as shares...  It also seems
> that number two is a typical zero knowledge situation -

No its not. Its easy to conduct a zero knowledge interactive theorem
proof for things that are mathematically expressable, like "I know a
Hamiltonial circuit of this graph", but it won't work for anything
that can't be expressed that way.

Example: construct a zero knowledge proof for the proposition "I know
something interesting about George Bush that you would be willing to
pay $100 to know".

> BTW, what is fungible?

A fungible thing, sometimes called "a commodity", is one for which the
all are oblivious to substitution. As an example, when you request a
dollar bill from me, you don't care WHICH dollar bill you get. When
you ask for a one kilo gold ingot, which ingot from the space of all
ingots doesn't matter to you.

Only fungibles can be traded in securities markets or deposited in
accounts. I can trade shares of IBM because you have no care which 100
shares of IBM you get. I can trade futures contracts for West Texas
Intermediate Crude because thats a very well specified substance.

Currency is ALWAYS fungible. That which is not fungible cannot be used
as a currency. In particular, "information" is not fungible. It is not
a commodity. Two pieces of information are not indistinguishable.

Perry