From: "Perry E. Metzger" <pmetzger@lehman.com>
Date: Thu, 18 Nov 93 16:54:37 PST
To: Jim_Miller@suite.com
Subject: Re: All our eggs in one basket?
In-Reply-To: <9311190031.AA22296@bilbo.suite.com>
Message-ID: <9311190052.AA29960@snark.lehman.com>
MIME-Version: 1.0
Content-Type: text/plain



Jim Miller says:
> So to prove that the bank is lying you show a third party your copy
> of the digitally signed receipt of the disputed transaction?  I
> assume the third party uses the bank's public key and your public
> key to verify the receipt.

Presumably something like that.

> 
> This brings up a good question: How does the withdraw of digital
> money from a bank account work?  In particular, how does the bank
> simultaneously give you money and a receipt that neither party could
> repudiate?

> I can see how they could give you the money and a receipt signed by the bank.
   
> I do not yet see how they could simultaneously give you the money
> and a receipt signed by both parties.

It needn't be signed by both parties. The bank could always simply
claim that you'd never given them an order to withdraw money and
refuse to give it to you -- cheating halfway into giving you a receipt
isn't interesting, so it also needn't be simultaneous. 

What needed is a) the bank has to be able to show a third party a
signed request for every transaction they've performed, and b) you
have to be able to show a third party a signed (by the bank) receipt
for every transaction you've performed. In other words, you are
protected because the bank can't simply claim to the arbitrator "oh,
he withdrew all his money yesterday" because they can't show an order.
The bank is protected because you can't claim "oh, I deposited ten
million dollars yesterday" if you can't show a receipt.

Perry