Re: All our eggs in one basket?

Perry Metzger writes

> Jim Miller says:
> > However, proving them wrong while also retaining your anonymity may
> > be a trick.
> 

> If all transactions require digitally signed confirmation from the
> bank, you have an audit trail from them that they can't deny was theirs.
> 


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.

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. 


I imagine the bank would use one of the simultaneous contract signing protocols  
and somehow produce an encryption key as the last step.  The key would be used  
to decrypt the digital money, which was sent in an earlier step in an encrypted  
form.

However, how can the person withdrawing the money verify the digital money is  
for the amount stated in the receipt if they only get the key after the last  
step in the receipt signing protocol.  I am confused.  I must not be thinking  
of the correct protocol.

How is this situation handled?


Jim_Miller@suite.com

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