Your source code, for sale

Hal Finney hal at finney.org
Mon Nov 8 10:51:24 PST 2004


Ben Laurie writes:
> How do you make the payment already "gone" without using a third party?

Of course there has to be a third party in the form of the currency
issuer.  If it is someone like e-gold, they could do as I suggested and
add a feature where the buyer could transfer funds irrevocably into
an escrow account which would be jointly controlled by the buyer and
the seller.  This way the payment is already "gone" from the POV of the
buyer and if the seller completes the transaction, the buyer has less
incentive to cheat him.

In the case of an ecash mint, a simple method would be for the seller to
give the buyer a proto-coin, that is, the value to be signed at the mint,
but in blinded form.  The buyer could take this to the mint and pay to
get it signed.  The resulting value is no good to the buyer because he
doesn't know the blinding factors, so from his POV the money (he paid
to get it signed) is already "gone".  He can prove to the seller that
he did it by using the Guillou-Quisquater protocol to prove in ZK that
he knows the mint's signature on the value the seller gave him.

The seller thereby knows that the buyer's costs are sunk, and so the
seller is motivated to complete the transaction.  The buyer has nothing
to lose and might as well pay the seller by giving him the signed value
from the mint, which the seller can unblind and (provably, verifiably)
be able to deposit.

Hal





More information about the cypherpunks-legacy mailing list