Your source code, for sale

[Ben Laurie]

Hal Finney wrote:
> 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.

Cute. You could adapt Lucre to do this.

Cheers,

Ben.

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