<p dir="ltr">Hi Jorge,</p>
<p dir="ltr">I don't think I understand the question. Proof of Payment is used to prove that you have the credentials needed for a certain transaction. It does not care where in the blockchain the transaction is. Or if it's in the blockchain at all. </p>
<p dir="ltr">/Kalle</p>
<div class="gmail_quot<blockquote class=" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">So at the low level, how does a "proof of payment" differ from just proving that a given transaction is in a given block (what SPV nodes take as proof of payment today)?</p>
<div class="gmail_quote">On Apr 27, 2015 2:42 PM, "Kalle Rosenbaum" <<a href="mailto:kalle@rosenbaum.se" target="_blank">kalle@rosenbaum.se</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr">"Or a really high lock_time, but it would not make it invalid, just delayed." </p>
<p dir="ltr">Ok, this was a bad idea, since nodes would have to keep it in memory. Please disregard that idea... </p>
<p dir="ltr">Kalle </p>
<p dir="ltr">Den 27 apr 2015 14:35 skrev "Kalle Rosenbaum" <<a href="mailto:kalle@rosenbaum.se" target="_blank">kalle@rosenbaum.se</a>>:<br>
><br>
> ><br>
> > Some more use cases might be:<br>
> > Waiting in comfort:<br>
> > - Send a payment ahead of time, then wander over and collect the goods<br>
> > after X confirmations.<br>
> ><br>
> > Authorized pickup :<br>
> > - Hot wallet software used by related people could facilitate the use<br>
> > of 1 of N multisig funds. Any one of the N wallets could collect goods<br>
> > and services purchased by any of the others.<br>
><br>
> I like this one, because it shows the power of reusing the transaction data structure.<br>
><br>
> ><br>
> > Non-monetary gifts:<br>
> > - Sender exports spent keys to a beneficiary, enabling PoP to work as a<br>
> > gift claim<br>
> ><br>
> > Contingent services:<br>
> > - Without Bob's permission, a 3rd party conditions action on a payment<br>
> > made from Alice to Bob. For example, if you donated at least .02 BTC to<br>
> > Dorian, you (or combining scenarios, any of your N authorized family<br>
> > members), can come to my dinner party.<br>
><br>
> This is an interesting one.<br>
><br>
> ><br>
> > I tried out your demo wallet and service and it worked as advertised.<br>
> ><br>
> > Could the same standard also be used to prove that a transaction COULD<br>
> > BE created? To generalize the concept beyond actual payments, you could<br>
> > call it something like proof of payment potential.<br>
><br>
> I guess it's possible, but we'd have to remove the txid from the output, since there is none. This is a way of saying "I'm in control of these addresses". The other party/parties can then verify the funds on the blockchain and watch those addresses for changes. Maybe there are some interesting use cases here. Ideas?<br>
><br>
> ><br>
> > Why not make these proofs permanently INVALID transactions, to remove<br>
> > any possibility of their being mined and spending everything to fees<br>
> > when used in this way, and also in cases involving reorganizations?<br>
><br>
> Yes. Initially I thought it would be enough that the funds are already spent, but I think you're right here. Reorgs could be a problem. Worse, you also might want to prove 0-confirmation transactions, in which case it's a huge security problem. Someone might intercept the PoP and publish it on the bitcoin network, spending all the funds. But I still would like wallets to be able to build/verify PoPs with little or no modifications. Could we possibly change the version number on the PoP to something other than 1? Maybe 2^4-1? Or a really high lock_time, but it would not make it invalid, just delayed. Any suggestions here?<br>
><br>
> ><br>
> > I agree that PoP seems complementary to BIP70.<br>
> ><br>
> ><br>
><br>
> Thank you very much for your comments!<br>
><br>
> /Kalle</p>
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