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)?
On Apr 27, 2015 2:42 PM, "Kalle Rosenbaum" <kalle@rosenbaum.se> wrote:

> "Or a really high lock_time, but it would not make it invalid, just
> delayed."
>
> Ok, this was a bad idea, since nodes would have to keep it in memory.
> Please disregard that idea...
>
> Kalle
>
> Den 27 apr 2015 14:35 skrev "Kalle Rosenbaum" <kalle@rosenbaum.se>:
> >
> > >
> > > Some more use cases might be:
> > > Waiting in comfort:
> > >  - Send a payment ahead of time, then wander over and collect the goods
> > > after X confirmations.
> > >
> > > Authorized pickup :
> > >  - Hot wallet software used by related people could facilitate the use
> > > of 1 of N multisig funds.  Any one of the N wallets could collect goods
> > > and services purchased by any of the others.
> >
> > I like this one, because it shows the power of reusing the transaction
> data structure.
> >
> > >
> > > Non-monetary gifts:
> > >  - Sender exports spent keys to a beneficiary, enabling PoP to work as
> a
> > > gift claim
> > >
> > > Contingent services:
> > >  - Without Bob's permission, a 3rd party conditions action on a payment
> > > made from Alice to Bob.  For example, if you donated at least .02 BTC
> to
> > > Dorian, you (or combining scenarios, any of your N authorized family
> > > members), can come to my dinner party.
> >
> > This is an interesting one.
> >
> > >
> > > I tried out your demo wallet and service and it worked as advertised.
> > >
> > > Could the same standard also be used to prove that a transaction COULD
> > > BE created?  To generalize the concept beyond actual payments, you
> could
> > > call it something like proof of payment potential.
> >
> > 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?
> >
> > >
> > > Why not make these proofs permanently INVALID transactions, to remove
> > > any possibility of their being mined and spending everything to fees
> > > when used in this way, and also in cases involving reorganizations?
> >
> > 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?
> >
> > >
> > > I agree that PoP seems complementary to BIP70.
> > >
> > >
> >
> > Thank you very much for your comments!
> >
> > /Kalle
>
>
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