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Date: Mon, 27 Apr 2015 14:35:27 +0200
Message-ID: <CAPswA9xUfr1D6New3hm+1Z1OqSfkAZ8L+VnbFZayG+uJecgaeA@mail.gmail.com>
From: Kalle Rosenbaum <kalle@rosenbaum.se>
To: Tom Harding <tomh@thinlink.com>
Content-Type: multipart/alternative; boundary=001a114005320eaa4a0514b3fbcf
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Proof of Payment
Precedence: list

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>
> 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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<p dir=3D"ltr">&gt;<br>
&gt; Some more use cases might be:<br>
&gt; Waiting in comfort:<br>
&gt; =C2=A0- Send a payment ahead of time, then wander over and collect the=
 goods<br>
&gt; after X confirmations.<br>
&gt;<br>
&gt; Authorized pickup :<br>
&gt; =C2=A0- Hot wallet software used by related people could facilitate th=
e use<br>
&gt; of 1 of N multisig funds.=C2=A0 Any one of the N wallets could collect=
 goods<br>
&gt; and services purchased by any of the others.</p>
<p dir=3D"ltr">I like this one, because it shows the power of reusing the t=
ransaction data structure.</p>
<p dir=3D"ltr">&gt;<br>
&gt; Non-monetary gifts:<br>
&gt; =C2=A0- Sender exports spent keys to a beneficiary, enabling PoP to wo=
rk as a<br>
&gt; gift claim<br>
&gt;<br>
&gt; Contingent services:<br>
&gt; =C2=A0- Without Bob&#39;s permission, a 3rd party conditions action on=
 a payment<br>
&gt; made from Alice to Bob.=C2=A0 For example, if you donated at least .02=
 BTC to<br>
&gt; Dorian, you (or combining scenarios, any of your N authorized family<b=
r>
&gt; members), can come to my dinner party.</p>
<p dir=3D"ltr">This is an interesting one.</p>
<p dir=3D"ltr">&gt;<br>
&gt; I tried out your demo wallet and service and it worked as advertised.<=
br>
&gt;<br>
&gt; Could the same standard also be used to prove that a transaction COULD=
<br>
&gt; BE created?=C2=A0 To generalize the concept beyond actual payments, yo=
u could<br>
&gt; call it something like proof of payment potential.</p>
<p dir=3D"ltr">I guess it&#39;s possible, but we&#39;d have to remove the t=
xid from the output, since there is none. This is a way of saying &quot;I&#=
39;m in control of these addresses&quot;. The other party/parties can then =
verify the funds on the blockchain and watch those addresses for changes. M=
aybe there are some interesting use cases here. Ideas?</p>
<p dir=3D"ltr">&gt;<br>
&gt; Why not make these proofs permanently INVALID transactions, to remove<=
br>
&gt; any possibility of their being mined and spending everything to fees<b=
r>
&gt; when used in this way, and also in cases involving reorganizations?</p=
>
<p dir=3D"ltr">Yes. Initially I thought it would be enough that the funds a=
re already spent, but I think you&#39;re right here. Reorgs could be a prob=
lem. Worse, you also might want to prove 0-confirmation transactions, in wh=
ich case it&#39;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 modifi=
cations. Could we possibly change the version number on the PoP to somethin=
g other than 1? Maybe 2^4-1? Or a really high lock_time, but it would not m=
ake it invalid, just delayed. Any suggestions here? </p>
<p dir=3D"ltr">&gt;<br>
&gt; I agree that PoP seems complementary to BIP70.<br>
&gt;<br>
&gt;</p>
<p dir=3D"ltr">Thank you very much for your comments!</p>
<p dir=3D"ltr">/Kalle </p>

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