Date: Wed, 9 May 2018 16:59:14 -0400
From: Peter Todd <pete@petertodd.org>
To: Johnson Lau <jl2012@xbt.hk>
Message-ID: <20180509205913.5vpivaudj5e3bnih@petertodd.org>
References: <87po25lmzs.fsf@rustcorp.com.au>
	<F8C553EE-9AF5-4348-90B7-3EC55FC46B4C@xbt.hk>
	<20180509192733.6aif4wapolbb5z7c@petertodd.org>
	<4E64F59E-3367-4C4E-A9FB-48ED568BC2D3@xbt.hk>
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Cc: bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Making OP_TRUE standard?
Precedence: list


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On Thu, May 10, 2018 at 04:19:31AM +0800, Johnson Lau wrote:
>=20
>=20
> > On 10 May 2018, at 3:27 AM, Peter Todd <pete@petertodd.org> wrote:
> >=20
> > On Thu, May 10, 2018 at 01:56:46AM +0800, Johnson Lau via bitcoin-dev w=
rote:
> >> You should make a =E2=80=9C0 fee tx with exactly one OP_TRUE output=E2=
=80=9D standard, but nothing else. This makes sure CPFP will always be need=
ed, so the OP_TRUE output won=E2=80=99t pollute the UTXO set
> >>=20
> >> Instead, would you consider to use ANYONECANPAY to sign the tx, so it =
is possible add more inputs for fees? The total tx size is bigger than the =
OP_TRUE approach, but you don=E2=80=99t need to ask for any protocol change.
> >>=20
> >> In long-term, I think the right way is to have a more flexible SIGHASH=
 system to allow people to add more inputs and outputs easily.
> >=20
> > I don't think that will work, as a zero-fee tx won't get relayed even w=
ith
> > CPFP, due to the fact that we haven't yet implemented package-based tx
> > relaying.
> >=20
> > --=20
> > https://petertodd.org 'peter'[:-1]@petertodd.org
>=20
> My only concern is UTXO pollution. There could be a =E2=80=9CCPFP anchor=
=E2=80=9D softfork that outputs with empty scriptPubKey and 0 value are spe=
ndable only in the same block. If not spent immediately, they become invali=
d and are removed from UTXO. But I still think the best solution is a more =
flexible SIGHASH system, which doesn=E2=80=99t need CPFP at all.

I don't see any reason why UTXO pollution would be a special concern so lon=
g as
those outputs are subject to the same dust rules as any other output is.

--=20
https://petertodd.org 'peter'[:-1]@petertodd.org

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