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From: Johnson Lau <jl2012@xbt.hk>
In-Reply-To: <20180509192733.6aif4wapolbb5z7c@petertodd.org>
Date: Thu, 10 May 2018 04:19:31 +0800
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Message-Id: <4E64F59E-3367-4C4E-A9FB-48ED568BC2D3@xbt.hk>
References: <87po25lmzs.fsf@rustcorp.com.au>
	<F8C553EE-9AF5-4348-90B7-3EC55FC46B4C@xbt.hk>
	<20180509192733.6aif4wapolbb5z7c@petertodd.org>
To: Peter Todd <pete@petertodd.org>
Cc: bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Making OP_TRUE standard?
Precedence: list


> 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 =
wrote:
>> 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 needed, 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 =
with
> CPFP, due to the fact that we haven't yet implemented package-based tx
> relaying.
>=20
> --=20
> https://petertodd.org 'peter'[:-1]@petertodd.org

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 spendable only in the same block. If not spent immediately, =
they become invalid 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.=