Date: Thu, 17 May 2018 06:28:54 -0400
To: Rusty Russell <rusty@rustcorp.com.au>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Reply-To: ZmnSCPxj <ZmnSCPxj@protonmail.com>
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Subject: Re: [bitcoin-dev] Making OP_TRUE standard?
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Good morning Rusty and list,

> Your zero-val-OP_TRUE-can't-be-spent-after-same-block SF is interesting,
>=20
> but if we want a SF just give us SIGHASH_NOINPUT and we'll not need this
>=20
> at all (though others still might).

We might still want this in general in Lightning; for instance we could mak=
e every funding transaction include such an output.  If it turns out, our i=
nitial feerate estimate for the funding transaction is low, we can use the =
`OP_TRUE` for fee-bumping.  This is a win for Lightning since the funding t=
ransaction ID remains the same (even in Decker-Russell-Osuntokun, the trigg=
er transaction is signed with `SIGHASH_ALL`, and refers to a fixed funding =
transaction ID).

Without the `OP_TRUE`-for-fee-bump, we would have to pretend to open a new =
different channel and RBF the old funding transaction with a new higher-fee=
rate funding transaction, then keep track of which one gets confirmed deepl=
y (there is a race where a miner discovers a block using the older funding =
transaction before our broadcast of the new funding transaction reaches it)=
.

(we could also feebump using the change output of the funding transaction, =
but such a change output might not exist for all funding transactions.)

Regards,
ZmnSCPxj