Date: Mon, 25 Apr 2022 16:35:14 +0000
To: darosior <darosior@protonmail.com>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
From: darosior <darosior@protonmail.com>
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Subject: Re: [bitcoin-dev] ANYPREVOUT in place of CTV
Precedence: list

Just a correction to my previous mail. Sorry for the non-attribution, i did=
n't recall APO covenants had been discussed in the context of CTV.

> > a write-up that explains how APO-AS w/out ANYONECANPAY approximates CTV=
?
>
> I'm not aware of any specific to CTV. It's just that the fields covered i=
n the CTV hash are very close to what

The comparison was already done by Anthony Towns.
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2019-June/017036.ht=
ml

Jeremy Rubin already pointed out that it missed committing to the nSequence=
s hash and number of inputs (and optionally scriptSigs).
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2019-June/017038.ht=
ml


------- Original Message -------
Le lundi 25 avril 2022 =C3=A0 3:35 PM, darosior via bitcoin-dev <bitcoin-de=
v@lists.linuxfoundation.org> a =C3=A9crit :


> Hi Richard,
>
> > Sounds good to me. Although from an activation perspective it may not b=
e either/or, both proposals do
>
> compete for scarce reviewer time
>
> Yes, of course. Let's say i was more interested in knowing if people who =
oppose CTV would oppose
> SIGHASH_ANYPREVOUT too. I think talking about activation of anything at t=
his point is premature.
>
> > For someone not as versed in CTV, why is it necessary that ANYONECANPAY=
 be optional to emulate CTV? Is there
>
> a write-up that explains how APO-AS w/out ANYONECANPAY approximates CTV?
>
> I'm not aware of any specific to CTV. It's just that the fields covered i=
n the CTV hash are very close to what
> ANYPREVOUT_ANYSCRIPT's signature hash covers [0]. The two things that CTV=
 commits to that APO_AS does not are
> the number of inputs and the hash of the inputs' sequences [1].
> Not committing to the number of inputs and other inputs' data is today's =
behaviour of ANYONECANPAY that can
> be combined with other signature hash types [1]. Thus APO_AS makes ACP ma=
ndatory, and to emulate CTV
> completely it should be optional.
>
>
> Antoine
>
> [0] https://github.com/bitcoin/bips/blob/master/bip-0119.mediawiki#Detail=
ed_Specification
> [1] https://github.com/bitcoin/bips/blob/master/bip-0118.mediawiki#signat=
ure-message
> [2] https://github.com/bitcoin/bitcoin/blob/10a626a1d6776447525f50d3e1a97=
b3c5bbad7d6/src/script/interpreter.cpp#L1327, https://github.com/bitcoin/bi=
tcoin/blob/10a626a1d6776447525f50d3e1a97b3c5bbad7d6/src/script/interpreter.=
cpp#L1517-L1522
>
>
> ------- Original Message -------
> Le dimanche 24 avril 2022 =C3=A0 10:41 PM, Richard Myers remyers@yakshave=
r.org a =C3=A9crit :
>
>
>
> > Hi darosior,
> >
> > Thanks for sharing your thoughts on this.
> >
> > > I would like to know people's sentiment about doing (a very slightly =
tweaked version of) BIP118 in place of
> > > (or before doing) BIP119.
> >
> > Sounds good to me. Although from an activation perspective it may not b=
e either/or, both proposals do compete for scarce reviewer time so their or=
dering will necessarily be driven by reviewer's priorities. My priority is =
eltoo which is why I focus on BIP-118.
> >
> > > SIGHASH_ANYPREVOUTANYSCRIPT, if its "ANYONECANPAY" behaviour is made =
optional [0], can emulate CTV just fine.
> >
> > For someone not as versed in CTV, why is it necessary that ANYONECANPAY=
 be optional to emulate CTV? Is there a write-up that explains how APO-AS w=
/out ANYONECANPAY approximates CTV?
> >
> > In the case of eltoo commit txs, we use bring-your-own-fee (BYOF) to la=
te-bind fees; that means ANYONECANPAY will always be paired with APO-AS for=
 eltoo. Settlement txs in eltoo use just APO and do not necessarily need to=
 be paired with ANYONECANPAY.
> >
> > I would guess making ANYONECANPAY the default for APO-AS was a way to s=
queeze in one more sighash flag. Perhaps there's another way to do it?
> >
> > Including SIGHASH_GROUP with APO for eltoo is also tempting. Specifical=
ly so the counter-party who commits a settlement tx can use for fees their =
settled to_self balance. How to rejigger the sighash flags to accommodate b=
oth APO and GROUP may be worth some discussion.
> >
> > The BIP-118 proposal will certainly benefit from having input from revi=
ewers looking at other protocols than eltoo.
> >
> > -- Richard
>
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