Hi pushd.
Would you mind clarifying what you mean by BIP118 being a premature idea?
SIGHASH_ANYPREVOUT, or SIGHASH_NOINPUT, as it was called back then, was first proposed in the original Lightning Network whitepaper back in 2015.
It has been discussed on and off for many years now. I would not call it a premature idea.

Now, the revised "Taprooted" version called ANYPREVOUT is a couple of years old, so going with the NOINPUT version could be a safer bet (though that's a bit ridiculous in my opinion).

Regarding that you do not find use-cases interesting. That's all fine I suppose, but in the Lightning Network scene, I think it's fair to say that there's widespread enthusiasm in getting a working eltoo solution, which necessitates something like NOINPUT/ANYPREVOUT.
And even if eltoo wouldn't happen, enabling spacechains, covenants and blind statechains seem like sufficient use-cases to me.

Cheers
Hampus

On Fri, Apr 22, 2022 at 9:32 PM pushd via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

I would like to know people's sentiment about doing (a very slightly tweaked version of) BIP118 in place of (or before doing) BIP119.


NACK for the below reasons:

- Premature idea
- I do not find use cases interesting
- We are still in research phase of implementing covenants in bitcoin and looking for the best proposal
- Taproot soft fork was recently activated and its too soon
- Not enough documentation available
- Could not find any pull request in core for BIP 118 that can be reviewed
- Not enough tools available for testing


pushd
---

parallel lines meet at infinity?

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On Friday, April 22nd, 2022 at 5:30 PM, bitcoin-dev-request@lists.linuxfoundation.org wrote:

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Today's Topics:

1. ANYPREVOUT in place of CTV (darosior)

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Message: 1
Date: Fri, 22 Apr 2022 11:11:41 +0000
From: darosior darosior@protonmail.com

To: Bitcoin Protocol Discussion
bitcoin-dev@lists.linuxfoundation.org

Subject: [bitcoin-dev] ANYPREVOUT in place of CTV
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I would like to know people's sentiment about doing (a very slightly tweaked version of) BIP118 in place of
(or before doing) BIP119.

SIGHASH_ANYPREVOUT and its precedent iterations have been discussed for over 6 years. It presents proven and
implemented usecases, that are demanded and (please someone correct me if i'm wrong) more widely accepted than
CTV's.

SIGHASH_ANYPREVOUTANYSCRIPT, if its "ANYONECANPAY" behaviour is made optional [0], can emulate CTV just fine.
Sure then you can't have bare or Segwit v0 CTV, and it's a bit more expensive to use. But we can consider CTV
an optimization of APO-AS covenants.

CTV advocates have been presenting vaults as the flagship usecase. Although as someone who've been trying to
implement practical vaults for the past 2 years i doubt CTV is necessary nor sufficient for this (but still
useful!), using APO-AS covers it. And it's not a couple dozen more virtual bytes that are going to matter for
a potential vault user.

If after some time all of us who are currently dubious about CTV's stated usecases are proven wrong by onchain
usage of a less efficient construction to achieve the same goal, we could roll-out CTV as an optimization. In
the meantime others will have been able to deploy new applications leveraging ANYPREVOUT (Eltoo, blind
statechains, etc..[1]).

Given the interest in, and demand for, both simple covenants and better offchain protocols it seems to me that
BIP118 is a soft fork candidate that could benefit more (if not most of) Bitcoin users.
Actually i'd also be interested in knowing if people would oppose the APO-AS part of BIP118, since it enables
CTV's features, for the same reason they'd oppose BIP119.

[0] That is, to not commit to the other inputs of the transaction (via sha_sequences and maybe also
sha_amounts). Cf https://github.com/bitcoin/bips/blob/master/bip-0118.mediawiki#signature-message.

[1] https://anyprevout.xyz/ "Use Cases" section

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