Re: [bitcoin-dev] ANYPREVOUT in place of CTV

From: Nadav Ivgi <nadav@shesek•info>
To: darosior <darosior@protonmail•com>,
	 Bitcoin Protocol Discussion
	<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] ANYPREVOUT in place of CTV
Date: Mon, 25 Apr 2022 19:35:17 +0300	[thread overview]
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darosior via bitcoin-dev wrote:

> 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.

Some potential vault users looking to store funds for long time periods
(say of decades) might have quantumphobia and prefer to avoid Taproot for
that reason.

One of the arguments presented for not using pubkey hashes in Taproot is
that quantumphobic people could choose to continue using non-Taproot
outputs. Making a feature that's targeted for long-term cold-storage vaults
available on Taproot only might be less ideal in that view.

Cheers
shesek

On Fri, Apr 22, 2022 at 2:23 PM darosior 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.
>
> 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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