Good morning darosior,

Do you know if there is a working implementation of APO somewhere that people can use to try out some of the proposed usecases? For example, it would be great to see what eltoo would actually look like on an APO signet. Or to see some working code for a vault using covenants in an APO world.

I haven’t seen much in the way of APO implementations recently, but I also haven’t gone looking, so would appreciate any links!

Thanks

On Fri, Apr 22, 2022 at 7:11 AM, 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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