Subject: [bitcoindev] Summary: Covenants Support - Bitcoin Wiki

From: /dev /fd0 <[email-masked]>
Date: Tue, 31 Dec 2024 00:23:28 -0800 (PST)

Hi Bitcoin Developers,

I had shared covenants support wiki page link here on [mailing list][1] in 
the last week of November 2024. Multiple changes were made based on the 
feedback:

- Removed 'community support' from 'No'. Rephrased definitions for 'Prefer' 
and 'Evaluating'.
- Added LNHANCE category for a combination of opcodes.
- Added links for BIP drafts and a column for 'rationale'.
- Created a separate table for evaluations without a rationale.

Murch and Gloria shared their feedback in the bitcoin optech [podcast 
333][2]. I have started working on a [page][3] that lists use cases, 
prototype links and primitives used. We can still add more use cases in it. 
This list does not include use cases enabled by [OP_CHECKSIGFROMSTACK][4] 
alone or in combination with other opcodes like [LN SYMMETRY][5].

I had verified each entry to avoid spam and fake evaluations. Rearden was 
assigned moderator permissions on 8 December 2024 by Theymos to help me 
with the moderations. Some edits have been approved by other moderators.

Some insights from the table that could help developers working on 
different covenant proposals:

1. Multiple ways to achieve LN symmetry were discovered. SIGHASH_APO lacks 
interest among developers, contrary to the belief prior to this exercise.
2. OP_CHECKSIGFROMSTACK has unanimous support and is a part of multiple 
covenant proposals.
3. OP_PAIRCOMMIT, OP_INTERNALKEY and OP_CHECKCONTRACTVERIFY are not 
reviewed by enough developers. OP_PARCOMMIT seems to be controversial at 
this moment.

Objections:

```
======================
SIGHASH_APO
======================

LN SYMMETRY is possible with combination of a few opcodes which is more 
efficient. Its not the best option for covenants and cannot be used to 
improve Ark. Some developers prefer opcodes and not sighash flags.

Seems to be the result of an attempt to fix signatures to make them work 
for a specific use-case, but the end-result is hard-to-reason (for me) and 
not flexible. In general, SIGHASH flags are an encoding of specific 
predicates on the transaction, and I think the Script is better suited to 
carry the predicate. There is no interesting SIGHASH flag that couldn't be 
functionally simulated by introspection + CHECKSIGFROMSTACK (or other 
Script-based approaches), and that seems to me a much cleaner and ergonomic 
way to achieve the same goals.

======================
OP_TXHASH
======================

More expressive, many flag configurations, untested and undesirable use 
cases. Unaddressed comments in the BIP and the delay doesn't make sense 
because OP_CHECKTEMPLATEVERIFY can be upgraded later to achieve the same 
thing. Makes hash caching complex, potentially opening up DoS vectors or 
quadratic sighash.

Most templates you'd obtain with various combinations of parameters are 
meaningless. It implements state-carrying UTXOs in a very dirty way: adding 
additional inputs/outputs with no other meaning than "storing some state". 
This is ugly, inefficient, and bloats the UTXO set - and it definitely will 
happen if TXHASH is enabled without also enabling a clean way to carry 
state.

Follow up with an upgrade to OP_CHECKTEMPLATEVERIFY can fine tune it to 
what people are actually using covenants for, instead of prematurely 
optimizing everything with no data.

======================
OP_VAULT
======================

No demand for vaults. Customized for a specific use case.

======================
OP_CAT
======================

Can be used for various complex scripts including undesirable use cases 
(DEX, AMM and Hashrate Escrow). Enables granular transaction introspection 
through abuse of schnorr signatures and OP_CHECKSIG. Can be used for 
interesting use cases but alone does it poorly and inefficiently.

People can and will litter the chain with inefficient/ugly Scripts if 
activated alone. Since it happens to enable generic introspection by 
accident, and therefore an ugly version of state-carrying UTXOs, it 
shouldn't be enabled without more ergonomic opcodes for those use cases.

======================
OP_INTERNALKEY
======================

There are 3 'No' in the table, I couldn't find anything relevant in the 
rationales.

======================
OP_PAIRCOMMIT
======================

Adds unnecessary complexity, redundant if OP_CAT is activated in future and 
added for specific use case. LN SYMMETRY is possible without this opcode. 
It does not compose with anything that involves transaction introspection 
due to its specified tagged hash. Some developers prefer OP_CAT.

Not convinced it is impossible that there is no way to simulate CAT with 
PAIRCOMMIT, nor confident how much less powerful PAIRCOMMIT is than CAT.

======================
OP_CHECKTEMPLATEVERIFY
======================

Limited in scope and not recursive.
```

I have tried my best to remain unbiased in writing this summary and 
approving edits. There are a few things that I want to share and it could 
be a result of the aggressive marketing:

- A spammer had edited the table to remove all evaluations except in favor 
of OP_CAT and it was rejected.
- [Rationale][6] added by Aaron (sCrypt) does not mention anything about 
other opcodes and SIGHASH_APO. It is only focused on OP_CAT however 
evaluations exist in the table.
- I [requested][7] Udev (CatSwap) to add details about evaluation of other 
opcodes and SIGHASH_APO.
- Last [edit][8] by Roujiamo (bitdollar) has a rationale with incorrect 
signet stats and seems to be rephrased version of another rationale. 
Evaluation had 'weak' for OP_CTV before adding the rationale.
- An edit with duplicate rationale (in support of OP_CAT) was rejected 
because sharing the link for a rationale submitted by other developer adds 
no value in the table.

Evaluations without a rationale have some 'No' in different cells. Although 
none of them are backed by a rationale so cannot be considered for 
consensus discussion. The table is still updated regularly so you may see 
some of them with a rationale in 2025. Any suggestions to help achieve 
technical consensus are most welcome.

What's next?

- More rationales in the table
- Discuss objections on mailing list (if any)
- Workshops
- Add a table for economic nodes and their opinion
- Build activation client and discuss parameters

Finally, I would thank all the developers who added their evaluations in 
the table and everyone who shared updates on twitter. It was a coordinated 
effort to reach some technical consensus. You can read all the rationales 
in detail to understand different perspectives and reasons to support a 
combination of opcodes over others.

[1]: https://groups.google.com/g/bitcoindev/c/fdxkE1Al4TI/m/CeEuls2IAQAJ
[2]: https://bitcoinops.org/en/podcast/2024/12/17/
[3]: https://en.bitcoin.it/wiki/Covenants_Uses
[4]: https://github.com/bitcoin/bips/blob/master/bip-0348.md
[5]: https://gist.github.com/Ademan/4a14614fa850511d63a5b2a9b5104cb7
[6]: https://gist.github.com/gitzhou/dc92c41db1987db16fe665c26bc56dd9
[7]: 
https://gist.github.com/udevswap/b768d20d62549922b9e72428ef9eb608?permalink_comment_id=5359072#gistcomment-5359072
[8]: 
https://en.bitcoin.it/w/index.php?title=Covenants_support&diff=prev&oldid=70520

/dev/fd0
floppy disk guy

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