Add BIP 349: OP_INTERNALKEY #1534

reardencode · 2024-01-07T18:30:14Z

OP_INTERNALKEY is a new BIP342 tapscript only opcode (upgraded using OP_SUCCESS semantics) that takes bytes 1-32 (0-index, inclusive) from the BIP341 taproot control block and places them on the stack. This BIP describes that behavior.

vostrnad · 2024-01-17T01:51:14Z

bip-internalkey.mediawiki

+
+When building taproot outputs, especially those secured by an aggregate key
+representing more than 1 signer; the parties may wish to collaborate on signing
+with the taproot internal key, but only with additional script restrictions. In


Can you give an example where using the key path with an aggregate key and having every participant enforce the additional restrictions themselves (i.e. only signing if they're met) wouldn't suffice?

The most obvious case would be lightning symmetry where the parties want to pre-sign with CTV+CSFS to create a rebindable update transaction.

bip-internalkey.mediawiki

reardencode · 2024-04-24T21:59:26Z

Updated to match the BIN.

murchandamus

Has this proposal been discussed on the mailing list?

bip-internalkey.md

halseth · 2024-05-13T08:27:13Z

bip-internalkey.md

+[BIP 342]), `OP_INTERNALKEY` replaces `OP_SUCCESS203` (0xcb). `OP_INTERNALKEY`
+pushes the taproot internal key, as defined in [BIP 341], to the stack.
+
+## Motivation


Additional useful feature: ability to inspect the tweak to a key (in combination with some OP_TWEAKVERIFY).

That would require additional introspection beyond just INTERNALKEY too, wouldn't it?

Yes, something like TWEAKADD or TWEAKVERIFY.

ProofOfKeags · 2024-05-22T19:14:25Z

bip-internalkey.md

+
+When verifying taproot script spends having leaf version `0xc0` (as defined in
+[BIP 342]), `OP_INTERNALKEY` replaces `OP_SUCCESS203` (0xcb). `OP_INTERNALKEY`
+pushes the taproot internal key, as defined in [BIP 341], to the stack.


nit: might be nice to mark "taproot internal key" as a formal term, either by italicizing, backticks or the like. I find that marking terms that invoke a suite of definitions and properties is really helpful. We do it a lot in the BOLTs and I'd recommend doing it in the BIPs as much as we can.

murchandamus

This seems close to ready for a merge, although I am wondering whether it has gotten enough review from the community. I noticed that both this PR and the mailing list thread were not that active.

murchandamus · 2024-05-22T19:16:06Z

bip-internalkey.md

+
+## Specification
+
+When verifying taproot script spends having leaf version `0xc0` (as defined in


Suggested change

When verifying taproot script spends having leaf version `0xc0` (as defined in

When verifying taproot script path spends having leaf version `0xc0` (as defined in

murchandamus · 2024-05-22T19:20:05Z

bip-internalkey.md

+When building taproot outputs, especially those secured by an aggregate key
+representing more than one signer, the parties may wish to collaborate on
+signing with the taproot internal key, but only with additional script
+restrictions. In this case, `OP_INTERNALKEY` saves 8 vBytes.


Perhaps you could elaborate how OP_INTERNALKEY would save 8 vB, for example in a footnote. (I assume it’s an x-only key of 32 bytes, and otherwise you’d need a PUSH and the 32 bytes, but with OP_INTERNALKEY you only need only that one byte instead. But if I had to think about that, maybe others would also appreciate an explanation.

murchandamus · 2024-05-22T19:22:20Z

bip-internalkey.md

+
+### Mitigated control block overhead for scripts using hash locks
+
+In cases where script path spending is not desired, the internal key may be set


Did you mean:

Suggested change

In cases where script path spending is not desired, the internal key may be set

In cases where key path spending is not desired, the internal key may be set

murchandamus · 2024-05-22T19:42:09Z

bip-internalkey.md

+
+When verifying taproot script spends having leaf version `0xc0` (as defined in
+[BIP 342]), `OP_INTERNALKEY` replaces `OP_SUCCESS203` (0xcb). `OP_INTERNALKEY`
+pushes the taproot internal key, as defined in [BIP 341], to the stack.


It seems to me that this should be perhaps a bit more specific what exactly is being pushed to the stack. I assume this is referring to

Let p = c[1:33] and let P = lift_x(int(p)) where lift_x and [:] are defined as in BIP340. Fail if this point is not on the curve. […] q is referred to as taproot output key and p as taproot internal key.

but it would not hurt to clarify.

"the taproot internal key denoted as P in [BIP 341]"?

My point is that the "taproot internal key" refers to an abstract object in BIP 341 that is denoted as p:

"q is referred to as taproot output key and p as taproot internal key."

and it wouldn’t hurt to simply describe what you are referring to, instead of sending people to parse another BIP to get clued in.

How about:

"pushes the 32-byte x-only representation P of the taproot internal key p, as defined in [BIP 341], to the stack."

How about?

When verifying taproot script path spends having leaf version 0xc0 (as defined in [BIP 342]), OP_INTERNALKEY replaces OP_SUCCESS203 (0xcb). OP_INTERNALKEY pushes the 32-byte x-only representation (referred to as P) of the taproot internal key (referred to as p), as defined in [BIP 341], to the stack.

Note that BIP341 already defines the taproot internal key p (note the lowercase) as a 32-byte array (as opposed to, say, a point on the secp256k1 curve), so it's not necessary to reinterpret it in any way before pushing it to the stack.

If others feel that this passage is sufficiently clear, I don’t feel strongly about it.

So then:

When verifying taproot script path spends having leaf version 0xc0 (as defined in [BIP 342]), OP_INTERNALKEY replaces OP_SUCCESS203 (0xcb). OP_INTERNALKEY pushes the 32-byte taproot internal key (referred to as p), as defined in [BIP 341], to the stack.

?

Yes, we can add the "32-byte" qualifier for additional clarity. I would use slightly different phrasing, but that's just a suggestion:

When verifying taproot script path spends having leaf version 0xc0 (as defined in [BIP 342]), OP_INTERNALKEY replaces OP_SUCCESS203 (0xcb). OP_INTERNALKEY pushes the 32-byte taproot internal key p, as defined in [BIP 341], to the stack.

I find it weird that both taproot internal key and p are in italic and together like that. No hard preference just feels off somehow!

I understand that, but it's not unprecedented, for example in BIP341 you'll find "annex a". Also notice that they're in separate italic blocks, even though you can't tell from the rendered version.

moonsettler · 2024-11-11T22:05:41Z

So what exactly needs to be done to get this BIP unstuck?

murchandamus · 2024-11-12T21:17:35Z

There do seem to be several unaddressed review comments. Happy to review again when the open review comments have been addressed.

murchandamus · 2024-11-14T17:00:30Z

Let’s call this BIP 349. Could you please rename the file, add the number to the preamble, and update the README table accordingly?

murchandamus

CI isn’t passing, I think the problem are two little issues with the Preamble.

murchandamus · 2024-11-14T20:41:59Z

bip-0349.md

+```
+BIP: 349
+Layer: Consensus (soft fork)
+Title: OP_INTERNALKEY
+Author: Brandon Black <[email protected]>, Jeremy Rubin <[email protected]>
+Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0349
+Status: Draft
+Type: Standards Track
+Created: 2023-12-22
+License: BSD-3-Clause
+```


I think these changes should make the CI pass:

use <pre> and </pre> instead of ```

put each author on a separate line

I also suggest updating the date in the Created header to the day that the proposal was assigned a number as that’s the meaning of the field according to BIP 2.

Suggested change

```

BIP: 349

Layer: Consensus (soft fork)

Title: OP_INTERNALKEY

Author: Brandon Black <[email protected]>, Jeremy Rubin <[email protected]>

Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0349

Status: Draft

Type: Standards Track

Created: 2023-12-22

License: BSD-3-Clause

```

<pre>

BIP: 349

Layer: Consensus (soft fork)

Title: OP_INTERNALKEY

Author: Brandon Black <[email protected]>

Jeremy Rubin <[email protected]>

Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0349

Status: Draft

Type: Standards Track

Created: 2024-11-14

License: BSD-3-Clause

</pre>

reardencode · 2024-11-14T21:38:31Z

Thanks @murchandamus !

murchandamus · 2024-11-14T21:38:52Z

I updated the Preamble formatting:

Move authors to separate lines
Use <pre> formatting
Correct the background color in README table
Updated the "Created" header to use the date of the number assignment as prescribed by BIP 2.

This should now be good to go unless you wanted to make more changes before it is merged.

reardencode mentioned this pull request Jan 7, 2024

OP_CHECKTEMPLATEVERIFY, OP_CHECKSIGFROMSTACK(VERIFY), OP_INTERNALKEY validation (LNHANCE) bitcoin/bitcoin#29198

Closed

Davidson-Souza mentioned this pull request Jan 8, 2024

Topicos Janeiro saopaulobitdevs/saopaulobitdevs.org#17

Closed

reardencode force-pushed the internalkey branch from 4d448cc to a24aca4 Compare January 13, 2024 17:18

vostrnad reviewed Jan 17, 2024

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reardencode force-pushed the internalkey branch 2 times, most recently from c9842c4 to 729276c Compare April 24, 2024 21:34

jonatack added Needs number assignment New BIP and removed Needs number assignment labels Apr 24, 2024

reardencode force-pushed the internalkey branch 3 times, most recently from 978f4cd to efd4bd9 Compare April 25, 2024 05:17

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reardencode force-pushed the internalkey branch from efd4bd9 to e7dfa7e Compare May 14, 2024 21:44

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Starco1001 approved these changes Jun 4, 2024

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murchandamus removed the Needs number assignment label Nov 14, 2024

murchandamus changed the title ~~Add bip-internalkey~~ Add BIP 349: OP_INTERNALKEY Nov 14, 2024

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reardencode and others added 2 commits November 14, 2024 16:30

Add bip-internalkey

75351f2

Fixes and clarifications to address PR comments

b35383b

BIP-349

329b0d3

murchandamus force-pushed the internalkey branch from 4f25671 to 3c147cc Compare November 14, 2024 21:31

murchandamus removed the PR Author action required Needs updates, has unaddressed review comments, or is otherwise waiting for PR author label Nov 14, 2024

murchandamus added 2 commits November 14, 2024 16:36

BIP349: Fix preamble for CI issues

669d3b3

BIP349: Set Created header to number assignment

217ae0d

murchandamus force-pushed the internalkey branch from 3c147cc to 217ae0d Compare November 14, 2024 21:37

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Add BIP 349: OP_INTERNALKEY #1534

Add BIP 349: OP_INTERNALKEY #1534

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murchandamus commented Nov 14, 2024


		## Specification

		When verifying taproot script spends having leaf version `0xc0` (as defined in

	When verifying taproot script spends having leaf version `0xc0` (as defined in
	When verifying taproot script path spends having leaf version `0xc0` (as defined in


		### Mitigated control block overhead for scripts using hash locks

		In cases where script path spending is not desired, the internal key may be set

	In cases where script path spending is not desired, the internal key may be set
	In cases where key path spending is not desired, the internal key may be set

Add BIP 349: OP_INTERNALKEY #1534

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Add BIP 349: OP_INTERNALKEY #1534

Add BIP 349: OP_INTERNALKEY #1534

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