multi: add ability to fund+use musig2 channels that commit to a tapscript root #8546

Roasbeef · 2024-03-13T15:01:18Z

In this PR, we add the initial plumbing that'll allow users to create and use musig2 channels that also commit to a tapscript root. Along the way, we start to store a new optional tapscript root in the channeldb.OpenChannel struct within the existing TLV stream appended to the older hard coded byte stream. The musig2 session itself will now conditionally pass in a tapscript root to the key aggregation and signing operations. We've also hooked up the lower half of the funding flow (lnwallet reservations) as well to ensure the new field gets propagated all the way down the relevant call stacks.

In this commit, we rename the files as assembler.go houses the primary interfaces/abstractions of the package. In the rest of the codebase, this file is near uniformly called interface.go, so we rename the file to make the repo more digestible at a scan.

In this commit, we consolidate the root bucket TLVs into a new struct. This makes it easier to see all the new TLV fields at a glance. We also convert TLV usage to use the new type param based APis.

This'll allow us to create a funding output that uses musig2, but uses a tapscript tweak rather than a normal BIP 86 tweak.

coderabbitai · 2024-03-13T15:01:23Z

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In most cases, we won't yet be passing a root. The option usage helps us keep the control flow mostly unchanged.

This isn't hooked up yet to the funding manager, but with this commit, we can now start to write internal unit tests that handle musig2 channels with a tapscript root.

With this commit, the channel is now aware of if it's a musig2 channel, that also has a tapscript root. We'll need to always pass in the tapscript root each time we: make the funding output, sign a new state, and also verify a new state.

guggero

Great work, can really see the pieces coming together now 💯

guggero · 2024-03-19T11:36:48Z

channeldb/channel.go


+	// TapscriptRoot is an optional tapscript root used to derive the
+	// musig2 funding output.
+	TapscriptRoot fn.Option[chainhash.Hash]


nit: move this to next commit since it's not yet used here?

guggero · 2024-03-19T11:39:56Z

channeldb/channel.go

+		),
+	}
+
+	if len(openChan.Memo) == 0 {


nit: fix the != 0 in this commit?

guggero · 2024-03-19T11:41:36Z

channeldb/channel.go

 	auxData.memo.WhenSome(func(memo tlv.RecordT[tlv.TlvType5, []byte]) {
 		tlvRecords = append(tlvRecords, memo.Record())
 	})
+	auxData.tapscriptRoot.WhenSome(func(root tlv.RecordT[tlv.TlvType6, [32]byte]) { //nolint:lll


nit: format as:

auxData.tapscriptRoot.WhenSome( func(root tlv.RecordT[tlv.TlvType6, [32]byte]) { tlvRecords = append(tlvRecords, root.Record()) } )

instead? Or place the //nolint:lll above the line instead of at the end to make it even longer?

guggero · 2024-03-19T11:42:28Z

channeldb/channel_test.go

 	op := wire.OutPoint{Hash: key, Index: uniqueOutputIndex.Load()}

+	var tapscriptRoot chainhash.Hash
+	copy(tapscriptRoot[:], bytes.Repeat([]byte{1}, 32))


While we're at it, should we also throw in a value for the memo since that doesn't seem to be covered yet?

guggero · 2024-03-19T11:49:19Z

lnwallet/chanfunding/wallet_assembler.go

 				// don't have to provide for it during coin
-				// selection. The manually selected coins can be
-				// spent entirely on the channel funding. If
+				// selection. The manually selected coins can


Just asking out of curiousity, did you change your editor's settings? Because it looks to me like this fit perfectly before...

guggero · 2024-03-19T11:54:48Z

contractcourt/chain_watcher.go

 		err error
 	)
 	if chanState.ChanType.IsTaproot() {
+		fundingOpts := fn.MapOptionZ(


Nice trick 😎

guggero · 2024-03-19T11:59:38Z

lnwallet/musig_session.go

 func NewMusigPartialSig(sig *musig2.PartialSignature,
 	signerNonce, combinedNonce lnwire.Musig2Nonce,
-	signerKeys []*btcec.PublicKey) *MusigPartialSig {
+	signerKeys []*btcec.PublicKey, tapscriptTweak fn.Option[chainhash.Hash],


nit: break before tapscriptTweak instead?

guggero · 2024-03-19T12:08:16Z

lnwallet/reservation.go

+	// tapscriptRoot is the root of the tapscript tree that will be used to
+	// create the musig2 funding output. This is only used for taproot
+	// channels.
+	tapscriptRoot fn.Option[chainhash.Hash]


Unused since it's already in partialState?

GeorgeTsagk

had a look, beautiful usage of fn package

GeorgeTsagk · 2024-03-20T15:03:42Z

channeldb/channel.go

 		),
 	}

-	if len(openChan.Memo) == 0 {


was this some unrelated old typo?

GeorgeTsagk · 2024-03-20T15:40:46Z

channeldb/channel.go

+		),
+	}
+
+	if len(openChan.Memo) == 0 {


GeorgeTsagk · 2024-03-20T15:43:54Z

channeldb/channel.go

+		revokeKeyLoc: tlv.NewRecordT[tlv.TlvType1, keyLocRecord](
+			keyLocRecord{openChan.RevocationKeyLocator},
+		),
+		initialLocalBalance: tlv.NewPrimitiveRecord[tlv.TlvType2, uint64](


nit: line length here and below

GeorgeTsagk · 2024-03-20T17:05:02Z

lnwallet/channel_test.go

 			anchorAmt:            anchorSize * 2,
 		})
 	})
+	t.Run("taproot with tapscript root", func(t *testing.T) {


IIUC these tests only check that the aux tapscript root can co-exist within the channel, but doesn't use the tapscript root in any way

correct?

guggero · 2024-04-03T10:45:17Z

channeldb/channel.go

-// DKeyLocator is a decoder for keychain.KeyLocator.
-func DKeyLocator(r io.Reader, val interface{}, buf *[8]byte, l uint64) error {
+// dKeyLocator is a decoder for keychain.KeyLocator.
+func dKeyLocator(r io.Reader, val interface{}, buf *[8]byte, l uint64) error {


We shouldn't un-export these two functions, since we apparently use them in Loop.

lightninglabs-deploy · 2024-04-17T12:41:34Z

@Roasbeef, remember to re-request review from reviewers when ready

guggero · 2024-04-24T09:40:29Z

Replacement version of this PR with all current review comments applied and rebased on the 0-19-staging branch created here: #8683

Roasbeef added 5 commits March 12, 2024 10:17

channeldb: consolidate root bucket TLVs into new struct

784d236

In this commit, we consolidate the root bucket TLVs into a new struct. This makes it easier to see all the new TLV fields at a glance. We also convert TLV usage to use the new type param based APis.

channeldb: add optional TapscriptRoot field + feature bit

5d18c65

input: add new tapscript root func op to GenTaprootFundingScript

733e192

This'll allow us to create a funding output that uses musig2, but uses a tapscript tweak rather than a normal BIP 86 tweak.

lnwallet/chanfunding: add optional tapscript root

1e07ba3

Roasbeef added taproot musig2 taproot chans labels Mar 13, 2024

guggero self-requested a review March 13, 2024 15:22

GeorgeTsagk self-requested a review March 13, 2024 20:34

dstadulis mentioned this pull request Mar 14, 2024

[feature]: enable funding+use of musig2 channels that commit to a tapscript root lightninglabs/taproot-assets#838

Closed

Roasbeef added 3 commits March 15, 2024 09:54

multi: update GenTaprootFundingScript to pass tapscript root

7d3c83b

In most cases, we won't yet be passing a root. The option usage helps us keep the control flow mostly unchanged.

lnwallet: update internal funding flow w/ tapscript root

b8cb4e6

This isn't hooked up yet to the funding manager, but with this commit, we can now start to write internal unit tests that handle musig2 channels with a tapscript root.

Roasbeef force-pushed the funding-tapcript branch from 3176b9c to fa13125 Compare March 15, 2024 14:03

lnwallet: add initial unit tests for musig2+tapscript root chans

33e0cea

Roasbeef force-pushed the funding-tapcript branch from fa13125 to 33e0cea Compare March 15, 2024 14:05

guggero reviewed Mar 19, 2024

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GeorgeTsagk reviewed Mar 20, 2024

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guggero reviewed Apr 3, 2024

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guggero mentioned this pull request Apr 24, 2024

[1/?]: multi: add ability to fund+use musig2 channels that commit to a tapscript root #8683

Merged

guggero closed this Apr 24, 2024

multi: add ability to fund+use musig2 channels that commit to a tapscript root #8546

multi: add ability to fund+use musig2 channels that commit to a tapscript root #8546

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Roasbeef commented Mar 13, 2024

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lightninglabs-deploy commented Apr 17, 2024

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