multi: add ability to specify local nonces for musig2 signer rpc, add itest for remote signer taproot chans

docs/release-notes/release-notes-0.17.0.md

@@ -244,6 +244,13 @@ None
 * Add [`--unused`](https://github.com/lightningnetwork/lnd/pull/6387) to
   `lncli newaddr` command.
 
+* [The `MuSig2SessionRequest` proto message now contains a field to allow a
+  caller to specify a custom signing
+  nonce](https://github.com/lightningnetwork/lnd/pull/7994). This can be useful
+  for protocol where an external nonces must be pre-generated before the full
+  session can be completed.
+
+
 ## Code Health
 * Updated [our fork for serializing protobuf as JSON to be based on the
   latest version of `google.golang.org/protobuf` instead of the deprecated

input/musig2.go

@@ -49,12 +49,13 @@ type MuSig2Signer interface {
 	// already known, they can be submitted as well to reduce the number of
 	// method calls necessary later on.
 	//
-	// The set of sessionOpts are _optional_ and allow a caller to modify
-	// the generated sessions. As an example the local nonce might already
-	// be generated ahead of time.
+	// The localNonces field is optional. If it is set, then the specified
+	// nonces will be used instead of generating from scratch.  This is
+	// useful in instances where the nonces are generated ahead of time
+	// before the set of signers is known.
 	MuSig2CreateSession(MuSig2Version, keychain.KeyLocator,
 		[]*btcec.PublicKey, *MuSig2Tweaks, [][musig2.PubNonceSize]byte,
-		...musig2.SessionOption) (*MuSig2SessionInfo, error)
+		*musig2.Nonces) (*MuSig2SessionInfo, error)
 
 	// MuSig2RegisterNonces registers one or more public nonces of other
 	// signing participants for a session identified by its ID. This method
@@ -379,18 +380,18 @@ func combineKeysV040(allSignerPubKeys []*btcec.PublicKey, sortKeys bool,
 // MuSig2CreateContext creates a new MuSig2 signing context.
 func MuSig2CreateContext(bipVersion MuSig2Version, privKey *btcec.PrivateKey,
 	allSignerPubKeys []*btcec.PublicKey, tweaks *MuSig2Tweaks,
-	sessionOpts ...musig2.SessionOption,
+	localNonces *musig2.Nonces,
 ) (MuSig2Context, MuSig2Session, error) {
 
 	switch bipVersion {
 	case MuSig2Version040:
 		return createContextV040(
-			privKey, allSignerPubKeys, tweaks, sessionOpts...,
+			privKey, allSignerPubKeys, tweaks, localNonces,
 		)
 
 	case MuSig2Version100RC2:
 		return createContextV100RC2(
-			privKey, allSignerPubKeys, tweaks, sessionOpts...,
+			privKey, allSignerPubKeys, tweaks, localNonces,
 		)
 
 	default:
@@ -403,7 +404,7 @@ func MuSig2CreateContext(bipVersion MuSig2Version, privKey *btcec.PrivateKey,
 // BIP draft version 1.0.0rc2.
 func createContextV100RC2(privKey *btcec.PrivateKey,
 	allSignerPubKeys []*btcec.PublicKey, tweaks *MuSig2Tweaks,
-	sessionOpts ...musig2.SessionOption,
+	localNonces *musig2.Nonces,
 ) (*musig2.Context, *musig2.Session, error) {
 
 	// The context keeps track of all signing keys and our local key.
@@ -419,6 +420,13 @@ func createContextV100RC2(privKey *btcec.PrivateKey,
 			"context: %v", err)
 	}
 
+	var sessionOpts []musig2.SessionOption
+	if localNonces != nil {
+		sessionOpts = append(
+			sessionOpts, musig2.WithPreGeneratedNonce(localNonces),
+		)
+	}
+
 	muSigSession, err := muSigContext.NewSession(sessionOpts...)
 	if err != nil {
 		return nil, nil, fmt.Errorf("error creating MuSig2 signing "+
@@ -432,7 +440,7 @@ func createContextV100RC2(privKey *btcec.PrivateKey,
 // draft version 0.4.0.
 func createContextV040(privKey *btcec.PrivateKey,
 	allSignerPubKeys []*btcec.PublicKey, tweaks *MuSig2Tweaks,
-	_ ...musig2.SessionOption,
+	_ *musig2.Nonces,
 ) (*musig2v040.Context, *musig2v040.Session, error) {
 
 	// The context keeps track of all signing keys and our local key.

input/musig2_session_manager.go

@@ -63,7 +63,7 @@ func NewMusigSessionManager(keyFetcher PrivKeyFetcher) *MusigSessionManager {
 func (m *MusigSessionManager) MuSig2CreateSession(bipVersion MuSig2Version,
 	keyLoc keychain.KeyLocator, allSignerPubKeys []*btcec.PublicKey,
 	tweaks *MuSig2Tweaks, otherSignerNonces [][musig2.PubNonceSize]byte,
-	sessionOpts ...musig2.SessionOption) (*MuSig2SessionInfo, error) {
+	localNonces *musig2.Nonces) (*MuSig2SessionInfo, error) {
 
 	// We need to derive the private key for signing. In the remote signing
 	// setup, this whole RPC call will be forwarded to the signing
@@ -78,7 +78,7 @@ func (m *MusigSessionManager) MuSig2CreateSession(bipVersion MuSig2Version,
 	// Create a signing context and session with the given private key and
 	// list of all known signer public keys.
 	musigContext, musigSession, err := MuSig2CreateContext(
-		bipVersion, privKey, allSignerPubKeys, tweaks, sessionOpts...,
+		bipVersion, privKey, allSignerPubKeys, tweaks, localNonces,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("error creating signing context: %w",

itest/lnd_payment_test.go

@@ -233,19 +233,34 @@ func testAsyncPayments(ht *lntest.HarnessTest) {
 	ht.EnsureConnected(alice, bob)
 	ht.FundCoins(btcutil.SatoshiPerBitcoin, alice)
 
-	runAsyncPayments(ht, alice, bob)
+	runAsyncPayments(ht, alice, bob, nil)
 }
 
 // runAsyncPayments tests the performance of the async payments.
-func runAsyncPayments(ht *lntest.HarnessTest, alice, bob *node.HarnessNode) {
+func runAsyncPayments(ht *lntest.HarnessTest, alice, bob *node.HarnessNode,
+	commitType *lnrpc.CommitmentType) {
+
 	const paymentAmt = 100
 
+	channelCapacity := btcutil.Amount(paymentAmt * 2000)
+
+	chanArgs := lntest.OpenChannelParams{
+		Amt: channelCapacity,
+	}
+
+	if commitType != nil {
+		chanArgs.CommitmentType = *commitType
+
+		if *commitType == lnrpc.CommitmentType_SIMPLE_TAPROOT {
+			chanArgs.Private = true
+		}
+	}
+
 	// First establish a channel with a capacity equals to the overall
 	// amount of payments, between Alice and Bob, at the end of the test
 	// Alice should send all money from her side to Bob.
-	channelCapacity := btcutil.Amount(paymentAmt * 2000)
 	chanPoint := ht.OpenChannel(
-		alice, bob, lntest.OpenChannelParams{Amt: channelCapacity},
+		alice, bob, chanArgs,
 	)
 
 	info := ht.QueryChannelByChanPoint(alice, chanPoint)

itest/lnd_remote_signer_test.go

@@ -60,6 +60,7 @@ func testRemoteSigner(ht *lntest.HarnessTest) {
 		name       string
 		randomSeed bool
 		sendCoins  bool
+		commitType lnrpc.CommitmentType
 		fn         func(tt *lntest.HarnessTest,
 			wo, carol *node.HarnessNode)
 	}
@@ -94,8 +95,19 @@ func testRemoteSigner(ht *lntest.HarnessTest) {
 		name:      "async payments",
 		sendCoins: true,
 		fn: func(tt *lntest.HarnessTest, wo, carol *node.HarnessNode) {
-			runAsyncPayments(tt, wo, carol)
+			runAsyncPayments(tt, wo, carol, nil)
 		},
+	}, {
+		name:      "async payments taproot",
+		sendCoins: true,
+		fn: func(tt *lntest.HarnessTest, wo, carol *node.HarnessNode) {
+			commitType := lnrpc.CommitmentType_SIMPLE_TAPROOT
+
+			runAsyncPayments(
+				tt, wo, carol, &commitType,
+			)
+		},
+		commitType: lnrpc.CommitmentType_SIMPLE_TAPROOT,
 	}, {
 		name: "shared key",
 		fn: func(tt *lntest.HarnessTest, wo, carol *node.HarnessNode) {
@@ -199,11 +211,18 @@ func testRemoteSigner(ht *lntest.HarnessTest) {
 			require.NoError(st, err)
 		}
 
+		var commitArgs []string
+		if subTest.commitType == lnrpc.CommitmentType_SIMPLE_TAPROOT {
+			commitArgs = lntest.NodeArgsForCommitType(
+				subTest.commitType,
+			)
+		}
+
 		// WatchOnly is the node that has a watch-only wallet and uses
 		// the Signer node for any operation that requires access to
 		// private keys.
 		watchOnly := st.NewNodeRemoteSigner(
-			"WatchOnly", []string{
+			"WatchOnly", append([]string{
 				"--remotesigner.enable",
 				fmt.Sprintf(
 					"--remotesigner.rpchost=localhost:%d",
@@ -217,7 +236,8 @@ func testRemoteSigner(ht *lntest.HarnessTest) {
 					"--remotesigner.macaroonpath=%s",
 					signer.Cfg.AdminMacPath,
 				),
-			}, password, &lnrpc.WatchOnly{
+			}, commitArgs...),
+			password, &lnrpc.WatchOnly{
 				MasterKeyBirthdayTimestamp: 0,
 				MasterKeyFingerprint:       nil,
 				Accounts:                   watchOnlyAccounts,
@@ -235,7 +255,7 @@ func testRemoteSigner(ht *lntest.HarnessTest) {
 			)
 		}
 
-		carol := st.NewNode("carol", nil)
+		carol := st.NewNode("carol", commitArgs)
 		st.EnsureConnected(watchOnly, carol)
 
 		return signer, watchOnly, carol