waddrmgr: include master key fingerprint in derivation path

Following the previous commit, some external hardware signers require a
master key fingerprint to be present within the PSBT input derivation
paths so that the signer can recognize which inputs are relevant and
must be signed.

waddrmgr/manager.go

@@ -1218,7 +1218,7 @@ func (m *Manager) Unlock(ns walletdb.ReadBucket, passphrase []byte) error {
 		// We'll also derive any private keys that are pending due to
 		// them being created while the address manager was locked.
 		for _, info := range manager.deriveOnUnlock {
-			addressKey, _, err := manager.deriveKeyFromPath(
+			addressKey, _, _, err := manager.deriveKeyFromPath(
 				ns, info.managedAddr.InternalAccount(),
 				info.branch, info.index, true,
 			)

waddrmgr/scoped_manager.go

@@ -72,6 +72,12 @@ type DerivationPath struct {
 	// Index is the final child in the derivation path. This denotes the
 	// key index within as a child of the account and branch.
 	Index uint32
+
+	// MasterKeyFingerprint represents the fingerprint of the root key (also
+	// known as the key with derivation path m/) corresponding to the
+	// account public key. This may be required by some hardware wallets for
+	// proper identification and signing.
+	MasterKeyFingerprint uint32
 }
 
 // KeyScope represents a restricted key scope from the primary root key within
@@ -448,6 +454,7 @@ func (s *ScopedKeyManager) loadAccountInfo(ns walletdb.ReadBucket,
 		Account:              acctInfo.acctKeyPub.ChildIndex(),
 		Branch:               branch,
 		Index:                index,
+		MasterKeyFingerprint: acctInfo.masterKeyFingerprint,
 	}
 	lastExtKey, err := s.deriveKey(acctInfo, branch, index, hasPrivateKey)
 	if err != nil {
@@ -469,6 +476,7 @@ func (s *ScopedKeyManager) loadAccountInfo(ns walletdb.ReadBucket,
 		Account:              acctInfo.acctKeyPub.ChildIndex(),
 		Branch:               branch,
 		Index:                index,
+		MasterKeyFingerprint: acctInfo.masterKeyFingerprint,
 	}
 	lastIntKey, err := s.deriveKey(acctInfo, branch, index, hasPrivateKey)
 	if err != nil {
@@ -580,7 +588,7 @@ func (s *ScopedKeyManager) DeriveFromKeyPath(ns walletdb.ReadBucket,
 	watchOnly := s.rootManager.WatchOnly()
 	private := !s.rootManager.IsLocked() && !watchOnly
 
-	addrKey, _, err := s.deriveKeyFromPath(
+	addrKey, _, _, err := s.deriveKeyFromPath(
 		ns, kp.InternalAccount, kp.Branch, kp.Index, private,
 	)
 	if err != nil {
@@ -601,18 +609,18 @@ func (s *ScopedKeyManager) DeriveFromKeyPath(ns walletdb.ReadBucket,
 // This function MUST be called with the manager lock held for writes.
 func (s *ScopedKeyManager) deriveKeyFromPath(ns walletdb.ReadBucket,
 	internalAccount, branch, index uint32, private bool) (
-	*hdkeychain.ExtendedKey, *hdkeychain.ExtendedKey, error) {
+	*hdkeychain.ExtendedKey, *hdkeychain.ExtendedKey, uint32, error) {
 
 	// Look up the account key information.
 	acctInfo, err := s.loadAccountInfo(ns, internalAccount)
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, 0, err
 	}
 	private = private && acctInfo.acctKeyPriv != nil
 
 	addrKey, err := s.deriveKey(acctInfo, branch, index, private)
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, 0, err
 	}
 
 	acctKey := acctInfo.acctKeyPub
@@ -620,7 +628,7 @@ func (s *ScopedKeyManager) deriveKeyFromPath(ns walletdb.ReadBucket,
 		acctKey = acctInfo.acctKeyPriv
 	}
 
-	return addrKey, acctKey, nil
+	return addrKey, acctKey, acctInfo.masterKeyFingerprint, nil
 }
 
 // chainAddressRowToManaged returns a new managed address based on chained
@@ -634,7 +642,7 @@ func (s *ScopedKeyManager) chainAddressRowToManaged(ns walletdb.ReadBucket,
 	// function, we use the internal isLocked to avoid a deadlock.
 	private := !s.rootManager.isLocked() && !s.rootManager.watchOnly()
 
-	addressKey, acctKey, err := s.deriveKeyFromPath(
+	addressKey, acctKey, masterKeyFingerprint, err := s.deriveKeyFromPath(
 		ns, row.account, row.branch, row.index, private,
 	)
 	if err != nil {
@@ -651,6 +659,7 @@ func (s *ScopedKeyManager) chainAddressRowToManaged(ns walletdb.ReadBucket,
 			Account:              acctKey.ChildIndex(),
 			Branch:               row.branch,
 			Index:                row.index,
+			MasterKeyFingerprint: masterKeyFingerprint,
 		}, acctInfo,
 	)
 }

wallet/utxos.go

@@ -155,7 +155,7 @@ func (w *Wallet) FetchInputInfo(prevOut *wire.OutPoint) (*wire.MsgTx,
 			PkScript: pkScript,
 		}, &psbt.Bip32Derivation{
 			PubKey:               pubKeyAddr.PubKey().SerializeCompressed(),
-			MasterKeyFingerprint: 0, // TODO
+			MasterKeyFingerprint: derivationPath.MasterKeyFingerprint,
 			Bip32Path: []uint32{
 				keyScope.Purpose + hdkeychain.HardenedKeyStart,
 				keyScope.Coin + hdkeychain.HardenedKeyStart,