derivekey: show master fingerprint

Author: guggero

cmd/chantools/derivekey.go

@@ -12,6 +12,7 @@ import (
 const deriveKeyFormat = `
 Path:				%s
 Network: 			%s
+Master Fingerprint:             %x
 Public key: 			%x
 Extended public key (xpub): 	%v
 Address: 			%v
@@ -110,8 +111,13 @@ func deriveKey(extendedKey *hdkeychain.ExtendedKey, path string,
 		privKey, xPriv = wif.String(), child.String()
 	}
 
+	_, fingerPrintBytes, err := fingerprint(extendedKey)
+	if err != nil {
+		return fmt.Errorf("could not get fingerprint: %w", err)
+	}
+
 	result := fmt.Sprintf(
-		deriveKeyFormat, path, chainParams.Name,
+		deriveKeyFormat, path, chainParams.Name, fingerPrintBytes,
 		pubKey.SerializeCompressed(), neutered, addrP2WKH, addrP2PKH,
 		addrP2TR, privKey, xPriv,
 	)

cmd/chantools/signpsbt.go

@@ -221,14 +221,11 @@ func signPsbt(rootKey *hdkeychain.ExtendedKey,
 func findMatchingDerivationPath(rootKey *hdkeychain.ExtendedKey,
 	pIn *psbt.PInput) ([]uint32, error) {
 
-	pubKey, err := rootKey.ECPubKey()
+	masterFingerprint, _, err := fingerprint(rootKey)
 	if err != nil {
 		return nil, fmt.Errorf("error getting public key: %w", err)
 	}
 
-	pubKeyHash := btcutil.Hash160(pubKey.SerializeCompressed())
-	fingerprint := binary.LittleEndian.Uint32(pubKeyHash[:4])
-
 	if len(pIn.Bip32Derivation) == 0 {
 		return nil, errNoPathFound
 	}
@@ -246,10 +243,21 @@ func findMatchingDerivationPath(rootKey *hdkeychain.ExtendedKey,
 
 		// The normal case, where a derivation path has the master
 		// fingerprint set.
-		if derivation.MasterKeyFingerprint == fingerprint {
+		if derivation.MasterKeyFingerprint == masterFingerprint {
 			return derivation.Bip32Path, nil
 		}
 	}
 
 	return nil, errNoPathFound
 }
+
+func fingerprint(rootKey *hdkeychain.ExtendedKey) (uint32, []byte, error) {
+	pubKey, err := rootKey.ECPubKey()
+	if err != nil {
+		return 0, nil, fmt.Errorf("error getting public key: %w", err)
+	}
+
+	pubKeyHash := btcutil.Hash160(pubKey.SerializeCompressed())
+	fpBytes := pubKeyHash[:4]
+	return binary.LittleEndian.Uint32(fpBytes), fpBytes, nil
+}