lnrpc: add NoHash option to signer.SignMessage rpc

keychain/btcwallet.go

@@ -462,8 +462,8 @@ func (b *BtcWalletKeyRing) SignMessageCompact(keyLoc KeyLocator,
 //
 // NOTE: This is part of the keychain.MessageSignerRing interface.
 func (b *BtcWalletKeyRing) SignMessageSchnorr(keyLoc KeyLocator,
-	msg []byte, doubleHash bool, taprootTweak []byte) (*schnorr.Signature,
-	error) {
+	msg []byte, doubleHash bool, noHash bool, taprootTweak []byte,
+        ) (*schnorr.Signature, error) {
 
 	privKey, err := b.DerivePrivKey(KeyDescriptor{
 		KeyLocator: keyLoc,
@@ -477,7 +477,9 @@ func (b *BtcWalletKeyRing) SignMessageSchnorr(keyLoc KeyLocator,
 	}
 
 	var digest []byte
-	if doubleHash {
+	if noHash {
+                digest = msg
+        } else if doubleHash {
 		digest = chainhash.DoubleHashB(msg)
 	} else {
 		digest = chainhash.HashB(msg)

keychain/derivation.go

@@ -239,8 +239,8 @@ type MessageSignerRing interface {
 	// hashing it first, with the private key described in the key locator
 	// and the optional Taproot tweak applied to the private key.
 	SignMessageSchnorr(keyLoc KeyLocator, msg []byte,
-		doubleHash bool, taprootTweak []byte) (*schnorr.Signature,
-		error)
+		doubleHash bool, noHash bool, taprootTweak []byte,
+                ) (*schnorr.Signature, error)
 }
 
 // SingleKeyMessageSigner is an abstraction interface that hides the

lnrpc/signrpc/signer.proto

@@ -332,23 +332,27 @@ message SignMessageReq {
     // Double-SHA256 hash instead of just the default single round.
     bool double_hash = 3;
 
+    // Don't hash the message before signing it. This option is only available
+    // when using a Schnorr signature.
+    bool no_hash = 4;
+
     /*
     Use the compact (pubkey recoverable) format instead of the raw lnwire
     format. This option cannot be used with Schnorr signatures.
     */
-    bool compact_sig = 4;
+    bool compact_sig = 5;
 
     /*
     Use Schnorr signature. This option cannot be used with compact format.
     */
-    bool schnorr_sig = 5;
+    bool schnorr_sig = 6;
 
     /*
     The optional Taproot tweak bytes to apply to the private key before creating
     a Schnorr signature. The private key is tweaked as described in BIP-341:
     privKey + h_tapTweak(internalKey || tapTweak)
     */
-    bytes schnorr_sig_tap_tweak = 6;
+    bytes schnorr_sig_tap_tweak = 7;
 }
 message SignMessageResp {
     /*

lnrpc/signrpc/signer.swagger.json

@@ -808,6 +808,10 @@
           "type": "boolean",
           "description": "Double-SHA256 hash instead of just the default single round."
         },
+        "no_hash": {
+          "type": "boolean",
+          "description": "Don't hash the message before signing it. This option is only available\nwhen using a Schnorr signature."
+        },
         "compact_sig": {
           "type": "boolean",
           "description": "Use the compact (pubkey recoverable) format instead of the raw lnwire\nformat. This option cannot be used with Schnorr signatures."

lnrpc/signrpc/signer_server.go

@@ -615,7 +615,7 @@ func (s *Server) SignMessage(_ context.Context,
 	// Use the schnorr signature algorithm to sign the message.
 	if in.SchnorrSig {
 		sig, err := s.cfg.KeyRing.SignMessageSchnorr(
-			keyLocator, in.Msg, in.DoubleHash,
+			keyLocator, in.Msg, in.DoubleHash, in.NoHash,
 			in.SchnorrSigTapTweak,
 		)
 		if err != nil {

lnwallet/rpcwallet/rpcwallet.go

@@ -513,8 +513,8 @@ func (r *RPCKeyRing) SignMessageCompact(keyLoc keychain.KeyLocator,
 //
 // NOTE: This method is part of the keychain.MessageSignerRing interface.
 func (r *RPCKeyRing) SignMessageSchnorr(keyLoc keychain.KeyLocator,
-	msg []byte, doubleHash bool, taprootTweak []byte) (*schnorr.Signature,
-	error) {
+	msg []byte, doubleHash bool, noHash bool, taprootTweak []byte,
+        ) (*schnorr.Signature, error) {
 
 	ctxt, cancel := context.WithTimeout(context.Background(), r.rpcTimeout)
 	defer cancel()
@@ -526,6 +526,7 @@ func (r *RPCKeyRing) SignMessageSchnorr(keyLoc keychain.KeyLocator,
 			KeyIndex:  int32(keyLoc.Index),
 		},
 		DoubleHash:         doubleHash,
+                NoHash:             noHash,
 		SchnorrSig:         true,
 		SchnorrSigTapTweak: taprootTweak,
 	})