signrpc: add schnorr sig to sign and validate msg

lnrpc/signrpc/signer.proto

@@ -320,7 +320,10 @@ message InputScriptResp {
 }
 
 message SignMessageReq {
-    // The message to be signed.
+    /*
+    The message to be signed. When using REST, this field must be encoded as
+    base64.
+    */
     bytes msg = 1;
 
     // The key locator that identifies which key to use for signing.
@@ -331,9 +334,21 @@ message SignMessageReq {
 
     /*
     Use the compact (pubkey recoverable) format instead of the raw lnwire
-    format.
+    format. This option cannot be used with Schnorr signatures.
     */
     bool compact_sig = 4;
+
+    /*
+    Use Schnorr signature. This option cannot be used with compact format.
+    */
+    bool schnorr_sig = 5;
+
+    /*
+    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;
 }
 message SignMessageResp {
     /*
@@ -343,18 +358,30 @@ message SignMessageResp {
 }
 
 message VerifyMessageReq {
-    // The message over which the signature is to be verified.
+    // The message over which the signature is to be verified. When using
+    // REST, this field must be encoded as base64.
     bytes msg = 1;
 
     /*
     The fixed-size LN wire encoded signature to be verified over the given
-    message.
+    message. When using REST, this field must be encoded as base64.
     */
     bytes signature = 2;
 
-    // The public key the signature has to be valid for.
+    /*
+    The public key the signature has to be valid for. When using REST, this
+    field must be encoded as base64. If the is_schnorr_sig option is true, then
+    the public key is expected to be in the 32-byte x-only serialization
+    according to BIP-340.
+    */
     bytes pubkey = 3;
+
+    /*
+    Specifies if the signature is a Schnorr signature.
+    */
+    bool is_schnorr_sig = 4;
 }
+
 message VerifyMessageResp {
     // Whether the signature was valid over the given message.
     bool valid = 1;