fix(zcoin): don't force low r signing to generate htlc pubkey for zco…

…in (#2184)

This commit creates new `sign_low_r` function and keeps using regular sign for `derive_htlc_key_pair` of zcoin

mm2src/coins/utxo_signer/src/with_key_pair.rs

@@ -244,7 +244,7 @@ pub fn signature_hash_to_sign(
 }
 
 fn sign_message(message: &H256, key_pair: &KeyPair) -> UtxoSignWithKeyPairResult<Bytes> {
-    let signature = key_pair.private().sign(message)?;
+    let signature = key_pair.private().sign_low_r(message)?;
     Ok(Bytes::from(signature.to_vec()))
 }
 

mm2src/mm2_bitcoin/keys/src/keypair.rs

@@ -124,7 +124,7 @@ mod tests {
     fn check_sign(secret: &'static str, raw_message: &[u8], signature: &'static str) -> bool {
         let message = dhash256(raw_message);
         let kp = KeyPair::from_private(secret.into()).unwrap();
-        kp.private().sign(&message).unwrap() == signature.into()
+        kp.private().sign_low_r(&message).unwrap() == signature.into()
     }
 
     fn check_verify(secret: &'static str, raw_message: &[u8], signature: &'static str) -> bool {

mm2src/mm2_bitcoin/keys/src/private.rs

@@ -27,7 +27,16 @@ impl Private {
     pub fn sign(&self, message: &Message) -> Result<Signature, Error> {
         let secret = SecretKey::from_slice(&*self.secret)?;
         let message = SecpMessage::from_slice(&**message)?;
-        // use low R signing from bitcoin which reduces signature malleability
+        let signature = SECP_SIGN.sign(&message, &secret);
+        let data = signature.serialize_der();
+        Ok(data.as_ref().to_vec().into())
+    }
+
+    /// Sign a message with a low R value, this reduces signature malleability for Bitcoin transactions
+    /// and makes fee estimation more reliable.
+    pub fn sign_low_r(&self, message: &Message) -> Result<Signature, Error> {
+        let secret = SecretKey::from_slice(&*self.secret)?;
+        let message = SecpMessage::from_slice(&**message)?;
         let signature = SECP_SIGN.sign_low_r(&message, &secret);
         let data = signature.serialize_der();
         Ok(data.as_ref().to_vec().into())

mm2src/mm2_bitcoin/script/src/sign.rs

@@ -262,7 +262,7 @@ impl TransactionInputSigner {
     ) -> TransactionInput {
         let hash = self.signature_hash(input_index, input_amount, script_pubkey, sigversion, sighash);
 
-        let mut signature: Vec<u8> = keypair.private().sign(&hash).unwrap().into();
+        let mut signature: Vec<u8> = keypair.private().sign_low_r(&hash).unwrap().into();
         signature.push(sighash as u8);
         let script_sig = Builder::default()
             .push_data(&signature)