fix R verification (#413)

closes: babylonlabs-io/pm#157

CHANGELOG.md

@@ -43,6 +43,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
   0.50.11
 - [#404](https://github.com/babylonlabs-io/babylon/pull/404) Improve adaptor
 signature nonce generation to match reference implementation
+- [#413](https://github.com/babylonlabs-io/babylon/pull/413) Fix adaptor
+signature R verification
 
 ## v1.0.0-rc3
 

crypto/schnorr-adaptor-signature/sign_utils.go

@@ -126,11 +126,9 @@ func encVerify(
 
 	expRHat.ToAffine()
 
-	// fail if expected R'.y is odd
-	if expRHat.Y.IsOdd() {
-		return fmt.Errorf("expected R'.y is odd")
+	if R.Y.IsOdd() {
+		return fmt.Errorf("expected R.y is odd")
 	}
-
 	// ensure R' is same as the expected R' = s'*G - e*P
 	if !expRHat.X.Equals(&RHat.X) {
 		return fmt.Errorf("expected R' = s'*G - e*P is different from the actual R'")