btcsuite · Roasbeef · Jun 19, 2025 · Dec 3, 2024
diff --git a/txscript/taproot.go b/txscript/taproot.go
@@ -353,7 +353,10 @@ func VerifyTaprootLeafCommitment(controlBlock *ControlBlock,
 	expectedWitnessProgram := schnorr.SerializePubKey(taprootKey)
 	if !bytes.Equal(expectedWitnessProgram, taprootWitnessProgram) {
 
-		return scriptError(ErrTaprootMerkleProofInvalid, "")
+		str := fmt.Sprintf("derived witness program: %x, expected: "+
+			"%x, using tapscript_root: %x", expectedWitnessProgram,
+			taprootWitnessProgram, rootHash)
+		return scriptError(ErrTaprootMerkleProofInvalid, str)
 	}
 
 	// Finally, we'll verify that the parity of the y coordinate of the

diff --git a/txscript/taproot_test.go b/txscript/taproot_test.go
@@ -293,13 +293,15 @@ func TestTapscriptCommitmentVerification(t *testing.T) {
 	// make from 0 to 1 leaf
 	// ensure verifies properly
 	testCases := []struct {
+		treeMutateFunc func(*IndexedTapScriptTree)
+
+		ctrlBlockMutateFunc func(*ControlBlock)
+
 		numLeaves int
 
 		valid bool
 
-		treeMutateFunc func(*IndexedTapScriptTree)
-
-		ctrlBlockMutateFunc func(*ControlBlock)
+		expectedErr ErrorCode
 	}{
 		// A valid merkle proof of a single leaf.
 		{
@@ -322,11 +324,13 @@ func TestTapscriptCommitmentVerification(t *testing.T) {
 		// An invalid merkle proof, we modify the last byte of one of
 		// the leaves.
 		{
-			numLeaves: 4,
-			valid:     false,
+			numLeaves:   4,
+			valid:       false,
+			expectedErr: ErrTaprootMerkleProofInvalid,
 			treeMutateFunc: func(t *IndexedTapScriptTree) {
 				for _, leafProof := range t.LeafMerkleProofs {
-					leafProof.InclusionProof[0] ^= 1
+					proofLen := len(leafProof.InclusionProof)
+					leafProof.InclusionProof[proofLen-1] ^= 1
 				}
 			},
 		},
@@ -335,8 +339,9 @@ func TestTapscriptCommitmentVerification(t *testing.T) {
 			// An invalid series of proofs, we modify the control
 			// block to not match the parity of the final output
 			// key commitment.
-			numLeaves: 2,
-			valid:     false,
+			numLeaves:   2,
+			valid:       false,
+			expectedErr: ErrTaprootOutputKeyParityMismatch,
 			ctrlBlockMutateFunc: func(c *ControlBlock) {
 				c.OutputKeyYIsOdd = !c.OutputKeyYIsOdd
 			},
@@ -391,6 +396,15 @@ func TestTapscriptCommitmentVerification(t *testing.T) {
 						"valid=%v, got valid=%v", testCase.valid,
 						valid)
 				}
+
+				if !valid {
+					if !IsErrorCode(err, testCase.expectedErr) {
+						t.Fatalf("expected error "+
+							"code %v, got %v",
+							testCase.expectedErr,
+							err)
+					}
+				}
 			}
 
 			// TODO(roasbeef): index correctness