diff --git a/src/sm2_lib.c b/src/sm2_lib.c
index 8557d466..ea9d54d3 100644
--- a/src/sm2_lib.c
+++ b/src/sm2_lib.c
@@ -146,6 +146,23 @@ int sm2_do_verify(const SM2_KEY *key, const uint8_t dgst[32], const SM2_SIGNATUR
 	return 1;
 }
 
+// verify the xR of R = s * G + (s + r) * P
+// so (-r, -s) is also a valid SM2 signature
+int sm2_signature_conjugate(const SM2_SIGNATURE *sig, SM2_SIGNATURE *new_sig)
+{
+	SM2_Fn r;
+	SM2_Fn s;
+
+	sm2_bn_from_bytes(r, sig->r);
+	sm2_bn_from_bytes(s, sig->s);
+	sm2_fn_neg(r, r);
+	sm2_fn_neg(s, s);
+	sm2_bn_to_bytes(r, new_sig->r);
+	sm2_bn_to_bytes(s, new_sig->s);
+
+	return 1;
+}
+
 int sm2_signature_to_der(const SM2_SIGNATURE *sig, uint8_t **out, size_t *outlen)
 {
 	size_t len = 0;