diff --git a/src/tests/test_blindsig.py b/src/tests/test_blindsig.py
index ad44af98..b8d0248a 100644
--- a/src/tests/test_blindsig.py
+++ b/src/tests/test_blindsig.py
@@ -3,8 +3,10 @@ Test for ECC blind signatures
 """
 import os
 import unittest
+from ctypes import cast, c_char_p
 
 from pybitmessage.pyelliptic.eccblind import ECCBlind
+from pybitmessage.pyelliptic.openssl import OpenSSL
 
 
 class TestBlindSig(unittest.TestCase):
@@ -24,12 +26,27 @@ class TestBlindSig(unittest.TestCase):
         msg = os.urandom(64)
         msg_blinded = requester_obj.create_signing_request(point_r, msg)
 
+        # check
+        msg_blinded_str = OpenSSL.malloc(0, OpenSSL.BN_num_bytes(msg_blinded))
+        OpenSSL.BN_bn2bin(msg_blinded, msg_blinded_str)
+        self.assertNotEqual(msg, cast(msg_blinded_str, c_char_p).value)
+
         # (3) Signature Generation
         signature_blinded = signer_obj.blind_sign(msg_blinded)
 
         # (4) Extraction
         signature = requester_obj.unblind(signature_blinded)
 
+        # check
+        signature_blinded_str = OpenSSL.malloc(0,
+                                               OpenSSL.BN_num_bytes(
+                                                   signature_blinded))
+        signature_str = OpenSSL.malloc(0, OpenSSL.BN_num_bytes(signature[0]))
+        OpenSSL.BN_bn2bin(signature_blinded, signature_blinded_str)
+        OpenSSL.BN_bn2bin(signature[0], signature_str)
+        self.assertNotEqual(cast(signature_str, c_char_p).value,
+                            cast(signature_blinded_str, c_char_p).value)
+
         # (5) Verification
         verifier_obj = ECCBlind(pubkey=signer_obj.pubkey)
         self.assertTrue(verifier_obj.verify(msg, signature))