Limit SHA3 support to Python 3.6+

The third-party library that adds support for this to Python 3.5 is a
binary package, and thus breaks the pure-Python nature of Python-RSA.

This should fix [#147](https://github.com/sybrenstuvel/python-rsa/issues/147).

1 files changed, 7 insertions, 0 deletions

diff --git a/tests/test_pkcs1.py b/tests/test_pkcs1.py
index 702ce2d..f7baf7f 100644
--- a/tests/test_pkcs1.py
+++ b/tests/test_pkcs1.py
@@ -15,6 +15,7 @@
 """Tests string operations."""
 
 import struct
+import sys
 import unittest
 
 import rsa
@@ -101,6 +102,12 @@ class SignatureTest(unittest.TestCase):
         signature = pkcs1.sign(message, self.priv, 'SHA-256')
         self.assertEqual('SHA-256', pkcs1.verify(message, signature, self.pub))
 
+
+    @unittest.skipIf(sys.version_info < (3, 6), "SHA3 requires Python 3.6+")
+    def test_sign_verify_sha3(self):
+        """Test happy flow of sign and verify with SHA3-256"""
+
+        message = b'je moeder'
         signature = pkcs1.sign(message, self.priv, 'SHA3-256')
         self.assertEqual('SHA3-256', pkcs1.verify(message, signature, self.pub))