add aes cbc pkcs5 wycheproof tests (pyca#4347)

tests/wycheproof/test_aes.py

@@ -0,0 +1,42 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from __future__ import absolute_import, division, print_function
+
+import binascii
+
+import pytest
+
+from cryptography.hazmat.backends.interfaces import CipherBackend
+from cryptography.hazmat.primitives import padding
+from cryptography.hazmat.primitives.ciphers import (
+    Cipher, algorithms, modes
+)
+
+
+@pytest.mark.requires_backend_interface(interface=CipherBackend)
+@pytest.mark.wycheproof_tests("aes_cbc_pkcs5_test.json")
+def test_aes_cbc_pkcs5(backend, wycheproof):
+    key = binascii.unhexlify(wycheproof.testcase["key"])
+    iv = binascii.unhexlify(wycheproof.testcase["iv"])
+    msg = binascii.unhexlify(wycheproof.testcase["msg"])
+    ct = binascii.unhexlify(wycheproof.testcase["ct"])
+
+    padder = padding.PKCS7(128).padder()
+
+    cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend)
+    enc = cipher.encryptor()
+    computed_ct = enc.update(
+        padder.update(msg) + padder.finalize()) + enc.finalize()
+    dec = cipher.decryptor()
+    padded_msg = dec.update(ct) + dec.finalize()
+    unpadder = padding.PKCS7(128).unpadder()
+    if wycheproof.valid or wycheproof.acceptable:
+        assert computed_ct == ct
+        computed_msg = unpadder.update(padded_msg) + unpadder.finalize()
+        assert computed_msg == msg
+    else:
+        assert computed_ct != ct
+        with pytest.raises(ValueError):
+            unpadder.update(padded_msg) + unpadder.finalize()