Merge pull request #216 from alex/more-error-condition

Replaced an assertion in the OpenSSL backend with a proper exception

2 files changed, 26 insertions, 1 deletions

diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index 7367818a..ea1073b9 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -147,7 +147,9 @@ class _CipherContext(object):
             raise UnsupportedAlgorithm
 
         evp_cipher = adapter(self._backend, cipher, mode)
-        assert evp_cipher != self._backend.ffi.NULL
+        if evp_cipher == self._backend.ffi.NULL:
+            raise UnsupportedAlgorithm
+
         if isinstance(mode, interfaces.ModeWithInitializationVector):
             iv_nonce = mode.initialization_vector
         elif isinstance(mode, interfaces.ModeWithNonce):
diff --git a/tests/hazmat/bindings/test_openssl.py b/tests/hazmat/bindings/test_openssl.py
index fb01c10a..f283a7dd 100644
--- a/tests/hazmat/bindings/test_openssl.py
+++ b/tests/hazmat/bindings/test_openssl.py
@@ -13,11 +13,21 @@
 
 import pytest
 
+from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.bindings.openssl.backend import backend, Backend
+from cryptography.hazmat.primitives.block import BlockCipher
 from cryptography.hazmat.primitives.block.ciphers import AES
 from cryptography.hazmat.primitives.block.modes import CBC
 
 
+class FakeMode(object):
+    pass
+
+
+class FakeCipher(object):
+    pass
+
+
 class TestOpenSSL(object):
     def test_backend_exists(self):
         assert backend
@@ -44,3 +54,16 @@ class TestOpenSSL(object):
         b = Backend()
         assert b.ffi is backend.ffi
         assert b.lib is backend.lib
+
+    def test_nonexistent_cipher(self):
+        b = Backend()
+        b.ciphers.register_cipher_adapter(
+            FakeCipher,
+            FakeMode,
+            lambda backend, cipher, mode: backend.ffi.NULL
+        )
+        cipher = BlockCipher(
+            FakeCipher(), FakeMode(), backend=b,
+        )
+        with pytest.raises(UnsupportedAlgorithm):
+            cipher.encryptor()