modify modes to use abc so api can determine what attribute to call

* Due to a circular dependency issue I had to put the abcs in
  cryptography.primitives.abc.block.modes
* The ABCs look like they do because that is the form that is compatible
  with 2.x and 3.x

6 files changed, 36 insertions, 12 deletions

diff --git a/cryptography/bindings/openssl/api.py b/cryptography/bindings/openssl/api.py
index fd54a8ff..f95e4d62 100644
--- a/cryptography/bindings/openssl/api.py
+++ b/cryptography/bindings/openssl/api.py
@@ -13,6 +13,8 @@
 
 from __future__ import absolute_import, division, print_function
 
+from cryptography.primitives.abc.block import modes
+
 import cffi
 
 
@@ -72,7 +74,7 @@ class API(object):
         )
         evp_cipher = self._lib.EVP_get_cipherbyname(ciphername.encode("ascii"))
         assert evp_cipher != self._ffi.NULL
-        iv_nonce = mode.get_iv_or_nonce(self)
+        iv_nonce = self._introspect(mode)
 
         # TODO: Sometimes this needs to be a DecryptInit, when?
         res = self._lib.EVP_EncryptInit_ex(
@@ -86,8 +88,13 @@ class API(object):
         self._lib.EVP_CIPHER_CTX_set_padding(ctx, 0)
         return ctx
 
-    def get_iv_for_ecb(self):
-        return self._ffi.NULL
+    def _introspect(self, mode):
+        if isinstance(mode, modes.ModeWithInitializationVector):
+            return mode.initialization_vector
+        elif isinstance(mode, modes.ModeWithNonce):
+            return mode.nonce
+        else:
+            return self._ffi.NULL
 
     def update_encrypt_context(self, ctx, plaintext):
         buf = self._ffi.new("unsigned char[]", len(plaintext))
diff --git a/cryptography/primitives/abc/__init__.py b/cryptography/primitives/abc/__init__.py
new file mode 100644
index 00000000..e69de29b
--- /dev/null
+++ b/cryptography/primitives/abc/__init__.py
diff --git a/cryptography/primitives/abc/block/__init__.py b/cryptography/primitives/abc/block/__init__.py
new file mode 100644
index 00000000..e69de29b
--- /dev/null
+++ b/cryptography/primitives/abc/block/__init__.py
diff --git a/cryptography/primitives/abc/block/modes.py b/cryptography/primitives/abc/block/modes.py
new file mode 100644
index 00000000..609a2ae3
--- /dev/null
+++ b/cryptography/primitives/abc/block/modes.py
@@ -0,0 +1,21 @@
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import absolute_import, division, print_function
+
+import abc
+
+
+ModeWithInitializationVector = abc.ABCMeta('ModeWithInitializationVector',
+                                           (object, ), {})
+ModeWithNonce = abc.ABCMeta('ModeWithNonce', (object, ), {})
diff --git a/cryptography/primitives/block/modes.py b/cryptography/primitives/block/modes.py
index e4fc886e..1e9b14b7 100644
--- a/cryptography/primitives/block/modes.py
+++ b/cryptography/primitives/block/modes.py
@@ -13,6 +13,8 @@
 
 from __future__ import absolute_import, division, print_function
 
+from cryptography.primitives.abc.block import modes
+
 
 class CBC(object):
     name = "CBC"
@@ -21,12 +23,9 @@ class CBC(object):
         super(CBC, self).__init__()
         self.initialization_vector = initialization_vector
 
-    def get_iv_or_nonce(self, api):
-        return self.initialization_vector
-
 
 class ECB(object):
     name = "ECB"
 
-    def get_iv_or_nonce(self, api):
-        return api.get_iv_for_ecb()
+
+modes.ModeWithInitializationVector.register(CBC)
diff --git a/tests/bindings/test_openssl.py b/tests/bindings/test_openssl.py
index f25236cc..b23c4ccc 100644
--- a/tests/bindings/test_openssl.py
+++ b/tests/bindings/test_openssl.py
@@ -11,7 +11,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from cryptography.bindings.openssl import api
+from cryptography.bindings.openssl.api import api
 
 
 class TestOpenSSL(object):
@@ -28,6 +28,3 @@ class TestOpenSSL(object):
         for every OpenSSL.
         """
         assert api.openssl_version_text().startswith("OpenSSL")
-
-    def test_get_iv_for_ecb(self):
-        assert api.get_iv_for_ecb() == api._ffi.NULL