move abc, inline introspect method, use six for abcs

* abc moved to cryptography.primitive.interfaces
* six added to dependencies
* six used to have py2x/py3x compatible abc
* nonce abc removed for now

cryptography/bindings/openssl/api.py

@@ -13,7 +13,7 @@
 
 from __future__ import absolute_import, division, print_function
 
-from cryptography.primitives.abc.block import modes
+from cryptography.primitives import interfaces
 
 import cffi
 
@@ -74,12 +74,14 @@ class API(object):
         )
         evp_cipher = self._lib.EVP_get_cipherbyname(ciphername.encode("ascii"))
         assert evp_cipher != self._ffi.NULL
-        iv_nonce = self._introspect(mode)
+        if isinstance(mode, interfaces.ModeWithInitializationVector):
+            iv_nonce = mode.initialization_vector
+        else:
+            iv_nonce = self._ffi.NULL
 
         # TODO: Sometimes this needs to be a DecryptInit, when?
         res = self._lib.EVP_EncryptInit_ex(
-            ctx, evp_cipher, self._ffi.NULL, cipher.key,
-            iv_nonce
+            ctx, evp_cipher, self._ffi.NULL, cipher.key, iv_nonce
         )
         assert res != 0
 
@@ -88,14 +90,6 @@ class API(object):
         self._lib.EVP_CIPHER_CTX_set_padding(ctx, 0)
         return ctx
 
-    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))
         outlen = self._ffi.new("int *")

cryptography/primitives/block/modes.py

@@ -13,7 +13,7 @@
 
 from __future__ import absolute_import, division, print_function
 
-from cryptography.primitives.abc.block import modes
+from cryptography.primitives import interfaces
 
 
 class CBC(object):
@@ -28,4 +28,4 @@ class ECB(object):
     name = "ECB"
 
 
-modes.ModeWithInitializationVector.register(CBC)
+interfaces.ModeWithInitializationVector.register(CBC)

cryptography/primitives/interfaces.py

@@ -14,8 +14,8 @@
 from __future__ import absolute_import, division, print_function
 
 import abc
+import six
 
 
-ModeWithInitializationVector = abc.ABCMeta('ModeWithInitializationVector',
-                                           (object, ), {})
-ModeWithNonce = abc.ABCMeta('ModeWithNonce', (object, ), {})
+class ModeWithInitializationVector(six.with_metaclass(abc.ABCMeta)):
+    pass

setup.py

@@ -21,9 +21,11 @@ with open("cryptography/__about__.py") as fp:
 
 
 CFFI_DEPENDENCY = "cffi>=0.6"
+SIX_DEPENDENCY = "six>=1.4.1"
 
 install_requires = [
     CFFI_DEPENDENCY,
+    SIX_DEPENDENCY
 ]
 
 setup_requires = [

tox.ini

@@ -5,6 +5,7 @@ envlist = py26,py27,pypy,py32,py33,docs,pep8
 deps =
     pytest-cov
     pretend
+    six
 commands = py.test --cov=cryptography/ --cov=tests/
 
 [testenv:docs]