Implement and document an interface for cipher algorithms

3 files changed, 25 insertions, 0 deletions

diff --git a/cryptography/hazmat/primitives/ciphers/algorithms.py b/cryptography/hazmat/primitives/ciphers/algorithms.py
index c135f563..1ed487b6 100644
--- a/cryptography/hazmat/primitives/ciphers/algorithms.py
+++ b/cryptography/hazmat/primitives/ciphers/algorithms.py
@@ -13,7 +13,10 @@
 
 from __future__ import absolute_import, division, print_function
 
+from cryptography.hazmat.primitives import interfaces
 
+
+@interfaces.register(interfaces.CipherAlgorithm)
 class AES(object):
     name = "AES"
     block_size = 128
@@ -33,6 +36,7 @@ class AES(object):
         return len(self.key) * 8
 
 
+@interfaces.register(interfaces.CipherAlgorithm)
 class Camellia(object):
     name = "camellia"
     block_size = 128
@@ -52,6 +56,7 @@ class Camellia(object):
         return len(self.key) * 8
 
 
+@interfaces.register(interfaces.CipherAlgorithm)
 class TripleDES(object):
     name = "3DES"
     block_size = 64
@@ -75,6 +80,7 @@ class TripleDES(object):
         return len(self.key) * 8
 
 
+@interfaces.register(interfaces.CipherAlgorithm)
 class Blowfish(object):
     name = "Blowfish"
     block_size = 64
@@ -94,6 +100,7 @@ class Blowfish(object):
         return len(self.key) * 8
 
 
+@interfaces.register(interfaces.CipherAlgorithm)
 class CAST5(object):
     name = "CAST5"
     block_size = 64
@@ -113,6 +120,7 @@ class CAST5(object):
         return len(self.key) * 8
 
 
+@interfaces.register(interfaces.CipherAlgorithm)
 class ARC4(object):
     name = "RC4"
     block_size = 1
diff --git a/cryptography/hazmat/primitives/ciphers/base.py b/cryptography/hazmat/primitives/ciphers/base.py
index 0fe11996..78bf7e0c 100644
--- a/cryptography/hazmat/primitives/ciphers/base.py
+++ b/cryptography/hazmat/primitives/ciphers/base.py
@@ -24,6 +24,9 @@ class Cipher(object):
                 _default_backend as backend,
             )
 
+        if not isinstance(algorithm, interfaces.CipherAlgorithm):
+            raise TypeError("Expected interface of interfaces.CipherAlgorithm")
+
         self.algorithm = algorithm
         self.mode = mode
         self._backend = backend
diff --git a/cryptography/hazmat/primitives/interfaces.py b/cryptography/hazmat/primitives/interfaces.py
index 67dbe6fa..bbbb266c 100644
--- a/cryptography/hazmat/primitives/interfaces.py
+++ b/cryptography/hazmat/primitives/interfaces.py
@@ -25,6 +25,20 @@ def register(iface):
     return register_decorator
 
 
+class CipherAlgorithm(six.with_metaclass(abc.ABCMeta)):
+    @abc.abstractproperty
+    def name(self):
+        """
+        A string naming this mode.  (e.g. AES, Camellia)
+        """
+
+    @abc.abstractproperty
+    def key_size(self):
+        """
+        The size of the key being used as an integer in bits.  (e.g. 128, 256)
+        """
+
+
 class Mode(six.with_metaclass(abc.ABCMeta)):
     @abc.abstractproperty
     def name(self):