Added backend check to cipher primitives

1 files changed, 7 insertions, 1 deletions

diff --git a/cryptography/hazmat/primitives/ciphers/base.py b/cryptography/hazmat/primitives/ciphers/base.py
index d366e4cf..2c804cac 100644
--- a/cryptography/hazmat/primitives/ciphers/base.py
+++ b/cryptography/hazmat/primitives/ciphers/base.py
@@ -16,12 +16,18 @@ from __future__ import absolute_import, division, print_function
 from cryptography import utils
 from cryptography.exceptions import (
     AlreadyFinalized, NotYetFinalized, AlreadyUpdated,
-)
+    UnsupportedInterface)
+
+from cryptography.hazmat.backends.interfaces import CipherBackend
 from cryptography.hazmat.primitives import interfaces
 
 
 class Cipher(object):
     def __init__(self, algorithm, mode, backend):
+        if not isinstance(backend, CipherBackend):
+            raise UnsupportedInterface(
+                "Backend object does not implement CipherBackend")
+
         if not isinstance(algorithm, interfaces.CipherAlgorithm):
             raise TypeError("Expected interface of interfaces.CipherAlgorithm")