1 files changed, 14 insertions, 0 deletions
diff --git a/cryptography/hazmat/primitives/asymmetric/rsa.py b/cryptography/hazmat/primitives/asymmetric/rsa.py
index dfb43340..cbef8e32 100644
--- a/cryptography/hazmat/primitives/asymmetric/rsa.py
+++ b/cryptography/hazmat/primitives/asymmetric/rsa.py
@@ -16,6 +16,8 @@ from __future__ import absolute_import, division, print_function
 import six
 
 from cryptography import utils
+from cryptography.exceptions import UnsupportedInterface
+from cryptography.hazmat.backends.interfaces import RSABackend
 from cryptography.hazmat.primitives import interfaces
 
 
@@ -41,6 +43,10 @@ class RSAPublicKey(object):
         self._modulus = modulus
 
     def verifier(self, signature, padding, algorithm, backend):
+        if not isinstance(backend, RSABackend):
+            raise UnsupportedInterface(
+                "Backend object does not implement RSABackend")
+
         return backend.create_rsa_verification_ctx(self, signature, padding,
                                                    algorithm)
 
@@ -128,9 +134,17 @@ class RSAPrivateKey(object):
 
     @classmethod
     def generate(cls, public_exponent, key_size, backend):
+        if not isinstance(backend, RSABackend):
+            raise UnsupportedInterface(
+                "Backend object does not implement RSABackend")
+
         return backend.generate_rsa_private_key(public_exponent, key_size)
 
     def signer(self, padding, algorithm, backend):
+        if not isinstance(backend, RSABackend):
+            raise UnsupportedInterface(
+                "Backend object does not implement RSABackend")
+
         return backend.create_rsa_signature_ctx(self, padding, algorithm)
 
     @property