add basic multibackend so we can do signatures using default_backend

2 files changed, 18 insertions, 0 deletions

diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
index 4de02026..eb58dd68 100644
--- a/cryptography/hazmat/backends/multibackend.py
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -24,6 +24,7 @@ from cryptography.hazmat.backends.interfaces import (
 @utils.register_interface(HashBackend)
 @utils.register_interface(HMACBackend)
 @utils.register_interface(PBKDF2HMACBackend)
+@utils.register_interface(RSABackend)
 class MultiBackend(object):
     name = "multibackend"
 
@@ -106,3 +107,9 @@ class MultiBackend(object):
         for b in self._filtered_backends(RSABackend):
             return b.generate_rsa_private_key(public_exponent, key_size)
         raise UnsupportedAlgorithm
+
+    def create_rsa_signature_ctx(self, private_key, padding, algorithm):
+        for b in self._filtered_backends(RSABackend):
+            return b.create_rsa_signature_ctx(private_key, padding, algorithm)
+        raise UnsupportedAlgorithm
+
diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index ce77ce2f..e3f83d3a 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -20,6 +20,7 @@ from cryptography.hazmat.backends.interfaces import (
 )
 from cryptography.hazmat.backends.multibackend import MultiBackend
 from cryptography.hazmat.primitives import hashes, hmac
+from cryptography.hazmat.primitives.asymmetric import padding
 from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
 
 
@@ -85,6 +86,9 @@ class DummyRSABackend(object):
     def generate_rsa_private_key(self, public_exponent, private_key):
         pass
 
+    def create_rsa_signature_ctx(self, private_key, padding, algorithm):
+        pass
+
 
 class TestMultiBackend(object):
     def test_ciphers(self):
@@ -158,6 +162,13 @@ class TestMultiBackend(object):
             key_size=1024, public_exponent=65537
         )
 
+        backend.create_rsa_signature_ctx("private_key", padding.PKCS1(),
+                                         hashes.MD5())
+
         backend = MultiBackend([])
         with pytest.raises(UnsupportedAlgorithm):
             backend.generate_rsa_private_key(key_size=1024, public_exponent=3)
+
+        with pytest.raises(UnsupportedAlgorithm):
+            backend.create_rsa_signature_ctx("private_key", padding.PKCS1(),
+                                             hashes.MD5())