Add _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM

3 files changed, 16 insertions, 6 deletions

diff --git a/cryptography/exceptions.py b/cryptography/exceptions.py
index d2782be6..b4ee8feb 100644
--- a/cryptography/exceptions.py
+++ b/cryptography/exceptions.py
@@ -20,6 +20,7 @@ class _Reasons(object):
     UNSUPPORTED_CIPHER = object()
     UNSUPPORTED_PADDING = object()
     UNSUPPORTED_MGF = object()
+    UNSUPPORTED_PUBLIC_KEY_ALGORITHM = object()
 
 
 class UnsupportedAlgorithm(Exception):
diff --git a/cryptography/hazmat/backends/multibackend.py b/cryptography/hazmat/backends/multibackend.py
index 2a1ec439..aa649dd3 100644
--- a/cryptography/hazmat/backends/multibackend.py
+++ b/cryptography/hazmat/backends/multibackend.py
@@ -126,16 +126,19 @@ class MultiBackend(object):
     def generate_rsa_private_key(self, public_exponent, key_size):
         for b in self._filtered_backends(RSABackend):
             return b.generate_rsa_private_key(public_exponent, key_size)
-        raise UnsupportedAlgorithm("RSA is not supported by the backend")
+        raise UnsupportedAlgorithm("RSA is not supported by the backend",
+                                   _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM)
 
     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("RSA is not supported by the backend")
+        raise UnsupportedAlgorithm("RSA is not supported by the backend",
+                                   _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM)
 
     def create_rsa_verification_ctx(self, public_key, signature, padding,
                                     algorithm):
         for b in self._filtered_backends(RSABackend):
             return b.create_rsa_verification_ctx(public_key, signature,
                                                  padding, algorithm)
-        raise UnsupportedAlgorithm("RSA is not supported by the backend")
+        raise UnsupportedAlgorithm("RSA is not supported by the backend",
+                                   _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM)
diff --git a/tests/hazmat/backends/test_multibackend.py b/tests/hazmat/backends/test_multibackend.py
index b7bcaf69..c91cb471 100644
--- a/tests/hazmat/backends/test_multibackend.py
+++ b/tests/hazmat/backends/test_multibackend.py
@@ -179,13 +179,19 @@ class TestMultiBackend(object):
                                             padding.PKCS1v15(), hashes.MD5())
 
         backend = MultiBackend([])
-        with pytest.raises(UnsupportedAlgorithm):
+        with raises_unsupported_algorithm(
+            _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM
+        ):
             backend.generate_rsa_private_key(key_size=1024, public_exponent=3)
 
-        with pytest.raises(UnsupportedAlgorithm):
+        with raises_unsupported_algorithm(
+            _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM
+        ):
             backend.create_rsa_signature_ctx("private_key", padding.PKCS1v15(),
                                              hashes.MD5())
 
-        with pytest.raises(UnsupportedAlgorithm):
+        with raises_unsupported_algorithm(
+            _Reasons.UNSUPPORTED_PUBLIC_KEY_ALGORITHM
+        ):
             backend.create_rsa_verification_ctx(
                 "public_key", "sig", padding.PKCS1v15(), hashes.MD5())