diff --git a/cryptography/exceptions.py b/cryptography/exceptions.py
index 8825d3b..86082e4 100644
--- a/cryptography/exceptions.py
+++ b/cryptography/exceptions.py
@@ -16,6 +16,9 @@
 
 class _Reasons(object):
     BACKEND_MISSING_INTERFACE = object()
+    UNSUPPORTED_HASH = object()
+    UNSUPPORTED_CIPHER = object()
+    UNSUPPORTED_PADDING = object()
 
 
 class UnsupportedAlgorithm(Exception):