Require cryptography<2.0 for Python 3.3, as >=2.0 only supports 3.4+.

requirements.txt

@@ -1,3 +1,4 @@
-cryptography>=1.5
+cryptography>=1.5 ; python_version!="3.3"
+cryptography>=1.5,<2.0 ; python_version=="3.3"
 requests
 future

tox.ini

@@ -11,9 +11,7 @@ commands = nosetests
 
 deps =
     nose
-    requests
+    -r{toxinidir}/requirements.txt
-    cryptography
-    future
 
 [testenv:cover]
 deps =