Fixes #784 -- bump minimum cryptography version (#785)

diff --git a/setup.py b/setup.py
index 29c11f4..3728795 100755
--- a/setup.py
+++ b/setup.py
@@ -95,7 +95,7 @@
         package_dir={"": "src"},
         install_requires=[
             # Fix cryptographyMinimum in tox.ini when changing this!
-            "cryptography>=2.2.1",
+            "cryptography>=2.3",
             "six>=1.5.2"
         ],
         extras_require={
diff --git a/tox.ini b/tox.ini
index eda9e4e..8400a5d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -10,7 +10,7 @@
 deps =
     coverage>=4.2
     cryptographyMaster: git+https://github.com/pyca/cryptography.git
-    cryptographyMinimum: cryptography==2.2.1
+    cryptographyMinimum: cryptography==2.3.0
 setenv =
     # Do not allow the executing environment to pollute the test environment
     # with extra packages.