diff --git a/cryptography/bindings/openssl/api.py b/cryptography/bindings/openssl/api.py
index 93863b3..cb5afe3 100644
--- a/cryptography/bindings/openssl/api.py
+++ b/cryptography/bindings/openssl/api.py
@@ -68,6 +68,8 @@
 
     def create_block_cipher_context(self, cipher, mode):
         ctx = self.ffi.new("EVP_CIPHER_CTX *")
+        res = self.lib.EVP_CIPHER_CTX_init(ctx)
+        assert res != 0
         ctx = self.ffi.gc(ctx, self.lib.EVP_CIPHER_CTX_cleanup)
         # TODO: compute name using a better algorithm
         ciphername = "{0}-{1}-{2}".format(
diff --git a/cryptography/bindings/openssl/evp.py b/cryptography/bindings/openssl/evp.py
index 740f125..8afaf34 100644
--- a/cryptography/bindings/openssl/evp.py
+++ b/cryptography/bindings/openssl/evp.py
@@ -35,6 +35,7 @@
 int EVP_CIPHER_CTX_cleanup(EVP_CIPHER_CTX *);
 const EVP_CIPHER *EVP_CIPHER_CTX_cipher(const EVP_CIPHER_CTX *);
 int EVP_CIPHER_block_size(const EVP_CIPHER *);
+void EVP_CIPHER_CTX_init(EVP_CIPHER_CTX *);
 """
 
 MACROS = """
diff --git a/dev-requirements.txt b/dev-requirements.txt
new file mode 100644
index 0000000..01030e8
--- /dev/null
+++ b/dev-requirements.txt
@@ -0,0 +1,5 @@
+flake8
+pretend
+pytest-cov
+sphinx
+tox
diff --git a/docs/contributing.rst b/docs/contributing.rst
index b4c72ba..9dd14c2 100644
--- a/docs/contributing.rst
+++ b/docs/contributing.rst
@@ -73,8 +73,81 @@
 - No blank line at the end.
 - Use Sphinx parameter/attribute documentation `syntax`_.
 
+Development Environment
+-----------------------
+
+Working on ``cryptography`` requires the installation of a small number of
+development dependencies. These are listed in ``dev-requirements.txt`` and they
+can be installed in a `virtualenv`_ using `pip`_. Once you've installed the
+dependencies, install ``cryptography`` in ``editable`` mode. For example:
+
+.. code-block:: sh
+
+   # Create a virtualenv and activate it
+   $ pip install --requirement dev-requirements.txt
+   $ pip install --editable .
+
+You are now ready to run the tests and build the documentation.
+
+Running Tests
+-------------
+
+``cryptography`` unit tests are found in the ``tests/`` directory and are
+designed to be run using `pytest`_. `pytest`_ will discover the tests
+automatically, so all you have to do is:
+
+.. code-block:: sh
+
+   $ py.test
+   ...
+   4294 passed in 15.24 seconds
+
+This runs the tests with the default Python interpreter.
+
+You can also verify that the tests pass on other supported Python interpreters.
+For this we use `tox`_, which will automatically create a `virtualenv`_ for
+each supported Python version and run the tests. For example:
+
+.. code-block:: sh
+
+   $ tox
+   ...
+   ERROR:   py26: InterpreterNotFound: python2.6
+    py27: commands succeeded
+   ERROR:   pypy: InterpreterNotFound: pypy
+   ERROR:   py32: InterpreterNotFound: python3.2
+    py33: commands succeeded
+    docs: commands succeeded
+    pep8: commands succeeded
+
+You may not have all the required Python versions installed, in which case you
+will see one or more ``InterpreterNotFound`` errors.
+
+Building Documentation
+----------------------
+
+``cryptography`` documentation is stored in the ``docs/`` directory. It is
+written in `reStructured Text`_ and rendered using `Sphinx`_.
+
+Use `tox`_ to build the documentation. For example:
+
+.. code-block:: sh
+
+   $ tox -e docs
+   ...
+   docs: commands succeeded
+   congratulations :)
+
+The HTML documentation index can now be found at ``docs/_build/html/index.html``
+
 
 .. _`GitHub`: https://github.com/alex/cryptography
 .. _`our mailing list`: https://mail.python.org/mailman/listinfo/cryptography-dev
 .. _`PEP 8`: http://www.peps.io/8/
 .. _`syntax`: http://sphinx-doc.org/domains.html#info-field-lists
+.. _`pytest`: https://pypi.python.org/pypi/pytest
+.. _`tox`: https://pypi.python.org/pypi/tox
+.. _`virtualenv`: https://pypi.python.org/pypi/virtualenv
+.. _`pip`: https://pypi.python.org/pypi/pip
+.. _`sphinx`: https://pypi.python.org/pypi/sphinx
+.. _`reStructured Text`: http://docutils.sourceforge.net/rst.html