Add documentation and changelog

CHANGELOG.rst

@@ -25,6 +25,8 @@ Changes:
 
 - Enable use of CRL (and more) in verify context.
   `#483 <https://github.com/pyca/pyopenssl/pull/483>`_
+- ``OpenSSL.crypto.PKey`` can now be constructed from ``cryptography`` objects and also exported as such.
+  `#439 <https://github.com/pyca/pyopenssl/pull/439>`_
 
 
 ----

src/OpenSSL/crypto.py

@@ -171,13 +171,33 @@ def __init__(self):
         self._initialized = False
 
     def to_cryptography_key(self):
+        """
+        Export as a ``cryptography`` key.
+
+        :rtype: One of ``cryptography``'s `key interfaces`_.
+
+        .. _key interfaces: https://cryptography.io/en/latest/hazmat/\
+            primitives/asymmetric/rsa/#key-interfaces
+
+        .. versionadded:: 16.1.0
+        """
         if self._only_public:
             return backend._evp_pkey_to_public_key(self._pkey)
         else:
             return backend._evp_pkey_to_private_key(self._pkey)
 
     @classmethod
     def from_cryptography_key(cls, crypto_key):
+        """
+        Construct based on a ``cryptography`` *crypto_key*.
+
+        :param crypto_key: A ``cryptography`` key.
+        :type crypto_key: One of ``cryptography``'s `key interfaces`_.
+
+        :rtype: PKey
+
+        .. versionadded:: 16.1.0
+        """
         pkey = cls()
         pkey._pkey = crypto_key._evp_pkey
         if isinstance(crypto_key, (rsa.RSAPublicKey, dsa.DSAPublicKey)):

tests/test_crypto.py

@@ -762,7 +762,7 @@ class TestPKey(object):
 
     def test_convert_from_cryptography_private_key(self):
         """
-        Convert from a cryptography private key to a pyOpenSSL PKey.
+        PKey.from_cryptography_key creates a proper private PKey.
         """
         key = serialization.load_pem_private_key(
             intermediate_key_pem, None, backend
@@ -776,7 +776,7 @@ def test_convert_from_cryptography_private_key(self):
 
     def test_convert_from_cryptography_public_key(self):
         """
-        Convert from a cryptography public key to a pyOpenSSL PKey.
+        PKey.from_cryptography_key creates a proper public PKey.
         """
         key = serialization.load_pem_public_key(cleartextPublicKeyPEM, backend)
         pkey = PKey.from_cryptography_key(key)
@@ -788,7 +788,7 @@ def test_convert_from_cryptography_public_key(self):
 
     def test_convert_public_pkey_to_cryptography_key(self):
         """
-        Convert from a pyOpenSSL PKey to a cryptography public key.
+        PKey.to_cryptography_key creates a proper cryptography public key.
         """
         pkey = load_publickey(FILETYPE_PEM, cleartextPublicKeyPEM)
         key = pkey.to_cryptography_key()
@@ -798,7 +798,7 @@ def test_convert_public_pkey_to_cryptography_key(self):
 
     def test_convert_private_pkey_to_cryptography_key(self):
         """
-        Convert from a pyOpenSSL PKey to a cryptography private key.
+        PKey.to_cryptography_key creates a proper cryptography private key.
         """
         pkey = load_privatekey(FILETYPE_PEM, cleartextPrivateKeyPEM)
         key = pkey.to_cryptography_key()