PBKDF2 support for OpenSSL backend
diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst
index 11e2f2a..fa4f800 100644
--- a/docs/hazmat/backends/interfaces.rst
+++ b/docs/hazmat/backends/interfaces.rst
@@ -131,3 +131,42 @@
:returns:
:class:`~cryptography.hazmat.primitives.interfaces.HashContext`
+
+
+
+.. class:: PBKDF2Backend
+
+ A backend with methods for using PBKDF2.
+
+ .. method:: pbkdf2_hash_supported(algorithm)
+
+ Check if the specified ``algorithm`` is supported by this backend.
+
+ :param algorithm: An instance of a
+ :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+ provider.
+
+ :returns: ``True`` if the specified ``algorithm`` is supported for
+ PBKDF2 by this backend, otherwise ``False``.
+
+ .. method:: derive_pbkdf2(self, algorithm, length, salt, iterations,
+ key_material)
+
+ :param algorithm: An instance of a
+ :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+ provider.
+
+ :param int length: The desired length of the derived key. Maximum is
+ 2\ :sup:`31` - 1.
+
+ :param bytes salt: A salt. `RFC 2898`_ recommends 64-bits or longer.
+
+ :param int iterations: The number of iterations to perform of the hash
+ function.
+
+ :param bytes key_material: The key material to use as a basis for
+ the derived key. This is typically a password.
+
+ :return bytes: Derived key.
+
+.. _`RFC 2898`: https://www.ietf.org/rfc/rfc2898.txt