DH backend interfaces
diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst
index 8866cf7..4da0d75 100644
--- a/docs/hazmat/backends/interfaces.rst
+++ b/docs/hazmat/backends/interfaces.rst
@@ -518,3 +518,88 @@
:returns: An instance of
:class:`~cryptography.x509.CertificateSigningRequest`.
+
+
+.. class:: DHBackend
+
+ .. versionadded:: 0.9
+
+ A backend with methods for doing Diffie-Hellman key exchange.
+
+ .. method:: generate_dh_parameters(key_size)
+
+ :param int key_size: The bit length of the prime modulus to generate.
+
+ :return: A new instance of a
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHParameters`
+ provider.
+
+ :raises ValueError: If ``key_size`` is not at least 512.
+
+ .. method:: generate_dh_private_key(parameters)
+
+ :param parameters: A
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHParameters`
+ provider.
+
+ :return: A new instance of a
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKey`
+ provider.
+
+ .. method:: generate_dh_private_key_and_parameters(self, key_size)
+
+ :param int key_size: The bit length of the prime modulus to generate.
+
+ :return: A new instance of a
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKey`
+ provider.
+
+ :raises ValueError: If ``key_size`` is not at least 512.
+
+ .. method:: load_dh_private_numbers(numbers)
+
+ :param numbers: A
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateNumbers`
+ instance.
+
+ :return: A new instance of a
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHPrivateKey`
+ provider.
+
+ :raises cryptography.exceptions.UnsupportedAlgorithm: This is raised
+ when any backend specific criteria are not met.
+
+ .. method:: load_dh_public_numbers(numbers)
+
+ :param numbers: A
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHPublicNumbers`
+ instance.
+
+ :return: A new instance of a
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHPublicKey`
+ provider.
+
+ :raises cryptography.exceptions.UnsupportedAlgorithm: This is raised
+ when any backend specific criteria are not met.
+
+ .. method:: load_dh_parameter_numbers(numbers)
+
+ :param numbers: A
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHParameterNumbers`
+ instance.
+
+ :return: A new instance of a
+ :class:`~cryptography.hazmat.primitives.asymmetric.dh.DHParameters`
+ provider.
+
+ :raises cryptography.exceptions.UnsupportedAlgorithm: This is raised
+ when any backend specific criteria are not met.
+
+ .. method:: dh_parameters_supported(p, g)
+
+ :param int p: The p value of the DH key.
+
+ :param int g: The g value of the DH key.
+
+ :returns: ``True`` if the given values of ``p`` and ``g`` are supported
+ by this backend, otherwise ``False``.