Added support for padding ANSI X.923
diff --git a/docs/hazmat/primitives/padding.rst b/docs/hazmat/primitives/padding.rst
index a60f5ac..37e4252 100644
--- a/docs/hazmat/primitives/padding.rst
+++ b/docs/hazmat/primitives/padding.rst
@@ -54,6 +54,47 @@
provider.
+.. class:: ANSIX923(block_size)
+
+ ANSI X.923 padding works by appending ``N-1`` bytes with the value of ``0``
+ and a last byte with the value of ``chr(N)``, where ``N`` is the number of
+ bytes required to make the final block of data the same size as the block
+ size. A simple example of padding is:
+
+ .. doctest::
+
+ >>> padder = padding.ANSIX923(128).padder()
+ >>> padded_data = padder.update(b"11111111111111112222222222")
+ >>> padded_data
+ '1111111111111111'
+ >>> padded_data += padder.finalize()
+ >>> padded_data
+ '11111111111111112222222222\x00\x00\x00\x00\x00\x06'
+ >>> unpadder = padding.ANSIX923(128).unpadder()
+ >>> data = unpadder.update(padded_data)
+ >>> data
+ '1111111111111111'
+ >>> data + unpadder.finalize()
+ '11111111111111112222222222'
+
+ :param block_size: The size of the block in bits that the data is being
+ padded to.
+ :raises ValueError: Raised if block size is not a multiple of 8 or is not
+ between 0 and 256.
+
+ .. method:: padder()
+
+ :returns: A padding
+ :class:`~cryptography.hazmat.primitives.padding.PaddingContext`
+ provider
+
+ .. method:: unpadder()
+
+ :returns: An unpadding
+ :class:`~cryptography.hazmat.primitives.padding.PaddingContext`
+ provider.
+
+
.. class:: PaddingContext
When calling ``padder()`` or ``unpadder()`` the result will conform to the