add output feedback mode support + test vectors (aes)
diff --git a/docs/primitives/symmetric-encryption.rst b/docs/primitives/symmetric-encryption.rst
index d0429d4..7ec42a3 100644
--- a/docs/primitives/symmetric-encryption.rst
+++ b/docs/primitives/symmetric-encryption.rst
@@ -68,6 +68,19 @@
reuse an ``initialization_vector`` with
a given ``key``.
+.. class:: cryptography.primitives.block.modes.OFB(initialization_vector)
+
+ OFB (Output Feedback) is a mode of operation for block ciphers. It
+ transforms a block cipher into a stream cipher.
+
+ :param bytes initialization_vector: Must be random bytes. They do not need
+ to be kept secret (they can be included
+ in a transmitted message). Must be the
+ same number of bytes as the
+ ``block_size`` of the cipher. Do not
+ reuse an ``initialization_vector`` with
+ a given ``key``.
+
Insecure Modes
--------------