Documentation!

1 files changed, 16 insertions, 0 deletions

diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index eef359d6..35b0d9a8 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -75,6 +75,15 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_.
     everything into the context. Once that is done call ``finalize()`` to
     finish the operation and obtain the remainder of the data.
 
+    Block ciphers require that plaintext or ciphertext always be a multiple of
+    their block size, because of that **padding** is often required to make a
+    message the correct size. ``CipherContext`` will not automatically apply
+    any padding; you'll need to add your own. For block ciphers the reccomended
+    padding is :class:`cryptography.hazmat.primitives.padding.PKCS7`. If you
+    are using a stream cipher mode (such as
+    :class:`cryptography.hazmat.primitives.modes.CTR`) you don't have to worry
+    about this.
+
     .. method:: update(data)
 
         :param bytes data: The data you wish to pass into the context.
@@ -90,6 +99,13 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_.
     .. method:: finalize()
 
         :return bytes: Returns the remainder of the data.
+        :raises cryptography.exceptions.IncorrectPadding: This is raised when
+                                                          the data provided
+                                                          isn't correctly
+                                                          padded to be a
+                                                          multiple of the
+                                                          algorithm's block
+                                                          size.
 
         Once ``finalize`` is called this object can no longer be used and
         :meth:`update` and :meth:`finalize` will raise