gcm doc improvements
diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index bd9a3f6..4e7990b 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -137,7 +137,8 @@
.. attribute:: tag
:return bytes: Returns the tag value as bytes.
- :raises: :class:`~cryptography.exceptions.NotFinalized`
+ :raises: :class:`~cryptography.exceptions.NotYetFinalized` if called
+ before the context is finalized.
.. _symmetric-encryption-algorithms:
@@ -319,7 +320,10 @@
.. class:: GCM(initialization_vector, tag=None)
GCM (Galois Counter Mode) is a mode of operation for block ciphers. It
- is an AEAD (authenticated encryption with additional data) mode.
+ is an AEAD (authenticated encryption with additional data) mode. AEAD
+ is a type of block cipher mode that encrypts the message as well as
+ authenticating it (and optionally additional data that is not encrypted)
+ simultaneously.
:param bytes initialization_vector: Must be random bytes. They do not need
to be kept secret (they can be included