document invalidtag (#3675)
* document invalidtag
* move invalidtag
diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index 8b047b8..8c6087e 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -690,6 +690,17 @@
Exact requirements of the tag are described by the documentation of
individual modes.
+Exceptions
+~~~~~~~~~~
+
+.. currentmodule:: cryptography.exceptions
+
+
+.. class:: InvalidTag
+
+ This is raised if an authenticated encryption tag fails to verify during
+ decryption.
+
.. _`described by Colin Percival`: http://www.daemonology.net/blog/2009-06-11-cryptographic-right-answers.html