Validate the IV/nonce length for a given algorithm.
Fixes #159
diff --git a/docs/hazmat/primitives/interfaces.rst b/docs/hazmat/primitives/interfaces.rst
index 11cff51..e798c0e 100644
--- a/docs/hazmat/primitives/interfaces.rst
+++ b/docs/hazmat/primitives/interfaces.rst
@@ -56,6 +56,18 @@
The name may be used by a backend to influence the operation of a
cipher in conjunction with the algorithm's name.
+ .. method:: validate_for_algorithm(algorithm)
+
+ :param CipherAlgorithm algorithm:
+
+ Checks that the combination of this mode with the provided algorithm
+ meets any necessary invariants. This should raise an exception if they
+ are not met.
+
+ For example, the :class:`~cryptography.hazmat.primitives.modes.CBC`
+ mode uses this method to check that the provided initialization
+ vector's length matches the block size of the algorithm.
+
.. class:: ModeWithInitializationVector