update docs to roughly describe many time pad attack & link cbc
diff --git a/docs/primitives/symmetric-encryption.rst b/docs/primitives/symmetric-encryption.rst
index 52bd6a4..9520d6e 100644
--- a/docs/primitives/symmetric-encryption.rst
+++ b/docs/primitives/symmetric-encryption.rst
@@ -87,8 +87,11 @@
message). Must be the same number of bytes as the
``block_size`` of the cipher. It is critical to
never reuse a ``nonce`` with a given ``key``. Unlike
- CBC, reusing a nonce compromises the security of
- all data encrypted under the key (see: two time pad).
+ :class:`~cryptography.primitives.block.modes.CBC`,
+ reusing a nonce compromises the security of all data
+ encrypted under the key. Specifically,
+ (pt1 xor keystream) xor (pt2 xor keystream) is
+ equivalent to (pt1 xor pt2).
.. class:: cryptography.primitives.block.modes.OFB(initialization_vector)