Document that IVs should not be reused.
diff --git a/docs/primitives/symmetric-encryption.rst b/docs/primitives/symmetric-encryption.rst
index c0b3608..be6ed2b 100644
--- a/docs/primitives/symmetric-encryption.rst
+++ b/docs/primitives/symmetric-encryption.rst
@@ -55,3 +55,5 @@
                                         in a transmitted message). Should be
                                         the same number of bytes as the ``key``
                                         for the cipher.
+                                        ``initialization_vectors`` should never
+                                        be reused across different messages.