Merge branch 'master' into triple-des

1 files changed, 19 insertions, 0 deletions

diff --git a/docs/primitives/symmetric-encryption.rst b/docs/primitives/symmetric-encryption.rst
index b1b40486..cf251c91 100644
--- a/docs/primitives/symmetric-encryption.rst
+++ b/docs/primitives/symmetric-encryption.rst
@@ -94,6 +94,25 @@ Modes
                                         reuse an ``initialization_vector`` with
                                         a given ``key``.
 
+
+.. class:: cryptography.primitives.block.modes.CTR(nonce)
+
+    .. warning::
+
+        Counter mode is not recommended for use with block ciphers that have a
+        block size of less than 128-bits.
+
+    CTR (Counter) is a mode of operation for block ciphers. It is considered
+    cryptographically strong.
+
+    :param bytes nonce: Should be random bytes. It is critical to never reuse a
+                        ``nonce`` with a given key.  Any reuse of a nonce
+                        with the same key compromises the security of every
+                        message encrypted with that key. Must be the same
+                        number of bytes as the ``block_size`` of the cipher
+                        with a given key. The nonce does not need to be kept
+                        secret and may be included alongside the ciphertext.
+
 .. class:: cryptography.primitives.block.modes.OFB(initialization_vector)
 
     OFB (Output Feedback) is a mode of operation for block ciphers. It