Iinital work on 3DES. No tests and no implementation yet.
diff --git a/docs/primitives/symmetric-encryption.rst b/docs/primitives/symmetric-encryption.rst
index 1b8d1d7..91f3b7a 100644
--- a/docs/primitives/symmetric-encryption.rst
+++ b/docs/primitives/symmetric-encryption.rst
@@ -52,6 +52,25 @@
This must be kept secret.
+Insecure Ciphers
+----------------
+
+.. class:: cryptography.primitives.block.ciphers.TripleDES(key)
+
+ Triple DES (Data encryption standard), sometimes refered to as 3DES, is a
+ block cipher standardized by NIST. Triple DES should be considered to be
+ cryptographically broken and should not be used for new applications, old
+ applications should strongly consider moving away from it.
+
+ :param bytes key: The secret key, either ``64``, ``128``, or ``192`` bits
+ (note that DES functionally uses ``56``, ``112``, or
+ ``168`` bits of the key, there is a parity byte in each
+ component of the key), in some materials these are
+ referred to as being up to three separate keys (each
+ ``56`` bits long), they can simply be concatenated to
+ produce the full key. This must be kept secret.
+
+
Modes
~~~~~