From fc73e2d04315e21011869fbd925df9e7a99d21ae Mon Sep 17 00:00:00 2001 From: Paul Kehrer Date: Sat, 21 Dec 2013 18:41:38 -0600 Subject: prose updates for GCM tag --- docs/hazmat/primitives/symmetric-encryption.rst | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) (limited to 'docs/hazmat') diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst index 85d7d5b1..f009bb78 100644 --- a/docs/hazmat/primitives/symmetric-encryption.rst +++ b/docs/hazmat/primitives/symmetric-encryption.rst @@ -354,10 +354,12 @@ Modes .. note:: - `NIST SP-800-38D`_ recommends that GCM tags be 128, 120, 122, 104, or - 96-bits in length. Tags are shortened by truncating bytes. Longer tags - provide better security margins. If you must shorten the tag the minimum - allowed length is 4 bytes (32 bits). + Cryptography will emit a 128-bit tag when finalizing encryption. + You can shorten a tag by truncating it to the desired length, but this + is **not recommended** as it lowers the security margins of the + authentication (`NIST SP-800-38D`_ recommends 96-bit or greater). + If you must shorten the tag the minimum allowed length is 4 bytes + (32 bit). :param bytes tag: The tag bytes to verify during decryption. When encrypting this must be None. -- cgit v1.2.3