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| author | Alex Gaynor <alex.gaynor@gmail.com> | 2014-01-01 08:11:13 -0800 |
|---|---|---|
| committer | Alex Gaynor <alex.gaynor@gmail.com> | 2014-01-01 08:11:13 -0800 |
| commit | 2a160d6a159817dd9d08a84e77d102e328f9af4f (patch) | |
| tree | 461b7c607367f243bb46996ec16ad7424e48d440 /docs/hazmat/primitives/symmetric-encryption.rst | |
| parent | 62aefffb1396190930074bf04c91459d1536bd0e (diff) | |
| parent | 522487e5a7dd3004747da85c9f6c53fc5dc4de06 (diff) | |
| download | cryptography-2a160d6a159817dd9d08a84e77d102e328f9af4f.tar.gz cryptography-2a160d6a159817dd9d08a84e77d102e328f9af4f.tar.bz2 cryptography-2a160d6a159817dd9d08a84e77d102e328f9af4f.zip | |
Merge branch 'master' into validate-iv
Conflicts:
tests/hazmat/backends/test_openssl.py
tests/hazmat/primitives/test_block.py
Diffstat (limited to 'docs/hazmat/primitives/symmetric-encryption.rst')
| -rw-r--r-- | docs/hazmat/primitives/symmetric-encryption.rst | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst index f4d0457a..30896a05 100644 --- a/docs/hazmat/primitives/symmetric-encryption.rst +++ b/docs/hazmat/primitives/symmetric-encryption.rst @@ -61,7 +61,7 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_. provider. If the backend doesn't support the requested combination of ``cipher`` - and ``mode`` an :class:`cryptography.exceptions.UnsupportedAlgorithm` + and ``mode`` an :class:`~cryptography.exceptions.UnsupportedAlgorithm` will be raised. .. method:: decryptor() @@ -352,6 +352,16 @@ Modes Do not reuse an ``initialization_vector`` with a given ``key``. + .. note:: + + 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-bits or greater). + If you must shorten the tag the minimum allowed length is 4 bytes + (32-bits). Applications **must** verify the tag is the expected length + to guarantee the expected security margin. + :param bytes tag: The tag bytes to verify during decryption. When encrypting this must be None. @@ -390,3 +400,4 @@ Insecure Modes .. _`described by Colin Percival`: http://www.daemonology.net/blog/2009-06-11-cryptographic-right-answers.html .. _`recommends 96-bit IV length`: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf +.. _`NIST SP-800-38D`: http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf |