Update cryptography to 2.3

[pyup-bot]

This PR updates cryptography from 2.2.2 to 2.3.

Changelog

2.3

~~~~~~~~~~~~~~~~

* **SECURITY ISSUE:**
:meth:`~cryptography.hazmat.primitives.ciphers.AEADDecryptionContext.finalize_with_tag`
allowed tag truncation by default which can allow tag forgery in some cases.
The method now enforces the ``min_tag_length`` provided to the
:class:`~cryptography.hazmat.primitives.ciphers.modes.GCM` constructor.
* Added support for Python 3.7.
* Added :meth:`~cryptography.fernet.Fernet.extract_timestamp` to get the
authenticated timestamp of a :doc:`Fernet </fernet>` token.
* Support for Python 2.7.x without ``hmac.compare_digest`` has been deprecated.
We will require Python 2.7.7 or higher (or 2.7.6 on Ubuntu) in the next
``cryptography`` release.
* Fixed multiple issues preventing ``cryptography`` from compiling against
LibreSSL 2.7.x.
* Added
:class:`~cryptography.x509.CertificateRevocationList.get_revoked_certificate_by_serial_number`
for quick serial number searches in CRLs.
* The :class:`~cryptography.x509.RelativeDistinguishedName` class now
preserves the order of attributes. Duplicate attributes now raise an error
instead of silently discarding duplicates.
* :func:`~cryptography.hazmat.primitives.keywrap.aes_key_unwrap` and
:func:`~cryptography.hazmat.primitives.keywrap.aes_key_unwrap_with_padding`
now raise :class:`~cryptography.hazmat.primitives.keywrap.InvalidUnwrap` if
the wrapped key is an invalid length, instead of ``ValueError``.

.. _v2-2-2:

Links

• PyPI: https://pypi.org/project/cryptography
• Changelog: https://pyup.io/changelogs/cryptography/
• Repo: https://github.com/pyca/cryptography