Random number generation
========================

When generating random data for use in cryptographic operations, such as an
initialization vector for encryption in
:class:`~cryptography.hazmat.primitives.ciphers.modes.CBC` mode, you do not
want to use the standard :mod:`random` module APIs. This is because they do not
provide a cryptographically secure random number generator, resulting in
various security issues in different algorithms.

Therefore, it is our recommendation to always use your operating system's
provided random number generator, which is available as ``os.urandom()``. For
example, if you need 16 bytes of random data for an initialization vector, you
can obtain them with:

.. doctest::

    >>> import os
    >>> os.urandom(16)
    '...'