FM / docs

/usr/share/doc/python3-cryptography/docs/

/usr/share/doc/python3-cryptography/docs

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development/	-	0755	rm
hazmat/	-	0755	rm
x509/	-	0755	rm
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api-stability.rst	2330	0644	edit dl rm
changelog.rst	30	0644	edit dl rm
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conf.py	6216	0644	edit dl rm
cryptography-docs.py	1698	0644	edit dl rm
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exceptions.rst	853	0644	edit dl rm
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random-numbers.rst	1584	0644	edit dl rm
security.rst	3668	0644	edit dl rm
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Edit: /usr/share/doc/python3-cryptography/docs/random-numbers.rst (1584B)

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, which can result in
major security issues depending on the algorithms in use.

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

.. doctest::

>>> import os
    >>> iv = os.urandom(16)

This will use ``/dev/urandom`` on UNIX platforms, and ``CryptGenRandom`` on
Windows.

If you need your random number as an integer (for example, for
:meth:`~cryptography.x509.CertificateBuilder.serial_number`), you can use
``int.from_bytes`` to convert the result of ``os.urandom``:

.. code-block:: pycon

>>> serial = int.from_bytes(os.urandom(20), byteorder="big")

Starting with Python 3.6 the `standard library includes`_ the ``secrets``
module, which can be used for generating cryptographically secure random
numbers, with specific helpers for text-based formats.

.. _`always use your operating system's provided random number generator`: https://sockpuppet.org/blog/2014/02/25/safely-generate-random-numbers/
.. _`standard library includes`: https://docs.python.org/3/library/secrets.html

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, which can result in major security issues depending on the algorithms in use. Therefore, it is our recommendation to `always use your operating system's provided random number generator`_, which is available as :func:`os.urandom`. For example, if you need 16 bytes of random data for an initialization vector, you can obtain them with: .. doctest:: >>> import os >>> iv = os.urandom(16) This will use ``/dev/urandom`` on UNIX platforms, and ``CryptGenRandom`` on Windows. If you need your random number as an integer (for example, for :meth:`~cryptography.x509.CertificateBuilder.serial_number`), you can use ``int.from_bytes`` to convert the result of ``os.urandom``: .. code-block:: pycon >>> serial = int.from_bytes(os.urandom(20), byteorder="big") Starting with Python 3.6 the `standard library includes`_ the ``secrets`` module, which can be used for generating cryptographically secure random numbers, with specific helpers for text-based formats. .. _`always use your operating system's provided random number generator`: https://sockpuppet.org/blog/2014/02/25/safely-generate-random-numbers/ .. _`standard library includes`: https://docs.python.org/3/library/secrets.html