:mod:`secrets` --- Generate secure random numbers for managing secrets
.. module:: secrets :synopsis: Generate secure random numbers for managing secrets.
.. moduleauthor:: Steven D'Aprano <steve+python@pearwood.info>
.. sectionauthor:: Steven D'Aprano <steve+python@pearwood.info>
.. versionadded:: 3.6
.. testsetup:: from secrets import * __name__ = '<doctest>'
Source code: :source:`Lib/secrets.py`
The :mod:`secrets` module is used for generating cryptographically strong random numbers suitable for managing data such as passwords, account authentication, security tokens, and related secrets.
In particularly, :mod:`secrets` should be used in preference to the default pseudo-random number generator in the :mod:`random` module, which is designed for modelling and simulation, not security or cryptography.
.. seealso:: :pep:`506`
The :mod:`secrets` module provides access to the most secure source of randomness that your operating system provides.
A class for generating random numbers using the highest-quality sources provided by the operating system. See :class:`random.SystemRandom` for additional details.
.. function:: choice(sequence) Return a randomly-chosen element from a non-empty sequence.
.. function:: randbelow(n) Return a random int in the range [0, *n*).
.. function:: randbits(k) Return an int with *k* random bits.
The :mod:`secrets` module provides functions for generating secure tokens, suitable for applications such as password resets, hard-to-guess URLs, and similar.
.. function:: token_bytes([nbytes=None]) Return a random byte string containing *nbytes* number of bytes. If *nbytes* is ``None`` or not supplied, a reasonable default is used. .. doctest:: >>> token_bytes(16) #doctest:+SKIP b'\xebr\x17D*t\xae\xd4\xe3S\xb6\xe2\xebP1\x8b'
.. function:: token_hex([nbytes=None]) Return a random text string, in hexadecimal. The string has *nbytes* random bytes, each byte converted to two hex digits. If *nbytes* is ``None`` or not supplied, a reasonable default is used. .. doctest:: >>> token_hex(16) #doctest:+SKIP 'f9bf78b9a18ce6d46a0cd2b0b86df9da'
.. function:: token_urlsafe([nbytes=None]) Return a random URL-safe text string, containing *nbytes* random bytes. The text is Base64 encoded, so on average each byte results in approximately 1.3 characters. If *nbytes* is ``None`` or not supplied, a reasonable default is used. .. doctest:: >>> token_urlsafe(16) #doctest:+SKIP 'Drmhze6EPcv0fN_81Bj-nA'
To be secure against brute-force attacks, tokens need to have sufficient randomness. Unfortunately, what is considered sufficient will necessarily increase as computers get more powerful and able to make more guesses in a shorter period. As of 2015, it is believed that 32 bytes (256 bits) of randomness is sufficient for the typical use-case expected for the :mod:`secrets` module.
For those who want to manage their own token length, you can explicitly
specify how much randomness is used for tokens by giving an :class:`int`
argument to the various token_*
functions. That argument is taken
as the number of bytes of randomness to use.
Otherwise, if no argument is provided, or if the argument is None
,
the token_*
functions will use a reasonable default instead.
Note
That default is subject to change at any time, including during maintenance releases.
.. function:: compare_digest(a, b) Return ``True`` if strings *a* and *b* are equal, otherwise ``False``, in such a way as to reduce the risk of `timing attacks <http://codahale.com/a-lesson-in-timing-attacks/>`_. See :func:`hmac.compare_digest` for additional details.
This section shows recipes and best practices for using :mod:`secrets` to manage a basic level of security.
Generate an eight-character alphanumeric password:
.. testcode:: import string alphabet = string.ascii_letters + string.digits password = ''.join(choice(alphabet) for i in range(8))
Note
Applications should not store passwords in a recoverable format, whether plain text or encrypted. They should be salted and hashed using a cryptographically-strong one-way (irreversible) hash function.
Generate a ten-character alphanumeric password with at least one lowercase character, at least one uppercase character, and at least three digits:
.. testcode:: import string alphabet = string.ascii_letters + string.digits while True: password = ''.join(choice(alphabet) for i in range(10)) if (any(c.islower() for c in password) and any(c.isupper() for c in password) and sum(c.isdigit() for c in password) >= 3): break
Generate an XKCD-style passphrase:
.. testcode:: # On standard Linux systems, use a convenient dictionary file. # Other platforms may need to provide their own word-list. with open('/usr/share/dict/words') as f: words = [word.strip() for word in f] password = ' '.join(choice(words) for i in range(4))
Generate a hard-to-guess temporary URL containing a security token suitable for password recovery applications:
.. testcode:: url = 'https://mydomain.com/reset=' + token_urlsafe()