secrets — Generate secure random numbers for managing secrets
New in version 3.6.
Source code: Lib/secrets.py
The 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 particular, secrets
should be used in preference to the default pseudo-random number generator in the random
module, which is designed for modelling and simulation, not security or cryptography.
See also
Random numbers
The secrets
module provides access to the most secure source of randomness that your operating system provides.
-
class secrets.SystemRandom
-
A class for generating random numbers using the highest-quality sources provided by the operating system. See
random.SystemRandom
for additional details.
-
secrets.choice(sequence)
-
Return a randomly-chosen element from a non-empty sequence.
-
secrets.randbelow(n)
-
Return a random int in the range [0, n).
-
secrets.randbits(k)
-
Return an int with k random bits.
Generating tokens
The secrets
module provides functions for generating secure tokens, suitable for applications such as password resets, hard-to-guess URLs, and similar.
-
secrets.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.pycon3Copy Code>>> token_bytes(16) b'\xebr\x17D*t\xae\xd4\xe3S\xb6\xe2\xebP1\x8b'
-
secrets.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.pycon3Copy Code>>> token_hex(16) 'f9bf78b9a18ce6d46a0cd2b0b86df9da'
-
secrets.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.pycon3Copy Code>>> token_urlsafe(16) 'Drmhze6EPcv0fN_81Bj-nA'
How many bytes should tokens use?
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 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 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.
Other functions
-
secrets.compare_digest(a, b)
-
Return
True
if strings a and b are equal, otherwiseFalse
, in such a way as to reduce the risk of timing attacks. Seehmac.compare_digest()
for additional details.
Recipes and best practices
This section shows recipes and best practices for using secrets
to manage a basic level of security.
Generate an eight-character alphanumeric password:
import string import secrets alphabet = string.ascii_letters + string.digits password = ''.join(secrets.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:
import string import secrets alphabet = string.ascii_letters + string.digits while True: password = ''.join(secrets.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:
import secrets # 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(secrets.choice(words) for i in range(4))
Generate a hard-to-guess temporary URL containing a security token suitable for password recovery applications:
import secrets url = 'https://mydomain.com/reset=' + secrets.token_urlsafe()
License
© 2001–2021 Python Software Foundation
Licensed under the PSF License.
https://docs.python.org/3.9/library/secrets.html