secrets — Generate secure random numbers for managing secrets (original) (raw)

Added 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.

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. Seerandom.SystemRandom for additional details.

secrets.choice(seq)¶

Return a randomly chosen element from a non-empty sequence.

secrets.randbelow(exclusive_upper_bound)¶

Return a random int in the range [0, exclusive_upper_bound).

secrets.randbits(k)¶

Return a non-negative 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.

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 isNone or not supplied, a reasonable default is used.

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.

token_urlsafe(16) 'Drmhze6EPcv0fN_81Bj-nA'

How many bytes should tokens use?¶

To be secure againstbrute-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 intargument 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 orbytes-like objects a and b are equal, otherwise False, using a “constant-time compare” to reduce the risk oftiming attacks. See hmac.compare_digest() for additional details.

Recipes and best practices¶

This section shows recipes and best practices for using secretsto 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 notstore 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://example.com/reset=' + secrets.token_urlsafe()