secrets —- Generate secure random numbers for managing secrets

3.6 新版功能.

Source code:Lib/secrets.py

The secrets module is used for generating cryptographically strongrandom numbers suitable for managing data such as passwords, accountauthentication, security tokens, and related secrets.

In particularly, secrets should be used in preference to thedefault pseudo-random number generator in the random module, whichis designed for modelling and simulation, not security or cryptography.

参见

PEP 506

Random numbers

The secrets module provides access to the most secure source ofrandomness that your operating system provides.

  • class secrets.SystemRandom

  • A class for generating random numbers using the highest-qualitysources provided by the operating system. Seerandom.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 securetokens, suitable for applications such as password resets,hard-to-guess URLs, and similar.

  • secrets.tokenbytes([_nbytes=None])
  • Return a random byte string containing nbytes number of bytes.If nbytes is None or not supplied, a reasonable default isused.
  1. >>> token_bytes(16)  
  2. b'\xebr\x17D*t\xae\xd4\xe3S\xb6\xe2\xebP1\x8b'
  • secrets.tokenhex([_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.
  1. >>> token_hex(16)  
  2. 'f9bf78b9a18ce6d46a0cd2b0b86df9da'
  • secrets.tokenurlsafe([_nbytes=None])
  • Return a random URL-safe text string, containing nbytes randombytes. The text is Base64 encoded, so on average each byte resultsin approximately 1.3 characters. If nbytes is None or notsupplied, a reasonable default is used.
  1. >>> token_urlsafe(16)  
  2. 'Drmhze6EPcv0fN_81Bj-nA'

How many bytes should tokens use?

To be secure againstbrute-force attacks,tokens need to have sufficient randomness. Unfortunately, what isconsidered sufficient will necessarily increase as computers get morepowerful 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 forthe typical use-case expected for the secrets module.

For those who want to manage their own token length, you can explicitlyspecify how much randomness is used for tokens by giving an intargument to the various token_* functions. That argument is takenas 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.

注解

That default is subject to change at any time, including duringmaintenance releases.

其他功能

  • secrets.comparedigest(_a, b)
  • Return True if strings a and b are equal, otherwise False,in such a way as 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:

  1. import string
  2. import secrets
  3. alphabet = string.ascii_letters + string.digits
  4. password = ''.join(secrets.choice(alphabet) for i in range(8))

注解

Applications should notstore passwords in a recoverable format,whether plain text or encrypted. They should be salted and hashedusing a cryptographically-strong one-way (irreversible) hash function.

Generate a ten-character alphanumeric password with at least onelowercase character, at least one uppercase character, and at leastthree digits:

  1. import string
  2. import secrets
  3. alphabet = string.ascii_letters + string.digits
  4. while True:
  5.     password = ''.join(secrets.choice(alphabet) for i in range(10))
  6.     if (any(c.islower() for c in password)
  7.             and any(c.isupper() for c in password)
  8.             and sum(c.isdigit() for c in password) >= 3):
  9.         break

Generate an XKCD-style passphrase:

  1. import secrets
  2. # On standard Linux systems, use a convenient dictionary file.
  3. # Other platforms may need to provide their own word-list.
  4. with open('/usr/share/dict/words') as f:
  5.     words = [word.strip() for word in f]
  6.     password = ' '.join(secrets.choice(words) for i in range(4))

Generate a hard-to-guess temporary URL containing a security tokensuitable for password recovery applications:

  1. import secrets
  2. url = 'https://mydomain.com/reset=' + secrets.token_urlsafe()