# `secrets` — Generate secure random numbers for managing secrets

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.

See also

PEP 506

## 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(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 not specified or `None`, `DEFAULT_ENTROPY` is used instead.

      >>> 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 not specified or `None`, `DEFAULT_ENTROPY` is used instead.

      >>> 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 not specified or `None`, `DEFAULT_ENTROPY` is used instead.

      >>> 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 use `DEFAULT_ENTROPY` instead.

secrets.DEFAULT_ENTROPY

  Default number of bytes of randomness used by the `token_*` functions.

  The exact value is subject to change at any time, including during maintenance releases.

## Other functions

secrets.compare_digest(a, b)

  Return `True` if strings or bytes-like objects a and b are equal, otherwise `False`, using a “constant-time compare” to reduce the risk of timing attacks. See `hmac.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://example.com/reset=' + secrets.token_urlsafe()