secrets — Generate secure random numbers for managing secrets

Added in version 3.6.

Código fuente: 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.

Ver también

PEP 506

Números aleatorios

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

class secrets.SystemRandom

Una clase para generar números aleatorios utilizando las fuentes de mayor calidad que proporciona el sistema operativo. Ver random.SystemRandom para más detalles.

secrets.choice(seq)

Retorna un elemento elegido aleatoriamente a partir de una secuencia no vacía.

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.

Generando 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'

¿Cuántos bytes deben tener los tokens?

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.

Para quienes quieran gestionar la longitud de sus propios tokens, pueden especificar explícitamente cuánta aleatoriedad se utiliza para los tokens dando un argumento int a las funciones token_*. Ese argumento se toma como el número de bytes de aleatoriedad a utilizar.

Otherwise, if no argument is provided, or if the argument is None, the token_* functions uses 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.

Otras funciones

secrets.compare_digest(a, b)

Retorna True si las cadenas de caracteres o objetos tipo-bytes a y b son iguales, de lo contrario False, usando una «comparación de tiempo constante» para reducir el riesgo de ataques de análisis temporal. Ver hmac.compare_digest`() para detalles adicionales.

Recetas y mejores prácticas

This section shows recipes and best practices for using secrets to manage a basic level of security.

Generar una contraseña alfanumérica de ocho caracteres:

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

Nota

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.

Generar una contraseña alfanumérica de diez caracteres con al menos un carácter en minúscula, al menos un carácter en mayúscula y al menos tres dígitos:

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

Generar una contraseña al estilo XKCD:

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))

Generar una URL temporal difícil de adivinar que contenga un token de seguridad adecuado para la recuperación de contraseñas:

import secrets
url = 'https://example.com/reset=' + secrets.token_urlsafe()