1"""Generate cryptographically strong pseudo-random numbers suitable for 2managing secrets such as account authentication, tokens, and similar. 3 4See PEP 506 for more information. 5https://www.python.org/dev/peps/pep-0506/ 6 7""" 8 9__all__ = ['choice', 'randbelow', 'randbits', 'SystemRandom', 10 'token_bytes', 'token_hex', 'token_urlsafe', 11 'compare_digest', 12 ] 13 14 15import base64 16import binascii 17 18from hmac import compare_digest 19from random import SystemRandom 20 21_sysrand = SystemRandom() 22 23randbits = _sysrand.getrandbits 24choice = _sysrand.choice 25 26def randbelow(exclusive_upper_bound): 27 """Return a random int in the range [0, n).""" 28 if exclusive_upper_bound <= 0: 29 raise ValueError("Upper bound must be positive.") 30 return _sysrand._randbelow(exclusive_upper_bound) 31 32DEFAULT_ENTROPY = 32 # number of bytes to return by default 33 34def token_bytes(nbytes=None): 35 """Return a random byte string containing *nbytes* bytes. 36 37 If *nbytes* is ``None`` or not supplied, a reasonable 38 default is used. 39 40 >>> token_bytes(16) #doctest:+SKIP 41 b'\\xebr\\x17D*t\\xae\\xd4\\xe3S\\xb6\\xe2\\xebP1\\x8b' 42 43 """ 44 if nbytes is None: 45 nbytes = DEFAULT_ENTROPY 46 return _sysrand.randbytes(nbytes) 47 48def token_hex(nbytes=None): 49 """Return a random text string, in hexadecimal. 50 51 The string has *nbytes* random bytes, each byte converted to two 52 hex digits. If *nbytes* is ``None`` or not supplied, a reasonable 53 default is used. 54 55 >>> token_hex(16) #doctest:+SKIP 56 'f9bf78b9a18ce6d46a0cd2b0b86df9da' 57 58 """ 59 return binascii.hexlify(token_bytes(nbytes)).decode('ascii') 60 61def token_urlsafe(nbytes=None): 62 """Return a random URL-safe text string, in Base64 encoding. 63 64 The string has *nbytes* random bytes. If *nbytes* is ``None`` 65 or not supplied, a reasonable default is used. 66 67 >>> token_urlsafe(16) #doctest:+SKIP 68 'Drmhze6EPcv0fN_81Bj-nA' 69 70 """ 71 tok = token_bytes(nbytes) 72 return base64.urlsafe_b64encode(tok).rstrip(b'=').decode('ascii') 73