1 """Generate cryptographically strong pseudo-random numbers suitable for 2 managing secrets such as account authentication, tokens, and similar. 3 4 See PEP 506 for more information. 5 https://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 15 import base64 16 import binascii 17 import os 18 19 from hmac import compare_digest 20 from random import SystemRandom 21 22 _sysrand = SystemRandom() 23 24 randbits = _sysrand.getrandbits 25 choice = _sysrand.choice 26 27 def randbelow(exclusive_upper_bound): 28 """Return a random int in the range [0, n).""" 29 if exclusive_upper_bound <= 0: 30 raise ValueError("Upper bound must be positive.") 31 return _sysrand._randbelow(exclusive_upper_bound) 32 33 DEFAULT_ENTROPY = 32 # number of bytes to return by default 34 35 def token_bytes(nbytes=None): 36 """Return a random byte string containing *nbytes* bytes. 37 38 If *nbytes* is ``None`` or not supplied, a reasonable 39 default is used. 40 41 >>> token_bytes(16) #doctest:+SKIP 42 b'\\xebr\\x17D*t\\xae\\xd4\\xe3S\\xb6\\xe2\\xebP1\\x8b' 43 44 """ 45 if nbytes is None: 46 nbytes = DEFAULT_ENTROPY 47 return os.urandom(nbytes) 48 49 def token_hex(nbytes=None): 50 """Return a random text string, in hexadecimal. 51 52 The string has *nbytes* random bytes, each byte converted to two 53 hex digits. If *nbytes* is ``None`` or not supplied, a reasonable 54 default is used. 55 56 >>> token_hex(16) #doctest:+SKIP 57 'f9bf78b9a18ce6d46a0cd2b0b86df9da' 58 59 """ 60 return binascii.hexlify(token_bytes(nbytes)).decode('ascii') 61 62 def token_urlsafe(nbytes=None): 63 """Return a random URL-safe text string, in Base64 encoding. 64 65 The string has *nbytes* random bytes. If *nbytes* is ``None`` 66 or not supplied, a reasonable default is used. 67 68 >>> token_urlsafe(16) #doctest:+SKIP 69 'Drmhze6EPcv0fN_81Bj-nA' 70 71 """ 72 tok = token_bytes(nbytes) 73 return base64.urlsafe_b64encode(tok).rstrip(b'=').decode('ascii') 74
