/usr/lib/python3/dist-packages/twisted/python/randbytes.py is in python3-twisted-experimental 13.2.0-0ubuntu1.
This file is owned by root:root, with mode 0o644.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 | # -*- test-case-name: twisted.test.test_randbytes -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Cryptographically secure random implementation, with fallback on normal random.
"""
from __future__ import division, absolute_import
import warnings, os, random, string
from twisted.python.compat import _PY3
getrandbits = getattr(random, 'getrandbits', None)
if _PY3:
_fromhex = bytes.fromhex
else:
def _fromhex(hexBytes):
return hexBytes.decode('hex')
class SecureRandomNotAvailable(RuntimeError):
"""
Exception raised when no secure random algorithm is found.
"""
class SourceNotAvailable(RuntimeError):
"""
Internal exception used when a specific random source is not available.
"""
class RandomFactory(object):
"""
Factory providing L{secureRandom} and L{insecureRandom} methods.
You shouldn't have to instantiate this class, use the module level
functions instead: it is an implementation detail and could be removed or
changed arbitrarily.
"""
# This variable is no longer used, and will eventually be removed.
randomSources = ()
getrandbits = getrandbits
def _osUrandom(self, nbytes):
"""
Wrapper around C{os.urandom} that cleanly manage its absence.
"""
try:
return os.urandom(nbytes)
except (AttributeError, NotImplementedError) as e:
raise SourceNotAvailable(e)
def secureRandom(self, nbytes, fallback=False):
"""
Return a number of secure random bytes.
@param nbytes: number of bytes to generate.
@type nbytes: C{int}
@param fallback: Whether the function should fallback on non-secure
random or not. Default to C{False}.
@type fallback: C{bool}
@return: a string of random bytes.
@rtype: C{str}
"""
try:
return self._osUrandom(nbytes)
except SourceNotAvailable:
pass
if fallback:
warnings.warn(
"urandom unavailable - "
"proceeding with non-cryptographically secure random source",
category=RuntimeWarning,
stacklevel=2)
return self.insecureRandom(nbytes)
else:
raise SecureRandomNotAvailable("No secure random source available")
def _randBits(self, nbytes):
"""
Wrapper around C{os.getrandbits}.
"""
if self.getrandbits is not None:
n = self.getrandbits(nbytes * 8)
hexBytes = ("%%0%dx" % (nbytes * 2)) % n
return _fromhex(hexBytes)
raise SourceNotAvailable("random.getrandbits is not available")
if _PY3:
_maketrans = bytes.maketrans
def _randModule(self, nbytes):
"""
Wrapper around the C{random} module.
"""
return b"".join([
bytes([random.choice(self._BYTES)]) for i in range(nbytes)])
else:
_maketrans = string.maketrans
def _randModule(self, nbytes):
"""
Wrapper around the C{random} module.
"""
return b"".join([
random.choice(self._BYTES) for i in range(nbytes)])
_BYTES = _maketrans(b'', b'')
def insecureRandom(self, nbytes):
"""
Return a number of non secure random bytes.
@param nbytes: number of bytes to generate.
@type nbytes: C{int}
@return: a string of random bytes.
@rtype: C{str}
"""
for src in ("_randBits", "_randModule"):
try:
return getattr(self, src)(nbytes)
except SourceNotAvailable:
pass
factory = RandomFactory()
secureRandom = factory.secureRandom
insecureRandom = factory.insecureRandom
del factory
__all__ = ["secureRandom", "insecureRandom", "SecureRandomNotAvailable"]
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