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# -*- coding: utf-8 -*-
#
# Random/_UserFriendlyRNG.py : A user-friendly random number generator
#
# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
#
# ===================================================================
# The contents of this file are dedicated to the public domain. To
# the extent that dedication to the public domain is not available,
# everyone is granted a worldwide, perpetual, royalty-free,
# non-exclusive license to exercise all rights associated with the
# contents of this file for any purpose whatsoever.
# No rights are reserved.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
# ===================================================================
__revision__ = "$Id$"
import sys
if sys.version_info[0] == 2 and sys.version_info[1] == 1:
from Crypto.Util.py21compat import *
import os
import threading
import struct
import time
from math import floor
from Crypto.Random import OSRNG
from Crypto.Random.Fortuna import FortunaAccumulator
class _EntropySource(object):
def __init__(self, accumulator, src_num):
self._fortuna = accumulator
self._src_num = src_num
self._pool_num = 0
def feed(self, data):
self._fortuna.add_random_event(self._src_num, self._pool_num, data)
self._pool_num = (self._pool_num + 1) & 31
class _EntropyCollector(object):
def __init__(self, accumulator):
self._osrng = OSRNG.new()
self._osrng_es = _EntropySource(accumulator, 255)
self._time_es = _EntropySource(accumulator, 254)
self._clock_es = _EntropySource(accumulator, 253)
def reinit(self):
# Add 256 bits to each of the 32 pools, twice. (For a total of 16384
# bits collected from the operating system.)
for i in range(2):
block = self._osrng.read(32*32)
for p in range(32):
self._osrng_es.feed(block[p*32:(p+1)*32])
block = None
self._osrng.flush()
def collect(self):
# Collect 64 bits of entropy from the operating system and feed it to Fortuna.
self._osrng_es.feed(self._osrng.read(8))
# Add the fractional part of time.time()
t = time.time()
self._time_es.feed(struct.pack("@I", int(2**30 * (t - floor(t)))))
# Add the fractional part of time.clock()
t = time.clock()
self._clock_es.feed(struct.pack("@I", int(2**30 * (t - floor(t)))))
class _UserFriendlyRNG(object):
def __init__(self):
self.closed = False
self._fa = FortunaAccumulator.FortunaAccumulator()
self._ec = _EntropyCollector(self._fa)
self.reinit()
def reinit(self):
"""Initialize the random number generator and seed it with entropy from
the operating system.
"""
# Save the pid (helps ensure that Crypto.Random.atfork() gets called)
self._pid = os.getpid()
# Collect entropy from the operating system and feed it to
# FortunaAccumulator
self._ec.reinit()
# Override FortunaAccumulator's 100ms minimum re-seed interval. This
# is necessary to avoid a race condition between this function and
# self.read(), which that can otherwise cause forked child processes to
# produce identical output. (e.g. CVE-2013-1445)
#
# Note that if this function can be called frequently by an attacker,
# (and if the bits from OSRNG are insufficiently random) it will weaken
# Fortuna's ability to resist a state compromise extension attack.
self._fa._forget_last_reseed()
def close(self):
self.closed = True
self._osrng = None
self._fa = None
def flush(self):
pass
def read(self, N):
"""Return N bytes from the RNG."""
if self.closed:
raise ValueError("I/O operation on closed file")
if not isinstance(N, int):
raise TypeError("an integer is required")
if N < 0:
raise ValueError("cannot read to end of infinite stream")
# Collect some entropy and feed it to Fortuna
self._ec.collect()
# Ask Fortuna to generate some bytes
retval = self._fa.random_data(N)
# Check that we haven't forked in the meantime. (If we have, we don't
# want to use the data, because it might have been duplicated in the
# parent process.
self._check_pid()
# Return the random data.
return retval
def _check_pid(self):
# Lame fork detection to remind developers to invoke Random.atfork()
# after every call to os.fork(). Note that this check is not reliable,
# since process IDs can be reused on most operating systems.
#
# You need to do Random.atfork() in the child process after every call
# to os.fork() to avoid reusing PRNG state. If you want to avoid
# leaking PRNG state to child processes (for example, if you are using
# os.setuid()) then you should also invoke Random.atfork() in the
# *parent* process.
if os.getpid() != self._pid:
raise AssertionError("PID check failed. RNG must be re-initialized after fork(). Hint: Try Random.atfork()")
class _LockingUserFriendlyRNG(_UserFriendlyRNG):
def __init__(self):
self._lock = threading.Lock()
_UserFriendlyRNG.__init__(self)
def close(self):
self._lock.acquire()
try:
return _UserFriendlyRNG.close(self)
finally:
self._lock.release()
def reinit(self):
self._lock.acquire()
try:
return _UserFriendlyRNG.reinit(self)
finally:
self._lock.release()
def read(self, bytes):
self._lock.acquire()
try:
return _UserFriendlyRNG.read(self, bytes)
finally:
self._lock.release()
class RNGFile(object):
def __init__(self, singleton):
self.closed = False
self._singleton = singleton
# PEP 343: Support for the "with" statement
def __enter__(self):
"""PEP 343 support"""
def __exit__(self):
"""PEP 343 support"""
self.close()
def close(self):
# Don't actually close the singleton, just close this RNGFile instance.
self.closed = True
self._singleton = None
def read(self, bytes):
if self.closed:
raise ValueError("I/O operation on closed file")
return self._singleton.read(bytes)
def flush(self):
if self.closed:
raise ValueError("I/O operation on closed file")
_singleton_lock = threading.Lock()
_singleton = None
def _get_singleton():
global _singleton
_singleton_lock.acquire()
try:
if _singleton is None:
_singleton = _LockingUserFriendlyRNG()
return _singleton
finally:
_singleton_lock.release()
def new():
return RNGFile(_get_singleton())
def reinit():
_get_singleton().reinit()
def get_random_bytes(n):
"""Return the specified number of cryptographically-strong random bytes."""
return _get_singleton().read(n)
# vim:set ts=4 sw=4 sts=4 expandtab: