Edit File: _UserFriendlyRNG.py
# -*- 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: