basic functionalty

modules/Crypto/Random/_UserFriendlyRNG.py

@@ -0,0 +1,230 @@
+# -*- 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, (long, 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: