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+# -*- coding: utf-8 -*-
+#
+# Random/random.py : Strong alternative for the standard 'random' module
+#
+# 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.
+# ===================================================================
+
+"""A cryptographically strong version of Python's standard "random" module."""
+
+__revision__ = "$Id$"
+__all__ = ['StrongRandom', 'getrandbits', 'randrange', 'randint', 'choice', 'shuffle', 'sample']
+
+from Crypto import Random
+import sys
+if sys.version_info[0] == 2 and sys.version_info[1] == 1:
+ from Crypto.Util.py21compat import *
+
+class StrongRandom(object):
+ def __init__(self, rng=None, randfunc=None):
+ if randfunc is None and rng is None:
+ self._randfunc = None
+ elif randfunc is not None and rng is None:
+ self._randfunc = randfunc
+ elif randfunc is None and rng is not None:
+ self._randfunc = rng.read
+ else:
+ raise ValueError("Cannot specify both 'rng' and 'randfunc'")
+
+ def getrandbits(self, k):
+ """Return a python long integer with k random bits."""
+ if self._randfunc is None:
+ self._randfunc = Random.new().read
+ mask = (1 << k) - 1
+ return mask & bytes_to_long(self._randfunc(ceil_div(k, 8)))
+
+ def randrange(self, *args):
+ """randrange([start,] stop[, step]):
+ Return a randomly-selected element from range(start, stop, step)."""
+ if len(args) == 3:
+ (start, stop, step) = args
+ elif len(args) == 2:
+ (start, stop) = args
+ step = 1
+ elif len(args) == 1:
+ (stop,) = args
+ start = 0
+ step = 1
+ else:
+ raise TypeError("randrange expected at most 3 arguments, got %d" % (len(args),))
+ if (not isinstance(start, int)
+ or not isinstance(stop, int)
+ or not isinstance(step, int)):
+ raise TypeError("randrange requires integer arguments")
+ if step == 0:
+ raise ValueError("randrange step argument must not be zero")
+
+ num_choices = ceil_div(stop - start, step)
+ if num_choices < 0:
+ num_choices = 0
+ if num_choices < 1:
+ raise ValueError("empty range for randrange(%r, %r, %r)" % (start, stop, step))
+
+ # Pick a random number in the range of possible numbers
+ r = num_choices
+ while r >= num_choices:
+ r = self.getrandbits(size(num_choices))
+
+ return start + (step * r)
+
+ def randint(self, a, b):
+ """Return a random integer N such that a <= N <= b."""
+ if not isinstance(a, int) or not isinstance(b, int):
+ raise TypeError("randint requires integer arguments")
+ N = self.randrange(a, b+1)
+ assert a <= N <= b
+ return N
+
+ def choice(self, seq):
+ """Return a random element from a (non-empty) sequence.
+
+ If the seqence is empty, raises IndexError.
+ """
+ if len(seq) == 0:
+ raise IndexError("empty sequence")
+ return seq[self.randrange(len(seq))]
+
+ def shuffle(self, x):
+ """Shuffle the sequence in place."""
+ # Make a (copy) of the list of objects we want to shuffle
+ items = list(x)
+
+ # Choose a random item (without replacement) until all the items have been
+ # chosen.
+ for i in range(len(x)):
+ x[i] = items.pop(self.randrange(len(items)))
+
+ def sample(self, population, k):
+ """Return a k-length list of unique elements chosen from the population sequence."""
+
+ num_choices = len(population)
+ if k > num_choices:
+ raise ValueError("sample larger than population")
+
+ retval = []
+ selected = {} # we emulate a set using a dict here
+ for i in range(k):
+ r = None
+ while r is None or r in selected:
+ r = self.randrange(num_choices)
+ retval.append(population[r])
+ selected[r] = 1
+ return retval
+
+_r = StrongRandom()
+getrandbits = _r.getrandbits
+randrange = _r.randrange
+randint = _r.randint
+choice = _r.choice
+shuffle = _r.shuffle
+sample = _r.sample
+
+# These are at the bottom to avoid problems with recursive imports
+from Crypto.Util.number import ceil_div, bytes_to_long, long_to_bytes, size
+
+# vim:set ts=4 sw=4 sts=4 expandtab: