143 lines
5.3 KiB
Python
143 lines
5.3 KiB
Python
# -*- coding: utf-8 -*-
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#
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# Random/random.py : Strong alternative for the standard 'random' module
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#
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# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
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#
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# ===================================================================
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# The contents of this file are dedicated to the public domain. To
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# the extent that dedication to the public domain is not available,
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# everyone is granted a worldwide, perpetual, royalty-free,
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# non-exclusive license to exercise all rights associated with the
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# contents of this file for any purpose whatsoever.
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# No rights are reserved.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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# SOFTWARE.
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# ===================================================================
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"""A cryptographically strong version of Python's standard "random" module."""
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__revision__ = "$Id$"
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__all__ = ['StrongRandom', 'getrandbits', 'randrange', 'randint', 'choice', 'shuffle', 'sample']
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from Crypto import Random
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import sys
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if sys.version_info[0] == 2 and sys.version_info[1] == 1:
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from Crypto.Util.py21compat import *
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class StrongRandom(object):
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def __init__(self, rng=None, randfunc=None):
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if randfunc is None and rng is None:
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self._randfunc = None
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elif randfunc is not None and rng is None:
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self._randfunc = randfunc
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elif randfunc is None and rng is not None:
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self._randfunc = rng.read
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else:
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raise ValueError("Cannot specify both 'rng' and 'randfunc'")
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def getrandbits(self, k):
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"""Return a python long integer with k random bits."""
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if self._randfunc is None:
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self._randfunc = Random.new().read
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mask = (1 << k) - 1
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return mask & bytes_to_long(self._randfunc(ceil_div(k, 8)))
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def randrange(self, *args):
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"""randrange([start,] stop[, step]):
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Return a randomly-selected element from range(start, stop, step)."""
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if len(args) == 3:
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(start, stop, step) = args
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elif len(args) == 2:
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(start, stop) = args
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step = 1
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elif len(args) == 1:
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(stop,) = args
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start = 0
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step = 1
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else:
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raise TypeError("randrange expected at most 3 arguments, got %d" % (len(args),))
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if (not isinstance(start, int)
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or not isinstance(stop, int)
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or not isinstance(step, int)):
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raise TypeError("randrange requires integer arguments")
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if step == 0:
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raise ValueError("randrange step argument must not be zero")
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num_choices = ceil_div(stop - start, step)
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if num_choices < 0:
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num_choices = 0
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if num_choices < 1:
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raise ValueError("empty range for randrange(%r, %r, %r)" % (start, stop, step))
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# Pick a random number in the range of possible numbers
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r = num_choices
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while r >= num_choices:
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r = self.getrandbits(size(num_choices))
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return start + (step * r)
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def randint(self, a, b):
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"""Return a random integer N such that a <= N <= b."""
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if not isinstance(a, int) or not isinstance(b, int):
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raise TypeError("randint requires integer arguments")
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N = self.randrange(a, b+1)
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assert a <= N <= b
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return N
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def choice(self, seq):
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"""Return a random element from a (non-empty) sequence.
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If the seqence is empty, raises IndexError.
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"""
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if len(seq) == 0:
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raise IndexError("empty sequence")
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return seq[self.randrange(len(seq))]
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def shuffle(self, x):
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"""Shuffle the sequence in place."""
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# Make a (copy) of the list of objects we want to shuffle
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items = list(x)
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# Choose a random item (without replacement) until all the items have been
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# chosen.
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for i in range(len(x)):
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x[i] = items.pop(self.randrange(len(items)))
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def sample(self, population, k):
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"""Return a k-length list of unique elements chosen from the population sequence."""
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num_choices = len(population)
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if k > num_choices:
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raise ValueError("sample larger than population")
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retval = []
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selected = {} # we emulate a set using a dict here
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for i in range(k):
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r = None
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while r is None or r in selected:
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r = self.randrange(num_choices)
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retval.append(population[r])
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selected[r] = 1
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return retval
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_r = StrongRandom()
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getrandbits = _r.getrandbits
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randrange = _r.randrange
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randint = _r.randint
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choice = _r.choice
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shuffle = _r.shuffle
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sample = _r.sample
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# These are at the bottom to avoid problems with recursive imports
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from Crypto.Util.number import ceil_div, bytes_to_long, long_to_bytes, size
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# vim:set ts=4 sw=4 sts=4 expandtab:
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