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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 = (1L << 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, long))
or not isinstance(stop, (int, long))
or not isinstance(step, (int, long))):
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, long)) or not isinstance(b, (int, long)):
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."""
# Fisher-Yates shuffle. O(n)
# See http://en.wikipedia.org/wiki/Fisher-Yates_shuffle
# Working backwards from the end of the array, we choose a random item
# from the remaining items until all items have been chosen.
for i in xrange(len(x)-1, 0, -1): # iterate from len(x)-1 downto 1
j = self.randrange(0, i+1) # choose random j such that 0 <= j <= i
x[i], x[j] = x[j], x[i] # exchange x[i] and x[j]
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 xrange(k):
r = None
while r is None or selected.has_key(r):
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:
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