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Diffstat (limited to 'lib/Python/Lib/Crypto/Random/random.py')
-rw-r--r-- | lib/Python/Lib/Crypto/Random/random.py | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/lib/Python/Lib/Crypto/Random/random.py b/lib/Python/Lib/Crypto/Random/random.py new file mode 100644 index 000000000..bef02e651 --- /dev/null +++ b/lib/Python/Lib/Crypto/Random/random.py @@ -0,0 +1,142 @@ +# -*- 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.""" + # 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 xrange(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 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: |