/usr/lib/python2.7/dist-packages/Crypto/Random/Fortuna/FortunaGenerator.py is in python-crypto 2.6.1-6build1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 | # -*- coding: ascii -*-
#
# FortunaGenerator.py : Fortuna's internal PRNG
#
# 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] is 2 and sys.version_info[1] is 1:
from Crypto.Util.py21compat import *
from Crypto.Util.py3compat import *
import struct
from Crypto.Util.number import ceil_shift, exact_log2, exact_div
from Crypto.Util import Counter
from Crypto.Cipher import AES
import SHAd256
class AESGenerator(object):
"""The Fortuna "generator"
This is used internally by the Fortuna PRNG to generate arbitrary amounts
of pseudorandom data from a smaller amount of seed data.
The output is generated by running AES-256 in counter mode and re-keying
after every mebibyte (2**16 blocks) of output.
"""
block_size = AES.block_size # output block size in octets (128 bits)
key_size = 32 # key size in octets (256 bits)
# Because of the birthday paradox, we expect to find approximately one
# collision for every 2**64 blocks of output from a real random source.
# However, this code generates pseudorandom data by running AES in
# counter mode, so there will be no collisions until the counter
# (theoretically) wraps around at 2**128 blocks. Thus, in order to prevent
# Fortuna's pseudorandom output from deviating perceptibly from a true
# random source, Ferguson and Schneier specify a limit of 2**16 blocks
# without rekeying.
max_blocks_per_request = 2**16 # Allow no more than this number of blocks per _pseudo_random_data request
_four_kiblocks_of_zeros = b("\0") * block_size * 4096
def __init__(self):
self.counter = Counter.new(nbits=self.block_size*8, initial_value=0, little_endian=True)
self.key = None
# Set some helper constants
self.block_size_shift = exact_log2(self.block_size)
assert (1 << self.block_size_shift) == self.block_size
self.blocks_per_key = exact_div(self.key_size, self.block_size)
assert self.key_size == self.blocks_per_key * self.block_size
self.max_bytes_per_request = self.max_blocks_per_request * self.block_size
def reseed(self, seed):
if self.key is None:
self.key = b("\0") * self.key_size
self._set_key(SHAd256.new(self.key + seed).digest())
self.counter() # increment counter
assert len(self.key) == self.key_size
def pseudo_random_data(self, bytes):
assert bytes >= 0
num_full_blocks = bytes >> 20
remainder = bytes & ((1<<20)-1)
retval = []
for i in xrange(num_full_blocks):
retval.append(self._pseudo_random_data(1<<20))
retval.append(self._pseudo_random_data(remainder))
return b("").join(retval)
def _set_key(self, key):
self.key = key
self._cipher = AES.new(key, AES.MODE_CTR, counter=self.counter)
def _pseudo_random_data(self, bytes):
if not (0 <= bytes <= self.max_bytes_per_request):
raise AssertionError("You cannot ask for more than 1 MiB of data per request")
num_blocks = ceil_shift(bytes, self.block_size_shift) # num_blocks = ceil(bytes / self.block_size)
# Compute the output
retval = self._generate_blocks(num_blocks)[:bytes]
# Switch to a new key to avoid later compromises of this output (i.e.
# state compromise extension attacks)
self._set_key(self._generate_blocks(self.blocks_per_key))
assert len(retval) == bytes
assert len(self.key) == self.key_size
return retval
def _generate_blocks(self, num_blocks):
if self.key is None:
raise AssertionError("generator must be seeded before use")
assert 0 <= num_blocks <= self.max_blocks_per_request
retval = []
for i in xrange(num_blocks >> 12): # xrange(num_blocks / 4096)
retval.append(self._cipher.encrypt(self._four_kiblocks_of_zeros))
remaining_bytes = (num_blocks & 4095) << self.block_size_shift # (num_blocks % 4095) * self.block_size
retval.append(self._cipher.encrypt(self._four_kiblocks_of_zeros[:remaining_bytes]))
return b("").join(retval)
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