lib/dnspython/dns/entropy.py

   1 # Copyright (C) 2009, 2011 Nominum, Inc.
   2 #
   3 # Permission to use, copy, modify, and distribute this software and its
   4 # documentation for any purpose with or without fee is hereby granted,
   5 # provided that the above copyright notice and this permission notice
   6 # appear in all copies.
   7 #
   8 # THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
   9 # WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10 # MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
  11 # ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12 # WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13 # ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
  14 # OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15
  16 import os
  17 import time
  18 try:
  19     import threading as _threading
  20 except ImportError:
  21     import dummy_threading as _threading
  22
  23 class EntropyPool(object):
  24     def __init__(self, seed=None):
  25         self.pool_index = 0
  26         self.digest = None
  27         self.next_byte = 0
  28         self.lock = _threading.Lock()
  29         try:
  30             import hashlib
  31             self.hash = hashlib.sha1()
  32             self.hash_len = 20
  33         except:
  34             try:
  35                 import sha
  36                 self.hash = sha.new()
  37                 self.hash_len = 20
  38             except:
  39                 import md5
  40                 self.hash = md5.new()
  41                 self.hash_len = 16
  42         self.pool = '\0' * self.hash_len
  43         if not seed is None:
  44             self.stir(seed)
  45             self.seeded = True
  46         else:
  47             self.seeded = False
  48
  49     def stir(self, entropy, already_locked=False):
  50         if not already_locked:
  51             self.lock.acquire()
  52         try:
  53             bytes = [ord(c) for c in self.pool]
  54             for c in entropy:
  55                 if self.pool_index == self.hash_len:
  56                     self.pool_index = 0
  57                 b = ord(c) & 0xff
  58                 bytes[self.pool_index] ^= b
  59                 self.pool_index += 1
  60             self.pool = ''.join([chr(c) for c in bytes])
  61         finally:
  62             if not already_locked:
  63                 self.lock.release()
  64
  65     def _maybe_seed(self):
  66         if not self.seeded:
  67             try:
  68                 seed = os.urandom(16)
  69             except:
  70                 try:
  71                     r = file('/dev/urandom', 'r', 0)
  72                     try:
  73                         seed = r.read(16)
  74                     finally:
  75                         r.close()
  76                 except:
  77                     seed = str(time.time())
  78             self.seeded = True
  79             self.stir(seed, True)
  80
  81     def random_8(self):
  82         self.lock.acquire()
  83         self._maybe_seed()
  84         try:
  85             if self.digest is None or self.next_byte == self.hash_len:
  86                 self.hash.update(self.pool)
  87                 self.digest = self.hash.digest()
  88                 self.stir(self.digest, True)
  89                 self.next_byte = 0
  90             value = ord(self.digest[self.next_byte])
  91             self.next_byte += 1
  92         finally:
  93             self.lock.release()
  94         return value
  95
  96     def random_16(self):
  97         return self.random_8() * 256 + self.random_8()
  98
  99     def random_32(self):
 100         return self.random_16() * 65536 + self.random_16()
 101
 102     def random_between(self, first, last):
 103         size = last - first + 1
 104         if size > 4294967296L:
 105             raise ValueError('too big')
 106         if size > 65536:
 107             rand = self.random_32
 108             max = 4294967295L
 109         elif size > 256:
 110             rand = self.random_16
 111             max = 65535
 112         else:
 113             rand = self.random_8
 114             max = 255
 115         return (first + size * rand() // (max + 1))
 116
 117 pool = EntropyPool()
 118
 119 def random_16():
 120     return pool.random_16()
 121
 122 def between(first, last):
 123     return pool.random_between(first, last)