Source Code for Module paramiko.rng

  1  #!/usr/bin/python 
  2  # -*- coding: ascii -*- 
  3  # Copyright (C) 2008  Dwayne C. Litzenberger <dlitz@dlitz.net> 
  4  # 
  5  # This file is part of paramiko. 
  6  # 
  7  # Paramiko is free software; you can redistribute it and/or modify it under the 
  8  # terms of the GNU Lesser General Public License as published by the Free 
  9  # Software Foundation; either version 2.1 of the License, or (at your option) 
 10  # any later version. 
 11  # 
 12  # Paramiko is distrubuted in the hope that it will be useful, but WITHOUT ANY 
 13  # WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR 
 14  # A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more 
 15  # details. 
 16  # 
 17  # You should have received a copy of the GNU Lesser General Public License 
 18  # along with Paramiko; if not, write to the Free Software Foundation, Inc., 
 19  # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. 
 20   
 21  import sys 
 22  import threading 
 23  from Crypto.Util.randpool import RandomPool as _RandomPool 
 24   
 25  try: 
 26      import platform 
 27  except ImportError: 
 28      platform = None     # Not available using Python 2.2 
 29   
 30 -def _strxor(a, b): 
 31      assert len(a) == len(b) 
 32      return "".join(map(lambda x, y: chr(ord(x) ^ ord(y)), a, b)) 
 33   
 34  ## 
 35  ## Find a strong random entropy source, depending on the detected platform. 
 36  ## WARNING TO DEVELOPERS: This will fail on some systems, but do NOT use 
 37  ## Crypto.Util.randpool.RandomPool as a fall-back.  RandomPool will happily run 
 38  ## with very little entropy, thus _silently_ defeating any security that 
 39  ## Paramiko attempts to provide.  (This is current as of PyCrypto 2.0.1). 
 40  ## See http://www.lag.net/pipermail/paramiko/2008-January/000599.html 
 41  ## and http://www.lag.net/pipermail/paramiko/2008-April/000678.html 
 42  ## 
 43   
 44  if ((platform is not None and platform.system().lower() == 'windows') or 
 45          sys.platform == 'win32'): 
 46      # MS Windows 
 47      from paramiko import rng_win32 
 48      rng_device = rng_win32.open_rng_device() 
 49  else: 
 50      # Assume POSIX (any system where /dev/urandom exists) 
 51      from paramiko import rng_posix 
 52      rng_device = rng_posix.open_rng_device() 
 53   
 54   
 55 -class StrongLockingRandomPool(object): 
 56      """Wrapper around RandomPool guaranteeing strong random numbers. 
 57       
 58      Crypto.Util.randpool.RandomPool will silently operate even if it is seeded 
 59      with little or no entropy, and it provides no prediction resistance if its 
 60      state is ever compromised throughout its runtime.  It is also not thread-safe. 
 61   
 62      This wrapper augments RandomPool by XORing its output with random bits from 
 63      the operating system, and by controlling access to the underlying 
 64      RandomPool using an exclusive lock. 
 65      """ 
 66   
 67 -    def __init__(self, instance=None): 
 68          if instance is None: 
 69              instance = _RandomPool() 
 70          self.randpool = instance 
 71          self.randpool_lock = threading.Lock() 
 72          self.entropy = rng_device 
 73   
 74          # Stir 256 bits of entropy from the RNG device into the RandomPool. 
 75          self.randpool.stir(self.entropy.read(32)) 
 76          self.entropy.randomize() 
 77   
 78 -    def stir(self, s=''): 
 79          self.randpool_lock.acquire() 
 80          try: 
 81              self.randpool.stir(s) 
 82          finally: 
 83              self.randpool_lock.release() 
 84          self.entropy.randomize() 
 85   
 86 -    def randomize(self, N=0): 
 87          self.randpool_lock.acquire() 
 88          try: 
 89              self.randpool.randomize(N) 
 90          finally: 
 91              self.randpool_lock.release() 
 92          self.entropy.randomize() 
 93   
 94 -    def add_event(self, s=''): 
 95          self.randpool_lock.acquire() 
 96          try: 
 97              self.randpool.add_event(s) 
 98          finally: 
 99              self.randpool_lock.release() 
100   
101 -    def get_bytes(self, N): 
102          self.randpool_lock.acquire() 
103          try: 
104              randpool_data = self.randpool.get_bytes(N) 
105          finally: 
106              self.randpool_lock.release() 
107          entropy_data = self.entropy.read(N) 
108          result = _strxor(randpool_data, entropy_data) 
109          assert len(randpool_data) == N and len(entropy_data) == N and len(result) == N 
110          return result 
111   
112  # vim:set ts=4 sw=4 sts=4 expandtab: 
113