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annotate roundup/anypy/random_.py @ 5726:e199d0ae4a25

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issue2551033: prevent reverse engineering hidden data by using etags as an oracle to identify when the right data has been guessed. Identified by Joseph Myers who also suggested remediation methods. Implemented John Rouillard.
author John Rouillard <rouilj@ieee.org>
date Thu, 23 May 2019 18:56:57 -0400
parents 52cb53eedf77
children adf54478cdaf
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5488
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1 try:
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2 from secrets import choice, randbelow, token_bytes
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3 def seed(v = None):
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4 pass
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5
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6 is_weak = False
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7 except ImportError:
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8 import os as _os
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9 import random as _random
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10
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11 # prefer to use SystemRandom if it is available
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12 if hasattr(_random, 'SystemRandom'):
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13 def seed(v = None):
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14 pass
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15
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16 _r = _random.SystemRandom()
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17 is_weak = False
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18 else:
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19 # don't completely throw away the existing state, but add some
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20 # more random state to the existing state
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21 def seed(v = None):
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22 import os, time
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23 _r.seed((_r.getstate(),
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24 v,
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25 hasattr(os, 'getpid') and os.getpid(),
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26 time.time()))
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27
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28 # create our own instance so we don't mess with the global
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29 # random number generator
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30 _r = _random.Random()
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31 seed()
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32 is_weak = True
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33
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34 choice = _r.choice
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35
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36 def randbelow(i):
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37 return _r.randint(0, i - 1)
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38
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39 if hasattr(_os, 'urandom'):
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40 def token_bytes(l):
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41 return _os.urandom(l)
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42 else:
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43 def token_bytes(l):
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44 _bchr = chr if str == bytes else lambda x: bytes((x,))
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45 return b''.join([_bchr(_r.getrandbits(8)) for i in range(l)])
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