75 lines
2.7 KiB
Python
75 lines
2.7 KiB
Python
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#
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# Random/OSRNG/nt.py : OS entropy source for MS Windows
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#
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# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
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#
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# ===================================================================
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# The contents of this file are dedicated to the public domain. To
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# the extent that dedication to the public domain is not available,
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# everyone is granted a worldwide, perpetual, royalty-free,
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# non-exclusive license to exercise all rights associated with the
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# contents of this file for any purpose whatsoever.
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# No rights are reserved.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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# SOFTWARE.
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# ===================================================================
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__revision__ = "$Id$"
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__all__ = ['WindowsRNG']
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from . import winrandom
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from .rng_base import BaseRNG
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class WindowsRNG(BaseRNG):
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name = "<CryptGenRandom>"
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def __init__(self):
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self.__winrand = winrandom.new()
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BaseRNG.__init__(self)
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def flush(self):
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"""Work around weakness in Windows RNG.
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The CryptGenRandom mechanism in some versions of Windows allows an
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attacker to learn 128 KiB of past and future output. As a workaround,
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this function reads 128 KiB of 'random' data from Windows and discards
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it.
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For more information about the weaknesses in CryptGenRandom, see
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_Cryptanalysis of the Random Number Generator of the Windows Operating
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System_, by Leo Dorrendorf and Zvi Gutterman and Benny Pinkas
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http://eprint.iacr.org/2007/419
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"""
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if self.closed:
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raise ValueError("I/O operation on closed file")
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data = self.__winrand.get_bytes(128*1024)
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assert (len(data) == 128*1024)
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BaseRNG.flush(self)
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def _close(self):
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self.__winrand = None
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def _read(self, N):
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# Unfortunately, research shows that CryptGenRandom doesn't provide
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# forward secrecy and fails the next-bit test unless we apply a
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# workaround, which we do here. See http://eprint.iacr.org/2007/419
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# for information on the vulnerability.
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self.flush()
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data = self.__winrand.get_bytes(N)
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self.flush()
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return data
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def new(*args, **kwargs):
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return WindowsRNG(*args, **kwargs)
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# vim:set ts=4 sw=4 sts=4 expandtab:
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