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#
# Random/OSRNG/rng_base.py : Base class for OSRNG
#
# 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__ = "$Id$"
from Crypto.Util.python_compat import *
class BaseRNG(object):
def __init__(self):
self.closed = False
self._selftest()
def __del__(self):
self.close()
def _selftest(self):
# Test that urandom can return data
data = self.read(16)
if len(data) != 16:
raise AssertionError("read truncated")
# Test that we get different data every time (if we don't, the RNG is
# probably malfunctioning)
data2 = self.read(16)
if data == data2:
raise AssertionError("OS RNG returned duplicate data")
# PEP 343: Support for the "with" statement
def __enter__(self):
pass
def __exit__(self):
"""PEP 343 support"""
self.close()
def close(self):
if not self.closed:
self._close()
self.closed = True
def flush(self):
pass
def read(self, N=-1):
"""Return N bytes from the RNG."""
if self.closed:
raise ValueError("I/O operation on closed file")
if not isinstance(N, (long, int)):
raise TypeError("an integer is required")
if N < 0:
raise ValueError("cannot read to end of infinite stream")
elif N == 0:
return ""
data = self._read(N)
if len(data) != N:
raise AssertionError("%s produced truncated output (requested %d, got %d)" % (self.name, N, len(data)))
return data
def _close(self):
raise NotImplementedError("child class must implement this")
def _read(self, N):
raise NotImplementedError("child class must implement this")
# vim:set ts=4 sw=4 sts=4 expandtab:
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