mirror of
https://github.com/Legrandin/pycryptodome.git
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65 lines
2.6 KiB
Python
65 lines
2.6 KiB
Python
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# -*- coding: ascii -*-
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#
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# Util/Counter.py : Fast counter for use with CTR-mode ciphers
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#
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# Copyright (C) 2008 Dwayne C. Litzenberger <dlitz@dlitz.net>
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#
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# =======================================================================
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# Permission is hereby granted, free of charge, to any person obtaining
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# a copy of this software and associated documentation files (the
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# "Software"), to deal in the Software without restriction, including
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# without limitation the rights to use, copy, modify, merge, publish,
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# distribute, sublicense, and/or sell copies of the Software, and to
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# permit persons to whom the Software is furnished to do so.
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#
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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# =======================================================================
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from Crypto.Util.python_compat import *
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from Crypto.Util import _counter
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import struct
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# Factory function
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def new(nbits, prefix="", suffix="", initial_value=1, overflow=0, little_endian=False):
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# TODO: Document this
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# Sanity-check the message size
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(nbytes, remainder) = divmod(nbits, 8)
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if remainder != 0:
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# In the future, we might support arbitrary bit lengths, but for now we don't.
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raise ValueError("nbits must be a multiple of 8; got %d" % (nbits,))
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if nbytes < 1:
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raise ValueError("nbits too small")
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elif nbytes > 0xffff:
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raise ValueError("nbits too large")
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initval = _encode(initial_value, nbytes, little_endian)
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if little_endian:
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return _counter.CounterLE(str(prefix), str(suffix), initval)
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else:
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return _counter.CounterBE(str(prefix), str(suffix), initval)
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def _encode(n, nbytes, little_endian=False):
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retval = []
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n = long(n)
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for i in range(nbytes):
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if little_endian:
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retval.append(chr(n & 0xff))
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else:
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retval.insert(0, chr(n & 0xff))
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n >>= 8
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return "".join(retval)
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# vim:set ts=4 sw=4 sts=4 expandtab:
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