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107 lines
4.1 KiB
107 lines
4.1 KiB
#
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# Util/Padding.py : Functions to manage padding
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#
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# ===================================================================
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#
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# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
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# All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions
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# are met:
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#
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# 1. Redistributions of source code must retain the above copyright
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# notice, this list of conditions and the following disclaimer.
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# 2. Redistributions in binary form must reproduce the above copyright
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# notice, this list of conditions and the following disclaimer in
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# the documentation and/or other materials provided with the
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# distribution.
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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
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# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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# POSSIBILITY OF SUCH DAMAGE.
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# ===================================================================
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__all__ = [ 'pad', 'unpad' ]
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from Crypto.Util.py3compat import *
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def pad(data_to_pad, block_size, style='pkcs7'):
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"""Apply standard padding.
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Args:
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data_to_pad (byte string):
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The data that needs to be padded.
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block_size (integer):
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The block boundary to use for padding. The output length is guaranteed
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to be a multiple of :data:`block_size`.
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style (string):
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Padding algorithm. It can be *'pkcs7'* (default), *'iso7816'* or *'x923'*.
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Return:
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byte string : the original data with the appropriate padding added at the end.
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"""
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padding_len = block_size-len(data_to_pad)%block_size
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if style == 'pkcs7':
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padding = bchr(padding_len)*padding_len
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elif style == 'x923':
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padding = bchr(0)*(padding_len-1) + bchr(padding_len)
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elif style == 'iso7816':
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padding = bchr(128) + bchr(0)*(padding_len-1)
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else:
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raise ValueError("Unknown padding style")
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return data_to_pad + padding
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def unpad(padded_data, block_size, style='pkcs7'):
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"""Remove standard padding.
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Args:
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padded_data (byte string):
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A piece of data with padding that needs to be stripped.
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block_size (integer):
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The block boundary to use for padding. The input length
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must be a multiple of :data:`block_size`.
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style (string):
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Padding algorithm. It can be *'pkcs7'* (default), *'iso7816'* or *'x923'*.
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Return:
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byte string : data without padding.
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Raises:
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ValueError: if the padding is incorrect.
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"""
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pdata_len = len(padded_data)
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if pdata_len % block_size:
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raise ValueError("Input data is not padded")
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if style in ('pkcs7', 'x923'):
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padding_len = bord(padded_data[-1])
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if padding_len<1 or padding_len>min(block_size, pdata_len):
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raise ValueError("Padding is incorrect.")
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if style == 'pkcs7':
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if padded_data[-padding_len:]!=bchr(padding_len)*padding_len:
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raise ValueError("PKCS#7 padding is incorrect.")
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else:
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if padded_data[-padding_len:-1]!=bchr(0)*(padding_len-1):
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raise ValueError("ANSI X.923 padding is incorrect.")
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elif style == 'iso7816':
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padding_len = pdata_len - padded_data.rfind(bchr(128))
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if padding_len<1 or padding_len>min(block_size, pdata_len):
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raise ValueError("Padding is incorrect.")
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if padding_len>1 and padded_data[1-padding_len:]!=bchr(0)*(padding_len-1):
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raise ValueError("ISO 7816-4 padding is incorrect.")
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else:
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raise ValueError("Unknown padding style")
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return padded_data[:-padding_len]
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