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