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629c26c Jun 23, 2014
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#
# -*- coding: utf-8 -*-
#
# Util/Padding.py : Functions to manage padding
#
# ===================================================================
# 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.
# ===================================================================
""" Functions to manage padding
This module provides minimal support for adding and removing standard padding
from data.
"""
__all__ = [ 'ValueError', 'pad', 'unpad' ]
from Crypto.Util.py3compat import *
def pad(data_to_pad, block_size, style='pkcs7'):
"""Apply standard padding.
:Parameters:
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 ``block_size``.
style : string
Padding algorithm. It can be *'pkcs7'* (default), *'iso7816'* or *'x923'*.
:Return:
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.
:Parameters:
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 ``block_size``.
style : string
Padding algorithm. It can be *'pkcs7'* (default), *'iso7816'* or *'x923'*.
:Return:
Data without padding.
:Raises ValueError:
if the padding is incorrect.
"""
pdata_len = len(padded_data)
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]