2 # PyGOST -- Pure Python GOST cryptographic functions library
3 # Copyright (C) 2015-2016 Sergey Matveev <stargrave@stargrave.org>
5 # This program is free software: you can redistribute it and/or modify
6 # it under the terms of the GNU General Public License as published by
7 # the Free Software Foundation, either version 3 of the License, or
8 # (at your option) any later version.
10 # This program is distributed in the hope that it will be useful,
11 # but WITHOUT ANY WARRANTY; without even the implied warranty of
12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 # GNU General Public License for more details.
15 # You should have received a copy of the GNU General Public License
16 # along with this program. If not, see <http://www.gnu.org/licenses/>.
17 """ GOST R 34.13-2015: Modes of operation for block ciphers
19 This module currently includes only padding methods.
23 def pad_size(data_size, blocksize):
24 """Calculate required pad size to full up BLOCKSIZE
26 if data_size < blocksize:
27 return blocksize - data_size
28 if data_size % blocksize == 0:
30 return blocksize - data_size % blocksize
33 def pad1(data, blocksize):
36 Just fill up with zeros if necessary.
38 return data + b"\x00" * pad_size(len(data), blocksize)
41 def pad2(data, blocksize):
42 """Padding method 2 (also known as ISO/IEC 7816-4)
44 Add one bit and then fill up with zeros.
46 return data + b"\x80" + b"\x00" * pad_size(len(data) + 1, blocksize)
49 def pad3(data, blocksize):
52 if pad_size(len(data), blocksize) == 0:
54 return pad2(data, blocksize)