git.zerfleddert.de Git - proxmark3-svn/blob - tools/xorcheck.py

   1 #!/usr/bin/python
   2
   3 #  xorcheck.py - find xor values for 8-bit CRC
   4 #
   5 #  Adam Laurie <adam@algroup.co.uk>
   6 #  http://rfidiot.org/
   7 #
   8 #  This code is copyright (c) Adam Laurie, 2009, All rights reserved.
   9 #  For non-commercial use only, the following terms apply - for all other
  10 #  uses, please contact the author:
  11 #
  12 #    This code is free software; you can redistribute it and/or modify
  13 #    it under the terms of the GNU General Public License as published by
  14 #    the Free Software Foundation; either version 2 of the License, or
  15 #    (at your option) any later version.
  16 #
  17 #    This code is distributed in the hope that it will be useful,
  18 #    but WITHOUT ANY WARRANTY; without even the implied warranty of
  19 #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20 #    GNU General Public License for more details.
  21 #
  22
  23 import sys
  24 import os
  25
  26 if(len(sys.argv) < 3):
  27         print
  28         print '\t'+sys.argv[0] + ' - Generate final byte for XOR CRC'
  29         print
  30         print 'Usage: ' + sys.argv[0] + ' <ID Byte1> <ID Byte2> ... <CRC>'
  31         print
  32         print '\tSpecifying the bytes of a UID with a known CRC will find the last byte value'
  33         print '\tneeded to generate that CRC with a rolling XOR. All bytes should be specified in HEX.'
  34         print
  35         print 'Example:'
  36         print
  37         print '\txorcheck.py 04 00 80 64 ba'
  38         print
  39         print 'Should produce the output:'
  40         print
  41         print '\tTarget (BA) matched with final byte value: 5A'
  42         print
  43         os._exit(True)
  44
  45 target= int(sys.argv[len(sys.argv) - 1],16)
  46
  47 for candidate in range(256):
  48         crc= 0x00
  49         for i in range(len(sys.argv) - 2):
  50                 crc ^= int(sys.argv[i + 1],16)
  51         crc ^= candidate
  52         if (crc == target):
  53                 print
  54                 print 'Target (%02X) matched with final byte value: %02X' % (target,candidate)
  55                 print
  56