]>
Commit | Line | Data |
---|---|---|
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 | ||
28 | print sys.argv[0] + ' - generate final byte for XOR CRC' | |
29 | print 'Usage: ' + sys.argv[0] + ' <ID Byte1> <ID Byte2> ... <CRC>' | |
30 | ||
31 | print '\tSpecifying the bytes of a UID with a known CRC will generate the last byte value' | |
32 | print '\tneeded to generate that CRC with a rolling XOR. All bytes should be specified in HEX.' | |
33 | ||
34 | print 'Example:' | |
35 | ||
36 | print '\txorcheck.py 04 00 80 64 ba' | |
37 | ||
38 | print 'Should produce the output:' | |
39 | ||
40 | print '\tTarget matched with Byte value: 5A' | |
41 | ||
42 | os._exit(True) | |
43 | ||
44 | target= int(sys.argv[len(sys.argv) - 1],16) | |
45 | ||
46 | for candidate in range(256): | |
47 | crc= 0x00 | |
48 | for i in range(len(sys.argv) - 2): | |
49 | crc ^= int(sys.argv[i + 1],16) | |
50 | crc ^= candidate | |
51 | if (crc == target): | |
52 | ||
53 | print 'Target matched with Byte value: %02X' % candidate | |
54 | ||
55 |