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Commit | Line | Data |
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4962d414 | 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 | ||
c5847014 | 28 | print '\t'+sys.argv[0] + ' - Generate final byte for XOR CRC' |
29 | ||
4962d414 | 30 | print 'Usage: ' + sys.argv[0] + ' <ID Byte1> <ID Byte2> ... <CRC>' |
31 | ||
c5847014 | 32 | print '\tSpecifying the bytes of a UID with a known CRC will find the last byte value' |
4962d414 | 33 | print '\tneeded to generate that CRC with a rolling XOR. All bytes should be specified in HEX.' |
34 | ||
35 | print 'Example:' | |
36 | ||
37 | print '\txorcheck.py 04 00 80 64 ba' | |
38 | ||
39 | print 'Should produce the output:' | |
40 | ||
c5847014 | 41 | print '\tTarget (BA) matched with final byte value: 5A' |
4962d414 | 42 | |
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 | ||
c5847014 | 54 | print 'Target (%02X) matched with final byte value: %02X' % (target,candidate) |
4962d414 | 55 | |
56 |