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1 | #!/usr/bin/python |
2 | |
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3 | # xorcheck.py - find xor values for 8-bit LRC |
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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 |
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28 | print '\t'+sys.argv[0] + ' - Generate final byte for XOR LRC' |
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29 | print |
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30 | print 'Usage: ' + sys.argv[0] + ' <ID Byte1> <ID Byte2> ... <LRC>' |
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31 | print |
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32 | print '\tSpecifying the bytes of a UID with a known LRC will find the last byte value' |
33 | print '\tneeded to generate that LRC with a rolling XOR. All bytes should be specified in HEX.' |
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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 |
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41 | print '\tTarget (BA) requires final LRC XOR byte value: 5A' |
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42 | print |
43 | os._exit(True) |
44 | |
45 | target= int(sys.argv[len(sys.argv) - 1],16) |
46 | |
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47 | lrc= 0x00 |
48 | for i in range(len(sys.argv) - 1): |
49 | lrc ^= int(sys.argv[i + 1],16) |
50 | print |
51 | print 'Target (%02X) requires final LRC XOR byte value: %02X' % (target,lrc) |
52 | print |