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fix wrong terminology - LRC/CRC and calulate result instead of matching (thanks Henryk!)

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adam@algroup.co.uk 2009-09-05 13:10:17 +00:00
parent c5847014fd
commit 98af9ddf8c
1 changed files with 12 additions and 16 deletions
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28
tools/xorcheck.py
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@ -1,6 +1,6 @@
#!/usr/bin/python
# xorcheck.py - find xor values for 8-bit CRC
# xorcheck.py - find xor values for 8-bit LRC
#
# Adam Laurie <adam@algroup.co.uk>
# http://rfidiot.org/
@ -25,12 +25,12 @@ import os
if(len(sys.argv) < 3):
print
print '\t'+sys.argv[0] + ' - Generate final byte for XOR CRC'
print '\t'+sys.argv[0] + ' - Generate final byte for XOR LRC'
print
print 'Usage: ' + sys.argv[0] + ' <ID Byte1> <ID Byte2> ... <CRC>'
print 'Usage: ' + sys.argv[0] + ' <ID Byte1> <ID Byte2> ... <LRC>'
print
print '\tSpecifying the bytes of a UID with a known CRC will find the last byte value'
print '\tneeded to generate that CRC with a rolling XOR. All bytes should be specified in HEX.'
print '\tSpecifying the bytes of a UID with a known LRC will find the last byte value'
print '\tneeded to generate that LRC with a rolling XOR. All bytes should be specified in HEX.'
print
print 'Example:'
print
@ -38,19 +38,15 @@ if(len(sys.argv) < 3):
print
print 'Should produce the output:'
print
print '\tTarget (BA) matched with final byte value: 5A'
print '\tTarget (BA) matched with final LRC XOR byte value: 5A'
print
os._exit(True)
target= int(sys.argv[len(sys.argv) - 1],16)
for candidate in range(256):
crc= 0x00
for i in range(len(sys.argv) - 2):
crc ^= int(sys.argv[i + 1],16)
crc ^= candidate
if (crc == target):
print
print 'Target (%02X) matched with final byte value: %02X' % (target,candidate)
print
lrc= 0x00
for i in range(len(sys.argv) - 1):
lrc ^= int(sys.argv[i + 1],16)
print
print 'Target (%02X) requires final LRC XOR byte value: %02X' % (target,lrc)
print