#!/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/
if(len(sys.argv) < 3):
print
- print sys.argv[0] + ' - generate final byte for XOR CRC'
- print 'Usage: ' + sys.argv[0] + ' <ID Byte1> <ID Byte2> ... <CRC>'
+ print '\t'+sys.argv[0] + ' - Generate final byte for XOR LRC'
print
- print '\tSpecifying the bytes of a UID with a known CRC will generate the last byte value'
- print '\tneeded to generate that CRC with a rolling XOR. All bytes should be specified in HEX.'
+ print 'Usage: ' + sys.argv[0] + ' <ID Byte1> <ID Byte2> ... <LRC>'
+ print
+ 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
print
print 'Should produce the output:'
print
- print '\tTarget matched with Byte value: 5A'
+ print '\tTarget (BA) requires 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 matched with Byte value: %02X' % 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