@marshmellow42 ideas

[proxmark3-svn] / tools / xorcheck.py

diff --git a/tools/xorcheck.py b/tools/xorcheck.py
index ddfcf82a035cf183aacfcdf39e837295e394324d..3a7c8d66cad3f45a8cf80a0cc5563e038d85b61d 100755 (executable)
--- a/tools/xorcheck.py
+++ b/tools/xorcheck.py
@@ -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/
@@ -25,11 +25,12 @@ import os
 
 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
@@ -37,19 +38,15 @@ if(len(sys.argv) < 3):
        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