X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/4962d41420e10c9e05238b97065236d50d7c624d..3b2fee43ea7d9e08b7729d662d8d010ee0e2a2e3:/tools/xorcheck.py

diff --git a/tools/xorcheck.py b/tools/xorcheck.py
index ddfcf82a..3a7c8d66 100755
--- 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