From ee4e2816753bbc28ca10c20cbfbbc7eff404cab9 Mon Sep 17 00:00:00 2001
From: iceman1001 <iceman@iuse.se>
Date: Fri, 12 Feb 2016 12:34:05 +0100
Subject: [PATCH 1/1] FIX:  legic_prng.c according to user on forum ref:
 http://www.proxmark.org/forum/viewtopic.php?pid=5437#p5437  needs to be "&
 0x7F"

ADD:  method for calculating the storage crc8.
---
 common/crc.c        | 29 +++++++++++++++++++++++++----
 common/crc.h        |  9 +++++++--
 common/legic_prng.c |  4 +++-
 3 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/common/crc.c b/common/crc.c
index 0c73474f..21019da9 100644
--- a/common/crc.c
+++ b/common/crc.c
@@ -6,6 +6,8 @@
 // Generic CRC calculation code.
 //-----------------------------------------------------------------------------
 #include "crc.h"
+#include "util.h"
+#include <stdio.h>
 #include <stdint.h>
 #include <stddef.h>
 
@@ -21,8 +23,7 @@ void crc_init(crc_t *crc, int order, uint32_t polynom, uint32_t initial_value, u
 
 void crc_update(crc_t *crc, uint32_t data, int data_width)
 {
-	int i;
-	for(i=0; i<data_width; i++) {
+	for( int i=0; i < data_width; i++) {
 		int oldstate = crc->state;
 		crc->state = crc->state >> 1;
 		if( (oldstate^data) & 1 ) {
@@ -49,8 +50,28 @@ uint32_t CRC8Maxim(uint8_t *buff, size_t size)
 	crc_init(&crc, 9, 0x8c, 0x00, 0x00);
 	crc_clear(&crc);
 
-	for (size_t i=0; i < size; ++i){
+	for (size_t i=0; i < size; ++i)
 		crc_update(&crc, buff[i], 8);
-	}
+
 	return crc_finish(&crc);
 }
+
+uint32_t CRC8Legic(uint8_t *buff, size_t size) {
+
+	// Poly 0x63,   reversed poly 0xC6,  Init 0x55,  Final 0x00
+	crc_t crc;
+	crc_init(&crc, 8, 0xC6, 0x55, 0);
+	crc_clear(&crc);
+	
+	for ( int i = 0; i < size; ++i)
+		crc_update(&crc, buff[i], 8);
+	return SwapBits(crc_finish(&crc), 8);
+}
+
+uint32_t SwapBits(uint32_t value, int nrbits) {
+	uint32_t newvalue = 0;
+	for(int i = 0; i < nrbits; i++) {
+		newvalue ^= ((value >> i) & 1) << (nrbits - 1 - i);
+	}
+	return newvalue;
+}
diff --git a/common/crc.h b/common/crc.h
index adbfb237..0c0770a4 100644
--- a/common/crc.h
+++ b/common/crc.h
@@ -26,7 +26,7 @@ typedef struct crc {
  * final_xor is XORed onto the state before returning it from crc_result(). */
 extern void crc_init(crc_t *crc, int order, uint32_t polynom, uint32_t initial_value, uint32_t final_xor);
 
-/* Update the crc state. data is the data of length data_width bits (only the the
+/* Update the crc state. data is the data of length data_width bits (only the
  * data_width lower-most bits are used).
  */
 extern void crc_update(crc_t *crc, uint32_t data, int data_width);
@@ -38,7 +38,12 @@ extern void crc_clear(crc_t *crc);
 extern uint32_t crc_finish(crc_t *crc);
 
 // Calculate CRC-8/Maxim checksum
-uint32_t CRC8Maxim(uint8_t *buff, size_t size  );
+uint32_t CRC8Maxim(uint8_t *buff, size_t size);
+
+// Calculate CRC-8/Legic checksum
+uint32_t CRC8Legic(uint8_t *buff, size_t size);
+uint32_t SwapBits(uint32_t value, int nrbits);
+
 /* Static initialization of a crc structure */
 #define CRC_INITIALIZER(_order, _polynom, _initial_value, _final_xor) { \
 	.state = ((_initial_value) & ((1L<<(_order))-1)), \
diff --git a/common/legic_prng.c b/common/legic_prng.c
index 4f3b1ffe..1f12873c 100644
--- a/common/legic_prng.c
+++ b/common/legic_prng.c
@@ -26,7 +26,9 @@ void legic_prng_init(uint8_t init) {
 void legic_prng_forward(int count) {
   lfsr.c += count;
   while(count--) {
-    lfsr.a = lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6;
+    //lfsr.a = lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6;
+	// According: http://www.proxmark.org/forum/viewtopic.php?pid=5437#p5437
+	lfsr.a = (lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6) & 0x7F;
     lfsr.b = lfsr.b >> 1 | (lfsr.b ^ lfsr.b >> 2 ^ lfsr.b >> 3 ^ lfsr.b >> 7) << 7;
   }
 }
-- 
2.39.5