crewID/libfreefare
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Fix MAD CRC algorithm.

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The CRC algorithm is not a standard CRC algorithm so rename it to nxp_crc() and adjust all related code.
This commit is contained in:
Romain Tartiere 2010-03-18 21:03:07 +00:00
parent 42692ccf54
commit feb240ee73
3 changed files with 110 additions and 136 deletions
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2
libfreefare/freefare_internal.h
View file

@ -39,7 +39,7 @@
struct mad_sector_0x00;
struct mad_sector_0x10;
void crc8 (uint8_t *crc, const uint8_t value);
void nxp_crc (uint8_t *crc, const uint8_t value);
MifareTag mifare_classic_tag_new (void);
void mifare_classic_tag_free (MifareTag tag);
MifareTag mifare_ultralight_tag_new (void);

31
libfreefare/mad.c
View file

@ -38,15 +38,10 @@
#include "freefare_internal.h"
/*
* XXX The documentation says the preset is 0xE3, but the various card dumps
* and the documentation example MAD CRC can be verified only with a CRC
* preset of 0x67.
*
* This is still under investigation:
* http://www.libnfc.org/community/post/667/
* http://discussion.forum.nokia.com/forum/showthread.php?t=181702#14
* The documentation says the preset is 0xE3 but the bits have to be mirrored:
* 0xe3 = 1110 0011 <=> 1100 0111 = 0xc7
*/
#define CRC_PRESET 0x67
#define CRC_PRESET 0xc7
#define SECTOR_0X00_AIDS 15
#define SECTOR_0X10_AIDS 23
@ -96,15 +91,15 @@ mad_new (uint8_t version)
* Compute CRC.
*/
void
crc8 (uint8_t *crc, const uint8_t value)
nxp_crc (uint8_t *crc, const uint8_t value)
{
/* x^8 + x^4 + x^3 + x^2 + 1 => 0x11d */
const uint8_t poly = 0x1d;
*crc ^= value;
for (int current_bit = 7; current_bit >= 0; current_bit--) {
int bit_out = (*crc) & 0x80;
*crc = ((*crc) << 1) | (( value >> (current_bit)) & 0x01);
*crc <<= 1;
if (bit_out)
*crc ^= poly;
@ -116,13 +111,12 @@ sector_0x00_crc8 (Mad mad)
{
uint8_t crc = CRC_PRESET;
crc8 (&crc, mad->sector_0x00.info);
nxp_crc (&crc, mad->sector_0x00.info);
for (int n = 0; n < SECTOR_0X00_AIDS; n++) {
crc8 (&crc, mad->sector_0x00.aids[n].application_code);
crc8 (&crc, mad->sector_0x00.aids[n].function_cluster_code);
nxp_crc (&crc, mad->sector_0x00.aids[n].application_code);
nxp_crc (&crc, mad->sector_0x00.aids[n].function_cluster_code);
}
crc8 (&crc, 0x00);
return crc;
}
@ -132,13 +126,12 @@ sector_0x10_crc8 (Mad mad)
{
uint8_t crc = CRC_PRESET;
crc8 (&crc, mad->sector_0x10.info);
nxp_crc (&crc, mad->sector_0x10.info);
for (int n = 0; n < SECTOR_0X10_AIDS; n++) {
crc8 (&crc, mad->sector_0x10.aids[n].application_code);
crc8 (&crc, mad->sector_0x10.aids[n].function_cluster_code);
nxp_crc (&crc, mad->sector_0x10.aids[n].application_code);
nxp_crc (&crc, mad->sector_0x10.aids[n].function_cluster_code);
}
crc8 (&crc, 0x00);
return crc;
}