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chg: 'lf nexwatch demod' - correct parity calc

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This commit is contained in:
iceman1001 2020-05-11 01:13:58 +02:00
parent f3293c9dcd
commit 280b7d9c46
1 changed files with 32 additions and 18 deletions
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50
client/src/cmdlfnexwatch.c
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@ -53,6 +53,16 @@ static int usage_lf_nexwatch_sim(void) {
return PM3_SUCCESS;
}
static inline uint32_t bitcount(uint32_t a) {
#if defined __GNUC__
return __builtin_popcountl(a);
#else
a = a - ((a >> 1) & 0x55555555);
a = (a & 0x33333333) + ((a >> 2) & 0x33333333);
return (((a + (a >> 4)) & 0x0f0f0f0f) * 0x01010101) >> 24;
#endif
}
int demodNexWatch(void) {
if (PSKDemod("", false) != PM3_SUCCESS) {
PrintAndLogEx(DEBUG, "DEBUG: Error - NexWatch can't demod signal");
@ -106,13 +116,14 @@ int demodNexWatch(void) {
32bit UID: 00100100011001000011111100010010
bits numbered from left (MSB):
1234567890 1234567890 1234567890 12
1234 5678 9012 34567 8901234567890 12
0010 0100 0110 0100 00111111000100 10
descramble:
b1 b5 b9 b13 b17 b21 b25 b29 b2 b6 b10 b14 b18 b22 b26 b30 b3 b7 b11 b15 b19 b23 b27 b31 b4 b8 b12 b16 b20 b24 b28 b32
00000100011101001010110100001100 = 74755340
gives:
0000 0100 0111 0100 1010 1101 0000 1110 = 74755342
*/
// Since the description is not zero indexed we adjust.
@ -167,18 +178,24 @@ int demodNexWatch(void) {
d_id |= DemodBuffer[DOFFSET + 24] << 2;
d_id |= DemodBuffer[DOFFSET + 28] << 1;
d_id |= DemodBuffer[DOFFSET + 32];
uint8_t mode = bytebits_to_byte(DemodBuffer + 72, 4);
// parity check
// from 8 preamble, 32 zeros, 32 id, 4 mode, comes EOEO parity.
/*
uint8_t even;
for (uint8_t p=0; p < 76; p++) {
even = (DemodBuffer[p] == 1);
// from 32 hex id, 4 mode, descramble par (1234) -> (4231)
uint8_t xor_par = 0;
for (uint8_t i = 40; i < 76; i +=4) {
xor_par ^= bytebits_to_byte(DemodBuffer + i, 4);
}
uint8_t calc_parity = (!even << 3 | even << 2 | !even << 1 | even);
uint8_t calc_parity ;
calc_parity = (((xor_par >> 3 ) & 1) );
calc_parity |= (((xor_par >> 1 ) & 1) << 1);
calc_parity |= (((xor_par >> 2 ) & 1) << 2);
calc_parity |= ((xor_par & 1) << 3);
uint8_t parity = bytebits_to_byte(DemodBuffer + 76, 4);
*/
/*
Checksum:::
1. Subtract every byte from ID field using an unsigned, one byte register:
@ -207,9 +224,7 @@ int demodNexWatch(void) {
PrintAndLogEx(NORMAL, "Sum: 0x%02x", calc);
uint8_t revpar = (even << 3 | !even << 2 | even << 1 | !even);
uint8_t a[] = {0xbe, 0xbc, 0x88, 0x86 };
uint8_t a[] = {0xbe, 0xbc, 0x88, 0x86 };
for (uint8_t c=0; c < ARRAYLEN(a); c++) {
uint8_t b = calc;
b -= a[c];
@ -227,19 +242,18 @@ int demodNexWatch(void) {
*/
// uint8_t chk = bytebits_to_byte(DemodBuffer + 80, 8);
uint8_t mode = bytebits_to_byte(DemodBuffer + 72, 4);
// output
PrintAndLogEx(SUCCESS, " NexWatch raw id : " _YELLOW_("0x%"PRIx32) , rawid);
PrintAndLogEx(SUCCESS, " descrambled id : " _YELLOW_("%"PRIu32) " " _YELLOW_("0x%"PRIx32), d_id, d_id);
PrintAndLogEx(SUCCESS, " 88bit id : " _YELLOW_("%"PRIu32) " " _YELLOW_("0x%"PRIx32), d_id, d_id);
PrintAndLogEx(SUCCESS, " mode : %x", mode);
// PrintAndLogEx(SUCCESS, " parity : %s [%X == %X]", (parity == calc_parity) ? _GREEN_("ok") : _RED_("fail"), parity, calc_parity);
PrintAndLogEx(SUCCESS, " parity : %s [%X == %X]", (parity == calc_parity) ? _GREEN_("ok") : _RED_("fail"), parity, calc_parity);
// PrintAndLogEx(NORMAL, " checksum : %02x == %02x", calc, chk);
// bits to hex (output used for SIM/CLONE cmd)
CmdPrintDemodBuff("x");
// PrintAndLogEx(INFO, "Raw: %s", sprint_hex_inrow(DemodBuffer, size));
//binarraytohex(char *target, const size_t targetlen, (char *)DemodBuffer, size);
return PM3_SUCCESS;
}