mirror of
https://github.com/RfidResearchGroup/proxmark3.git
synced 2025-01-08 09:10:06 +08:00
42 lines
805 B
C
42 lines
805 B
C
|
#include "legic_prng.h"
|
||
|
|
/* legic's obfuscation function */
|
||
|
|
|
||
|
|
struct lfsr {
|
||
|
|
uint8_t a;
|
||
|
|
uint8_t b;
|
||
|
|
} lfsr;
|
||
|
|
|
||
|
|
void legic_prng_init(uint8_t init) {
|
||
|
|
lfsr.a = init;
|
||
|
|
if(init == 0) /* hack to get a always 0 keystream */
|
||
|
|
lfsr.b = 0;
|
||
|
|
else
|
||
|
|
lfsr.b = (init << 1) | 1;
|
||
|
|
}
|
||
|
|
|
||
|
|
void legic_prng_forward(int count) {
|
||
|
|
uint8_t tmp;
|
||
|
|
while(count--) {
|
||
|
|
tmp = lfsr.a & 1;
|
||
|
|
tmp ^= (lfsr.a & 0x40) >> 6;
|
||
|
|
|
||
|
|
lfsr.a >>= 1;
|
||
|
|
lfsr.a |= tmp << 6;
|
||
|
|
|
||
|
|
tmp = lfsr.b & 1;
|
||
|
|
tmp ^= (lfsr.b & 4) >> 2;
|
||
|
|
tmp = ~tmp;
|
||
|
|
tmp ^= (lfsr.b & 8) >> 3;
|
||
|
|
tmp = ~tmp;
|
||
|
|
tmp ^= (lfsr.b & 0x80) >> 7;
|
||
|
|
|
||
|
|
lfsr.b >>= 1;
|
||
|
|
lfsr.b |= tmp << 7;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
uint8_t legic_prng_get_bit() {
|
||
|
|
uint8_t idx = 7-((lfsr.a & 4) | ((lfsr.a & 8) >> 2) | ((lfsr.a & 0x10) >> 4));
|
||
|
|
return ((lfsr.b >> idx) & 1);
|
||
|
|
}
|