github/proxmark3
1
0
Fork 0
mirror of https://github.com/Proxmark/proxmark3.git synced 2025-08-14 02:26:59 -07:00
Code Issues Projects Releases Packages Wiki Activity Actions

put legic back in the system and add rumpletux's fast legic / prng code from forum

Browse source
This commit is contained in:
adam@algroup.co.uk 2010-02-05 08:18:02 +00:00
commit 8e220a9126
8 changed files with 163 additions and 88 deletions
Download patch file Download diff file Expand all files Collapse all files

41
common/legic_prng.c Normal file
View file

@ -0,0 +1,41 @@
#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);
}