mirror of
https://github.com/Proxmark/proxmark3.git
synced 2024-12-03 10:40:27 -08:00
42 lines
1.1 KiB
C
42 lines
1.1 KiB
C
//-----------------------------------------------------------------------------
|
|
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
|
|
// at your option, any later version. See the LICENSE.txt file for the text of
|
|
// the license.
|
|
//-----------------------------------------------------------------------------
|
|
// LEFIC's obfuscation function
|
|
//-----------------------------------------------------------------------------
|
|
|
|
#include "legic_prng.h"
|
|
|
|
struct lfsr {
|
|
uint8_t a;
|
|
uint8_t b;
|
|
uint32_t c;
|
|
} lfsr;
|
|
|
|
void legic_prng_init(uint8_t init) {
|
|
lfsr.c = 0;
|
|
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) {
|
|
lfsr.c += count;
|
|
while(count--) {
|
|
lfsr.a = lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6;
|
|
lfsr.b = lfsr.b >> 1 | (lfsr.b ^ lfsr.b >> 2 ^ lfsr.b >> 3 ^ lfsr.b >> 7) << 7;
|
|
}
|
|
}
|
|
|
|
int legic_prng_count() {
|
|
return lfsr.c;
|
|
}
|
|
|
|
uint8_t legic_prng_get_bit() {
|
|
uint8_t idx = 7 - ( (lfsr.a & 4) | (lfsr.a >> 2 & 2) | (lfsr.a >> 4 & 1) );
|
|
return lfsr.b >> idx & 1;
|
|
}
|