mirror of
https://github.com/RfidResearchGroup/proxmark3.git
synced 2024-09-20 15:26:13 +08:00
bd20f8f478
I have kept whatever copyright notices exist. Please add your own copyright notice if you have made any nontrivial changes or additions to the code. There are several files without any attribution, currently.
49 lines
1.2 KiB
C
49 lines
1.2 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;
|
|
} 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);
|
|
}
|