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Merge branch 'master' of https://github.com/Proxmark/proxmark3
[proxmark3-svn] / common / legic_prng.c
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bd20f8f4 1//-----------------------------------------------------------------------------
2// This code is licensed to you under the terms of the GNU GPL, version 2 or,
3// at your option, any later version. See the LICENSE.txt file for the text of
4// the license.
5//-----------------------------------------------------------------------------
6// LEFIC's obfuscation function
7//-----------------------------------------------------------------------------
8
8e220a91 9#include "legic_prng.h"
8e220a91 10
11struct lfsr {
3612a8a8 12 uint8_t a;
13 uint8_t b;
14 uint32_t c;
8e220a91 15} lfsr;
16
17void legic_prng_init(uint8_t init) {
3612a8a8 18 lfsr.c = 0;
8e220a91 19 lfsr.a = init;
20 if(init == 0) /* hack to get a always 0 keystream */
21 lfsr.b = 0;
22 else
23 lfsr.b = (init << 1) | 1;
24}
25
26void legic_prng_forward(int count) {
3612a8a8 27 lfsr.c += count;
8e220a91 28 while(count--) {
538300ee 29 lfsr.a = lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6;
30 lfsr.b = lfsr.b >> 1 | (lfsr.b ^ lfsr.b >> 2 ^ lfsr.b >> 3 ^ lfsr.b >> 7) << 7;
8e220a91 31 }
32}
33
3612a8a8 34int legic_prng_count() {
35 return lfsr.c;
36}
37
8e220a91 38uint8_t legic_prng_get_bit() {
538300ee 39 uint8_t idx = 7 - ( (lfsr.a & 4) | (lfsr.a >> 2 & 2) | (lfsr.a >> 4 & 1) );
40 return lfsr.b >> idx & 1;
8e220a91 41}
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