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FIX: bug in nextwatch demod, which if the found psk bits was smaller than the preamb...
[proxmark3-svn] / common / legic_prng.c
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
9 #include "legic_prng.h"
10
11 struct lfsr {
12 uint8_t a;
13 uint8_t b;
14 uint32_t c;
15 } lfsr;
16
17 void legic_prng_init(uint8_t init) {
18 lfsr.c = 0;
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
26 void legic_prng_forward(int count) {
27 lfsr.c += count;
28 while(count--) {
29 //lfsr.a = lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6;
30 // According: http://www.proxmark.org/forum/viewtopic.php?pid=5437#p5437
31 lfsr.a = (lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6) & 0x7F;
32 lfsr.b = lfsr.b >> 1 | (lfsr.b ^ lfsr.b >> 2 ^ lfsr.b >> 3 ^ lfsr.b >> 7) << 7;
33 }
34 }
35
36 int legic_prng_count() {
37 return lfsr.c;
38 }
39
40 uint8_t legic_prng_get_bit() {
41 uint8_t idx = 7 - ( (lfsr.a & 4) | (lfsr.a >> 2 & 2) | (lfsr.a >> 4 & 1) );
42 return lfsr.b >> idx & 1;
43 }
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