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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 | ||
7838f4be | 9 | #include "legic_prng.h" |
8e220a91 | 10 | |
11 | struct lfsr { | |
c71c5ee1 | 12 | uint8_t a; |
13 | uint8_t b; | |
14 | uint32_t c; | |
8e220a91 | 15 | } lfsr; |
16 | ||
17 | void legic_prng_init(uint8_t init) { | |
c71c5ee1 | 18 | lfsr.a = init; |
19 | lfsr.b = 0; // hack to get a always 0 keystream | |
20 | lfsr.c = 0; | |
21 | if(init) | |
22 | lfsr.b = (init << 1) | 1; | |
8e220a91 | 23 | } |
24 | ||
25 | void legic_prng_forward(int count) { | |
c71c5ee1 | 26 | lfsr.c += count; |
27 | while(count--) { | |
28 | // According: http://www.proxmark.org/forum/viewtopic.php?pid=5437#p5437 | |
29 | lfsr.a = (lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6) & 0x7F; | |
30 | lfsr.b = lfsr.b >> 1 | (lfsr.b ^ lfsr.b >> 2 ^ lfsr.b >> 3 ^ lfsr.b >> 7) << 7; | |
31 | } | |
8e220a91 | 32 | } |
33 | ||
c71c5ee1 | 34 | uint32_t legic_prng_count() { |
35 | return lfsr.c; | |
3612a8a8 | 36 | } |
37 | ||
8e220a91 | 38 | uint8_t legic_prng_get_bit() { |
c71c5ee1 | 39 | uint8_t idx = 7 - ( (lfsr.a & 4) | (lfsr.a >> 2 & 2) | (lfsr.a >> 4 & 1) ); |
40 | return lfsr.b >> idx & 1; | |
41 | } |