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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 | |
11 | struct lfsr { | |
12 | uint8_t a; | |
13 | uint8_t b; | |
14 | } lfsr; | |
15 | ||
16 | void legic_prng_init(uint8_t init) { | |
17 | lfsr.a = init; | |
18 | if(init == 0) /* hack to get a always 0 keystream */ | |
19 | lfsr.b = 0; | |
20 | else | |
21 | lfsr.b = (init << 1) | 1; | |
22 | } | |
23 | ||
24 | void legic_prng_forward(int count) { | |
8e220a91 | 25 | while(count--) { |
538300ee | 26 | lfsr.a = lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6; |
27 | lfsr.b = lfsr.b >> 1 | (lfsr.b ^ lfsr.b >> 2 ^ lfsr.b >> 3 ^ lfsr.b >> 7) << 7; | |
8e220a91 | 28 | } |
29 | } | |
30 | ||
31 | uint8_t legic_prng_get_bit() { | |
538300ee | 32 | uint8_t idx = 7 - ( (lfsr.a & 4) | (lfsr.a >> 2 & 2) | (lfsr.a >> 4 & 1) ); |
33 | return lfsr.b >> idx & 1; | |
8e220a91 | 34 | } |