| 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 | lfsr.b = lfsr.b >> 1 | (lfsr.b ^ lfsr.b >> 2 ^ lfsr.b >> 3 ^ lfsr.b >> 7) << 7; |
| 31 | } |
| 32 | } |
| 33 | |
| 34 | int legic_prng_count() { |
| 35 | return lfsr.c; |
| 36 | } |
| 37 | |
| 38 | uint8_t legic_prng_get_bit() { |
| 39 | uint8_t idx = 7 - ( (lfsr.a & 4) | (lfsr.a >> 2 & 2) | (lfsr.a >> 4 & 1) ); |
| 40 | return lfsr.b >> idx & 1; |
| 41 | } |