| | 1 | #include "legic_prng.h" |
| | 2 | /* legic's obfuscation function */ |
| | 3 | |
| | 4 | struct lfsr { |
| | 5 | uint8_t a; |
| | 6 | uint8_t b; |
| | 7 | } lfsr; |
| | 8 | |
| | 9 | void legic_prng_init(uint8_t init) { |
| | 10 | lfsr.a = init; |
| | 11 | if(init == 0) /* hack to get a always 0 keystream */ |
| | 12 | lfsr.b = 0; |
| | 13 | else |
| | 14 | lfsr.b = (init << 1) | 1; |
| | 15 | } |
| | 16 | |
| | 17 | void legic_prng_forward(int count) { |
| | 18 | uint8_t tmp; |
| | 19 | while(count--) { |
| | 20 | tmp = lfsr.a & 1; |
| | 21 | tmp ^= (lfsr.a & 0x40) >> 6; |
| | 22 | |
| | 23 | lfsr.a >>= 1; |
| | 24 | lfsr.a |= tmp << 6; |
| | 25 | |
| | 26 | tmp = lfsr.b & 1; |
| | 27 | tmp ^= (lfsr.b & 4) >> 2; |
| | 28 | tmp = ~tmp; |
| | 29 | tmp ^= (lfsr.b & 8) >> 3; |
| | 30 | tmp = ~tmp; |
| | 31 | tmp ^= (lfsr.b & 0x80) >> 7; |
| | 32 | |
| | 33 | lfsr.b >>= 1; |
| | 34 | lfsr.b |= tmp << 7; |
| | 35 | } |
| | 36 | } |
| | 37 | |
| | 38 | uint8_t legic_prng_get_bit() { |
| | 39 | uint8_t idx = 7-((lfsr.a & 4) | ((lfsr.a & 8) >> 2) | ((lfsr.a & 0x10) >> 4)); |
| | 40 | return ((lfsr.b >> idx) & 1); |
| | 41 | } |
projects / proxmark3-svn / blame_incremental