X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/8e220a91260072f1483f1fb41d6ce64459667e4c..16a372ab75c10b0ffb3786adc4029cd1df2f6066:/common/legic_prng.c?ds=inline diff --git a/common/legic_prng.c b/common/legic_prng.c index ee8e0dc7..4f3b1ffe 100644 --- a/common/legic_prng.c +++ b/common/legic_prng.c @@ -1,12 +1,21 @@ +//----------------------------------------------------------------------------- +// This code is licensed to you under the terms of the GNU GPL, version 2 or, +// at your option, any later version. See the LICENSE.txt file for the text of +// the license. +//----------------------------------------------------------------------------- +// LEFIC's obfuscation function +//----------------------------------------------------------------------------- + #include "legic_prng.h" -/* legic's obfuscation function */ struct lfsr { - uint8_t a; - uint8_t b; + uint8_t a; + uint8_t b; + uint32_t c; } lfsr; void legic_prng_init(uint8_t init) { + lfsr.c = 0; lfsr.a = init; if(init == 0) /* hack to get a always 0 keystream */ lfsr.b = 0; @@ -15,27 +24,18 @@ void legic_prng_init(uint8_t init) { } void legic_prng_forward(int count) { - uint8_t tmp; + lfsr.c += count; while(count--) { - tmp = lfsr.a & 1; - tmp ^= (lfsr.a & 0x40) >> 6; - - lfsr.a >>= 1; - lfsr.a |= tmp << 6; - - tmp = lfsr.b & 1; - tmp ^= (lfsr.b & 4) >> 2; - tmp = ~tmp; - tmp ^= (lfsr.b & 8) >> 3; - tmp = ~tmp; - tmp ^= (lfsr.b & 0x80) >> 7; - - lfsr.b >>= 1; - lfsr.b |= tmp << 7; + lfsr.a = lfsr.a >> 1 | (lfsr.a ^ lfsr.a >> 6) << 6; + lfsr.b = lfsr.b >> 1 | (lfsr.b ^ lfsr.b >> 2 ^ lfsr.b >> 3 ^ lfsr.b >> 7) << 7; } } +int legic_prng_count() { + return lfsr.c; +} + uint8_t legic_prng_get_bit() { - uint8_t idx = 7-((lfsr.a & 4) | ((lfsr.a & 8) >> 2) | ((lfsr.a & 0x10) >> 4)); - return ((lfsr.b >> idx) & 1); + uint8_t idx = 7 - ( (lfsr.a & 4) | (lfsr.a >> 2 & 2) | (lfsr.a >> 4 & 1) ); + return lfsr.b >> idx & 1; }