/***************************************************************************** * WARNING * * THIS CODE IS CREATED FOR EXPERIMENTATION AND EDUCATIONAL USE ONLY. * * USAGE OF THIS CODE IN OTHER WAYS MAY INFRINGE UPON THE INTELLECTUAL * PROPERTY OF OTHER PARTIES, SUCH AS INSIDE SECURE AND HID GLOBAL, * AND MAY EXPOSE YOU TO AN INFRINGEMENT ACTION FROM THOSE PARTIES. * * THIS CODE SHOULD NEVER BE USED TO INFRINGE PATENTS OR INTELLECTUAL PROPERTY RIGHTS. * ***************************************************************************** * * This file is part of loclass. It is a reconstructon of the cipher engine * used in iClass, and RFID techology. * * The implementation is based on the work performed by * Flavio D. Garcia, Gerhard de Koning Gans, Roel Verdult and * Milosch Meriac in the paper "Dismantling IClass". * * Copyright (C) 2014 Martin Holst Swende * * This is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as published * by the Free Software Foundation, or, at your option, any later version. * * This file is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with loclass. If not, see . * * * ****************************************************************************/ /** This file contains an optimized version of the MAC-calculation algorithm. Some measurements on a std laptop showed it runs in about 1/3 of the time: Std: 0.428962 Opt: 0.151609 Additionally, it is self-reliant, not requiring e.g. bitstreams from the cipherutils, thus can be easily dropped into a code base. The optimizations have been performed in the following steps: * Parameters passed by reference instead of by value. * Iteration instead of recursion, un-nesting recursive loops into for-loops. * Handling of bytes instead of individual bits, for less shuffling and masking * Less creation of "objects", structs, and instead reuse of alloc:ed memory * Inlining some functions via #define:s As a consequence, this implementation is less generic. Also, I haven't bothered documenting this. For a thorough documentation, check out the MAC-calculation within cipher.c instead. -- MHS 2015 **/ #include "optimized_cipher.h" #define opt_T(s) (0x1 & ((s->t >> 15) ^ (s->t >> 14)^ (s->t >> 10)^ (s->t >> 8)^ (s->t >> 5)^ (s->t >> 4)^ (s->t >> 1)^ s->t)) #define opt_B(s) (((s->b >> 6) ^ (s->b >> 5) ^ (s->b >> 4) ^ (s->b)) & 0x1) #define opt__select(x,y,r) (4 & (((r & (r << 2)) >> 5) ^ ((r & ~(r << 2)) >> 4) ^ ( (r | r << 2) >> 3)))\ |(2 & (((r | r << 2) >> 6) ^ ( (r | r << 2) >> 1) ^ (r >> 5) ^ r ^ ((x^y) << 1)))\ |(1 & (((r & ~(r << 2)) >> 4) ^ ((r & (r << 2)) >> 3) ^ r ^ x)) /* * Some background on the expression above can be found here... uint8_t xopt__select(bool x, bool y, uint8_t r) { uint8_t r_ls2 = r << 2; uint8_t r_and_ls2 = r & r_ls2; uint8_t r_or_ls2 = r | r_ls2; //r: r0 r1 r2 r3 r4 r5 r6 r7 //r_ls2: r2 r3 r4 r5 r6 r7 0 0 // z0 // z1 // uint8_t z0 = (r0 & r2) ^ (r1 & ~r3) ^ (r2 | r4); // <-- original uint8_t z0 = (r_and_ls2 >> 5) ^ ((r & ~r_ls2) >> 4) ^ ( r_or_ls2 >> 3); // uint8_t z1 = (r0 | r2) ^ ( r5 | r7) ^ r1 ^ r6 ^ x ^ y; // <-- original uint8_t z1 = (r_or_ls2 >> 6) ^ ( r_or_ls2 >> 1) ^ (r >> 5) ^ r ^ ((x^y) << 1); // uint8_t z2 = (r3 & ~r5) ^ (r4 & r6 ) ^ r7 ^ x; // <-- original uint8_t z2 = ((r & ~r_ls2) >> 4) ^ (r_and_ls2 >> 3) ^ r ^ x; return (z0 & 4) | (z1 & 2) | (z2 & 1); } */ void opt_successor(const uint8_t *k, State *s, bool y, State *successor) { uint8_t Tt = 1 & opt_T(s); successor->t = (s->t >> 1); successor->t |= (Tt ^ (s->r >> 7 & 0x1) ^ (s->r >> 3 & 0x1)) << 15; successor->b = s->b >> 1; successor->b |= (opt_B(s) ^ (s->r & 0x1)) << 7; successor->r = (k[opt__select(Tt, y, s->r)] ^ successor->b) + s->l ; successor->l = successor->r + s->r; } void opt_suc(const uint8_t *k, State *s, uint8_t *in, uint8_t length, bool add32Zeroes) { State x2; int i; uint8_t head = 0; for (i = 0; i < length; i++) { head = 1 & (in[i] >> 7); opt_successor(k, s, head, &x2); head = 1 & (in[i] >> 6); opt_successor(k, &x2, head, s); head = 1 & (in[i] >> 5); opt_successor(k, s, head, &x2); head = 1 & (in[i] >> 4); opt_successor(k, &x2, head, s); head = 1 & (in[i] >> 3); opt_successor(k, s, head, &x2); head = 1 & (in[i] >> 2); opt_successor(k, &x2, head, s); head = 1 & (in[i] >> 1); opt_successor(k, s, head, &x2); head = 1 & in[i]; opt_successor(k, &x2, head, s); } //For tag MAC, an additional 32 zeroes if (add32Zeroes) { for (i = 0; i < 16; i++) { opt_successor(k, s, 0, &x2); opt_successor(k, &x2, 0, s); } } } void opt_output(const uint8_t *k, State *s, uint8_t *buffer) { uint8_t times = 0; uint8_t bout = 0; State temp = {0, 0, 0, 0}; for (; times < 4; times++) { bout = 0; bout |= (s->r & 0x4) << 5; opt_successor(k, s, 0, &temp); bout |= (temp.r & 0x4) << 4; opt_successor(k, &temp, 0, s); bout |= (s->r & 0x4) << 3; opt_successor(k, s, 0, &temp); bout |= (temp.r & 0x4) << 2; opt_successor(k, &temp, 0, s); bout |= (s->r & 0x4) << 1; opt_successor(k, s, 0, &temp); bout |= (temp.r & 0x4) ; opt_successor(k, &temp, 0, s); bout |= (s->r & 0x4) >> 1; opt_successor(k, s, 0, &temp); bout |= (temp.r & 0x4) >> 2; opt_successor(k, &temp, 0, s); buffer[times] = bout; } } void opt_MAC(uint8_t *k, uint8_t *input, uint8_t *out) { State _init = { ((k[0] ^ 0x4c) + 0xEC) & 0xFF,// l ((k[0] ^ 0x4c) + 0x21) & 0xFF,// r 0x4c, // b 0xE012 // t }; opt_suc(k, &_init, input, 12, false); opt_output(k, &_init, out); } uint8_t rev_byte(uint8_t b) { b = (b & 0xF0) >> 4 | (b & 0x0F) << 4; b = (b & 0xCC) >> 2 | (b & 0x33) << 2; b = (b & 0xAA) >> 1 | (b & 0x55) << 1; return b; } void opt_reverse_arraybytecpy(uint8_t *dest, uint8_t *src, size_t len) { uint8_t i; for (i = 0; i < len ; i++) dest[i] = rev_byte(src[i]); } void opt_doReaderMAC(uint8_t *cc_nr_p, uint8_t *div_key_p, uint8_t mac[4]) { static uint8_t cc_nr[12]; opt_reverse_arraybytecpy(cc_nr, cc_nr_p, 12); uint8_t dest [] = {0, 0, 0, 0, 0, 0, 0, 0}; opt_MAC(div_key_p, cc_nr, dest); //The output MAC must also be reversed opt_reverse_arraybytecpy(mac, dest, 4); return; } void opt_doTagMAC(uint8_t *cc_p, const uint8_t *div_key_p, uint8_t mac[4]) { static uint8_t cc_nr[8 + 4 + 4]; opt_reverse_arraybytecpy(cc_nr, cc_p, 12); State _init = { ((div_key_p[0] ^ 0x4c) + 0xEC) & 0xFF,// l ((div_key_p[0] ^ 0x4c) + 0x21) & 0xFF,// r 0x4c, // b 0xE012 // t }; opt_suc(div_key_p, &_init, cc_nr, 12, true); uint8_t dest [] = {0, 0, 0, 0}; opt_output(div_key_p, &_init, dest); //The output MAC must also be reversed opt_reverse_arraybytecpy(mac, dest, 4); return; } /** * The tag MAC can be divided (both can, but no point in dividing the reader mac) into * two functions, since the first 8 bytes are known, we can pre-calculate the state * reached after feeding CC to the cipher. * @param cc_p * @param div_key_p * @return the cipher state */ State opt_doTagMAC_1(uint8_t *cc_p, const uint8_t *div_key_p) { static uint8_t cc_nr[8]; opt_reverse_arraybytecpy(cc_nr, cc_p, 8); State _init = { ((div_key_p[0] ^ 0x4c) + 0xEC) & 0xFF,// l ((div_key_p[0] ^ 0x4c) + 0x21) & 0xFF,// r 0x4c, // b 0xE012 // t }; opt_suc(div_key_p, &_init, cc_nr, 8, false); return _init; } /** * The second part of the tag MAC calculation, since the CC is already calculated into the state, * this function is fed only the NR, and internally feeds the remaining 32 0-bits to generate the tag * MAC response. * @param _init - precalculated cipher state * @param nr - the reader challenge * @param mac - where to store the MAC * @param div_key_p - the key to use */ void opt_doTagMAC_2(State _init, uint8_t *nr, uint8_t mac[4], const uint8_t *div_key_p) { static uint8_t _nr[4]; opt_reverse_arraybytecpy(_nr, nr, 4); opt_suc(div_key_p, &_init, _nr, 4, true); uint8_t dest [] = {0, 0, 0, 0}; opt_output(div_key_p, &_init, dest); //The output MAC must also be reversed opt_reverse_arraybytecpy(mac, dest, 4); return; }