[proxmark3-svn] / armsrc / optimized_cipher.c

/*****************************************************************************
 * 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 <http://www.gnu.org/licenses/>.
 *
 *
 *
 ****************************************************************************/

/**

  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"
#include <stddef.h>
#include <stdbool.h>
#include <stdint.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;
        for (int i = 0; i < length; i++) {
                uint8_t head;
                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(int 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) {
        State temp = {0, 0, 0, 0};
        for (uint8_t times = 0; times < 4; times++) {
                uint8_t 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);
        //printf("\noutp ");
        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) {
        for (size_t 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);
        //opt_suc(div_key_p, &_init,nr, 4, false);
        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;
}