/*****************************************************************************
* 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.
*
* 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"
#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);
//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)
{
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);
//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;
}