git.zerfleddert.de Git - proxmark3-svn/blob - armsrc/legicrf.c

   1 /*
   2  * LEGIC RF simulation code
   3  *
   4  * (c) 2009 Henryk Plötz <henryk@ploetzli.ch>
   5  */
   6
   7 #include "proxmark3.h"
   8
   9 #include "apps.h"
  10 #include "legicrf.h"
  11 #include <stdint.h>
  12
  13 #include "legic_prng.h"
  14 #include "crc.h"
  15
  16 static struct legic_frame {
  17         int bits;
  18         uint32_t data;
  19 } current_frame;
  20
  21 static crc_t legic_crc;
  22
  23 AT91PS_TC timer;
  24
  25 static void setup_timer(void)
  26 {
  27         /* Set up Timer 1 to use for measuring time between pulses. Since we're bit-banging
  28          * this it won't be terribly accurate but should be good enough.
  29          */
  30         AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC1);
  31         timer = AT91C_BASE_TC1;
  32         timer->TC_CCR = AT91C_TC_CLKDIS;
  33         timer->TC_CMR = TC_CMR_TCCLKS_TIMER_CLOCK3;
  34         timer->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
  35
  36 /* At TIMER_CLOCK3 (MCK/32) */
  37 #define RWD_TIME_1 150     /* RWD_TIME_PAUSE off, 80us on = 100us */
  38 #define RWD_TIME_0 90      /* RWD_TIME_PAUSE off, 40us on = 60us */
  39 #define RWD_TIME_PAUSE 30  /* 20us */
  40 #define RWD_TIME_FUZZ 20   /* rather generous 13us, since the peak detector + hysteresis fuzz quite a bit */
  41 #define TAG_TIME_BIT 150   /* 100us for every bit */
  42 #define TAG_TIME_WAIT 490  /* time from RWD frame end to tag frame start, experimentally determined */
  43
  44 }
  45
  46 #define FUZZ_EQUAL(value, target, fuzz) ((value) > ((target)-(fuzz)) && (value) < ((target)+(fuzz)))
  47
  48 /* Send a frame in reader mode, the FPGA must have been set up by
  49  * LegicRfReader
  50  */
  51 static void frame_send_rwd(uint32_t data, int bits)
  52 {
  53         /* Start clock */
  54         timer->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
  55         while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
  56
  57         int i;
  58         for(i=0; i<bits; i++) {
  59                 int starttime = timer->TC_CV;
  60                 int pause_end = starttime + RWD_TIME_PAUSE, bit_end;
  61                 int bit = data & 1;
  62                 data = data >> 1;
  63
  64                 if(bit ^ legic_prng_get_bit()) {
  65                         bit_end = starttime + RWD_TIME_1;
  66                 } else {
  67                         bit_end = starttime + RWD_TIME_0;
  68                 }
  69
  70                 /* RWD_TIME_PAUSE time off, then some time on, so that the complete bit time is
  71                  * RWD_TIME_x, where x is the bit to be transmitted */
  72                 AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
  73                 while(timer->TC_CV < pause_end) ;
  74                 AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
  75                 legic_prng_forward(1); /* bit duration is longest. use this time to forward the lfsr */
  76
  77                 while(timer->TC_CV < bit_end) ;
  78         }
  79
  80         {
  81                 /* One final pause to mark the end of the frame */
  82                 int pause_end = timer->TC_CV + RWD_TIME_PAUSE;
  83                 AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
  84                 while(timer->TC_CV < pause_end) ;
  85                 AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
  86         }
  87
  88         /* Reset the timer, to measure time until the start of the tag frame */
  89         timer->TC_CCR = AT91C_TC_SWTRG;
  90         while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
  91 }
  92
  93 /* Receive a frame from the card in reader emulation mode, the FPGA and
  94  * timer must have been set up by LegicRfReader and frame_send_rwd.
  95  *
  96  * The LEGIC RF protocol from card to reader does not include explicit
  97  * frame start/stop information or length information. The reader must
  98  * know beforehand how many bits it wants to receive. (Notably: a card
  99  * sending a stream of 0-bits is indistinguishable from no card present.)
 100  *
 101  * Receive methodology: There is a fancy correlator in hi_read_rx_xcorr, but
 102  * I'm not smart enough to use it. Instead I have patched hi_read_tx to output
 103  * the ADC signal with hysteresis on SSP_DIN. Bit-bang that signal and look
 104  * for edges. Count the edges in each bit interval. If they are approximately
 105  * 0 this was a 0-bit, if they are approximately equal to the number of edges
 106  * expected for a 212kHz subcarrier, this was a 1-bit. For timing we use the
 107  * timer that's still running from frame_send_rwd in order to get a synchronization
 108  * with the frame that we just sent.
 109  *
 110  * FIXME: Because we're relying on the hysteresis to just do the right thing
 111  * the range is severely reduced (and you'll probably also need a good antenna).
 112  * So this should be fixed some time in the future for a proper receiver.
 113  */
 114 static void frame_receive_rwd(struct legic_frame * const f, int bits, int crypt)
 115 {
 116         uint32_t the_bit = 1;  /* Use a bitmask to save on shifts */
 117         uint32_t data=0;
 118         int i, old_level=0, edges=0;
 119         int next_bit_at = TAG_TIME_WAIT;
 120
 121
 122         if(bits > 16)
 123                 bits = 16;
 124
 125         AT91C_BASE_PIOA->PIO_ODR = GPIO_SSC_DIN;
 126         AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DIN;
 127
 128         /* we have some time now, precompute the cipher
 129          * since we cannot compute it on the fly while reading */
 130         legic_prng_forward(2);
 131
 132         if(crypt)
 133         {
 134                 for(i=0; i<bits; i++) {
 135                         data |= legic_prng_get_bit() << i;
 136                         legic_prng_forward(1);
 137                 }
 138         }
 139
 140         while(timer->TC_CV < next_bit_at) ;
 141
 142         next_bit_at += TAG_TIME_BIT;
 143
 144         for(i=0; i<bits; i++) {
 145                 edges = 0;
 146
 147                 while(timer->TC_CV < next_bit_at) {
 148                         int level = (AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_DIN);
 149                         if(level != old_level)
 150                                 edges++;
 151                         old_level = level;
 152                 }
 153                 next_bit_at += TAG_TIME_BIT;
 154
 155                 if(edges > 20 && edges < 60) { /* expected are 42 edges */
 156                         data ^= the_bit;
 157                 }
 158
 159                 the_bit <<= 1;
 160         }
 161
 162         f->data = data;
 163         f->bits = bits;
 164
 165         /* Reset the timer, to synchronize the next frame */
 166         timer->TC_CCR = AT91C_TC_SWTRG;
 167         while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
 168 }
 169
 170 static void frame_clean(struct legic_frame * const f)
 171 {
 172         f->data = 0;
 173         f->bits = 0;
 174 }
 175
 176 static uint32_t perform_setup_phase_rwd(int iv)
 177 {
 178
 179         /* Switch on carrier and let the tag charge for 1ms */
 180         AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
 181         SpinDelay(1);
 182
 183         legic_prng_init(0); /* no keystream yet */
 184         frame_send_rwd(iv, 7);
 185         legic_prng_init(iv);
 186
 187         frame_clean(&current_frame);
 188         frame_receive_rwd(&current_frame, 6, 1);
 189         legic_prng_forward(1); /* we wait anyways */
 190         while(timer->TC_CV < 387) ; /* ~ 258us */
 191         frame_send_rwd(0x19, 6);
 192
 193         return current_frame.data;
 194 }
 195
 196 static void LegicCommonInit(void) {
 197         SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
 198         FpgaSetupSsc();
 199         FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX);
 200
 201         /* Bitbang the transmitter */
 202         AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
 203         AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
 204         AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
 205
 206         setup_timer();
 207
 208         crc_init(&legic_crc, 4, 0x19 >> 1, 0x5, 0);
 209 }
 210
 211 static void switch_off_tag_rwd(void)
 212 {
 213         /* Switch off carrier, make sure tag is reset */
 214         AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
 215         SpinDelay(10);
 216
 217         WDT_HIT();
 218 }
 219 /* calculate crc for a legic command */
 220 static int LegicCRC(int byte_index, int value, int cmd_sz) {
 221         crc_clear(&legic_crc);
 222         crc_update(&legic_crc, 1, 1); /* CMD_READ */
 223         crc_update(&legic_crc, byte_index, cmd_sz-1);
 224         crc_update(&legic_crc, value, 8);
 225         return crc_finish(&legic_crc);
 226 }
 227
 228 int legic_read_byte(int byte_index, int cmd_sz) {
 229         int byte;
 230
 231         legic_prng_forward(4); /* we wait anyways */
 232         while(timer->TC_CV < 387) ; /* ~ 258us + 100us*delay */
 233
 234         frame_send_rwd(1 | (byte_index << 1), cmd_sz);
 235         frame_clean(&current_frame);
 236
 237         frame_receive_rwd(&current_frame, 12, 1);
 238
 239         byte = current_frame.data & 0xff;
 240         if( LegicCRC(byte_index, byte, cmd_sz) != (current_frame.data >> 8) ) {
 241                 Dbprintf("!!! crc mismatch: expected %x but got %x !!!", LegicCRC(byte_index, current_frame.data & 0xff, cmd_sz), current_frame.data >> 8);
 242                 return -1;
 243         }
 244
 245         return byte;
 246 }
 247
 248 /* legic_write_byte() is not included, however it's trivial to implement
 249  * and here are some hints on what remains to be done:
 250  *
 251  *  * assemble a write_cmd_frame with crc and send it
 252  *  * wait until the tag sends back an ACK ('1' bit unencrypted)
 253  *  * forward the prng based on the timing
 254  */
 255
 256
 257 void LegicRfReader(int offset, int bytes) {
 258         int byte_index=0, cmd_sz=0, card_sz=0;
 259
 260         LegicCommonInit();
 261
 262         memset(BigBuf, 0, 1024);
 263
 264         DbpString("setting up legic card");
 265         uint32_t tag_type = perform_setup_phase_rwd(0x55);
 266         switch(tag_type) {
 267                 case 0x1d:
 268                         DbpString("MIM 256 card found, reading card ...");
 269                         cmd_sz = 9;
 270                         card_sz = 256;
 271                         break;
 272                 case 0x3d:
 273                         DbpString("MIM 1024 card found, reading card ...");
 274                         cmd_sz = 11;
 275                         card_sz = 1024;
 276                         break;
 277                 default:
 278                         Dbprintf("Unknown card format: %x",tag_type);
 279                         switch_off_tag_rwd();
 280                         return;
 281         }
 282         if(bytes == -1) {
 283                 bytes = card_sz;
 284         }
 285         if(bytes+offset >= card_sz) {
 286                 bytes = card_sz-offset;
 287         }
 288
 289         switch_off_tag_rwd(); //we lost to mutch time with dprintf
 290         perform_setup_phase_rwd(0x55);
 291
 292         while(byte_index < bytes) {
 293                 int r = legic_read_byte(byte_index+offset, cmd_sz);
 294                 if(r == -1) {
 295                         Dbprintf("aborting");
 296                         switch_off_tag_rwd();
 297                         return;
 298                 }
 299                 ((uint8_t*)BigBuf)[byte_index] = r;
 300                 byte_index++;
 301         }
 302         switch_off_tag_rwd();
 303         Dbprintf("Card read, use 'hf legic decode' or 'data hexsamples %d' to view results", (bytes+7) & ~7);
 304 }
 305