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 "unistd.h"
  12 #include "stdint.h"
  13
  14 #include "legic_prng.h"
  15 #include "crc.h"
  16
  17 static struct legic_frame {
  18         int bits;
  19         uint16_t data;
  20 } current_frame;
  21
  22 static crc_t legic_crc;
  23
  24 AT91PS_TC timer;
  25
  26 static void setup_timer(void)
  27 {
  28         /* Set up Timer 1 to use for measuring time between pulses. Since we're bit-banging
  29          * this it won't be terribly accurate but should be good enough.
  30          */
  31         AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC1);
  32         timer = AT91C_BASE_TC1;
  33         timer->TC_CCR = AT91C_TC_CLKDIS;
  34         timer->TC_CMR = TC_CMR_TCCLKS_TIMER_CLOCK3;
  35         timer->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
  36
  37 /* At TIMER_CLOCK3 (MCK/32) */
  38 #define RWD_TIME_1 150     /* RWD_TIME_PAUSE off, 80us on = 100us */
  39 #define RWD_TIME_0 90      /* RWD_TIME_PAUSE off, 40us on = 60us */
  40 #define RWD_TIME_PAUSE 30  /* 20us */
  41 #define RWD_TIME_FUZZ 20   /* rather generous 13us, since the peak detector + hysteresis fuzz quite a bit */
  42 #define TAG_TIME_BIT 150   /* 100us for every bit */
  43 #define TAG_TIME_WAIT 490  /* time from RWD frame end to tag frame start, experimentally determined */
  44
  45 }
  46
  47 #define FUZZ_EQUAL(value, target, fuzz) ((value) > ((target)-(fuzz)) && (value) < ((target)+(fuzz)))
  48
  49 /* Send a frame in reader mode, the FPGA must have been set up by
  50  * LegicRfReader
  51  */
  52 static void frame_send_rwd(uint32_t data, int bits)
  53 {
  54         /* Start clock */
  55         timer->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
  56         while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
  57
  58         int i;
  59         for(i=0; i<bits; i++) {
  60                 int starttime = timer->TC_CV;
  61                 int pause_end = starttime + RWD_TIME_PAUSE, bit_end;
  62                 int bit = data & 1;
  63                 data = data >> 1;
  64
  65                 if(bit ^ legic_prng_get_bit()) {
  66                         bit_end = starttime + RWD_TIME_1;
  67                 } else {
  68                         bit_end = starttime + RWD_TIME_0;
  69                 }
  70
  71                 /* RWD_TIME_PAUSE time off, then some time on, so that the complete bit time is
  72                  * RWD_TIME_x, where x is the bit to be transmitted */
  73                 AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
  74                 while(timer->TC_CV < pause_end) ;
  75                 AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
  76                 legic_prng_forward(1); /* bit duration is longest. use this time to forward the lfsr */
  77
  78                 while(timer->TC_CV < bit_end) ;
  79         }
  80
  81         {
  82                 /* One final pause to mark the end of the frame */
  83                 int pause_end = timer->TC_CV + RWD_TIME_PAUSE;
  84                 AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
  85                 while(timer->TC_CV < pause_end) ;
  86                 AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
  87         }
  88
  89         /* Reset the timer, to measure time until the start of the tag frame */
  90         timer->TC_CCR = AT91C_TC_SWTRG;
  91         while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
  92 }
  93
  94 /* Receive a frame from the card in reader emulation mode, the FPGA and
  95  * timer must have been set up by LegicRfReader and frame_send_rwd.
  96  *
  97  * The LEGIC RF protocol from card to reader does not include explicit
  98  * frame start/stop information or length information. The reader must
  99  * know beforehand how many bits it wants to receive. (Notably: a card
 100  * sending a stream of 0-bits is indistinguishable from no card present.)
 101  *
 102  * Receive methodology: There is a fancy correlator in hi_read_rx_xcorr, but
 103  * I'm not smart enough to use it. Instead I have patched hi_read_tx to output
 104  * the ADC signal with hysteresis on SSP_DIN. Bit-bang that signal and look
 105  * for edges. Count the edges in each bit interval. If they are approximately
 106  * 0 this was a 0-bit, if they are approximately equal to the number of edges
 107  * expected for a 212kHz subcarrier, this was a 1-bit. For timing we use the
 108  * timer that's still running from frame_send_rwd in order to get a synchronization
 109  * with the frame that we just sent.
 110  *
 111  * FIXME: Because we're relying on the hysteresis to just do the right thing
 112  * the range is severely reduced (and you'll probably also need a good antenna).
 113  * So this should be fixed some time in the future for a proper receiver.
 114  */
 115 static void frame_receive_rwd(struct legic_frame * const f, int bits, int crypt)
 116 {
 117         uint16_t the_bit = 1;  /* Use a bitmask to save on shifts */
 118         uint16_t data=0;
 119         int i, old_level=0, edges=0;
 120         int next_bit_at = TAG_TIME_WAIT;
 121
 122
 123         if(bits > 16)
 124                 bits = 16;
 125
 126         AT91C_BASE_PIOA->PIO_ODR = GPIO_SSC_DIN;
 127         AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DIN;
 128
 129         /* we have some time now, precompute the cipher
 130          * since we cannot compute it on the fly while reading */
 131         legic_prng_forward(2);
 132
 133         if(crypt)
 134         {
 135                 for(i=0; i<bits; i++) {
 136                         data |= legic_prng_get_bit() << i;
 137                         legic_prng_forward(1);
 138                 }
 139         }
 140
 141         while(timer->TC_CV < next_bit_at) ;
 142
 143         next_bit_at += TAG_TIME_BIT;
 144
 145         for(i=0; i<bits; i++) {
 146                 edges = 0;
 147
 148                 while(timer->TC_CV < next_bit_at) {
 149                         int level = (AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_DIN);
 150                         if(level != old_level)
 151                                 edges++;
 152                         old_level = level;
 153                 }
 154                 next_bit_at += TAG_TIME_BIT;
 155
 156                 if(edges > 20 && edges < 60) { /* expected are 42 edges */
 157                         data ^= the_bit;
 158                 }
 159
 160                 the_bit <<= 1;
 161         }
 162
 163         f->data = data;
 164         f->bits = bits;
 165
 166         /* Reset the timer, to synchronize the next frame */
 167         timer->TC_CCR = AT91C_TC_SWTRG;
 168         while(timer->TC_CV > 1) ; /* Wait till the clock has reset */
 169 }
 170
 171 static void frame_clean(struct legic_frame * const f)
 172 {
 173         f->data = 0;
 174         f->bits = 0;
 175 }
 176
 177 static uint16_t perform_setup_phase_rwd(int iv)
 178 {
 179
 180         /* Switch on carrier and let the tag charge for 1ms */
 181         AT91C_BASE_PIOA->PIO_SODR = GPIO_SSC_DOUT;
 182         SpinDelay(1);
 183
 184         legic_prng_init(0); /* no keystream yet */
 185         frame_send_rwd(iv, 7);
 186         legic_prng_init(iv);
 187
 188         frame_clean(&current_frame);
 189         frame_receive_rwd(&current_frame, 6, 1);
 190         legic_prng_forward(1); /* we wait anyways */
 191         while(timer->TC_CV < 387) ; /* ~ 258us */
 192         frame_send_rwd(0x19, 6);
 193
 194         if(current_frame.data != 0x1d)
 195                 Dbprintf("probably don't know how to deal with %x card", current_frame.data);
 196         return current_frame.data;
 197 }
 198
 199 static void LegicCommonInit(void) {
 200         SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
 201         FpgaSetupSsc();
 202         FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX);
 203
 204         /* Bitbang the transmitter */
 205         AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
 206         AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
 207         AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
 208
 209         setup_timer();
 210
 211         crc_init(&legic_crc, 4, 0x19 >> 1, 0x5, 0);
 212 }
 213
 214 static void switch_off_tag_rwd(void)
 215 {
 216         /* Switch off carrier, make sure tag is reset */
 217         AT91C_BASE_PIOA->PIO_CODR = GPIO_SSC_DOUT;
 218         SpinDelay(10);
 219
 220         WDT_HIT();
 221 }
 222 /* calculate crc for a legic command */
 223 static int LegicCRC(int byte_index, int value) {
 224         crc_clear(&legic_crc);
 225         crc_update(&legic_crc, 1, 1); /* CMD_READ */
 226         crc_update(&legic_crc, byte_index, 8);
 227         crc_update(&legic_crc, value, 8);
 228         return crc_finish(&legic_crc);
 229 }
 230
 231 int legic_read_byte(int byte_index) {
 232         int byte;
 233
 234         legic_prng_forward(4); /* we wait anyways */
 235         while(timer->TC_CV < 387) ; /* ~ 258us + 100us*delay */
 236
 237         frame_send_rwd(1 | (byte_index << 1), 9);
 238         frame_clean(&current_frame);
 239
 240         frame_receive_rwd(&current_frame, 12, 1);
 241
 242         byte = current_frame.data & 0xff;
 243         if( LegicCRC(byte_index, byte) != (current_frame.data >> 8) )
 244                 Dbprintf("!!! crc mismatch: expected %x but got %x !!!", LegicCRC(byte_index, current_frame.data & 0xff), current_frame.data >> 8);
 245
 246         return byte;
 247 }
 248
 249 /* legic_write_byte() is not included, however it's trivial to implement
 250  * and here are some hints on what remains to be done:
 251  *
 252  *  * assemble a write_cmd_frame with crc and send it
 253  *  * wait until the tag sends back an ACK ('1' bit unencrypted)
 254  *  * forward the prng based on the timing
 255  */
 256
 257
 258 void LegicRfReader(int offset, int bytes) {
 259         int byte_index=0;
 260
 261         LegicCommonInit();
 262
 263         memset(BigBuf, 0, 256);
 264
 265         DbpString("setting up legic card");
 266         perform_setup_phase_rwd(0x55);
 267
 268         while(byte_index < bytes) {
 269                 ((uint8_t*)BigBuf)[byte_index] = legic_read_byte(byte_index+offset);
 270                 byte_index++;
 271         }
 272         switch_off_tag_rwd();
 273         Dbprintf("Card read, use 'data hexsamples %d' to view results", (bytes+7) & ~7);
 274 }