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

   1 //-----------------------------------------------------------------------------
   2 // (c) 2009 Henryk Plötz <henryk@ploetzli.ch>
   3 //     2016 Iceman
   4 //     2018 AntiCat
   5 //
   6 // This code is licensed to you under the terms of the GNU GPL, version 2 or,
   7 // at your option, any later version. See the LICENSE.txt file for the text of
   8 // the license.
   9 //-----------------------------------------------------------------------------
  10 // LEGIC RF simulation code
  11 //-----------------------------------------------------------------------------
  12
  13 #include "proxmark3.h"
  14 #include "apps.h"
  15 #include "util.h"
  16 #include "string.h"
  17
  18 #include "legicrf.h"
  19 #include "legic_prng.h"
  20 #include "legic.h"
  21 #include "crc.h"
  22
  23 static legic_card_select_t card;/* metadata of currently selected card */
  24 static crc_t legic_crc;
  25
  26 //-----------------------------------------------------------------------------
  27 // Frame timing and pseudorandom number generator
  28 //
  29 // The Prng is forwarded every 100us (TAG_BIT_PERIOD), except when the reader is
  30 // transmitting. In that case the prng has to be forwarded every bit transmitted:
  31 //  - 60us for a 0 (RWD_TIME_0)
  32 //  - 100us for a 1 (RWD_TIME_1)
  33 //
  34 // The data dependent timing makes writing comprehensible code significantly
  35 // harder. The current aproach forwards the prng data based if there is data on
  36 // air and time based, using GET_TICKS, during computational and wait periodes.
  37 //
  38 // To not have the necessity to calculate/guess exection time dependend timeouts
  39 // tx_frame and rx_frame use a shared timestamp to coordinate tx and rx timeslots.
  40 //-----------------------------------------------------------------------------
  41
  42 static uint32_t last_frame_end; /* ts of last bit of previews rx or tx frame */
  43
  44 #define RWD_TIME_PAUSE       30 /* 20us */
  45 #define RWD_TIME_1          150 /* READER_TIME_PAUSE 20us off + 80us on = 100us */
  46 #define RWD_TIME_0           90 /* READER_TIME_PAUSE 20us off + 40us on = 60us */
  47 #define RWD_FRAME_WAIT      330 /* 220us from TAG frame end to READER frame start */
  48 #define TAG_FRAME_WAIT      495 /* 330us from READER frame end to TAG frame start */
  49 #define TAG_BIT_PERIOD      150 /* 100us */
  50 #define TAG_WRITE_TIMEOUT    60 /* 40 * 100us (write should take at most 3.6ms) */
  51
  52 #define LEGIC_READ         0x01 /* Read Command */
  53 #define LEGIC_WRITE        0x00 /* Write Command */
  54
  55 #define SESSION_IV         0x55 /* An arbitrary chose session IV, all shoud work */
  56 #define OFFSET_LOG         1024 /* The largest Legic Prime card is 1k */
  57 #define WRITE_LOWERLIMIT      4 /* UID and MCC are not writable */
  58
  59 #define INPUT_THRESHOLD       8 /* heuristically determined, lower values */
  60                                 /* lead to detecting false ack during write */
  61
  62 //-----------------------------------------------------------------------------
  63 // I/O interface abstraction (FPGA -> ARM)
  64 //-----------------------------------------------------------------------------
  65
  66 static inline uint8_t rx_byte_from_fpga() {
  67   for(;;) {
  68     WDT_HIT();
  69
  70     // wait for byte be become available in rx holding register
  71     if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
  72       return AT91C_BASE_SSC->SSC_RHR;
  73     }
  74   }
  75 }
  76
  77 //-----------------------------------------------------------------------------
  78 // Demodulation (Reader)
  79 //-----------------------------------------------------------------------------
  80
  81 // Returns a demedulated bit
  82 //
  83 // The FPGA running xcorrelation samples the subcarrier at ~13.56 MHz. The mode
  84 // was initialy designed to receive BSPK/2-PSK. Hance, it reports an I/Q pair
  85 // every 4.7us (8 bits i and 8 bits q).
  86 //
  87 // The subcarrier amplitude can be calculated using Pythagoras sqrt(i^2 + q^2).
  88 // To reduce CPU time the amplitude is approximated by using linear functions:
  89 //   am = MAX(ABS(i),ABS(q)) + 1/2*MIN(ABS(i),ABSq))
  90 //
  91 // Note: The SSC receiver is never synchronized the calculation my be performed
  92 // on a I/Q pair from two subsequent correlations, but does not matter.
  93 //
  94 // The bit time is 99.1us (21 I/Q pairs). The receiver skips the first 5 samples
  95 // and averages the next (most stable) 8 samples. The final 8 samples are dropped
  96 // also.
  97 //
  98 // The demedulated should be alligned to the bit periode by the caller. This is
  99 // done in rx_bit and rx_ack.
 100 static inline bool rx_bit() {
 101   int32_t cq = 0;
 102   int32_t ci = 0;
 103
 104   // skip first 5 I/Q pairs
 105   for(size_t i = 0; i<5; ++i) {
 106     (int8_t)rx_byte_from_fpga();
 107     (int8_t)rx_byte_from_fpga();
 108   }
 109
 110   // sample next 8 I/Q pairs
 111   for(size_t i = 0; i<8; ++i) {
 112     cq += (int8_t)rx_byte_from_fpga();
 113     ci += (int8_t)rx_byte_from_fpga();
 114   }
 115
 116   // calculate power
 117   int32_t power = (MAX(ABS(ci), ABS(cq)) + (MIN(ABS(ci), ABS(cq)) >> 1));
 118
 119   // compare average (power / 8) to threshold
 120   return ((power >> 3) > INPUT_THRESHOLD);
 121 }
 122
 123 //-----------------------------------------------------------------------------
 124 // Modulation (Reader)
 125 //
 126 // I've tried to modulate the Legic specific pause-puls using ssc and the default
 127 // ssc clock of 105.4 kHz (bit periode of 9.4us) - previous commit. However,
 128 // the timing was not precise enough. By increasing the ssc clock this could
 129 // be circumvented, but the adventage over bitbang would be little.
 130 //-----------------------------------------------------------------------------
 131
 132 static inline void tx_bit(bool bit) {
 133   // insert pause
 134   LOW(GPIO_SSC_DOUT);
 135   last_frame_end += RWD_TIME_PAUSE;
 136   while(GET_TICKS < last_frame_end) { };
 137   HIGH(GPIO_SSC_DOUT);
 138
 139   // return to high, wait for bit periode to end
 140   last_frame_end += (bit ? RWD_TIME_1 : RWD_TIME_0) - RWD_TIME_PAUSE;
 141   while(GET_TICKS < last_frame_end) { };
 142 }
 143
 144 //-----------------------------------------------------------------------------
 145 // Frame Handling (Reader)
 146 //
 147 // The LEGIC RF protocol from card to reader does not include explicit frame
 148 // start/stop information or length information. The reader must know beforehand
 149 // how many bits it wants to receive.
 150 // Notably: a card sending a stream of 0-bits is indistinguishable from no card
 151 // present.
 152 //-----------------------------------------------------------------------------
 153
 154 static void tx_frame(uint32_t frame, uint8_t len) {
 155   FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX);
 156
 157   // wait for next tx timeslot
 158   last_frame_end += RWD_FRAME_WAIT;
 159   while(GET_TICKS < last_frame_end) { };
 160
 161   // transmit frame, MSB first
 162   for(uint8_t i = 0; i < len; ++i) {
 163     bool bit = (frame >> i) & 0x01;
 164     tx_bit(bit ^ legic_prng_get_bit());
 165     legic_prng_forward(1);
 166   };
 167
 168   // add pause to mark end of the frame
 169   LOW(GPIO_SSC_DOUT);
 170   last_frame_end += RWD_TIME_PAUSE;
 171   while(GET_TICKS < last_frame_end) { };
 172   HIGH(GPIO_SSC_DOUT);
 173 }
 174
 175 static uint32_t rx_frame(uint8_t len) {
 176   FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR
 177                   | FPGA_HF_READER_RX_XCORR_848_KHZ
 178                   | FPGA_HF_READER_RX_XCORR_QUARTER_FREQ);
 179
 180   // hold sampling until card is expected to respond
 181   last_frame_end += TAG_FRAME_WAIT;
 182   while(GET_TICKS < last_frame_end) { };
 183
 184   uint32_t frame = 0;
 185   for(uint8_t i = 0; i < len; ++i) {
 186     frame |= (rx_bit() ^ legic_prng_get_bit()) << i;
 187     legic_prng_forward(1);
 188
 189     // rx_bit runs only 95us, resync to TAG_BIT_PERIOD
 190     last_frame_end += TAG_BIT_PERIOD;
 191     while(GET_TICKS < last_frame_end) { };
 192   }
 193
 194   return frame;
 195 }
 196
 197 static bool rx_ack() {
 198   // change fpga into rx mode
 199   FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR
 200                   | FPGA_HF_READER_RX_XCORR_848_KHZ
 201                   | FPGA_HF_READER_RX_XCORR_QUARTER_FREQ);
 202
 203   // hold sampling until card is expected to respond
 204   last_frame_end += TAG_FRAME_WAIT;
 205   while(GET_TICKS < last_frame_end) { };
 206
 207   uint32_t ack = 0;
 208   for(uint8_t i = 0; i < TAG_WRITE_TIMEOUT; ++i) {
 209     // sample bit
 210     ack = rx_bit();
 211     legic_prng_forward(1);
 212
 213     // rx_bit runs only 95us, resync to TAG_BIT_PERIOD
 214     last_frame_end += TAG_BIT_PERIOD;
 215     while(GET_TICKS < last_frame_end) { };
 216
 217     // check if it was an ACK
 218     if(ack) {
 219       break;
 220     }
 221   }
 222
 223   return ack;
 224 }
 225
 226 //-----------------------------------------------------------------------------
 227 // Legic Reader
 228 //-----------------------------------------------------------------------------
 229
 230 static int init_card(uint8_t cardtype, legic_card_select_t *p_card) {
 231   p_card->tagtype = cardtype;
 232
 233   switch(p_card->tagtype) {
 234     case 0x0d:
 235       p_card->cmdsize = 6;
 236       p_card->addrsize = 5;
 237       p_card->cardsize = 22;
 238       break;
 239     case 0x1d:
 240       p_card->cmdsize = 9;
 241       p_card->addrsize = 8;
 242       p_card->cardsize = 256;
 243       break;
 244     case 0x3d:
 245       p_card->cmdsize = 11;
 246       p_card->addrsize = 10;
 247       p_card->cardsize = 1024;
 248       break;
 249     default:
 250       p_card->cmdsize = 0;
 251       p_card->addrsize = 0;
 252       p_card->cardsize = 0;
 253       return 2;
 254   }
 255   return 0;
 256 }
 257
 258 static void init_reader(bool clear_mem) {
 259   // configure FPGA
 260   FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
 261   FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR
 262                   | FPGA_HF_READER_RX_XCORR_848_KHZ
 263                   | FPGA_HF_READER_RX_XCORR_QUARTER_FREQ);
 264   SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
 265   LED_D_ON();
 266
 267   // configure SSC with defaults
 268   FpgaSetupSsc();
 269
 270   // re-claim GPIO_SSC_DOUT as GPIO and enable output
 271   AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
 272   AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
 273   HIGH(GPIO_SSC_DOUT);
 274
 275   // init crc calculator
 276   crc_init(&legic_crc, 4, 0x19 >> 1, 0x05, 0);
 277
 278   // start us timer
 279   StartTicks();
 280 }
 281
 282 // Setup reader to card connection
 283 //
 284 // The setup consists of a three way handshake:
 285 //  - Transmit initialisation vector 7 bits
 286 //  - Receive card type 6 bits
 287 //  - Transmit Acknowledge 6 bits
 288 static uint32_t setup_phase(uint8_t iv) {
 289   // init coordination timestamp
 290   last_frame_end = GET_TICKS;
 291
 292   // Switch on carrier and let the card charge for 5ms.
 293   last_frame_end += 7500;
 294   while(GET_TICKS < last_frame_end) { };
 295
 296   legic_prng_init(0);
 297   tx_frame(iv, 7);
 298
 299   // configure prng
 300   legic_prng_init(iv);
 301   legic_prng_forward(2);
 302
 303   // receive card type
 304   int32_t card_type = rx_frame(6);
 305   legic_prng_forward(3);
 306
 307   // send obsfuscated acknowledgment frame
 308   switch (card_type) {
 309     case 0x0D:
 310       tx_frame(0x19, 6); // MIM22 | READCMD = 0x18 | 0x01
 311       break;
 312     case 0x1D:
 313     case 0x3D:
 314       tx_frame(0x39, 6); // MIM256 | READCMD = 0x38 | 0x01
 315       break;
 316   }
 317
 318   return card_type;
 319 }
 320
 321 static uint8_t calc_crc4(uint16_t cmd, uint8_t cmd_sz, uint8_t value) {
 322   crc_clear(&legic_crc);
 323   crc_update(&legic_crc, (value << cmd_sz) | cmd, 8 + cmd_sz);
 324   return crc_finish(&legic_crc);
 325 }
 326
 327 static int16_t read_byte(uint16_t index, uint8_t cmd_sz) {
 328   uint16_t cmd = (index << 1) | LEGIC_READ;
 329
 330   // read one byte
 331   LED_B_ON();
 332   legic_prng_forward(2);
 333   tx_frame(cmd, cmd_sz);
 334   legic_prng_forward(2);
 335   uint32_t frame = rx_frame(12);
 336   LED_B_OFF();
 337
 338   // split frame into data and crc
 339   uint8_t byte = BYTEx(frame, 0);
 340   uint8_t crc = BYTEx(frame, 1);
 341
 342   // check received against calculated crc
 343   uint8_t calc_crc = calc_crc4(cmd, cmd_sz, byte);
 344   if(calc_crc != crc) {
 345     Dbprintf("!!! crc mismatch: %x != %x !!!",  calc_crc, crc);
 346     return -1;
 347   }
 348
 349   legic_prng_forward(1);
 350
 351   return byte;
 352 }
 353
 354 // Transmit write command, wait until (3.6ms) the tag sends back an unencrypted
 355 // ACK ('1' bit) and forward the prng time based.
 356 bool write_byte(uint16_t index, uint8_t byte, uint8_t addr_sz) {
 357   uint32_t cmd = index << 1 | LEGIC_WRITE;          // prepare command
 358   uint8_t  crc = calc_crc4(cmd, addr_sz + 1, byte); // calculate crc
 359   cmd |= byte << (addr_sz + 1);                     // append value
 360   cmd |= (crc & 0xF) << (addr_sz + 1 + 8);          // and crc
 361
 362   // send write command
 363   LED_C_ON();
 364   legic_prng_forward(2);
 365   tx_frame(cmd, addr_sz + 1 + 8 + 4); // sz = addr_sz + cmd + data + crc
 366   legic_prng_forward(3);
 367   LED_C_OFF();
 368
 369   // wait for ack
 370   return rx_ack();
 371 }
 372
 373 //-----------------------------------------------------------------------------
 374 // Command Line Interface
 375 //
 376 // Only this functions are public / called from appmain.c
 377 //-----------------------------------------------------------------------------
 378 void LegicRfReader(int offset, int bytes) {
 379   uint8_t *BigBuf = BigBuf_get_addr();
 380   memset(BigBuf, 0, 1024);
 381
 382   // configure ARM and FPGA
 383   init_reader(false);
 384
 385   // establish shared secret and detect card type
 386   DbpString("Reading card ...");
 387   uint8_t card_type = setup_phase(SESSION_IV);
 388   if(init_card(card_type, &card) != 0) {
 389     Dbprintf("No or unknown card found, aborting");
 390     goto OUT;
 391   }
 392
 393   // if no argument is specified create full dump
 394   if(bytes == -1) {
 395     bytes = card.cardsize;
 396   }
 397
 398   // do not read beyond card memory
 399   if(bytes + offset > card.cardsize) {
 400     bytes = card.cardsize - offset;
 401   }
 402
 403   for(uint16_t i = 0; i < bytes; ++i) {
 404     int16_t byte = read_byte(offset + i, card.cmdsize);
 405     if(byte == -1) {
 406       Dbprintf("operation failed @ 0x%03.3x", bytes);
 407       goto OUT;
 408     }
 409     BigBuf[i] = byte;
 410   }
 411
 412   // OK
 413   Dbprintf("Card (MIM %i) read, use 'hf legic decode' or", card.cardsize);
 414   Dbprintf("'data hexsamples %d' to view results", (bytes+7) & ~7);
 415
 416 OUT:
 417   FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
 418   LED_B_OFF();
 419   LED_C_OFF();
 420   LED_D_OFF();
 421   StopTicks();
 422 }
 423
 424 void LegicRfWriter(int bytes, int offset) {
 425   uint8_t *BigBuf = BigBuf_get_addr();
 426
 427   // configure ARM and FPGA
 428   init_reader(false);
 429
 430   // uid is not writeable
 431   if(offset <= WRITE_LOWERLIMIT) {
 432     goto OUT;
 433   }
 434
 435   // establish shared secret and detect card type
 436   Dbprintf("Writing 0x%02.2x - 0x%02.2x ...", offset, offset+bytes);
 437   uint8_t card_type = setup_phase(SESSION_IV);
 438   if(init_card(card_type, &card) != 0) {
 439     Dbprintf("No or unknown card found, aborting");
 440     goto OUT;
 441   }
 442
 443   // do not write beyond card memory
 444   if(bytes + offset > card.cardsize) {
 445     bytes = card.cardsize - offset;
 446   }
 447
 448   // write in reverse order, only then is DCF (decremental field) writable
 449   while(bytes-- > 0 && !BUTTON_PRESS()) {
 450     if(!write_byte(bytes + offset, BigBuf[bytes + offset], card.addrsize)) {
 451       Dbprintf("operation failed @ 0x%03.3x", bytes);
 452       goto OUT;
 453     }
 454   }
 455
 456   // OK
 457   DbpString("Write successful");
 458
 459 OUT:
 460   FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
 461   LED_B_OFF();
 462   LED_C_OFF();
 463   LED_D_OFF();
 464   StopTicks();
 465 }