+static legic_card_select_t card;/* metadata of currently selected card */
+
+//-----------------------------------------------------------------------------
+// Frame timing and pseudorandom number generator
+//
+// The Prng is forwarded every 100us (TAG_BIT_PERIOD), except when the reader is
+// transmitting. In that case the prng has to be forwarded every bit transmitted:
+// - 60us for a 0 (RWD_TIME_0)
+// - 100us for a 1 (RWD_TIME_1)
+//
+// The data dependent timing makes writing comprehensible code significantly
+// harder. The current aproach forwards the prng data based if there is data on
+// air and time based, using GET_TICKS, during computational and wait periodes.
+//
+// To not have the necessity to calculate/guess exection time dependend timeouts
+// tx_frame and rx_frame use a shared timestamp to coordinate tx and rx timeslots.
+//-----------------------------------------------------------------------------
+
+static uint32_t last_frame_end; /* ts of last bit of previews rx or tx frame */
+
+#define RWD_TIME_PAUSE 30 /* 20us */
+#define RWD_TIME_1 150 /* READER_TIME_PAUSE 20us off + 80us on = 100us */
+#define RWD_TIME_0 90 /* READER_TIME_PAUSE 20us off + 40us on = 60us */
+#define RWD_FRAME_WAIT 330 /* 220us from TAG frame end to READER frame start */
+#define TAG_FRAME_WAIT 495 /* 330us from READER frame end to TAG frame start */
+#define TAG_BIT_PERIOD 150 /* 100us */
+#define TAG_WRITE_TIMEOUT 60 /* 40 * 100us (write should take at most 3.6ms) */
+
+#define SIM_DIVISOR 586 /* prng_time/DIV count prng needs to be forwared */
+#define SIM_SHIFT 900 /* prng_time+SHIFT shift of delayed start */
+#define RWD_TIME_FUZZ 20 /* rather generous 13us, since the peak detector
+ /+ hysteresis fuzz quite a bit */
+
+#define LEGIC_READ 0x01 /* Read Command */
+#define LEGIC_WRITE 0x00 /* Write Command */
+
+#define SESSION_IV 0x55 /* An arbitrary chose session IV, all shoud work */
+#define OFFSET_LOG 1024 /* The largest Legic Prime card is 1k */
+#define WRITE_LOWERLIMIT 4 /* UID and MCC are not writable */
+
+#define INPUT_THRESHOLD 8 /* heuristically determined, lower values */
+ /* lead to detecting false ack during write */
+
+#define FUZZ_EQUAL(value, target, fuzz) ((value) > ((target)-(fuzz)) && (value) < ((target)+(fuzz)))
+
+//-----------------------------------------------------------------------------
+// I/O interface abstraction (FPGA -> ARM)
+//-----------------------------------------------------------------------------
+
+static inline uint8_t rx_byte_from_fpga() {
+ for(;;) {
+ WDT_HIT();
+
+ // wait for byte be become available in rx holding register
+ if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
+ return AT91C_BASE_SSC->SSC_RHR;
+ }
+ }
+}
+
+//-----------------------------------------------------------------------------
+// Demodulation (Reader)
+//-----------------------------------------------------------------------------
+
+// Returns a demedulated bit
+//
+// The FPGA running xcorrelation samples the subcarrier at ~13.56 MHz. The mode
+// was initialy designed to receive BSPK/2-PSK. Hance, it reports an I/Q pair
+// every 4.7us (8 bits i and 8 bits q).
+//
+// The subcarrier amplitude can be calculated using Pythagoras sqrt(i^2 + q^2).
+// To reduce CPU time the amplitude is approximated by using linear functions:
+// am = MAX(ABS(i),ABS(q)) + 1/2*MIN(ABS(i),ABSq))
+//
+// Note: The SSC receiver is never synchronized the calculation my be performed
+// on a I/Q pair from two subsequent correlations, but does not matter.
+//
+// The bit time is 99.1us (21 I/Q pairs). The receiver skips the first 5 samples
+// and averages the next (most stable) 8 samples. The final 8 samples are dropped
+// also.
+//
+// The demedulated should be alligned to the bit periode by the caller. This is
+// done in rx_bit_as_reader and rx_ack_as_reader.
+static inline bool rx_bit_as_reader() {
+ int32_t cq = 0;
+ int32_t ci = 0;
+
+ // skip first 5 I/Q pairs
+ for(size_t i = 0; i<5; ++i) {
+ (int8_t)rx_byte_from_fpga();
+ (int8_t)rx_byte_from_fpga();
+ }
+
+ // sample next 8 I/Q pairs
+ for(size_t i = 0; i<8; ++i) {
+ cq += (int8_t)rx_byte_from_fpga();
+ ci += (int8_t)rx_byte_from_fpga();
+ }
+
+ // calculate power
+ int32_t power = (MAX(ABS(ci), ABS(cq)) + (MIN(ABS(ci), ABS(cq)) >> 1));
+
+ // compare average (power / 8) to threshold
+ return ((power >> 3) > INPUT_THRESHOLD);
+}
+
+//-----------------------------------------------------------------------------
+// Modulation (Reader)
+//
+// I've tried to modulate the Legic specific pause-puls using ssc and the default
+// ssc clock of 105.4 kHz (bit periode of 9.4us) - previous commit. However,
+// the timing was not precise enough. By increasing the ssc clock this could
+// be circumvented, but the adventage over bitbang would be little.
+//-----------------------------------------------------------------------------
+
+static inline void tx_bit_as_reader(bool bit) {
+ // insert pause
+ LOW(GPIO_SSC_DOUT);
+ last_frame_end += RWD_TIME_PAUSE;
+ while(GET_TICKS < last_frame_end) { };
+ HIGH(GPIO_SSC_DOUT);
+
+ // return to high, wait for bit periode to end
+ last_frame_end += (bit ? RWD_TIME_1 : RWD_TIME_0) - RWD_TIME_PAUSE;
+ while(GET_TICKS < last_frame_end) { };
+}
+
+//-----------------------------------------------------------------------------
+// Frame Handling (Reader)
+//
+// The LEGIC RF protocol from card to reader does not include explicit frame
+// start/stop information or length information. The reader must know beforehand
+// how many bits it wants to receive.
+// Notably: a card sending a stream of 0-bits is indistinguishable from no card
+// present.
+//-----------------------------------------------------------------------------
+
+static void tx_frame_as_reader(uint32_t frame, uint8_t len) {
+ FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX);
+
+ // wait for next tx timeslot
+ last_frame_end += RWD_FRAME_WAIT;
+ while(GET_TICKS < last_frame_end) { };
+
+ // transmit frame, MSB first
+ for(uint8_t i = 0; i < len; ++i) {
+ bool bit = (frame >> i) & 0x01;
+ tx_bit_as_reader(bit ^ legic_prng_get_bit());
+ legic_prng_forward(1);
+ };
+
+ // add pause to mark end of the frame
+ LOW(GPIO_SSC_DOUT);
+ last_frame_end += RWD_TIME_PAUSE;
+ while(GET_TICKS < last_frame_end) { };
+ HIGH(GPIO_SSC_DOUT);
+}
+
+static uint32_t rx_frame_as_reader(uint8_t len) {
+ FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR
+ | FPGA_HF_READER_RX_XCORR_848_KHZ
+ | FPGA_HF_READER_RX_XCORR_QUARTER_FREQ);
+
+ // hold sampling until card is expected to respond
+ last_frame_end += TAG_FRAME_WAIT;
+ while(GET_TICKS < last_frame_end) { };
+
+ uint32_t frame = 0;
+ for(uint8_t i = 0; i < len; i++) {
+ frame |= (rx_bit_as_reader() ^ legic_prng_get_bit()) << i;
+ legic_prng_forward(1);
+
+ // rx_bit_as_reader runs only 95us, resync to TAG_BIT_PERIOD
+ last_frame_end += TAG_BIT_PERIOD;
+ while(GET_TICKS < last_frame_end) { };
+ }
+
+ return frame;
+}
+
+static bool rx_ack_as_reader() {
+ // change fpga into rx mode
+ FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR
+ | FPGA_HF_READER_RX_XCORR_848_KHZ
+ | FPGA_HF_READER_RX_XCORR_QUARTER_FREQ);
+
+ // hold sampling until card is expected to respond
+ last_frame_end += TAG_FRAME_WAIT;
+ while(GET_TICKS < last_frame_end) { };
+
+ uint32_t ack = 0;
+ for(uint8_t i = 0; i < TAG_WRITE_TIMEOUT; ++i) {
+ // sample bit
+ ack = rx_bit_as_reader();
+ legic_prng_forward(1);
+
+ // rx_bit_as_reader runs only 95us, resync to TAG_BIT_PERIOD
+ last_frame_end += TAG_BIT_PERIOD;
+ while(GET_TICKS < last_frame_end) { };
+
+ // check if it was an ACK
+ if(ack) {
+ break;
+ }
+ }
+
+ return ack;
+}
+
+//-----------------------------------------------------------------------------
+// Legic Reader
+//-----------------------------------------------------------------------------
+
+int init_card(uint8_t cardtype, legic_card_select_t *p_card) {
+ p_card->tagtype = cardtype;
+
+ switch(p_card->tagtype) {
+ case 0x0d:
+ p_card->cmdsize = 6;
+ p_card->addrsize = 5;
+ p_card->cardsize = 22;
+ break;
+ case 0x1d:
+ p_card->cmdsize = 9;
+ p_card->addrsize = 8;
+ p_card->cardsize = 256;
+ break;
+ case 0x3d:
+ p_card->cmdsize = 11;
+ p_card->addrsize = 10;
+ p_card->cardsize = 1024;
+ break;
+ default:
+ p_card->cmdsize = 0;
+ p_card->addrsize = 0;
+ p_card->cardsize = 0;
+ return 2;
+ }
+ return 0;
+}
+
+static void init_reader(bool clear_mem) {
+ // configure FPGA
+ FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
+ FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_RX_XCORR
+ | FPGA_HF_READER_RX_XCORR_848_KHZ
+ | FPGA_HF_READER_RX_XCORR_QUARTER_FREQ);
+ SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
+ LED_D_ON();
+
+ // configure SSC with defaults
+ FpgaSetupSsc();
+
+ // re-claim GPIO_SSC_DOUT as GPIO and enable output
+ AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
+ AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
+ HIGH(GPIO_SSC_DOUT);
+
+ // init crc calculator
+ crc_init(&legic_crc, 4, 0x19 >> 1, 0x05, 0);
+
+ // start us timer
+ StartTicks();
+}
+
+// Setup reader to card connection
+//
+// The setup consists of a three way handshake:
+// - Transmit initialisation vector 7 bits
+// - Receive card type 6 bits
+// - Acknowledge frame 6 bits
+static uint32_t setup_phase_reader(uint8_t iv) {
+ // init coordination timestamp
+ last_frame_end = GET_TICKS;
+
+ // Switch on carrier and let the card charge for 5ms.
+ last_frame_end += 7500;
+ while(GET_TICKS < last_frame_end) { };
+
+ legic_prng_init(0);
+ tx_frame_as_reader(iv, 7);
+
+ // configure iv
+ legic_prng_init(iv);
+ legic_prng_forward(2);
+
+ // receive card type
+ int32_t card_type = rx_frame_as_reader(6);
+ legic_prng_forward(3);
+
+ // send obsfuscated acknowledgment frame
+ switch (card_type) {
+ case 0x0D:
+ tx_frame_as_reader(0x19, 6); // MIM22 | READCMD = 0x18 | 0x01
+ break;
+ case 0x1D:
+ case 0x3D:
+ tx_frame_as_reader(0x39, 6); // MIM256 | READCMD = 0x38 | 0x01
+ break;
+ }
+
+ return card_type;
+}
+
+static uint8_t calc_crc4(uint16_t cmd, uint8_t cmd_sz, uint8_t value) {
+ crc_clear(&legic_crc);
+ crc_update(&legic_crc, (value << cmd_sz) | cmd, 8 + cmd_sz);
+ return crc_finish(&legic_crc);
+}
+
+static int16_t read_byte(uint16_t index, uint8_t cmd_sz) {
+ uint16_t cmd = (index << 1) | LEGIC_READ;
+
+ // read one byte
+ LED_B_ON();
+ legic_prng_forward(2);
+ tx_frame_as_reader(cmd, cmd_sz);
+ legic_prng_forward(2);
+ uint32_t frame = rx_frame_as_reader(12);
+ LED_B_OFF();
+
+ // split frame into data and crc
+ uint8_t byte = BYTEx(frame, 0);
+ uint8_t crc = BYTEx(frame, 1);
+
+ // check received against calculated crc
+ uint8_t calc_crc = calc_crc4(cmd, cmd_sz, byte);
+ if(calc_crc != crc) {
+ Dbprintf("!!! crc mismatch: %x != %x !!!", calc_crc, crc);
+ return -1;
+ }
+
+ legic_prng_forward(1);
+
+ return byte;
+}
+
+// Transmit write command, wait until (3.6ms) the tag sends back an unencrypted
+// ACK ('1' bit) and forward the prng time based.
+bool write_byte(uint16_t index, uint8_t byte, uint8_t addr_sz) {
+ uint32_t cmd = index << 1 | LEGIC_WRITE; // prepare command
+ uint8_t crc = calc_crc4(cmd, addr_sz + 1, byte); // calculate crc
+ cmd |= byte << (addr_sz + 1); // append value
+ cmd |= (crc & 0xF) << (addr_sz + 1 + 8); // and crc
+
+ // send write command
+ LED_C_ON();
+ legic_prng_forward(2);
+ tx_frame_as_reader(cmd, addr_sz + 1 + 8 + 4); // sz = addr_sz + cmd + data + crc
+ legic_prng_forward(3);
+ LED_C_OFF();
+
+ // wait for ack
+ return rx_ack_as_reader();
+}
+
+//-----------------------------------------------------------------------------
+// Command Line Interface
+//
+// Only this functions are public / called from appmain.c
+//-----------------------------------------------------------------------------
+void LegicRfReader(int offset, int bytes) {
+ uint8_t *BigBuf = BigBuf_get_addr();
+ memset(BigBuf, 0, 1024);
+
+ // configure ARM and FPGA
+ init_reader(false);
+
+ // establish shared secret and detect card type
+ DbpString("Reading card ...");
+ uint8_t card_type = setup_phase_reader(SESSION_IV);
+ if(init_card(card_type, &card) != 0) {
+ Dbprintf("No or unknown card found, aborting");
+ goto OUT;
+ }
+
+ // if no argument is specified create full dump
+ if(bytes == -1) {
+ bytes = card.cardsize;
+ }
+
+ // do not read beyond card memory
+ if(bytes + offset > card.cardsize) {
+ bytes = card.cardsize - offset;
+ }
+
+ for(uint16_t i = 0; i < bytes; ++i) {
+ int16_t byte = read_byte(offset + i, card.cmdsize);
+ if(byte == -1) {
+ Dbprintf("operation failed @ 0x%03.3x", bytes);
+ goto OUT;
+ }
+ BigBuf[i] = byte;
+ }
+
+ // OK
+ Dbprintf("Card (MIM %i) read, use 'hf legic decode' or", card.cardsize);
+ Dbprintf("'data hexsamples %d' to view results", (bytes+7) & ~7);
+
+OUT:
+ FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+ LED_B_OFF();
+ LED_C_OFF();
+ LED_D_OFF();
+ StopTicks();
+}
+
+void LegicRfWriter(int bytes, int offset) {
+ uint8_t *BigBuf = BigBuf_get_addr();
+
+ // configure ARM and FPGA
+ init_reader(false);
+
+ // uid is not writeable
+ if(offset <= WRITE_LOWERLIMIT) {
+ goto OUT;
+ }
+
+ // establish shared secret and detect card type
+ Dbprintf("Writing 0x%02.2x - 0x%02.2x ...", offset, offset+bytes);
+ uint8_t card_type = setup_phase_reader(SESSION_IV);
+ if(init_card(card_type, &card) != 0) {
+ Dbprintf("No or unknown card found, aborting");
+ goto OUT;
+ }
+
+ // do not write beyond card memory
+ if(bytes + offset > card.cardsize) {
+ bytes = card.cardsize - offset;
+ }
+
+ // write in reverse order, only then is DCF (decremental field) writable
+ while(bytes-- > 0 && !BUTTON_PRESS()) {
+ if(!write_byte(bytes + offset, BigBuf[bytes], card.addrsize)) {
+ Dbprintf("operation failed @ 0x%03.3x", bytes);
+ goto OUT;
+ }
+ }
+
+ // OK
+ DbpString("Write successful");
+
+OUT:
+ FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+ LED_B_OFF();
+ LED_C_OFF();
+ LED_D_OFF();
+ StopTicks();
+}
+
+//-----------------------------------------------------------------------------
+// Legic Simulator
+//-----------------------------------------------------------------------------
+
projects / proxmark3-svn / commitdiff