+//-----------------------------------------------------------------------------
+// (c) 2009 Henryk Plötz <henryk@ploetzli.ch>
+// 2016 Iceman
+// 2018 AntiCat
+//
+// This code is licensed to you under the terms of the GNU GPL, version 2 or,
+// at your option, any later version. See the LICENSE.txt file for the text of
+// the license.
+//-----------------------------------------------------------------------------
+// LEGIC RF simulation code
+//-----------------------------------------------------------------------------
+
+#include "proxmark3.h"
+#include "apps.h"
+#include "util.h"
+#include "string.h"
+
+#include "legicrfsim.h"
+#include "legic_prng.h"
+#include "legic.h"
+#include "crc.h"
+
+static uint8_t* legic_mem; /* card memory, used for sim */
+static legic_card_select_t card;/* metadata of currently selected card */
+static crc_t legic_crc;
+
+//-----------------------------------------------------------------------------
+// Frame timing and pseudorandom number generator
+//
+// The Prng is forwarded every 99.1us (TAG_BIT_PERIOD), except when the reader is
+// transmitting. In that case the prng has to be forwarded every bit transmitted:
+// - 31.3us for a 0 (RWD_TIME_0)
+// - 99.1us 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 GetCountSspClk(), during computational and wait
+// periodes. SSP Clock is clocked by the FPGA at 212 kHz (subcarrier frequency).
+//
+// 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 TAG_FRAME_WAIT 70 /* 330us from READER frame end to TAG frame start */
+#define TAG_ACK_WAIT 758 /* 3.57ms from READER frame end to TAG write ACK */
+#define TAG_BIT_PERIOD 21 /* 99.1us */
+
+#define RWD_TIME_PAUSE 4 /* 18.9us */
+#define RWD_TIME_1 21 /* RWD_TIME_PAUSE 18.9us off + 80.2us on = 99.1us */
+#define RWD_TIME_0 13 /* RWD_TIME_PAUSE 18.9us off + 42.4us on = 61.3us */
+#define RWD_CMD_TIMEOUT 40 /* 40 * 99.1us (arbitrary value) */
+#define RWD_MIN_FRAME_LEN 6 /* Shortest frame is 6 bits */
+#define RWD_MAX_FRAME_LEN 23 /* Longest frame is 23 bits */
+
+#define RWD_PULSE 1 /* Pulse is signaled with GPIO_SSC_DIN high */
+#define RWD_PAUSE 0 /* Pause is signaled with GPIO_SSC_DIN low */
+
+//-----------------------------------------------------------------------------
+// Demodulation
+//-----------------------------------------------------------------------------
+
+// Returns true if a pulse/pause is received within timeout
+static inline bool wait_for(bool value, const uint32_t timeout) {
+ while((bool)(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_DIN) != value) {
+ if(GetCountSspClk() > timeout) {
+ return false;
+ }
+ }
+ return true;
+}
+
+// Returns a demedulated bit or -1 on code violation
+//
+// rx_bit decodes bits using a thresholds. rx_bit has to be called by as soon as
+// a frame starts (first pause is received). rx_bit checks for a pause up to
+// 18.9us followed by a pulse of 80.2us or 42.4us:
+// - A bit length <18.9us is a code violation
+// - A bit length >80.2us is a 1
+// - A bit length <80.2us is a 0
+// - A bit length >148.6us is a code violation
+static inline int8_t rx_bit() {
+ // backup ts for threshold calculation
+ uint32_t bit_start = last_frame_end;
+
+ // wait for pause to end
+ if(!wait_for(RWD_PULSE, bit_start + RWD_TIME_1*3/2)) {
+ return -1;
+ }
+
+ // wait for next pause
+ if(!wait_for(RWD_PAUSE, bit_start + RWD_TIME_1*3/2)) {
+ return -1;
+ }
+
+ // update bit and frame end
+ last_frame_end = GetCountSspClk();
+
+ // check for code violation (bit to short)
+ if(last_frame_end - bit_start < RWD_TIME_PAUSE) {
+ return -1;
+ }
+
+ // apply threshold (average of RWD_TIME_0 and )
+ return (last_frame_end - bit_start > (RWD_TIME_0 + RWD_TIME_1) / 2);
+}
+
+//-----------------------------------------------------------------------------
+// Modulation
+//
+// LEGIC RF uses a very basic load modulation from card to reader:
+// - Subcarrier on for a 1
+// - Subcarrier off for for a 0
+//
+// The 212kHz subcarrier is generated by the FPGA as well as a mathcing ssp clk.
+// Each bit is transfered in a 99.1us slot and the first timeslot starts 330us
+// after the final 20us pause generated by the reader.
+//-----------------------------------------------------------------------------
+
+// Transmits a bit
+//
+// Note: The Subcarrier is not disabled during bits to prevent glitches. This is
+// not mandatory but results in a cleaner signal. tx_frame will disable
+// the subcarrier when the frame is done.
+static inline void tx_bit(bool bit) {
+ LED_C_ON();
+
+ if(bit) {
+ // modulate subcarrier
+ HIGH(GPIO_SSC_DOUT);
+ } else {
+ // do not modulate subcarrier
+ LOW(GPIO_SSC_DOUT);
+ }
+
+ // wait for tx timeslot to end
+ last_frame_end += TAG_BIT_PERIOD;
+ while(GetCountSspClk() < last_frame_end) { };
+ LED_C_OFF();
+}
+
+//-----------------------------------------------------------------------------
+// Frame Handling
+//
+// The LEGIC RF protocol from reader to card does not include explicit frame
+// start/stop information or length information. The tag detects end of frame
+// trough an extended pulse (>99.1us) without a pause.
+// In reverse direction (card to reader) the number of bites is well known
+// and depends only the command received (IV, ACK, READ or WRITE).
+//-----------------------------------------------------------------------------
+
+static void tx_frame(uint32_t frame, uint8_t len) {
+ // wait for next tx timeslot
+ last_frame_end += TAG_FRAME_WAIT;
+ legic_prng_forward(TAG_FRAME_WAIT/TAG_BIT_PERIOD - 1);
+ while(GetCountSspClk() < last_frame_end) { };
+
+ // transmit frame, MSB first
+ for(uint8_t i = 0; i < len; ++i) {
+ bool bit = (frame >> i) & 0x01;
+ tx_bit(bit ^ legic_prng_get_bit());
+ legic_prng_forward(1);
+ };
+
+ // disable subcarrier
+ LOW(GPIO_SSC_DOUT);
+}
+
+static void tx_ack() {
+ // wait for ack timeslot
+ last_frame_end += TAG_ACK_WAIT;
+ legic_prng_forward(TAG_ACK_WAIT/TAG_BIT_PERIOD - 1);
+ while(GetCountSspClk() < last_frame_end) { };
+
+ // transmit ack (ack is not encrypted)
+ tx_bit(true);
+ legic_prng_forward(1);
+
+ // disable subcarrier
+ LOW(GPIO_SSC_DOUT);
+}
+
+// Returns a demedulated frame or -1 on code violation
+//
+// Since TX to RX delay is arbitrary rx_frame has to:
+// - detect start of frame (first pause)
+// - forward prng based on ts/TAG_BIT_PERIOD
+// - receive the frame
+// - detect end of frame (last pause)
+static int32_t rx_frame(uint8_t *len) {
+ int32_t frame = 0;
+
+ // add 2 SSP clock cycles (1 for tx and 1 for rx pipeline delay)
+ // those will be substracted at the end of the rx phase
+ last_frame_end -= 2;
+
+ // wait for first pause (start of frame)
+ for(uint8_t i = 0; true; ++i) {
+ // increment prng every TAG_BIT_PERIOD
+ last_frame_end += TAG_BIT_PERIOD;
+ legic_prng_forward(1);
+
+ // if start of frame was received exit delay loop
+ if(wait_for(RWD_PAUSE, last_frame_end)) {
+ last_frame_end = GetCountSspClk();
+ break;
+ }
+
+ // check for code violation
+ if(i > RWD_CMD_TIMEOUT) {
+ return -1;
+ }
+ }
+
+ // receive frame
+ for(*len = 0; true; ++(*len)) {
+ // receive next bit
+ LED_D_ON();
+ int8_t bit = rx_bit();
+ LED_D_OFF();
+
+ // check for code violation and to short / long frame
+ if((bit < 0) && ((*len < RWD_MIN_FRAME_LEN) || (*len > RWD_MAX_FRAME_LEN))) {
+ return -1;
+ }
+
+ // check for code violation caused by end of frame
+ if(bit < 0) {
+ break;
+ }
+
+ // append bit
+ frame |= (bit ^ legic_prng_get_bit()) << (*len);
+ legic_prng_forward(1);
+ }
+
+ // rx_bit sets coordination timestamp to start of pause, append pause duration
+ // and substract 2 SSP clock cycles (1 for rx and 1 for tx pipeline delay) to
+ // obtain exact end of frame.
+ last_frame_end += RWD_TIME_PAUSE - 2;
+
+ return frame;
+}
+
+//-----------------------------------------------------------------------------
+// Legic Simulator
+//-----------------------------------------------------------------------------
+
+static int32_t init_card(uint8_t cardtype, legic_card_select_t *p_card) {
+ p_card->tagtype = cardtype;
+
+ switch(p_card->tagtype) {
+ case 0:
+ p_card->cmdsize = 6;
+ p_card->addrsize = 5;
+ p_card->cardsize = 22;
+ break;
+ case 1:
+ p_card->cmdsize = 9;
+ p_card->addrsize = 8;
+ p_card->cardsize = 256;
+ break;
+ case 2:
+ 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_tag() {
+ // configure FPGA
+ FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
+ FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_SIMULATOR
+ | FPGA_HF_SIMULATOR_MODULATE_212K);
+ SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
+
+ // configure SSC with defaults
+ FpgaSetupSsc();
+
+ // first pull output to low to prevent glitches then re-claim GPIO_SSC_DOUT
+ LOW(GPIO_SSC_DOUT);
+ AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
+ AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
+
+ // reserve a cardmem, meaning we can use the tracelog function in bigbuff easier.
+ legic_mem = BigBuf_get_addr();
+
+ // init crc calculator
+ crc_init(&legic_crc, 4, 0x19 >> 1, 0x05, 0);
+
+ // start 212kHz timer (running from SSP Clock)
+ StartCountSspClk();
+}
+
+// Setup reader to card connection
+//
+// The setup consists of a three way handshake:
+// - Receive initialisation vector 7 bits
+// - Transmit card type 6 bits
+// - Receive Acknowledge 6 bits
+static int32_t setup_phase(legic_card_select_t *p_card) {
+ uint8_t len = 0;
+
+ // init coordination timestamp
+ last_frame_end = GetCountSspClk();
+
+ // reset prng
+ legic_prng_init(0);
+
+ // wait for iv
+ int32_t iv = rx_frame(&len);
+ if((len != 7) || (iv < 0)) {
+ return -1;
+ }
+
+ // configure prng
+ legic_prng_init(iv);
+
+ // reply with card type
+ switch(p_card->tagtype) {
+ case 0:
+ tx_frame(0x0D, 6);
+ break;
+ case 1:
+ tx_frame(0x1D, 6);
+ break;
+ case 2:
+ tx_frame(0x3D, 6);
+ break;
+ }
+
+ // wait for ack
+ int32_t ack = rx_frame(&len);
+ if((len != 6) || (ack < 0)) {
+ return -1;
+ }
+
+ // validate data
+ switch(p_card->tagtype) {
+ case 0:
+ if(ack != 0x19) return -1;
+ break;
+ case 1:
+ if(ack != 0x39) return -1;
+ break;
+ case 2:
+ if(ack != 0x39) return -1;
+ break;
+ }
+
+ // During rx the prng is clocked using the variable reader period.
+ // Since rx_frame detects end of frame by detecting a code violation,
+ // the prng is off by one bit period after each rx phase. Hence, tx
+ // code advances the prng by (TAG_FRAME_WAIT/TAG_BIT_PERIOD - 1).
+ // This is not possible for back to back rx, so this quirk reduces
+ // the gap by one period.
+ last_frame_end += TAG_BIT_PERIOD;
+
+ return 0;
+}
+
+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 int32_t connected_phase(legic_card_select_t *p_card) {
+ uint8_t len = 0;
+
+ // wait for command
+ int32_t cmd = rx_frame(&len);
+ if(cmd < 0) {
+ return -1;
+ }
+
+ // check if command is LEGIC_READ
+ if(len == p_card->cmdsize) {
+ // prepare data
+ uint8_t byte = legic_mem[cmd >> 1];
+ uint8_t crc = calc_crc4(cmd, p_card->cmdsize, byte);
+
+ // transmit data
+ tx_frame((crc << 8) | byte, 12);
+
+ return 0;
+ }
+
+ // check if command is LEGIC_WRITE
+ if(len == p_card->cmdsize + 8 + 4) {
+ // decode data
+ uint16_t mask = (1 << p_card->addrsize) - 1;
+ uint16_t addr = (cmd >> 1) & mask;
+ uint8_t byte = (cmd >> p_card->cmdsize) & 0xff;
+ uint8_t crc = (cmd >> (p_card->cmdsize + 8)) & 0xf;
+
+ // check received against calculated crc
+ uint8_t calc_crc = calc_crc4(addr << 1, p_card->cmdsize, byte);
+ if(calc_crc != crc) {
+ Dbprintf("!!! crc mismatch: %x != %x !!!", calc_crc, crc);
+ return -1;
+ }
+
+ // store data
+ legic_mem[addr] = byte;
+
+ // transmit ack
+ tx_ack();
+
+ return 0;
+ }
+
+ return -1;
+}
+
+//-----------------------------------------------------------------------------
+// Command Line Interface
+//
+// Only this function is public / called from appmain.c
+//-----------------------------------------------------------------------------
+
+void LegicRfSimulate(uint8_t cardtype) {
+ // configure ARM and FPGA
+ init_tag();
+
+ // verify command line input
+ if(init_card(cardtype, &card) != 0) {
+ DbpString("Unknown tagtype.");
+ goto OUT;
+ }
+
+ LED_A_ON();
+ DbpString("Starting Legic emulator, press button to end");
+ while(!BUTTON_PRESS()) {
+ WDT_HIT();
+
+ // wait for carrier, restart after timeout
+ if(!wait_for(RWD_PULSE, GetCountSspClk() + TAG_BIT_PERIOD)) {
+ continue;
+ }
+
+ // wait for connection, restart on error
+ if(setup_phase(&card)) {
+ continue;
+ }
+
+ // conection is established, process commands until one fails
+ while(!connected_phase(&card)) {
+ WDT_HIT();
+ }
+ }
+
+OUT:
+ DbpString("Stopped");
+ FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+ LED_A_OFF();
+ LED_C_OFF();
+ LED_D_OFF();
+ StopTicks();
+}
projects / proxmark3-svn / commitdiff