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proxmark3/armsrc/em4x70.c

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//-----------------------------------------------------------------------------
// Copyright (C) 2020 sirloins based on em4x50
//
// 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.
//-----------------------------------------------------------------------------
// Low frequency EM4170 commands
//-----------------------------------------------------------------------------
#include "fpgaloader.h"
#include "ticks.h"
#include "dbprint.h"
#include "lfadc.h"
#include "commonutil.h"
#include "em4x70.h"
#include "appmain.h" // tear
static em4x70_tag_t tag = { 0 };
// EM4170 requires a parity bit on commands, other variants do not.
static bool command_parity = true;
// Conversion from Ticks to RF periods
// 1 us = 1.5 ticks
// 1RF Period = 8us = 12 Ticks
#define TICKS_PER_FC 12
// Chip timing from datasheet
// Converted into Ticks for timing functions
#define EM4X70_T_TAG_QUARTER_PERIOD (8 * TICKS_PER_FC)
#define EM4X70_T_TAG_HALF_PERIOD (16 * TICKS_PER_FC)
#define EM4X70_T_TAG_THREE_QUARTER_PERIOD (24 * TICKS_PER_FC)
#define EM4X70_T_TAG_FULL_PERIOD (32 * TICKS_PER_FC) // 1 Bit Period
#define EM4X70_T_TAG_TWA (128 * TICKS_PER_FC) // Write Access Time
#define EM4X70_T_TAG_DIV (224 * TICKS_PER_FC) // Divergency Time
#define EM4X70_T_TAG_AUTH (4224 * TICKS_PER_FC) // Authentication Time
#define EM4X70_T_TAG_WEE (3072 * TICKS_PER_FC) // EEPROM write Time
#define EM4X70_T_TAG_TWALB (672 * TICKS_PER_FC) // Write Access Time of Lock Bits
#define EM4X70_T_TAG_BITMOD (4 * TICKS_PER_FC) // Initial time to stop modulation when sending 0
#define EM4X70_T_TAG_TOLERANCE (8 * TICKS_PER_FC) // Tolerance in RF periods for receive/LIW
#define EM4X70_T_TAG_TIMEOUT (4 * EM4X70_T_TAG_FULL_PERIOD) // Timeout if we ever get a pulse longer than this
#define EM4X70_T_WAITING_FOR_LIW 50 // Pulses to wait for listen window
#define EM4X70_T_READ_HEADER_LEN 16 // Read header length (16 bit periods)
#define EM4X70_COMMAND_RETRIES 5 // Attempts to send/read command
#define EM4X70_MAX_RECEIVE_LENGTH 96 // Maximum bits to expect from any command
/**
* These IDs are from the EM4170 datasheet
* Some versions of the chip require a
* (even) parity bit, others do not
*/
#define EM4X70_COMMAND_ID 0x01
#define EM4X70_COMMAND_UM1 0x02
#define EM4X70_COMMAND_AUTH 0x03
#define EM4X70_COMMAND_PIN 0x04
#define EM4X70_COMMAND_WRITE 0x05
#define EM4X70_COMMAND_UM2 0x07
// Constants used to determing high/low state of signal
#define EM4X70_NOISE_THRESHOLD 13 // May depend on noise in environment
#define HIGH_SIGNAL_THRESHOLD (127 + EM4X70_NOISE_THRESHOLD)
#define LOW_SIGNAL_THRESHOLD (127 - EM4X70_NOISE_THRESHOLD)
#define IS_HIGH(sample) (sample > LOW_SIGNAL_THRESHOLD ? true : false)
#define IS_LOW(sample) (sample < HIGH_SIGNAL_THRESHOLD ? true : false)
// Timing related macros
#define IS_TIMEOUT(timeout_ticks) (GetTicks() > timeout_ticks)
#define TICKS_ELAPSED(start_ticks) (GetTicks() - start_ticks)
static uint8_t bits2byte(const uint8_t *bits, int length);
static void bits2bytes(const uint8_t *bits, int length, uint8_t *out);
static int em4x70_receive(uint8_t *bits, size_t length);
static bool find_listen_window(bool command);
static void init_tag(void) {
memset(tag.data, 0x00, sizeof(tag.data) / sizeof(tag.data[0]));
}
static void em4x70_setup_read(void) {
FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_ADC | FPGA_LF_ADC_READER_FIELD);
// 50ms for the resonant antenna to settle.
SpinDelay(50);
// Now set up the SSC to get the ADC samples that are now streaming at us.
FpgaSetupSsc(FPGA_MAJOR_MODE_LF_READER);
FpgaSendCommand(FPGA_CMD_SET_DIVISOR, LF_DIVISOR_125);
// Connect the A/D to the peak-detected low-frequency path.
SetAdcMuxFor(GPIO_MUXSEL_LOPKD);
// Steal this pin from the SSP (SPI communication channel with fpga) and
// use it to control the modulation
AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
// Disable modulation at default, which means enable the field
LOW(GPIO_SSC_DOUT);
// Start the timer
StartTicks();
// Watchdog hit
WDT_HIT();
}
static bool get_signalproperties(void) {
// Simple check to ensure we see a signal above the noise threshold
uint32_t no_periods = 32;
// wait until signal/noise > 1 (max. 32 periods)
for (int i = 0; i < EM4X70_T_TAG_FULL_PERIOD * no_periods; i++) {
// about 2 samples per bit period
WaitTicks(EM4X70_T_TAG_HALF_PERIOD);
if (AT91C_BASE_SSC->SSC_RHR > HIGH_SIGNAL_THRESHOLD) {
return true;
}
}
return false;
}
/**
* get_falling_pulse_length
*
* Returns time between falling edge pulse in ticks
*/
static uint32_t get_falling_pulse_length(void) {
uint32_t timeout = GetTicks() + EM4X70_T_TAG_TIMEOUT;
while (IS_HIGH(AT91C_BASE_SSC->SSC_RHR) && !IS_TIMEOUT(timeout));
if (IS_TIMEOUT(timeout))
return 0;
uint32_t start_ticks = GetTicks();
while (IS_LOW(AT91C_BASE_SSC->SSC_RHR) && !IS_TIMEOUT(timeout));
if (IS_TIMEOUT(timeout))
return 0;
while (IS_HIGH(AT91C_BASE_SSC->SSC_RHR) && !IS_TIMEOUT(timeout));
if (IS_TIMEOUT(timeout))
return 0;
return TICKS_ELAPSED(start_ticks);
}
/**
* get_rising_pulse_length
*
* Returns time between rising edge pulse in ticks
*/
static uint32_t get_rising_pulse_length(void) {
uint32_t timeout = GetTicks() + EM4X70_T_TAG_TIMEOUT;
while (IS_LOW(AT91C_BASE_SSC->SSC_RHR) && !IS_TIMEOUT(timeout));
if (IS_TIMEOUT(timeout))
return 0;
uint32_t start_ticks = GetTicks();
while (IS_HIGH(AT91C_BASE_SSC->SSC_RHR) && !IS_TIMEOUT(timeout));
if (IS_TIMEOUT(timeout))
return 0;
while (IS_LOW(AT91C_BASE_SSC->SSC_RHR) && !IS_TIMEOUT(timeout));
if (IS_TIMEOUT(timeout))
return 0;
return TICKS_ELAPSED(start_ticks);
}
static uint32_t get_pulse_length(edge_detection_t edge) {
if(edge == RISING_EDGE)
return get_rising_pulse_length();
else if(edge == FALLING_EDGE)
return get_falling_pulse_length();
return 0;
}
static bool check_pulse_length(uint32_t pl, uint32_t length) {
// check if pulse length <pl> corresponds to given length <length>
return ((pl >= (length - EM4X70_T_TAG_TOLERANCE)) & (pl <= (length + EM4X70_T_TAG_TOLERANCE)));
}
static void em4x70_send_bit(bool bit) {
// send single bit according to EM4170 application note and datasheet
uint32_t start_ticks = GetTicks();
if (bit == 0) {
// disable modulation (drop the field) n cycles of carrier
LOW(GPIO_SSC_DOUT);
while (TICKS_ELAPSED(start_ticks) <= EM4X70_T_TAG_BITMOD);
// enable modulation (activates the field) for remaining first
// half of bit period
HIGH(GPIO_SSC_DOUT);
while (TICKS_ELAPSED(start_ticks) <= EM4X70_T_TAG_HALF_PERIOD);
// disable modulation for second half of bit period
LOW(GPIO_SSC_DOUT);
while (TICKS_ELAPSED(start_ticks) <= EM4X70_T_TAG_FULL_PERIOD);
} else {
// bit = "1" means disable modulation for full bit period
LOW(GPIO_SSC_DOUT);
while (TICKS_ELAPSED(start_ticks) <= EM4X70_T_TAG_FULL_PERIOD);
}
}
/**
* em4x70_send_nibble
*
* sends 4 bits of data + 1 bit of parity (with_parity)
*
*/
static void em4x70_send_nibble(uint8_t nibble, bool with_parity) {
int parity = 0;
int msb_bit = 0;
// Non automotive EM4x70 based tags are 3 bits + 1 parity.
// So drop the MSB and send a parity bit instead after the command
if (command_parity)
msb_bit = 1;
for (int i = msb_bit; i < 4; i++) {
int bit = (nibble >> (3 - i)) & 1;
em4x70_send_bit(bit);
parity ^= bit;
}
if (with_parity)
em4x70_send_bit(parity);
}
static void em4x70_send_byte(uint8_t byte) {
// Send byte msb first
for (int i = 0; i < 8; i++)
em4x70_send_bit((byte >> (7 - i)) & 1);
}
static void em4x70_send_word(const uint16_t word) {
// Split into nibbles
uint8_t nibbles[4];
uint8_t j = 0;
for (int i = 0; i < 2; i++) {
uint8_t byte = (word >> (8 * i)) & 0xff;
nibbles[j++] = (byte >> 4) & 0xf;
nibbles[j++] = byte & 0xf;
}
// send 16 bit word with parity bits according to EM4x70 datasheet
// sent as 4 x nibbles (4 bits + parity)
for (int i = 0; i < 4; i++) {
em4x70_send_nibble(nibbles[i], true);
}
// send column parities (4 bit)
em4x70_send_nibble(nibbles[0] ^ nibbles[1] ^ nibbles[2] ^ nibbles[3], false);
// send final stop bit (always "0")
em4x70_send_bit(0);
}
static bool check_ack(void) {
// returns true if signal structue corresponds to ACK, anything else is
// counted as NAK (-> false)
// ACK 64 + 64
// NACK 64 + 48
if (check_pulse_length(get_pulse_length(FALLING_EDGE), 2 * EM4X70_T_TAG_FULL_PERIOD) &&
check_pulse_length(get_pulse_length(FALLING_EDGE), 2 * EM4X70_T_TAG_FULL_PERIOD)) {
// ACK
return true;
}
// Othewise it was a NACK or Listen Window
return false;
}
static int authenticate(const uint8_t *rnd, const uint8_t *frnd, uint8_t *response) {
if (find_listen_window(true)) {
em4x70_send_nibble(EM4X70_COMMAND_AUTH, true);
// Send 56-bit Random number
for (int i = 0; i < 7; i++) {
em4x70_send_byte(rnd[i]);
}
// Send 7 x 0's (Diversity bits)
for (int i = 0; i < 7; i++) {
em4x70_send_bit(0);
}
// Send 28-bit f(RN)
// Send first 24 bits
for (int i = 0; i < 3; i++) {
em4x70_send_byte(frnd[i]);
}
// Send last 4 bits (no parity)
em4x70_send_nibble((frnd[3] >> 4) & 0xf, false);
// Receive header, 20-bit g(RN), LIW
uint8_t grnd[EM4X70_MAX_RECEIVE_LENGTH] = {0};
int num = em4x70_receive(grnd, 20);
if (num < 20) {
Dbprintf("Auth failed");
return PM3_ESOFT;
}
bits2bytes(grnd, 24, response);
return PM3_SUCCESS;
}
return PM3_ESOFT;
}
static int send_pin(const uint32_t pin) {
// sends pin code for unlocking
if (find_listen_window(true)) {
// send PIN command
em4x70_send_nibble(EM4X70_COMMAND_PIN, true);
// --> Send TAG ID (bytes 4-7)
for (int i = 0; i < 4; i++) {
em4x70_send_byte(tag.data[7 - i]);
}
// --> Send PIN
for (int i = 0; i < 4 ; i++) {
em4x70_send_byte((pin >> (i * 8)) & 0xff);
}
// Wait TWALB (write access lock bits)
WaitTicks(EM4X70_T_TAG_TWALB);
// <-- Receive ACK
if (check_ack()) {
// <w> Writes Lock Bits
WaitTicks(EM4X70_T_TAG_WEE);
// <-- Receive header + ID
uint8_t tag_id[EM4X70_MAX_RECEIVE_LENGTH];
int num = em4x70_receive(tag_id, 32);
if (num < 32) {
Dbprintf("Invalid ID Received");
return PM3_ESOFT;
}
bits2bytes(tag_id, num, &tag.data[4]);
return PM3_SUCCESS;
}
}
return PM3_ESOFT;
}
static int write(const uint16_t word, const uint8_t address) {
// writes <word> to specified <address>
if (find_listen_window(true)) {
// send write command
em4x70_send_nibble(EM4X70_COMMAND_WRITE, true);
// send address data with parity bit
em4x70_send_nibble(address, true);
// send data word
em4x70_send_word(word);
// Wait TWA
WaitTicks(EM4X70_T_TAG_TWA);
// look for ACK sequence
if (check_ack()) {
// now EM4x70 needs EM4X70_T_TAG_TWEE (EEPROM write time)
// for saving data and should return with ACK
WaitTicks(EM4X70_T_TAG_WEE);
if (check_ack()) {
return PM3_SUCCESS;
}
}
}
return PM3_ESOFT;
}
static bool find_listen_window(bool command) {
int cnt = 0;
while (cnt < EM4X70_T_WAITING_FOR_LIW) {
/*
80 ( 64 + 16 )
80 ( 64 + 16 )
Flip Polarity
96 ( 64 + 32 )
64 ( 32 + 16 +16 )*/
if (check_pulse_length(get_pulse_length(RISING_EDGE), (2*EM4X70_T_TAG_FULL_PERIOD) + EM4X70_T_TAG_HALF_PERIOD) &&
check_pulse_length(get_pulse_length(RISING_EDGE), (2*EM4X70_T_TAG_FULL_PERIOD) + EM4X70_T_TAG_HALF_PERIOD) &&
check_pulse_length(get_pulse_length(FALLING_EDGE), (2*EM4X70_T_TAG_FULL_PERIOD) + EM4X70_T_TAG_FULL_PERIOD) &&
check_pulse_length(get_pulse_length(FALLING_EDGE), EM4X70_T_TAG_FULL_PERIOD + (2*EM4X70_T_TAG_HALF_PERIOD))) {
if (command) {
/* Here we are after the 64 duration edge.
* em4170 says we need to wait about 48 RF clock cycles.
* depends on the delay between tag and us
*
* I've found between 4-5 quarter periods (32-40) works best
*/
WaitTicks( 4 * EM4X70_T_TAG_QUARTER_PERIOD );
// Send RM Command
em4x70_send_bit(0);
em4x70_send_bit(0);
}
return true;
}
cnt++;
}
return false;
}
static void bits2bytes(const uint8_t *bits, int length, uint8_t *out) {
if (length % 8 != 0) {
Dbprintf("Should have a multiple of 8 bits, was sent %d", length);
}
int num_bytes = length / 8; // We should have a multiple of 8 here
for (int i = 1; i <= num_bytes; i++) {
out[num_bytes - i] = bits2byte(bits, 8);
bits += 8;
}
}
static uint8_t bits2byte(const uint8_t *bits, int length) {
// converts <length> separate bits into a single "byte"
uint8_t byte = 0;
for (int i = 0; i < length; i++) {
byte |= bits[i];
if (i != length - 1)
byte <<= 1;
}
return byte;
}
static bool send_command_and_read(uint8_t command, uint8_t *bytes, size_t length) {
int retries = EM4X70_COMMAND_RETRIES;
while (retries) {
retries--;
if (find_listen_window(true)) {
uint8_t bits[EM4X70_MAX_RECEIVE_LENGTH] = {0};
size_t out_length_bits = length * 8;
em4x70_send_nibble(command, command_parity);
int len = em4x70_receive(bits, out_length_bits);
if (len < out_length_bits) {
Dbprintf("Invalid data received length: %d, expected %d", len, out_length_bits);
return false;
}
bits2bytes(bits, len, bytes);
return true;
}
}
return false;
}
/**
* em4x70_read_id
*
* read pre-programmed ID (4 bytes)
*/
static bool em4x70_read_id(void) {
return send_command_and_read(EM4X70_COMMAND_ID, &tag.data[4], 4);
}
/**
* em4x70_read_um1
*
* read user memory 1 (4 bytes including lock bits)
*/
static bool em4x70_read_um1(void) {
return send_command_and_read(EM4X70_COMMAND_UM1, &tag.data[0], 4);
}
/**
* em4x70_read_um2
*
* read user memory 2 (8 bytes)
*/
static bool em4x70_read_um2(void) {
return send_command_and_read(EM4X70_COMMAND_UM2, &tag.data[24], 8);
}
static bool find_em4x70_tag(void) {
// function is used to check wether a tag on the proxmark is an
// EM4170 tag or not -> speed up "lf search" process
return find_listen_window(false);
}
static int em4x70_receive(uint8_t *bits, size_t length) {
uint32_t pl;
int bit_pos = 0;
edge_detection_t edge = RISING_EDGE;
bool foundheader = false;
// Read out the header
// 12 Manchester 1's (may miss some during settle period)
// 4 Manchester 0's
// Skip a few leading 1's as it could be noisy
WaitTicks(6 * EM4X70_T_TAG_FULL_PERIOD);
// wait until we get the transition from 1's to 0's which is 1.5 full windows
for(int i = 0; i < EM4X70_T_READ_HEADER_LEN; i++) {
pl = get_pulse_length(edge);
if (check_pulse_length(pl, 3 * EM4X70_T_TAG_HALF_PERIOD)) {
foundheader = true;
break;
}
}
if (!foundheader) {
Dbprintf("Failed to find read header");
return 0;
}
// Skip next 3 0's, header check consumes the first 0
for (int i = 0; i < 3; i++) {
// If pulse length is not 1 bit, then abort early
if(!check_pulse_length(get_pulse_length(edge), EM4X70_T_TAG_FULL_PERIOD)) {
return 0;
}
}
// identify remaining bits based on pulse lengths
// between listen windows only pulse lengths of 1, 1.5 and 2 are possible
while (bit_pos < length) {
pl = get_pulse_length(edge);
if (check_pulse_length(pl, EM4X70_T_TAG_FULL_PERIOD)) {
// pulse length 1 -> assign bit
bits[bit_pos++] = edge == FALLING_EDGE ? 1 : 0;
} else if (check_pulse_length(pl, 3 * EM4X70_T_TAG_HALF_PERIOD)) {
// pulse length 1.5 -> 2 bits + flip edge detection
if (edge == FALLING_EDGE) {
bits[bit_pos++] = 0;
bits[bit_pos++] = 0;
edge = RISING_EDGE;
} else {
bits[bit_pos++] = 1;
bits[bit_pos++] = 1;
edge = FALLING_EDGE;
}
} else if (check_pulse_length(pl, 2 * EM4X70_T_TAG_FULL_PERIOD)) {
// pulse length of 2 -> two bits
if (edge == FALLING_EDGE) {
bits[bit_pos++] = 0;
bits[bit_pos++] = 1;
} else {
bits[bit_pos++] = 1;
bits[bit_pos++] = 0;
}
} else {
// Listen Window, or invalid bit
break;
}
}
return bit_pos;
}
void em4x70_info(em4x70_data_t *etd) {
uint8_t status = 0;
// Support tags with and without command parity bits
command_parity = etd->parity;
init_tag();
em4x70_setup_read();
// Find the Tag
if (get_signalproperties() && find_em4x70_tag()) {
// Read ID, UM1 and UM2
status = em4x70_read_id() && em4x70_read_um1() && em4x70_read_um2();
}
StopTicks();
lf_finalize();
reply_ng(CMD_LF_EM4X70_INFO, status, tag.data, sizeof(tag.data));
}
void em4x70_write(em4x70_data_t *etd) {
uint8_t status = 0;
command_parity = etd->parity;
init_tag();
em4x70_setup_read();
// Find the Tag
if (get_signalproperties() && find_em4x70_tag()) {
// Write
status = write(etd->word, etd->address) == PM3_SUCCESS;
if (status) {
// Read Tag after writing
em4x70_read_id();
em4x70_read_um1();
em4x70_read_um2();
}
}
StopTicks();
lf_finalize();
reply_ng(CMD_LF_EM4X70_WRITE, status, tag.data, sizeof(tag.data));
}
void em4x70_unlock(em4x70_data_t *etd) {
uint8_t status = 0;
command_parity = etd->parity;
init_tag();
em4x70_setup_read();
// Find the Tag
if (get_signalproperties() && find_em4x70_tag()) {
// Read ID (required for send_pin command)
if (em4x70_read_id()) {
// Send PIN
status = send_pin(etd->pin) == PM3_SUCCESS;
// If the write succeeded, read the rest of the tag
if (status) {
// Read Tag
// ID doesn't change
em4x70_read_um1();
em4x70_read_um2();
}
}
}
StopTicks();
lf_finalize();
reply_ng(CMD_LF_EM4X70_UNLOCK, status, tag.data, sizeof(tag.data));
}
void em4x70_auth(em4x70_data_t *etd) {
uint8_t status = 0;
uint8_t response[3] = {0};
command_parity = etd->parity;
init_tag();
em4x70_setup_read();
// Find the Tag
if (get_signalproperties() && find_em4x70_tag()) {
// Authenticate and get tag response
status = authenticate(etd->rnd, etd->frnd, response) == PM3_SUCCESS;
}
StopTicks();
lf_finalize();
reply_ng(CMD_LF_EM4X70_AUTH, status, response, sizeof(response));
}
void em4x70_write_pin(em4x70_data_t *etd) {
uint8_t status = 0;
command_parity = etd->parity;
init_tag();
em4x70_setup_read();
// Find the Tag
if (get_signalproperties() && find_em4x70_tag()) {
// Read ID (required for send_pin command)
if (em4x70_read_id()) {
// Write new PIN
if( (write( etd->pin & 0xFFFF, EM4X70_PIN_WORD_UPPER) == PM3_SUCCESS) &&
(write((etd->pin >> 16) & 0xFFFF, EM4X70_PIN_WORD_LOWER) == PM3_SUCCESS)) {
// Now Try to authenticate using the new PIN
// Send PIN
status = send_pin(etd->pin) == PM3_SUCCESS;
// If the write succeeded, read the rest of the tag
if (status) {
// Read Tag
// ID doesn't change
em4x70_read_um1();
em4x70_read_um2();
}
}
}
}
StopTicks();
lf_finalize();
reply_ng(CMD_LF_EM4X70_WRITEPIN, status, tag.data, sizeof(tag.data));
}
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