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proxmark3/armsrc/em4x50.c
Henry Gabryjelski 1a8ef489c8 const for em4x50
2023-08-08 23:03:34 -07:00

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//-----------------------------------------------------------------------------
// Copyright (C) Proxmark3 contributors. See AUTHORS.md for details.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// See LICENSE.txt for the text of the license.
//-----------------------------------------------------------------------------
// Low frequency EM4x50 commands
//-----------------------------------------------------------------------------
#include "fpgaloader.h"
#include "ticks.h"
#include "dbprint.h"
#include "lfsampling.h"
#include "lfadc.h"
#include "lfdemod.h"
#include "commonutil.h"
#include "em4x50.h"
#include "BigBuf.h"
#include "spiffs.h"
#include "appmain.h" // tear
#include "bruteforce.h"
// Sam7s has several timers, we will use the source TIMER_CLOCK1 (aka AT91C_TC_CLKS_TIMER_DIV1_CLOCK)
// TIMER_CLOCK1 = MCK/2, MCK is running at 48 MHz, Timer is running at 48/2 = 24 MHz
// EM4x50 units (T0) have duration of 8 microseconds (us), which is 1/125000 per second (carrier)
// T0 = TIMER_CLOCK1 / 125000 = 192
#ifndef T0
#define T0 192
#endif
// conversions (carrier frequency 125 kHz):
// 1 us = 1.5 ticks
// 1 cycle = 1 period = 8 us = 12 ticks
// 1 bit = 64 cycles = 768 ticks = 512 us (for Opt64)
#define CYCLES2TICKS 12
#define CYCLES2MUSEC 8
// given in cycles/periods
#define EM4X50_T_TAG_QUARTER_PERIOD 16
#define EM4X50_T_TAG_HALF_PERIOD 32
#define EM4X50_T_TAG_THREE_QUARTER_PERIOD 48
#define EM4X50_T_TAG_FULL_PERIOD 64
#define EM4X50_T_TAG_TPP 64
#define EM4X50_T_TAG_TWA 64
#define EM4X50_T_TAG_TINIT 2112
#define EM4X50_T_TAG_TWEE 3200
#define EM4X50_T_TAG_WAITING_FOR_SIGNAL 75
#define EM4X50_T_WAITING_FOR_DBLLIW 1550
#define EM4X50_T_WAITING_FOR_ACK 4
#define EM4X50_T_TOLERANCE 8
#define EM4X50_T_ZERO_DETECTION 3
// timeout values (empirical) for simulation mode (may vary with regard to reader)
#define EM4X50_T_SIMULATION_TIMEOUT_READ 600
#define EM4X50_T_SIMULATION_TIMEOUT_WAIT 50
// the following value (pulses) seems to be critical; if it's too low
//(e.g. < 120) some cards are no longer readable although they're ok
#define EM4X50_T_WAITING_FOR_SNGLLIW 140
// div
#define EM4X50_TAG_WORD 45
#define EM4X50_TAG_MAX_NO_BYTES 136
#define EM4X50_TIMEOUT_PULSE_EVAL 2500
uint8_t g_High = 190;
uint8_t g_Low = 60;
// indication whether a previous login has been successful, so operations
// that require authentication can be handled
bool g_Login = false;
// WritePassword process in simulation mode is handled in a different way
// compared to operations like read, write, login, so it is necessary to
// to be able to identfiy it
bool g_WritePasswordProcess = false;
// if reader sends a different password than "expected" -> save it
uint32_t g_Password = 0;
// extract and check parities
// return result of parity check and extracted plain data
static bool extract_parities(uint64_t word, uint32_t *data) {
uint8_t row_parities = 0x0, col_parities = 0x0;
uint8_t row_parities_calculated = 0x0, col_parities_calculated = 0x0;
*data = 0x0;
// extract plain data (32 bits) from raw word (45 bits)
for (int i = 0; i < 4; i++) {
*data <<= 8;
*data |= (word >> ((4 - i) * 9 + 1)) & 0xFF;
}
// extract row parities (4 bits + stop bit) from raw word (45 bits)
for (int i = 0; i < 5; i++) {
row_parities <<= 1;
row_parities |= (word >> ((4 - i) * 9)) & 0x1;
}
// extract col_parities (8 bits, no stop bit) from raw word (45 bits)
col_parities = (word >> 1) & 0xFF;
// check extracted parities against extracted data
// calculate row parities from data
for (int i = 0; i < 4; i++) {
row_parities_calculated <<= 1;
for (int j = 0; j < 8; j++) {
row_parities_calculated ^= (*data >> ((3 - i) * 8 + (7 - j))) & 0x1;
}
}
// add stop bit (always zero)
row_parities_calculated <<= 1;
// calculate column parities from data
for (int i = 0; i < 8; i++) {
col_parities_calculated <<= 1;
for (int j = 0; j < 4; j++) {
col_parities_calculated ^= (*data >> ((3 - j) * 8 + (7 - i))) & 0x1;
}
}
if ((row_parities == row_parities_calculated) && (col_parities == col_parities_calculated))
return true;
return false;
}
void em4x50_setup_read(void) {
FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_ADC | FPGA_LF_ADC_READER_FIELD);
StartTicks();
// 50ms for the resonant antenna to settle.
WaitMS(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);
// Watchdog hit
WDT_HIT();
}
void em4x50_setup_sim(void) {
FpgaDownloadAndGo(FPGA_BITSTREAM_LF);
FpgaWriteConfWord(FPGA_MAJOR_MODE_LF_EDGE_DETECT);
FpgaSendCommand(FPGA_CMD_SET_DIVISOR, LF_DIVISOR_125);
AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT | GPIO_SSC_CLK;
AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
AT91C_BASE_PIOA->PIO_ODR = GPIO_SSC_CLK;
StartTicks();
// Watchdog hit
WDT_HIT();
}
// calculate signal properties (mean amplitudes) from measured data:
// 32 amplitudes (maximum values) -> mean amplitude value -> g_High -> g_Low
static bool get_signalproperties(void) {
bool signal_found = false;
int no_periods = 32, pct = 75, noise = 140;
uint8_t sample_ref = 127;
uint8_t sample_max_mean = 0;
uint8_t sample_max[no_periods];
uint32_t sample_max_sum = 0;
memset(sample_max, 0x00, sizeof(sample_max));
// wait until signal/noise > 1 (max. 32 periods)
for (int i = 0; i < EM4X50_T_TAG_WAITING_FOR_SIGNAL; i++) {
if (BUTTON_PRESS()) return false;
// about 2 samples per bit period
WaitUS(EM4X50_T_TAG_HALF_PERIOD * CYCLES2MUSEC);
// ignore first samples
if ((i > SIGNAL_IGNORE_FIRST_SAMPLES) && (AT91C_BASE_SSC->SSC_RHR > noise)) {
signal_found = true;
break;
}
}
if (signal_found == false) {
return false;
}
// calculate mean maximum value of 32 periods, each period has a length of
// 3 single "full periods" to eliminate the influence of a listen window
for (int i = 0; i < no_periods; i++) {
uint32_t tval = GetTicks();
while (GetTicks() - tval < 12 * 3 * EM4X50_T_TAG_FULL_PERIOD) {
if (BUTTON_PRESS()) return false;
volatile uint8_t sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
if (sample > sample_max[i])
sample_max[i] = sample;
}
sample_max_sum += sample_max[i];
}
sample_max_mean = sample_max_sum / no_periods;
// set global envelope variables
g_High = sample_ref + pct * (sample_max_mean - sample_ref) / 100;
g_Low = sample_ref - pct * (sample_max_mean - sample_ref) / 100;
return true;
}
// returns true if bit is undefined by evaluating a single sample within
// a bit period (given there is no LIW, ACK or NAK)
// This function is used for identifying a listen window in functions
// "find_double_listen_window" and "check_ack"
static bool invalid_bit(void) {
// get sample at 3/4 of bit period
WaitUS(EM4X50_T_TAG_THREE_QUARTER_PERIOD * CYCLES2MUSEC);
uint8_t sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
// wait until end of bit period
WaitUS(EM4X50_T_TAG_QUARTER_PERIOD * CYCLES2MUSEC);
// bit in "undefined" state?
if (sample <= g_High && sample >= g_Low)
return true;
return false;
}
static uint32_t get_pulse_length(void) {
int32_t timeout = EM4X50_TIMEOUT_PULSE_EVAL, tval = 0;
// iterates pulse lengths (low -> high -> low)
volatile uint8_t sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
while (sample > g_Low && (timeout--))
sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
if (timeout <= 0)
return 0;
tval = GetTicks();
timeout = EM4X50_TIMEOUT_PULSE_EVAL;
while (sample < g_High && (timeout--))
sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
if (timeout <= 0)
return 0;
timeout = EM4X50_TIMEOUT_PULSE_EVAL;
while (sample > g_Low && (timeout--))
sample = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
if (timeout <= 0)
return 0;
return GetTicks() - tval;
}
// check if pulse length <pl> corresponds to given length <length>
static bool check_pulse_length(uint32_t pl, int length) {
return ((pl >= (length - EM4X50_T_TOLERANCE) * CYCLES2TICKS) &&
(pl <= (length + EM4X50_T_TOLERANCE) * CYCLES2TICKS));
}
// send single bit according to EM4x50 application note and datasheet
static void em4x50_reader_send_bit(int bit) {
// reset clock for the next bit
uint32_t tval = GetTicks();
if (bit == 0) {
// disable modulation (activate the field) for 7 cycles of carrier
// period (Opt64)
LOW(GPIO_SSC_DOUT);
while (GetTicks() - tval < 7 * CYCLES2TICKS);
// enable modulation (drop the field) for remaining first
// half of bit period
HIGH(GPIO_SSC_DOUT);
while (GetTicks() - tval < EM4X50_T_TAG_HALF_PERIOD * CYCLES2TICKS);
// disable modulation for second half of bit period
LOW(GPIO_SSC_DOUT);
while (GetTicks() - tval < EM4X50_T_TAG_FULL_PERIOD * CYCLES2TICKS);
} else {
// bit = "1" means disable modulation for full bit period
LOW(GPIO_SSC_DOUT);
while (GetTicks() - tval < EM4X50_T_TAG_FULL_PERIOD * CYCLES2TICKS);
}
}
// send byte (without parity)
static void em4x50_reader_send_byte(uint8_t byte) {
for (int i = 0; i < 8; i++) {
em4x50_reader_send_bit((byte >> (7 - i)) & 1);
}
}
// send byte followed by its (even) parity bit
static void em4x50_reader_send_byte_with_parity(uint8_t byte) {
int parity = 0;
for (int i = 0; i < 8; i++) {
int bit = (byte >> (7 - i)) & 1;
em4x50_reader_send_bit(bit);
parity ^= bit;
}
em4x50_reader_send_bit(parity);
}
// send 32 bit word with parity bits according to EM4x50 datasheet
// word hast be sent in msb notation
static void em4x50_reader_send_word(const uint32_t word) {
uint8_t bytes[4] = {0x0, 0x0, 0x0, 0x0};
for (int i = 0; i < 4; i++) {
bytes[i] = (word >> (24 - (8 * i))) & 0xFF;
em4x50_reader_send_byte_with_parity(bytes[i]);
}
// send column parities
em4x50_reader_send_byte(bytes[0] ^ bytes[1] ^ bytes[2] ^ bytes[3]);
// send final stop bit (always "0")
em4x50_reader_send_bit(0);
}
// find single listen window
static bool find_single_listen_window(void) {
int cnt_pulses = 0;
while (cnt_pulses < EM4X50_T_WAITING_FOR_SNGLLIW) {
// identification of listen window is done via evaluation of
// pulse lengths
if (check_pulse_length(get_pulse_length(), 3 * EM4X50_T_TAG_FULL_PERIOD)) {
if (check_pulse_length(get_pulse_length(), 2 * EM4X50_T_TAG_FULL_PERIOD)) {
// found listen window
return true;
}
}
cnt_pulses++;
}
return false;
}
// find two successive listen windows that indicate the beginning of
// data transmission
// double listen window to be detected within 1600 pulses -> worst case
// reason: first detectable double listen window after 34 words
// -> 34 words + 34 single listen windows -> about 1600 pulses
static int find_double_listen_window(bool bcommand) {
int cnt_pulses = 0;
while (cnt_pulses < EM4X50_T_WAITING_FOR_DBLLIW) {
if (BUTTON_PRESS()) {
return PM3_EOPABORTED;
}
// identification of listen window is done via evaluation of
// pulse lengths
if (check_pulse_length(get_pulse_length(), 3 * EM4X50_T_TAG_FULL_PERIOD)) {
if (check_pulse_length(get_pulse_length(), 2 * EM4X50_T_TAG_FULL_PERIOD)) {
// first listen window found
if (bcommand) {
// data transmission from card has to be stopped, because
// a commamd shall be issued
// unfortunately the position in listen window (where
// command request has to be sent) has gone, so if a
// second window follows - sync on this to issue a command
// skip the next bit...
WaitUS(EM4X50_T_TAG_FULL_PERIOD * CYCLES2MUSEC);
// ...and check if the following bit does make sense
// (if not it is the correct position within the second
// listen window)
if (invalid_bit()) {
// send RM for request mode
em4x50_reader_send_bit(0);
em4x50_reader_send_bit(0);
return PM3_SUCCESS;
}
}
if (check_pulse_length(get_pulse_length(), 3 * EM4X50_T_TAG_FULL_PERIOD)) {
// return although second listen window consists of one
// more bit period but this period is necessary for
// evaluating further pulse lengths
return PM3_SUCCESS;
}
}
}
cnt_pulses++;
}
return PM3_EFAILED;
}
// function is used to check whether a tag on the proxmark is an
// EM4x50 tag or not -> speed up "lf search" process
static bool find_em4x50_tag(void) {
return find_single_listen_window();
}
// To issue a command we have to find a listen window first.
// Because identification and synchronization at the same time is not
// possible when using pulse lengths a double listen window is used.
static int request_receive_mode(void) {
return find_double_listen_window(true);
}
// returns true if signal structue corresponds to ACK, anything else is
// counted as NAK (-> false)
// Only relevant for password writing function:
// If <bliw> is true then within the single listen window right after the
// ack signal a RM request has to be sent.
static bool check_ack(bool bliw) {
int count_cycles = 0;
while (count_cycles < EM4X50_T_WAITING_FOR_ACK) {
if (BUTTON_PRESS())
return false;
if (check_pulse_length(get_pulse_length(), 2 * EM4X50_T_TAG_FULL_PERIOD)) {
// The received signal is either ACK or NAK.
if (check_pulse_length(get_pulse_length(), 2 * EM4X50_T_TAG_FULL_PERIOD)) {
// Now the signal must be ACK.
if (!bliw) {
return true;
} else {
// send RM request after ack signal
// wait for 2 bits (remaining "bit" of ACK signal + first
// "bit" of listen window)
WaitUS(2 * EM4X50_T_TAG_FULL_PERIOD * CYCLES2MUSEC);
// check for listen window (if first bit cannot be interpreted
// as a valid bit it must belong to a listen window)
if (invalid_bit()) {
// send RM for request mode
em4x50_reader_send_bit(0);
em4x50_reader_send_bit(0);
return true;
}
}
} else {
// It's NAK -> stop searching
break;
}
}
count_cycles++;
}
return false;
}
// decodes one word by evaluating pulse lengths and previous bit;
// word must have 45 bits in total:
// 32 data bits + 4 row parity bits + 8 column parity bits + 1 stop bit
static int get_word_from_bitstream(uint32_t *data) {
bool bitchange = false;
int cnt = 0;
uint32_t pl = 0;
uint64_t word = 0x0;
*data = 0x0;
// initial bit value depends on last pulse length of listen window
pl = get_pulse_length();
if (check_pulse_length(pl, 3 * EM4X50_T_TAG_HALF_PERIOD)) {
// pulse length = 1.5
word = 0x1;
} else if (check_pulse_length(pl, 2 * EM4X50_T_TAG_FULL_PERIOD)) {
// pulse length = 2
bitchange = true;
} else {
// pulse length = 2.5
word = 0x1;
cnt++;
}
// identify remaining bits based on pulse lengths
// between two listen windows only pulse lengths of 1, 1.5 and 2 are possible
while (BUTTON_PRESS() == false) {
cnt++;
word <<= 1;
pl = get_pulse_length();
if (check_pulse_length(pl, EM4X50_T_TAG_FULL_PERIOD)) {
// pulse length = 1 -> keep former bit value
word |= (word >> 1) & 0x1;
} else if (check_pulse_length(pl, 3 * EM4X50_T_TAG_HALF_PERIOD)) {
// pulse length = 1.5 -> decision on bit change
if (bitchange) {
// if number of pulse lengths with 1.5 periods is even -> add bit
word |= (word >> 1) & 0x1;
word <<= 1;
// pulse length of 1.5 changes bit value
word |= ((word >> 1) & 0x1) ^ 0x1;
cnt++;
// next time add only one bit
bitchange = false;
} else {
word |= ((word >> 1) & 0x1) ^ 0x1;
// next time two bits have to be added
bitchange = true;
}
} else if (check_pulse_length(pl, 2 * EM4X50_T_TAG_FULL_PERIOD)) {
// pulse length of 2 means: adding 2 bits "01"
cnt++;
word <<= 1;
word |= 0x1;
} else if (check_pulse_length(pl, 3 * EM4X50_T_TAG_FULL_PERIOD)) {
// pulse length of 3 indicates listen window -> clear last
// bit (= 0) and return (without parities)
word >>= 2;
return (extract_parities(word, data)) ? --cnt : 0;
}
}
return PM3_EOPABORTED;
}
// simple login to EM4x50,
// used in operations that require authentication
static int login(uint32_t password) {
if (request_receive_mode() == PM3_SUCCESS) {
// send login command
em4x50_reader_send_byte_with_parity(EM4X50_COMMAND_LOGIN);
// send password
em4x50_reader_send_word(password);
WaitUS(EM4X50_T_TAG_TPP * CYCLES2MUSEC);
// check if ACK is returned
if (check_ack(false))
return PM3_SUCCESS;
} else {
if (g_dbglevel >= DBG_DEBUG)
Dbprintf("error in command request");
}
return PM3_EFAILED;
}
// searching for password using chosen bruteforce algorithm
static bool brute(const em4x50_data_t *etd, uint32_t *pwd) {
generator_context_t ctx;
bool pwd_found = false;
int generator_ret = 0;
int cnt = 0;
bf_generator_init(&ctx, etd->bruteforce_mode);
if (etd->bruteforce_mode == BRUTEFORCE_MODE_CHARSET)
bf_generator_set_charset(&ctx, etd->bruteforce_charset);
while ((generator_ret = bf_generate32(&ctx)) == GENERATOR_NEXT) {
*pwd = ctx.current_key32;
WDT_HIT();
if (login(*pwd) == PM3_SUCCESS) {
pwd_found = true;
// to be safe login 5 more times
for (int i = 0; i < 5; i++) {
if (login(*pwd) != PM3_SUCCESS) {
pwd_found = false;
break;
}
}
if (pwd_found)
break;
}
// print password every 500 iterations
if ((++cnt % 500) == 0) {
// print header
if (cnt == 500) {
Dbprintf("|---------+------------+------------|");
Dbprintf("| no. | pwd (msb) | pwd (lsb) |");
Dbprintf("|---------+------------+------------|");
}
// print data
Dbprintf("|%8i | 0x%08x | 0x%08x |", cnt, reflect32(*pwd), *pwd);
}
if (BUTTON_PRESS())
break;
}
// print footer
if (cnt >= 500)
Dbprintf("|---------+------------+------------|");
return pwd_found;
}
// login into EM4x50
void em4x50_login(const uint32_t *password, bool ledcontrol) {
em4x50_setup_read();
int status = PM3_EFAILED;
if (ledcontrol) LED_C_ON();
if (get_signalproperties() && find_em4x50_tag()) {
if (ledcontrol) {
LED_C_OFF();
LED_D_ON();
}
status = login(*password);
}
if (ledcontrol) LEDsoff();
lf_finalize(ledcontrol);
reply_ng(CMD_LF_EM4X50_LOGIN, status, NULL, 0);
}
// invoke password search
void em4x50_brute(const em4x50_data_t *etd, bool ledcontrol) {
em4x50_setup_read();
bool bsuccess = false;
uint32_t pwd = 0x0;
if (ledcontrol) LED_C_ON();
if (get_signalproperties() && find_em4x50_tag()) {
if (ledcontrol) {
LED_C_OFF();
LED_D_ON();
}
bsuccess = brute(etd, &pwd);
}
if (ledcontrol) LEDsoff();
lf_finalize(ledcontrol);
reply_ng(CMD_LF_EM4X50_BRUTE, bsuccess ? PM3_SUCCESS : PM3_EFAILED, (uint8_t *)(&pwd), sizeof(pwd));
}
// check passwords from dictionary content in flash memory
void em4x50_chk(const char *filename, bool ledcontrol) {
int status = PM3_EFAILED;
uint32_t pwd = 0x0;
#ifdef WITH_FLASH
BigBuf_free();
int changed = rdv40_spiffs_lazy_mount();
uint16_t pwd_count = 0;
uint32_t size = size_in_spiffs(filename);
pwd_count = size / 4;
uint8_t *pwds = BigBuf_malloc(size);
rdv40_spiffs_read_as_filetype(filename, pwds, size, RDV40_SPIFFS_SAFETY_SAFE);
if (changed)
rdv40_spiffs_lazy_unmount();
em4x50_setup_read();
// set g_High and g_Low
if (ledcontrol) LED_C_ON();
if (get_signalproperties() && find_em4x50_tag()) {
if (ledcontrol) {
LED_C_OFF();
LED_D_ON();
}
// try to login with current password
for (int i = 0; i < pwd_count; i++) {
// manual interruption
if (BUTTON_PRESS()) {
status = PM3_EOPABORTED;
break;
}
// get next password
pwd = 0x0;
for (int j = 0; j < 4; j++)
pwd |= (*(pwds + 4 * i + j)) << ((3 - j) * 8);
if ((status = login(pwd)) == PM3_SUCCESS) {
SpinUp(50);
SpinDown(50);
break;
}
}
}
BigBuf_free();
#endif
if (ledcontrol) LEDsoff();
lf_finalize(ledcontrol);
reply_ng(CMD_LF_EM4X50_CHK, status, (uint8_t *)&pwd, sizeof(pwd));
}
// resets EM4x50 tag (used by write function)
static int reset(void) {
if (request_receive_mode() == PM3_SUCCESS) {
// send reset command
em4x50_reader_send_byte_with_parity(EM4X50_COMMAND_RESET);
if (check_ack(false))
return PM3_SUCCESS;
} else {
if (g_dbglevel >= DBG_DEBUG)
Dbprintf("error in command request");
}
return PM3_EFAILED;
}
// reads data that tag transmits when exposed to reader field
// (standard read mode); number of read words is saved in <now>
int standard_read(int *now, uint32_t *words) {
int fwr = *now, res = PM3_EFAILED;
// start with the identification of two successive listening windows
if ((res = find_double_listen_window(false)) == PM3_SUCCESS) {
// read and save words until following double listen window is detected
res = get_word_from_bitstream(&words[*now]);
while (res == EM4X50_TAG_WORD) {
(*now)++;
res = get_word_from_bitstream(&words[*now]);
}
// number of detected words
*now -= fwr;
} else {
if (g_dbglevel >= DBG_DEBUG)
Dbprintf("didn't find a listen window");
}
return res;
}
// reads from "first word read" (fwr) to "last word read" (lwr)
// result is verified by "standard read mode"
static int selective_read(uint32_t addresses, uint32_t *words) {
int status = PM3_EFAILED;
uint8_t fwr = addresses & 0xFF; // first word read (first byte)
uint8_t lwr = (addresses >> 8) & 0xFF; // last word read (second byte)
int now = fwr; // number of words
if (request_receive_mode() == PM3_SUCCESS) {
// send selective read command
em4x50_reader_send_byte_with_parity(EM4X50_COMMAND_SELECTIVE_READ);
// send address data
em4x50_reader_send_word(addresses);
// look for ACK sequence
if (check_ack(false))
// save and verify via standard read mode (compare number of words)
if ((status = standard_read(&now, words)) == PM3_SUCCESS)
if (now == (lwr - fwr + 1))
return status;
} else {
if (g_dbglevel >= DBG_DEBUG)
Dbprintf("error in command request");
}
return status;
}
// reads by using "selective read mode" -> bidirectional communication
void em4x50_read(const em4x50_data_t *etd, bool ledcontrol) {
int status = PM3_EFAILED;
uint32_t words[EM4X50_NO_WORDS] = {0x0};
em4x50_setup_read();
// set g_High and g_Low
if (ledcontrol) LED_C_ON();
if (get_signalproperties() && find_em4x50_tag()) {
if (ledcontrol) {
LED_C_OFF();
LED_D_ON();
}
bool blogin = true;
// try to login with given password
if (etd->pwd_given)
blogin = (login(etd->password1) == PM3_SUCCESS);
// only one word has to be read -> first word read = last word read
if (blogin)
status = selective_read(etd->addresses, words);
}
if (ledcontrol) LEDsoff();
LOW(GPIO_SSC_DOUT);
lf_finalize(ledcontrol);
reply_ng(CMD_LF_EM4X50_READ, status, (uint8_t *)words, EM4X50_TAG_MAX_NO_BYTES);
}
// collects as much information as possible via selective read mode
void em4x50_info(const em4x50_data_t *etd, bool ledcontrol) {
int status = PM3_EFAILED;
uint32_t words[EM4X50_NO_WORDS] = {0x0};
em4x50_setup_read();
if (ledcontrol) LED_C_ON();
if (get_signalproperties() && find_em4x50_tag()) {
if (ledcontrol) {
LED_C_OFF();
LED_D_ON();
}
bool blogin = true;
// login with given password
if (etd->pwd_given)
blogin = (login(etd->password1) == PM3_SUCCESS);
if (blogin) {
// read addresses from fwr = 0 to lwr = 33 (0x21)
status = selective_read(0x00002100, words);
}
}
if (ledcontrol) LEDsoff();
lf_finalize(ledcontrol);
reply_ng(CMD_LF_EM4X50_INFO, status, (uint8_t *)words, EM4X50_TAG_MAX_NO_BYTES);
}
// reads data that tag transmits "voluntarily" -> standard read mode
void em4x50_reader(bool ledcontrol) {
int now = 0;
uint32_t words[EM4X50_NO_WORDS] = {0x0};
em4x50_setup_read();
if (ledcontrol) LED_C_ON();
if (get_signalproperties() && find_em4x50_tag()) {
if (ledcontrol) {
LED_C_OFF();
LED_D_ON();
}
standard_read(&now, words);
}
if (ledcontrol) LEDsoff();
LOW(GPIO_SSC_DOUT);
lf_finalize(ledcontrol);
reply_ng(CMD_LF_EM4X50_READER, now, (uint8_t *)words, 4 * now);
}
// writes <word> to specified <addresses>
static int write(uint32_t word, uint32_t addresses) {
if (request_receive_mode() == PM3_SUCCESS) {
// send write command
em4x50_reader_send_byte_with_parity(EM4X50_COMMAND_WRITE);
// send address data
em4x50_reader_send_byte_with_parity(addresses & 0xFF);
// send data
em4x50_reader_send_word(word);
if (tearoff_hook() == PM3_ETEAROFF) { // tearoff occurred
reply_ng(CMD_LF_EM4X50_WRITE, PM3_ETEAROFF, NULL, 0);
return PM3_ETEAROFF;
} else {
// wait for T0 * EM4X50_T_TAG_TWA (write access time)
WaitUS(EM4X50_T_TAG_TWA * CYCLES2MUSEC);
// look for ACK sequence
if (check_ack(false)) {
// now EM4x50 needs T0 * EM4X50_T_TAG_TWEE (EEPROM write time = 3.2ms = 50 * 64 periods)
// for saving data and should return with ACK
for (int i = 0; i < 50; i++) {
WaitUS(EM4X50_T_TAG_FULL_PERIOD * CYCLES2MUSEC);
}
if (check_ack(false))
return PM3_SUCCESS;
}
}
} else {
if (g_dbglevel >= DBG_DEBUG)
Dbprintf("error in command request");
}
return PM3_EFAILED;
}
// changes password from <password> to <new_password>
static int write_password(uint32_t password, uint32_t new_password) {
if (request_receive_mode() == PM3_SUCCESS) {
// send write password command
em4x50_reader_send_byte_with_parity(EM4X50_COMMAND_WRITE_PASSWORD);
// send address data
em4x50_reader_send_word(password);
if (tearoff_hook() == PM3_ETEAROFF) { // tearoff occurred
reply_ng(CMD_LF_EM4X50_WRITE, PM3_ETEAROFF, NULL, 0);
return PM3_ETEAROFF;
} else {
// wait for T0 * EM4x50_T_TAG_TPP (processing pause time)
WaitUS(EM4X50_T_TAG_TPP * CYCLES2MUSEC);
// look for ACK sequence and send rm request
// during following listen window
if (check_ack(true)) {
// send new password
em4x50_reader_send_word(new_password);
// wait for T0 * EM4X50_T_TAG_TWA (write access time)
WaitUS(EM4X50_T_TAG_TWA * CYCLES2MUSEC);
if (check_ack(false)) {
// now EM4x50 needs T0 * EM4X50_T_TAG_TWEE (EEPROM write time = 3.2ms = 50 * 64 periods)
// for saving data and should return with ACK
for (int i = 0; i < 50; i++) {
WaitUS(EM4X50_T_TAG_FULL_PERIOD * CYCLES2MUSEC);
}
if (check_ack(false))
return PM3_SUCCESS;
}
}
}
} else {
if (g_dbglevel >= DBG_DEBUG)
Dbprintf("error in command request");
}
return PM3_EFAILED;
}
// write operation process for EM4x50 tag,
// single word is written to given address, verified by selective read operation
// wrong password -> return with PM3_EFAILED
void em4x50_write(const em4x50_data_t *etd, bool ledcontrol) {
int status = PM3_EFAILED;
uint32_t words[EM4X50_NO_WORDS] = {0x0};
em4x50_setup_read();
if (ledcontrol) LED_C_ON();
if (get_signalproperties() && find_em4x50_tag()) {
if (ledcontrol) {
LED_C_OFF();
LED_D_ON();
}
// if password is given try to login first
status = PM3_SUCCESS;
if (etd->pwd_given)
status = login(etd->password1);
if (status == PM3_SUCCESS) {
// write word to given address
status = write(etd->word, etd->addresses);
if (status == PM3_ETEAROFF) {
lf_finalize(ledcontrol);
return;
}
if (status == PM3_SUCCESS) {
// to verify result reset EM4x50
status = reset();
if (status == PM3_SUCCESS) {
// if password is given renew login after reset
if (etd->pwd_given)
status = login(etd->password1);
if (status == PM3_SUCCESS) {
// call a selective read
status = selective_read(etd->addresses, words);
if (status == PM3_SUCCESS) {
// compare result with given word
if (words[etd->addresses & 0xFF] != reflect32(etd->word))
status = PM3_EFAILED;
}
}
}
}
}
}
if (ledcontrol) LEDsoff();
lf_finalize(ledcontrol);
reply_ng(CMD_LF_EM4X50_WRITE, status, (uint8_t *)words, EM4X50_TAG_MAX_NO_BYTES);
}
// simple change of password
void em4x50_writepwd(const em4x50_data_t *etd, bool ledcontrol) {
int status = PM3_EFAILED;
em4x50_setup_read();
if (ledcontrol) LED_C_ON();
if (get_signalproperties() && find_em4x50_tag()) {
if (ledcontrol) {
LED_C_OFF();
LED_D_ON();
}
// login and change password
if (login(etd->password1) == PM3_SUCCESS) {
status = write_password(etd->password1, etd->password2);
if (status == PM3_ETEAROFF) {
lf_finalize(ledcontrol);
return;
}
}
}
if (ledcontrol) LEDsoff();
lf_finalize(ledcontrol);
reply_ng(CMD_LF_EM4X50_WRITEPWD, status, NULL, 0);
}
// send bit in receive mode by counting carrier cycles
static void em4x50_sim_send_bit(uint8_t bit) {
uint16_t timeout = EM4X50_T_SIMULATION_TIMEOUT_READ;
for (int t = 0; t < EM4X50_T_TAG_FULL_PERIOD; t++) {
// wait until SSC_CLK goes HIGH
// used as a simple detection of a reader field?
while ((timeout--) && !(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK));
if (timeout == 0) {
return;
}
timeout = EM4X50_T_SIMULATION_TIMEOUT_READ;
if (bit)
OPEN_COIL();
else
SHORT_COIL();
//wait until SSC_CLK goes LOW
while ((timeout--) && (AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK));
if (timeout == 0) {
return;
}
timeout = EM4X50_T_SIMULATION_TIMEOUT_READ;
if (t == EM4X50_T_TAG_HALF_PERIOD)
bit ^= 1;
}
}
// send byte in receive mode either with or without parity check (even)
static void em4x50_sim_send_byte(uint8_t byte, bool paritycheck) {
// send byte
for (int i = 0; i < 8; i++) {
em4x50_sim_send_bit((byte >> (7 - i)) & 1);
}
if (paritycheck) {
uint8_t parity = 0x0;
for (int i = 0; i < 8; i++) {
parity ^= (byte >> i) & 1;
}
em4x50_sim_send_bit(parity);
}
}
// send complete word in receive mode (including all parity checks)
static void em4x50_sim_send_word(uint32_t word) {
uint8_t cparity = 0x00;
// word has tobe sent in msb, not lsb
word = reflect32(word);
// 4 bytes each with even row parity bit
for (int i = 0; i < 4; i++) {
em4x50_sim_send_byte((word >> ((3 - i) * 8)) & 0xFF, true);
}
// column parity
for (int i = 0; i < 8; i++) {
cparity <<= 1;
for (int j = 0; j < 4; j++) {
cparity ^= (((word >> ((3 - j) * 8)) & 0xFF) >> (7 - i)) & 1;
}
}
em4x50_sim_send_byte(cparity, false);
// stop bit
em4x50_sim_send_bit(0);
}
// wait for <maxperiods> pulses of carrier frequency
static void wait_cycles(int maxperiods) {
int period = 0, timeout = EM4X50_T_SIMULATION_TIMEOUT_WAIT;
while (period < maxperiods) {
while ((timeout--) && !(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK));
if (timeout <= 0) {
return;
}
timeout = EM4X50_T_SIMULATION_TIMEOUT_WAIT;
while ((timeout--) && (AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK));
if (timeout <= 0) {
return;
}
timeout = EM4X50_T_SIMULATION_TIMEOUT_WAIT;
period++;
}
}
// read single bit in simulation mode
static int em4x50_sim_read_bit(void) {
int cycles = 0;
int timeout = EM4X50_T_SIMULATION_TIMEOUT_READ;
while (cycles < EM4X50_T_TAG_FULL_PERIOD) {
// wait until reader field disappears
while ((timeout--) && !(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK));
if (timeout <= 0) {
return PM3_ETIMEOUT;
}
timeout = EM4X50_T_SIMULATION_TIMEOUT_READ;
// now check until reader switches on carrier field
uint32_t tval = GetTicks();
while ((timeout--) && (AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK)) {
if (timeout <= 0) {
return PM3_ETIMEOUT;
}
// check if current cycle takes longer than "usual""
if (GetTicks() - tval > EM4X50_T_ZERO_DETECTION * CYCLES2TICKS) {
// gap detected; wait until reader field is switched on again
while ((timeout--) && (AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK));
if (timeout <= 0) {
return PM3_ETIMEOUT;
}
// now we have a reference "position", from here it will take
// slightly less than 32 cycles until the end of the bit period
wait_cycles(28);
// end of bit period is reached; return with bit value "0"
// (cf. datasheet)
return 0;
}
}
timeout = EM4X50_T_SIMULATION_TIMEOUT_READ;
// no gap detected, i.e. reader field is still up;
// continue with counting cycles
cycles++;
}
// reached 64 cycles (= EM4X50_T_TAG_FULL_PERIOD) -> return bit value "1"
return 1;
}
// read byte in simulation mode either with or without parity check (even)
static bool em4x50_sim_read_byte(uint8_t *byte, bool paritycheck) {
for (int i = 0; i < 8; i++) {
*byte <<= 1;
*byte |= em4x50_sim_read_bit();
}
if (paritycheck) {
int pval = em4x50_sim_read_bit();
uint8_t parity = 0;
for (int i = 0; i < 8; i++) {
parity ^= ((*byte) >> i) & 1;
}
if (parity != pval) {
return false;
}
}
return true;
}
// read complete word in simulation mode
static bool em4x50_sim_read_word(uint32_t *word) {
uint8_t stop_bit = 0;
uint8_t parities = 0, parities_calculated = 0;
uint8_t bytes[4] = {0};
// read plain data
for (int i = 0; i < 4; i++) {
em4x50_sim_read_byte(&bytes[i], true);
}
// read column parities and stop bit
em4x50_sim_read_byte(&parities, false);
stop_bit = em4x50_sim_read_bit();
// calculate column parities from data
for (int i = 0; i < 8; i++) {
parities_calculated <<= 1;
for (int j = 0; j < 4; j++) {
parities_calculated ^= (bytes[j] >> (7 - i)) & 1;
}
}
*word = BYTES2UINT32_BE(bytes);
// check parities
if ((parities == parities_calculated) && (stop_bit == 0)) {
return true;
}
return false;
}
// check if reader requests receive mode (rm) by sending two zeros
static int check_rm_request(const uint32_t *tag, bool ledcontrol) {
// look for first zero
int bit = em4x50_sim_read_bit();
if (bit == 0) {
// look for second zero
bit = em4x50_sim_read_bit();
if (bit == 0) {
if (ledcontrol) LED_C_ON();
// if command before was EM4X50_COMMAND_WRITE_PASSWORD
// switch to separate process
if (g_WritePasswordProcess) {
return EM4X50_COMMAND_WRITE_PASSWORD;
} else {
// read mode request detected, get command from reader
uint8_t command = 0;
em4x50_sim_read_byte(&command, true);
return command;
}
}
}
return (bit != PM3_ETIMEOUT) ? PM3_SUCCESS : PM3_ETIMEOUT;
}
// send single listen window in simulation mode
static int em4x50_sim_send_listen_window(const uint32_t *tag, bool ledcontrol) {
SHORT_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
OPEN_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
SHORT_COIL();
wait_cycles(2 * EM4X50_T_TAG_FULL_PERIOD);
OPEN_COIL();
int command = check_rm_request(tag, ledcontrol);
if (command != PM3_SUCCESS) {
return command;
}
SHORT_COIL();
wait_cycles(EM4X50_T_TAG_FULL_PERIOD);
return PM3_SUCCESS;
}
// send ack
static void em4x50_sim_send_ack(void) {
SHORT_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
OPEN_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
SHORT_COIL();
wait_cycles(3 * EM4X50_T_TAG_HALF_PERIOD);
OPEN_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
SHORT_COIL();
wait_cycles(3 * EM4X50_T_TAG_HALF_PERIOD);
OPEN_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
SHORT_COIL();
}
// send nak
static void em4x50_sim_send_nak(void) {
SHORT_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
OPEN_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
SHORT_COIL();
wait_cycles(3 * EM4X50_T_TAG_HALF_PERIOD);
OPEN_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
SHORT_COIL();
wait_cycles(EM4X50_T_TAG_FULL_PERIOD);
OPEN_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
SHORT_COIL();
wait_cycles(EM4X50_T_TAG_HALF_PERIOD);
}
// standard read mode process (simulation mode)
static int em4x50_sim_handle_standard_read_command(const uint32_t *tag, bool ledcontrol) {
// extract control data
int fwr = reflect32(tag[EM4X50_CONTROL]) & 0xFF; // first word read
int lwr = (reflect32(tag[EM4X50_CONTROL]) >> 8) & 0xFF; // last word read
// extract protection data:
// first word read protected
int fwrp = reflect32(tag[EM4X50_PROTECTION]) & 0xFF;
// last word read protected
int lwrp = (reflect32(tag[EM4X50_PROTECTION]) >> 8) & 0xFF;
while ((BUTTON_PRESS() == false) && (data_available() == false)) {
WDT_HIT();
int res = em4x50_sim_send_listen_window(tag, ledcontrol);
if (res != PM3_SUCCESS) {
return res;
}
for (int i = fwr; i <= lwr; i++) {
res = em4x50_sim_send_listen_window(tag, ledcontrol);
if (res != PM3_SUCCESS) {
return res;
}
if ((g_Login == false) && (i >= fwrp) && (i <= lwrp)) {
em4x50_sim_send_word(0x00);
} else {
em4x50_sim_send_word(reflect32(tag[i]));
}
}
}
return PM3_EOPABORTED;
}
// selective read mode process (simulation mode)
static int em4x50_sim_handle_selective_read_command(const uint32_t *tag, bool ledcontrol) {
// read password
uint32_t address = 0;
bool addr = em4x50_sim_read_word(&address);
// processing pause time (corresponds to a "1" bit)
em4x50_sim_send_bit(1);
if (addr) {
em4x50_sim_send_ack();
} else {
em4x50_sim_send_nak();
return EM4X50_COMMAND_STANDARD_READ;
}
// extract control data
int fwr = address & 0xFF; // first word read
int lwr = (address >> 8) & 0xFF; // last word read
// extract protection data:
// first word read protected
int fwrp = reflect32(tag[EM4X50_PROTECTION]) & 0xFF;
// last word read protected
int lwrp = (reflect32(tag[EM4X50_PROTECTION]) >> 8) & 0xFF;
while ((BUTTON_PRESS() == false) && (data_available() == false)) {
WDT_HIT();
int command = em4x50_sim_send_listen_window(tag, ledcontrol);
if (command != PM3_SUCCESS) {
return command;
}
for (int i = fwr; i <= lwr; i++) {
command = em4x50_sim_send_listen_window(tag, ledcontrol);
if (command != PM3_SUCCESS) {
return command;
}
// if not authenticated do not send read protected words
if ((g_Login == false) && (i >= fwrp) && (i <= lwrp)) {
em4x50_sim_send_word(0x00);
} else {
em4x50_sim_send_word(reflect32(tag[i]));
}
}
}
return PM3_EOPABORTED;
}
// login process (simulation mode)
static int em4x50_sim_handle_login_command(const uint32_t *tag, bool ledcontrol) {
// read password
uint32_t password = 0;
bool pwd = em4x50_sim_read_word(&password);
// processing pause time (corresponds to a "1" bit)
em4x50_sim_send_bit(1);
if (pwd && (password == reflect32(tag[EM4X50_DEVICE_PASSWORD]))) {
em4x50_sim_send_ack();
g_Login = true;
if (ledcontrol) LED_D_ON();
} else {
em4x50_sim_send_nak();
g_Login = false;
if (ledcontrol) LED_D_OFF();
// save transmitted password (to be used in standalone mode)
g_Password = password;
}
// continue with standard read mode
return EM4X50_COMMAND_STANDARD_READ;
}
// reset process (simulation mode)
static int em4x50_sim_handle_reset_command(const uint32_t *tag, bool ledcontrol) {
// processing pause time (corresponds to a "1" bit)
em4x50_sim_send_bit(1);
// send ACK
em4x50_sim_send_ack();
g_Login = false;
if (ledcontrol) LED_D_OFF();
// wait for initialization (tinit)
wait_cycles(EM4X50_T_TAG_TINIT);
// continue with standard read mode
return EM4X50_COMMAND_STANDARD_READ;
}
// write process (simulation mode)
static int em4x50_sim_handle_write_command(uint32_t *tag, bool ledcontrol) {
// read address
uint8_t address = 0;
bool addr = em4x50_sim_read_byte(&address, true);
// read data
uint32_t data = 0;
bool word = em4x50_sim_read_word(&data);
// write access time
wait_cycles(EM4X50_T_TAG_TWA);
if ((addr == false) || (word == false)) {
em4x50_sim_send_nak();
return EM4X50_COMMAND_STANDARD_READ;
}
// extract necessary control data
bool raw = (tag[EM4X50_CONTROL] >> CONFIG_BLOCK) & READ_AFTER_WRITE;
// extract protection data:
// first word write protected
int fwwp = reflect8((tag[EM4X50_PROTECTION] >> 24) & 0xFF);
// last word write protected
int lwwp = reflect8((tag[EM4X50_PROTECTION] >> 16) & 0xFF);
switch (address) {
case EM4X50_DEVICE_PASSWORD:
em4x50_sim_send_nak();
return EM4X50_COMMAND_STANDARD_READ;
break;
case EM4X50_PROTECTION:
if (g_Login) {
tag[address] = reflect32(data);
em4x50_sim_send_ack();
} else {
em4x50_sim_send_nak();
return EM4X50_COMMAND_STANDARD_READ;
}
break;
case EM4X50_CONTROL:
if (g_Login) {
tag[address] = reflect32(data);
em4x50_sim_send_ack();
} else {
em4x50_sim_send_nak();
return EM4X50_COMMAND_STANDARD_READ;
}
break;
case EM4X50_DEVICE_SERIAL:
em4x50_sim_send_nak();
return EM4X50_COMMAND_STANDARD_READ;
break;
case EM4X50_DEVICE_ID:
em4x50_sim_send_nak();
return EM4X50_COMMAND_STANDARD_READ;
break;
default:
if ((address >= fwwp) && (address <= lwwp)) {
if (g_Login) {
tag[address] = reflect32(data);
em4x50_sim_send_ack();
} else {
em4x50_sim_send_nak();
return EM4X50_COMMAND_STANDARD_READ;
}
} else {
tag[address] = reflect32(data);
em4x50_sim_send_ack();
}
break;
}
// EEPROM write time
// strange: need some sort of 'waveform correction', otherwise ack signal
// will not be detected; sending a single "1" as last "bit" of Twee
// seems to solve the problem
wait_cycles(EM4X50_T_TAG_TWEE - EM4X50_T_TAG_FULL_PERIOD);
em4x50_sim_send_bit(1);
em4x50_sim_send_ack();
// if "read after write" (raw) bit is set, send written data once
if (raw) {
int command = em4x50_sim_send_listen_window(tag, ledcontrol);
if (command != PM3_SUCCESS) {
return command;
}
command = em4x50_sim_send_listen_window(tag, ledcontrol);
if (command != PM3_SUCCESS) {
return command;
}
em4x50_sim_send_word(tag[address]);
}
// continue with standard read mode
return EM4X50_COMMAND_STANDARD_READ;
}
// write password process (simulation mode)
static int em4x50_sim_handle_writepwd_command(uint32_t *tag, bool ledcontrol) {
bool pwd = false;
g_WritePasswordProcess = true;
// read password
uint32_t act_password = 0;
pwd = em4x50_sim_read_word(&act_password);
// processing pause time tpp (corresponds to a "1" bit)
em4x50_sim_send_bit(1);
if (pwd && (act_password == reflect32(tag[EM4X50_DEVICE_PASSWORD]))) {
em4x50_sim_send_ack();
g_Login = true;
} else {
em4x50_sim_send_nak();
g_Login = false;
g_WritePasswordProcess = false;
// save transmitted password (to be used in standalone mode)
g_Password = act_password;
return EM4X50_COMMAND_STANDARD_READ;
}
int command = em4x50_sim_send_listen_window(tag, ledcontrol);
g_WritePasswordProcess = false;
if (command != EM4X50_COMMAND_WRITE_PASSWORD) {
return command;
}
// read new password
uint32_t new_password = 0;
pwd = em4x50_sim_read_word(&new_password);
// write access time twa
wait_cycles(EM4X50_T_TAG_TWA);
if (pwd) {
em4x50_sim_send_ack();
tag[EM4X50_DEVICE_PASSWORD] = reflect32(new_password);
g_Password = new_password;
} else {
em4x50_sim_send_nak();
return EM4X50_COMMAND_STANDARD_READ;
}
// EEPROM write time
// strange: need some sort of 'waveform correction', otherwise ack signal
// will not be detected; sending a single "1" as last part of Twee
// seems to solve the problem
wait_cycles(EM4X50_T_TAG_TWEE - EM4X50_T_TAG_FULL_PERIOD);
em4x50_sim_send_bit(1);
em4x50_sim_send_ack();
// continue with standard read mode
return EM4X50_COMMAND_STANDARD_READ;
}
void em4x50_handle_commands(int *command, uint32_t *tag, bool ledcontrol) {
switch (*command) {
case EM4X50_COMMAND_LOGIN:
*command = em4x50_sim_handle_login_command(tag, ledcontrol);
break;
case EM4X50_COMMAND_RESET:
*command = em4x50_sim_handle_reset_command(tag, ledcontrol);
break;
case EM4X50_COMMAND_WRITE:
*command = em4x50_sim_handle_write_command(tag, ledcontrol);
break;
case EM4X50_COMMAND_WRITE_PASSWORD:
*command = em4x50_sim_handle_writepwd_command(tag, ledcontrol);
break;
case EM4X50_COMMAND_SELECTIVE_READ:
*command = em4x50_sim_handle_selective_read_command(tag, ledcontrol);
break;
case EM4X50_COMMAND_STANDARD_READ:
if (ledcontrol) LED_C_OFF();
*command = em4x50_sim_handle_standard_read_command(tag, ledcontrol);
break;
// bit errors during reading may lead to unknown commands
// -> continue with standard read mode
default:
*command = EM4X50_COMMAND_STANDARD_READ;
break;
}
}
// simulate uploaded data in emulator memory
// LED C -> reader command has been detected
// LED D -> operations that require authentication are possible
void em4x50_sim(const uint32_t *password, bool ledcontrol) {
int command = PM3_ENODATA;
uint8_t *em4x50_mem = BigBuf_get_EM_addr();
uint32_t tag[EM4X50_NO_WORDS] = {0x0};
for (int i = 0; i < EM4X50_NO_WORDS; i++)
tag[i] = bytes_to_num(em4x50_mem + (i * 4), 4);
// via eload uploaded dump usually does not contain a password
if (tag[EM4X50_DEVICE_PASSWORD] == 0) {
tag[EM4X50_DEVICE_PASSWORD] = reflect32(*password);
}
// only if valid em4x50 data (e.g. uid == serial)
if (tag[EM4X50_DEVICE_SERIAL] != tag[EM4X50_DEVICE_ID]) {
// init
if (ledcontrol) LEDsoff();
em4x50_setup_sim();
g_Login = false;
g_WritePasswordProcess = false;
// start with initial command = standard read mode
command = EM4X50_COMMAND_STANDARD_READ;
for (;;) {
em4x50_handle_commands(&command, tag, ledcontrol);
// stop if key (pm3 button or enter key) has been pressed
if (command == PM3_EOPABORTED) {
break;
}
// if timeout (e.g. no reader field) continue with standard read
// mode and reset former authentication
if (command == PM3_ETIMEOUT) {
command = EM4X50_COMMAND_STANDARD_READ;
g_Login = false;
if (ledcontrol) LED_D_OFF();
}
}
}
BigBuf_free();
lf_finalize(ledcontrol);
reply_ng(CMD_LF_EM4X50_SIM, command, NULL, 0);
}
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