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1 //-----------------------------------------------------------------------------
2 // (c) 2009 Henryk Plötz <henryk@ploetzli.ch>
3 // 2016 Iceman
4 // 2018 AntiCat
5 //
6 // This code is licensed to you under the terms of the GNU GPL, version 2 or,
7 // at your option, any later version. See the LICENSE.txt file for the text of
8 // the license.
9 //-----------------------------------------------------------------------------
10 // LEGIC RF simulation code
11 //-----------------------------------------------------------------------------
12
13 #include "legicrf.h"
14
15 #include "proxmark3.h"
16 #include "apps.h"
17 #include "cmd.h"
18 #include "util.h"
19 #include "string.h"
20 #include "legic_prng.h"
21 #include "legic.h"
22 #include "crc.h"
23 #include "fpgaloader.h"
24
25 static legic_card_select_t card;/* metadata of currently selected card */
26 static crc_t legic_crc;
27
28 //-----------------------------------------------------------------------------
29 // Frame timing and pseudorandom number generator
30 //
31 // The Prng is forwarded every 100us (TAG_BIT_PERIOD), except when the reader is
32 // transmitting. In that case the prng has to be forwarded every bit transmitted:
33 // - 60us for a 0 (RWD_TIME_0)
34 // - 100us for a 1 (RWD_TIME_1)
35 //
36 // The data dependent timing makes writing comprehensible code significantly
37 // harder. The current aproach forwards the prng data based if there is data on
38 // air and time based, using GET_TICKS, during computational and wait periodes.
39 //
40 // To not have the necessity to calculate/guess exection time dependend timeouts
41 // tx_frame and rx_frame use a shared timestamp to coordinate tx and rx timeslots.
42 //-----------------------------------------------------------------------------
43
44 static uint32_t last_frame_end; /* ts of last bit of previews rx or tx frame */
45
46 #define RWD_TIME_PAUSE 30 /* 20us */
47 #define RWD_TIME_1 150 /* READER_TIME_PAUSE 20us off + 80us on = 100us */
48 #define RWD_TIME_0 90 /* READER_TIME_PAUSE 20us off + 40us on = 60us */
49 #define RWD_FRAME_WAIT 330 /* 220us from TAG frame end to READER frame start */
50 #define TAG_FRAME_WAIT 495 /* 330us from READER frame end to TAG frame start */
51 #define TAG_BIT_PERIOD 150 /* 100us */
52 #define TAG_WRITE_TIMEOUT 60 /* 40 * 100us (write should take at most 3.6ms) */
53
54 #define LEGIC_READ 0x01 /* Read Command */
55 #define LEGIC_WRITE 0x00 /* Write Command */
56
57 #define SESSION_IV 0x55 /* An arbitrary chose session IV, all shoud work */
58 #define OFFSET_LOG 1024 /* The largest Legic Prime card is 1k */
59 #define WRITE_LOWERLIMIT 4 /* UID and MCC are not writable */
60
61 #define INPUT_THRESHOLD 8 /* heuristically determined, lower values */
62 /* lead to detecting false ack during write */
63
64 //-----------------------------------------------------------------------------
65 // I/O interface abstraction (FPGA -> ARM)
66 //-----------------------------------------------------------------------------
67
68 static inline uint16_t rx_frame_from_fpga() {
69 for(;;) {
70 WDT_HIT();
71
72 // wait for frame be become available in rx holding register
73 if(AT91C_BASE_SSC->SSC_SR & (AT91C_SSC_RXRDY)) {
74 return AT91C_BASE_SSC->SSC_RHR;
75 }
76 }
77 }
78
79 //-----------------------------------------------------------------------------
80 // Demodulation (Reader)
81 //-----------------------------------------------------------------------------
82
83 // Returns a demedulated bit
84 //
85 // The FPGA running xcorrelation samples the subcarrier at ~13.56 MHz. The mode
86 // was initialy designed to receive BSPK/2-PSK. Hance, it reports an I/Q pair
87 // every 4.7us (8 bits i and 8 bits q).
88 //
89 // The subcarrier amplitude can be calculated using Pythagoras sqrt(i^2 + q^2).
90 // To reduce CPU time the amplitude is approximated by using linear functions:
91 // am = MAX(ABS(i),ABS(q)) + 1/2*MIN(ABS(i),ABSq))
92 //
93 // The bit time is 99.1us (21 I/Q pairs). The receiver skips the first 5 samples
94 // and averages the next (most stable) 8 samples. The final 8 samples are dropped
95 // also.
96 //
97 // The demodulated should be alligned to the bit period by the caller. This is
98 // done in rx_bit and rx_ack.
99 static inline bool rx_bit() {
100 int32_t sum_cq = 0;
101 int32_t sum_ci = 0;
102
103 // skip first 5 I/Q pairs
104 for(size_t i = 0; i<5; ++i) {
105 (void)rx_frame_from_fpga();
106 }
107
108 // sample next 8 I/Q pairs
109 for(size_t i = 0; i<8; ++i) {
110 uint16_t iq = rx_frame_from_fpga();
111 int8_t ci = (int8_t)(iq >> 8);
112 int8_t cq = (int8_t)(iq & 0xff);
113 sum_ci += ci;
114 sum_cq += cq;
115 }
116
117 // calculate power
118 int32_t power = (MAX(ABS(sum_ci), ABS(sum_cq)) + MIN(ABS(sum_ci), ABS(sum_cq))/2);
119
120 // compare average (power / 8) to threshold
121 return ((power >> 3) > INPUT_THRESHOLD);
122 }
123
124 //-----------------------------------------------------------------------------
125 // Modulation (Reader)
126 //
127 // I've tried to modulate the Legic specific pause-puls using ssc and the default
128 // ssc clock of 105.4 kHz (bit periode of 9.4us) - previous commit. However,
129 // the timing was not precise enough. By increasing the ssc clock this could
130 // be circumvented, but the adventage over bitbang would be little.
131 //-----------------------------------------------------------------------------
132
133 static inline void tx_bit(bool bit) {
134 // insert pause
135 HIGH(GPIO_SSC_DOUT);
136 last_frame_end += RWD_TIME_PAUSE;
137 while(GET_TICKS < last_frame_end) { };
138
139 // return to carrier on, wait for bit periode to end
140 LOW(GPIO_SSC_DOUT);
141 last_frame_end += (bit ? RWD_TIME_1 : RWD_TIME_0) - RWD_TIME_PAUSE;
142 while(GET_TICKS < last_frame_end) { };
143 }
144
145 //-----------------------------------------------------------------------------
146 // Frame Handling (Reader)
147 //
148 // The LEGIC RF protocol from card to reader does not include explicit frame
149 // start/stop information or length information. The reader must know beforehand
150 // how many bits it wants to receive.
151 // Notably: a card sending a stream of 0-bits is indistinguishable from no card
152 // present.
153 //-----------------------------------------------------------------------------
154
155 static void tx_frame(uint32_t frame, uint8_t len) {
156 FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_MODE_SEND_FULL_MOD);
157
158 // wait for next tx timeslot
159 last_frame_end += RWD_FRAME_WAIT;
160 while(GET_TICKS < last_frame_end) { };
161
162 // transmit frame, MSB first
163 for(uint8_t i = 0; i < len; ++i) {
164 bool bit = (frame >> i) & 0x01;
165 tx_bit(bit ^ legic_prng_get_bit());
166 legic_prng_forward(1);
167 };
168
169 // add pause to mark end of the frame
170 HIGH(GPIO_SSC_DOUT);
171 last_frame_end += RWD_TIME_PAUSE;
172 while(GET_TICKS < last_frame_end) { };
173 LOW(GPIO_SSC_DOUT);
174 }
175
176 static uint32_t rx_frame(uint8_t len) {
177 FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_SUBCARRIER_212_KHZ | FPGA_HF_READER_MODE_RECEIVE_IQ);
178
179 // hold sampling until card is expected to respond
180 last_frame_end += TAG_FRAME_WAIT;
181 while(GET_TICKS < last_frame_end) { };
182
183 uint32_t frame = 0;
184 for(uint8_t i = 0; i < len; ++i) {
185 frame |= (rx_bit() ^ legic_prng_get_bit()) << i;
186 legic_prng_forward(1);
187
188 // rx_bit runs only 95us, resync to TAG_BIT_PERIOD
189 last_frame_end += TAG_BIT_PERIOD;
190 while(GET_TICKS < last_frame_end) { };
191 }
192
193 return frame;
194 }
195
196 static bool rx_ack() {
197 // change fpga into rx mode
198 FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_SUBCARRIER_212_KHZ | FPGA_HF_READER_MODE_RECEIVE_IQ);
199
200 // hold sampling until card is expected to respond
201 last_frame_end += TAG_FRAME_WAIT;
202 while(GET_TICKS < last_frame_end) { };
203
204 uint32_t ack = 0;
205 for(uint8_t i = 0; i < TAG_WRITE_TIMEOUT; ++i) {
206 // sample bit
207 ack = rx_bit();
208 legic_prng_forward(1);
209
210 // rx_bit runs only 95us, resync to TAG_BIT_PERIOD
211 last_frame_end += TAG_BIT_PERIOD;
212 while(GET_TICKS < last_frame_end) { };
213
214 // check if it was an ACK
215 if(ack) {
216 break;
217 }
218 }
219
220 return ack;
221 }
222
223 //-----------------------------------------------------------------------------
224 // Legic Reader
225 //-----------------------------------------------------------------------------
226
227 static int init_card(uint8_t cardtype, legic_card_select_t *p_card) {
228 p_card->tagtype = cardtype;
229
230 switch(p_card->tagtype) {
231 case 0x0d:
232 p_card->cmdsize = 6;
233 p_card->addrsize = 5;
234 p_card->cardsize = 22;
235 break;
236 case 0x1d:
237 p_card->cmdsize = 9;
238 p_card->addrsize = 8;
239 p_card->cardsize = 256;
240 break;
241 case 0x3d:
242 p_card->cmdsize = 11;
243 p_card->addrsize = 10;
244 p_card->cardsize = 1024;
245 break;
246 default:
247 p_card->cmdsize = 0;
248 p_card->addrsize = 0;
249 p_card->cardsize = 0;
250 return 2;
251 }
252 return 0;
253 }
254
255 static void init_reader(bool clear_mem) {
256 // configure FPGA
257 FpgaDownloadAndGo(FPGA_BITSTREAM_HF);
258 FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER | FPGA_HF_READER_SUBCARRIER_212_KHZ | FPGA_HF_READER_MODE_RECEIVE_IQ);
259 SetAdcMuxFor(GPIO_MUXSEL_HIPKD);
260 LED_D_ON();
261
262 // configure SSC with defaults
263 FpgaSetupSsc(FPGA_MAJOR_MODE_HF_READER);
264
265 // re-claim GPIO_SSC_DOUT as GPIO and enable output
266 AT91C_BASE_PIOA->PIO_OER = GPIO_SSC_DOUT;
267 AT91C_BASE_PIOA->PIO_PER = GPIO_SSC_DOUT;
268 LOW(GPIO_SSC_DOUT);
269
270 // init crc calculator
271 crc_init(&legic_crc, 4, 0x19 >> 1, 0x05, 0);
272
273 // start us timer
274 StartTicks();
275 }
276
277 // Setup reader to card connection
278 //
279 // The setup consists of a three way handshake:
280 // - Transmit initialisation vector 7 bits
281 // - Receive card type 6 bits
282 // - Transmit Acknowledge 6 bits
283 static uint32_t setup_phase(uint8_t iv) {
284 // init coordination timestamp
285 last_frame_end = GET_TICKS;
286
287 // Switch on carrier and let the card charge for 5ms.
288 last_frame_end += 7500;
289 while(GET_TICKS < last_frame_end) { };
290
291 legic_prng_init(0);
292 tx_frame(iv, 7);
293
294 // configure prng
295 legic_prng_init(iv);
296 legic_prng_forward(2);
297
298 // receive card type
299 int32_t card_type = rx_frame(6);
300 legic_prng_forward(3);
301
302 // send obsfuscated acknowledgment frame
303 switch (card_type) {
304 case 0x0D:
305 tx_frame(0x19, 6); // MIM22 | READCMD = 0x18 | 0x01
306 break;
307 case 0x1D:
308 case 0x3D:
309 tx_frame(0x39, 6); // MIM256 | READCMD = 0x38 | 0x01
310 break;
311 }
312
313 return card_type;
314 }
315
316 static uint8_t calc_crc4(uint16_t cmd, uint8_t cmd_sz, uint8_t value) {
317 crc_clear(&legic_crc);
318 crc_update(&legic_crc, (value << cmd_sz) | cmd, 8 + cmd_sz);
319 return crc_finish(&legic_crc);
320 }
321
322 static int16_t read_byte(uint16_t index, uint8_t cmd_sz) {
323 uint16_t cmd = (index << 1) | LEGIC_READ;
324
325 // read one byte
326 LED_B_ON();
327 legic_prng_forward(2);
328 tx_frame(cmd, cmd_sz);
329 legic_prng_forward(2);
330 uint32_t frame = rx_frame(12);
331 LED_B_OFF();
332
333 // split frame into data and crc
334 uint8_t byte = BYTEx(frame, 0);
335 uint8_t crc = BYTEx(frame, 1);
336
337 // check received against calculated crc
338 uint8_t calc_crc = calc_crc4(cmd, cmd_sz, byte);
339 if(calc_crc != crc) {
340 Dbprintf("!!! crc mismatch: %x != %x !!!", calc_crc, crc);
341 return -1;
342 }
343
344 legic_prng_forward(1);
345
346 return byte;
347 }
348
349 // Transmit write command, wait until (3.6ms) the tag sends back an unencrypted
350 // ACK ('1' bit) and forward the prng time based.
351 bool write_byte(uint16_t index, uint8_t byte, uint8_t addr_sz) {
352 uint32_t cmd = index << 1 | LEGIC_WRITE; // prepare command
353 uint8_t crc = calc_crc4(cmd, addr_sz + 1, byte); // calculate crc
354 cmd |= byte << (addr_sz + 1); // append value
355 cmd |= (crc & 0xF) << (addr_sz + 1 + 8); // and crc
356
357 // send write command
358 LED_C_ON();
359 legic_prng_forward(2);
360 tx_frame(cmd, addr_sz + 1 + 8 + 4); // sz = addr_sz + cmd + data + crc
361 legic_prng_forward(3);
362 LED_C_OFF();
363
364 // wait for ack
365 return rx_ack();
366 }
367
368 //-----------------------------------------------------------------------------
369 // Command Line Interface
370 //
371 // Only this functions are public / called from appmain.c
372 //-----------------------------------------------------------------------------
373 void LegicRfReader(int offset, int bytes) {
374 uint8_t *BigBuf = BigBuf_get_addr();
375 memset(BigBuf, 0, 1024);
376
377 // configure ARM and FPGA
378 init_reader(false);
379
380 // establish shared secret and detect card type
381 DbpString("Reading card ...");
382 uint8_t card_type = setup_phase(SESSION_IV);
383 uint8_t result = 0;
384 if(init_card(card_type, &card) != 0) {
385 result = 1;
386 goto OUT;
387 }
388
389 // if no argument is specified create full dump
390 if(bytes == -1) {
391 bytes = card.cardsize;
392 }
393
394 // do not read beyond card memory
395 if(bytes + offset > card.cardsize) {
396 bytes = card.cardsize - offset;
397 }
398
399 for(uint16_t i = 0; i < bytes; ++i) {
400 int16_t byte = read_byte(offset + i, card.cmdsize);
401 if(byte == -1) {
402 result = 2;
403 goto OUT;
404 }
405 BigBuf[i] = byte;
406 }
407
408 OUT:
409 cmd_send(CMD_ACK, result, bytes, 0, &card, sizeof(card));
410 FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
411 LED_B_OFF();
412 LED_C_OFF();
413 LED_D_OFF();
414 StopTicks();
415 }
416
417 void LegicRfWriter(int bytes, int offset) {
418 uint8_t *BigBuf = BigBuf_get_addr();
419
420 // configure ARM and FPGA
421 init_reader(false);
422
423 // uid is not writeable
424 if(offset <= WRITE_LOWERLIMIT) {
425 goto OUT;
426 }
427
428 // establish shared secret and detect card type
429 Dbprintf("Writing 0x%02.2x - 0x%02.2x ...", offset, offset+bytes);
430 uint8_t card_type = setup_phase(SESSION_IV);
431 if(init_card(card_type, &card) != 0) {
432 Dbprintf("No or unknown card found, aborting");
433 goto OUT;
434 }
435
436 // do not write beyond card memory
437 if(bytes + offset > card.cardsize) {
438 bytes = card.cardsize - offset;
439 }
440
441 // write in reverse order, only then is DCF (decremental field) writable
442 while(bytes-- > 0 && !BUTTON_PRESS()) {
443 if(!write_byte(bytes + offset, BigBuf[bytes + offset], card.addrsize)) {
444 Dbprintf("operation failed @ 0x%03.3x", bytes);
445 goto OUT;
446 }
447 }
448
449 // OK
450 DbpString("Write successful");
451
452 OUT:
453 FpgaWriteConfWord(FPGA_MAJOR_MODE_OFF);
454 LED_B_OFF();
455 LED_C_OFF();
456 LED_D_OFF();
457 StopTicks();
458 }
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