summaryrefslogtreecommitdiff
path: root/openpicc/application/iso14443a_diffmiller.c
blob: cc895df9427e5f53fc93d0d12ba03a3e19068389 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
/* ISO14443A Miller decoder for OpenPICC, working with differential time samples
 *  
 * Copyright 2007 Milosch Meriac <meriac@bitmanufaktur.de>
 * Copyright 2007 Karsten Nohl <honk98@web.de>
 * Copyright 2007,2008 Henryk Plötz <henryk@ploetzli.ch>
 *
 *  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 2 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.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#include <openpicc.h>
#include <FreeRTOS.h>

#include <errno.h>
#include <stdlib.h>
#include <string.h>

#include "iso14443.h"
#include "iso14443a_diffmiller.h"
#include "usb_print.h"

#include "performance.h"

#define DEBUGP (void)
#define printf usb_print_string

/*
 * Decoding Methodology: We'll only see the edges for the start of modulation pauses and not
 * all symbols generate modulation pauses at all. Two phases:
 *  + Old state and next edge delta to sequence of symbols (might be more than one symbol per edge)
 *  + Symbols to EOF/SOF marker and bits
 * 
 * These are the possible old-state/delta combinations and the symbols they yield:
 * 
 * old_state  delta (in bit_len/4)  symbol(s)
 * none       3                     ZZ
 * none       5                     ZX
 * X          3                     X
 * X          5                     YZ
 * X          7                     YX
 * X          >=9                   YY
 * Y          3                     ZZ
 * Y          5                     ZX
 * Z          3                     Z
 * Z          5                     X
 * Z          >=7                   Y
 * 
 * All other combinations are invalid and likely en- or decoding errors. (Note that old_state
 * Y is exactly the same as old_state none.)
 * 
 * The mapping from symbol sequences to SOF/EOF/bit is as follows:
 *         X: 1
 * 0, then Y: EOF
 *   other Y: 0
 *   first Z: SOF
 *   other Z: 0
 */

#define BIT_LEN 128
/* The theoretical error margin for the timing measurement is about 7 (note: that is a jitter of 7 in
 * total, e.g. +/- 3.5), but we'll round that up to +/- 8. However, the specification allows pause
 * times from 2us to 3us, e.g. 1us difference, so we'll add another 13.
 */ 
#define BIT_LEN_ERROR_MAX (8+13)
#define PAUSE_LEN 20
/* Subtract the mean error margin (about 4, see comment above) from the bit length
 * Also subtract the pause length for the case when the clock is not counting during
 * a pause. Will subtract this length below for the when the clock *is* counting during
 * pauses.
 */
#define BIT_OFFSET (-4 -PAUSE_LEN)
#define BIT_LEN_3 ((BIT_LEN*3)/4 +BIT_OFFSET)
#define BIT_LEN_5 ((BIT_LEN*5)/4 +BIT_OFFSET)
#define BIT_LEN_7 ((BIT_LEN*7)/4 +BIT_OFFSET)
#define BIT_LEN_9 ((BIT_LEN*9)/4 +BIT_OFFSET)

#define ALMOST_EQUAL(a,b) ( abs(a-b) <= BIT_LEN_ERROR_MAX )
#define MUCH_GREATER_THAN(a,b) ( a > (b+BIT_LEN_ERROR_MAX) )
#define ALMOST_GREATER_THAN_OR_EQUAL(a,b) (a >= (b-BIT_LEN_ERROR_MAX))

enum symbol {NO_SYM=0, sym_x, sym_y, sym_z};
enum bit { BIT_ERROR, BIT_SOF, BIT_0, BIT_1, BIT_EOF };

struct diffmiller_state {
	int initialized, pauses_count;
	enum symbol old_state;
	enum bit last_bit;
	iso14443_frame *frame;
	u_int32_t counter;
	u_int16_t byte,crc;
	u_int8_t parity;
	struct {
		u_int8_t in_frame:1;
		u_int8_t frame_finished:1;
		u_int8_t overflow:1;
		u_int8_t error:1;
	} flags;
};

struct diffmiller_state _state;

inline void start_frame(struct diffmiller_state * const state)
{
	state->counter=0;
	state->byte=0;
	state->parity=0;
	state->crc=0x6363;
	
	performance_set_checkpoint("start_frame before memset");
	memset(&state->flags, 0, sizeof(state->flags));
	state->flags.in_frame = 1;
	
	//memset(state->frame, 0, sizeof(*state->frame));
	memset(state->frame, 0, (u_int32_t)&(((iso14443_frame*)0)->data) );
	performance_set_checkpoint("start_frame after memset");
}

static inline void append_to_frame(struct diffmiller_state *const state,
		const u_int8_t byte, const u_int8_t parity, const u_int8_t valid_bits) {

	iso14443_frame * const f = state->frame;
	
	if(f->numbytes >= sizeof(f->data)/sizeof(f->data[0])-1) { /* -1, because the last byte may be half filled */
		state->flags.overflow = 1;
		return;
	}

	if(f->numbits != 0) {
		DEBUGP("Appending to a frame with incomplete byte");
	}

	f->data[f->numbytes] = byte & 0xff;
	f->parity[f->numbytes/8] |= ((parity&1)<<(f->numbytes%8));

	if(valid_bits == 8) {
		f->numbytes++;
	} else {
		f->numbits += valid_bits;
	}
}


static inline void end_frame(struct diffmiller_state * const state)
{
	if(state->frame != NULL) {
		if(state->counter > 0) {
			append_to_frame(state, state->byte, 0, state->counter);
		}
		
		if(!state->crc)
			state->frame->parameters.a.crc = CRC_OK;
		else
			state->frame->parameters.a.crc = CRC_ERROR;
		
		state->flags.frame_finished = 1;
	}
}

static inline void Miller_Bit(struct diffmiller_state * const state, const int bit_value)
{
	
    if(state->counter<8) {
    	state->byte=state->byte | (bit_value<<state->counter);
    	if(bit_value)
    		state->parity++;
    } else DEBUGP((((~state->parity)&1)==bit_value) ? " ":"!" );

    if(++state->counter==9) {
    	state->counter=0;
    	append_to_frame(state, state->byte, bit_value, 8);

    	//DEBUGP(" ==0x%02X\n",byte);

    	state->byte=(state->byte ^ state->crc)&0xFF;
    	state->byte=(state->byte ^ state->byte<<4)&0xFF;
    	state->crc=((state->crc>>8)^(state->byte<<8)^(state->byte<<3)^(state->byte>>4))&0xFFFF;

    	//printf(" [%04X]\n",crc);

    	state->byte=0;        
    	state->parity=0;
    }
}

#define PRINT_BIT(a) if(0){(void)a;}
//#define PRINT_BIT(a) usb_print_string(a)

#define DO_BIT_0 { \
	Miller_Bit(state, 0); \
	PRINT_BIT(" 0"); \
	}

#define DO_BIT_1 { \
	Miller_Bit(state, 1); \
	PRINT_BIT(" 1"); \
	}

#define DO_SYMBOL_X \
	if(!in_frame) { \
		if(last_bit == BIT_0) DO_BIT_0; \
		error = 1; \
		end_frame(state); \
		PRINT_BIT(" ERROR\n"); \
		last_bit = BIT_ERROR; \
		in_frame = 0; \
	} else { \
		if(last_bit == BIT_0) DO_BIT_0; \
		DO_BIT_1; \
		last_bit = BIT_1; \
	}

#define DO_SYMBOL_Y \
	if(!in_frame) { \
		if(last_bit == BIT_0) DO_BIT_0; \
		error = 1; \
		end_frame(state); \
		PRINT_BIT(" ERROR\n"); \
		last_bit = BIT_ERROR; \
		in_frame = 0; \
	} else { \
		if(last_bit == BIT_0) { \
			end_frame(state); \
			PRINT_BIT(" EOF\n"); \
			last_bit = BIT_EOF; \
			in_frame = 0; \
		} else { \
			last_bit = BIT_0; \
		} \
	}

#define DO_SYMBOL_Z \
	if(!in_frame) { \
		if(last_bit == BIT_0) DO_BIT_0; \
		start_frame(state); \
		PRINT_BIT("SOF"); \
		in_frame = 1; \
		last_bit = BIT_ERROR; \
		last_bit = BIT_SOF; \
	} else { \
		if(last_bit == BIT_0) DO_BIT_0; \
		last_bit = BIT_0; \
	}


int iso14443a_decode_diffmiller(struct diffmiller_state * const state, iso14443_frame * const frame, 
	const u_int32_t buffer[], unsigned int * const offset, const unsigned int buflen)
{
	if(state == NULL || !state->initialized) return -EINVAL;
	if(state->frame != NULL && state->frame != frame) return -EINVAL;
	state->frame = frame;
	
	enum symbol old_state = state->old_state;
	enum bit last_bit = state->last_bit;
	int in_frame = state->flags.in_frame;
	int error = state->flags.error;
	
	for(; *offset < buflen; ) {
		int delta;
		if(state->pauses_count)
			delta = buffer[(*offset)++] - PAUSE_LEN;
		else
			delta = buffer[(*offset)++];

		switch(old_state) {
		case sym_x:
			if( ALMOST_EQUAL(delta, BIT_LEN_3) ) {
				DO_SYMBOL_X;
				old_state = sym_x;
			} else if( ALMOST_EQUAL(delta, BIT_LEN_5) ) {
				DO_SYMBOL_Y;
				DO_SYMBOL_Z;
				old_state = sym_z;
			} else if( ALMOST_EQUAL(delta, BIT_LEN_7) ) {
				DO_SYMBOL_Y;
				DO_SYMBOL_X;
				old_state = sym_x;
			} else if( ALMOST_GREATER_THAN_OR_EQUAL(delta, BIT_LEN_9)) {
				DO_SYMBOL_Y;
				DO_SYMBOL_Y;
				old_state = sym_y;
			}
			break;
		case NO_SYM: /* Fall-Through */
		case sym_y:
			if( ALMOST_EQUAL(delta, BIT_LEN_3) ) {
				DO_SYMBOL_Z;
				DO_SYMBOL_Z;
				old_state = sym_z;
			} else if( ALMOST_EQUAL(delta, BIT_LEN_5) ) {
				DO_SYMBOL_Z;
				DO_SYMBOL_X;
				old_state = sym_x;
			} 
			break;
		case sym_z:
			if( ALMOST_EQUAL(delta, BIT_LEN_3) ) {
				DO_SYMBOL_Z;
				old_state = sym_z;
			} else if( ALMOST_EQUAL(delta, BIT_LEN_5) ) {
				DO_SYMBOL_X;
				old_state = sym_x;
			} else if( ALMOST_GREATER_THAN_OR_EQUAL(delta, BIT_LEN_7)) {
				DO_SYMBOL_Y;
				old_state = sym_y;
			}
			break;
		}
		
		if(state->flags.frame_finished)  {
			state->flags.frame_finished = 0;
			state->old_state = old_state;
			state->last_bit = last_bit;
			state->flags.in_frame = in_frame;
			state->flags.error = error;
			performance_set_checkpoint("frame finished");
			return 0;
		}
	}
	
	state->old_state = old_state;
	state->last_bit = last_bit;
	state->flags.in_frame = in_frame;
	state->flags.error = error;
	
	return -EBUSY;
}

struct diffmiller_state *iso14443a_init_diffmiller(int pauses_count)
{
	if(_state.initialized) return NULL;
	struct diffmiller_state *state = &_state;
	state->initialized = 1;
	state->pauses_count = pauses_count;
	state->frame = NULL;
	state->flags.frame_finished = 0;
	
	return state;
}
personal git repositories of Harald Welte. Your mileage may vary