summaryrefslogtreecommitdiff
path: root/lib/util/asn1.c
blob: c687f8dc9a1d43ff0e0fec51dc385719f2cf4314 (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
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
/* 
   Unix SMB/CIFS implementation.
   simple ASN1 routines
   Copyright (C) Andrew Tridgell 2001
   
   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.
   
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "../lib/util/asn1.h"

/* allocate an asn1 structure */
struct asn1_data *asn1_init(TALLOC_CTX *mem_ctx)
{
	struct asn1_data *ret = talloc_zero(mem_ctx, struct asn1_data);
	if (ret == NULL) {
		DEBUG(0,("asn1_init failed! out of memory\n"));
	}
	return ret;
}

/* free an asn1 structure */
void asn1_free(struct asn1_data *data)
{
	talloc_free(data);
}

/* write to the ASN1 buffer, advancing the buffer pointer */
bool asn1_write(struct asn1_data *data, const void *p, int len)
{
	if (data->has_error) return false;
	if (data->length < data->ofs+len) {
		uint8_t *newp;
		newp = talloc_realloc(data, data->data, uint8_t, data->ofs+len);
		if (!newp) {
			asn1_free(data);
			data->has_error = true;
			return false;
		}
		data->data = newp;
		data->length = data->ofs+len;
	}
	memcpy(data->data + data->ofs, p, len);
	data->ofs += len;
	return true;
}

/* useful fn for writing a uint8_t */
bool asn1_write_uint8(struct asn1_data *data, uint8_t v)
{
	return asn1_write(data, &v, 1);
}

/* push a tag onto the asn1 data buffer. Used for nested structures */
bool asn1_push_tag(struct asn1_data *data, uint8_t tag)
{
	struct nesting *nesting;

	asn1_write_uint8(data, tag);
	nesting = talloc(data, struct nesting);
	if (!nesting) {
		data->has_error = true;
		return false;
	}

	nesting->start = data->ofs;
	nesting->next = data->nesting;
	data->nesting = nesting;
	return asn1_write_uint8(data, 0xff);
}

/* pop a tag */
bool asn1_pop_tag(struct asn1_data *data)
{
	struct nesting *nesting;
	size_t len;

	nesting = data->nesting;

	if (!nesting) {
		data->has_error = true;
		return false;
	}
	len = data->ofs - (nesting->start+1);
	/* yes, this is ugly. We don't know in advance how many bytes the length
	   of a tag will take, so we assumed 1 byte. If we were wrong then we 
	   need to correct our mistake */
	if (len > 0xFFFFFF) {
		data->data[nesting->start] = 0x84;
		if (!asn1_write_uint8(data, 0)) return false;
		if (!asn1_write_uint8(data, 0)) return false;
		if (!asn1_write_uint8(data, 0)) return false;
		if (!asn1_write_uint8(data, 0)) return false;
		memmove(data->data+nesting->start+5, data->data+nesting->start+1, len);
		data->data[nesting->start+1] = (len>>24) & 0xFF;
		data->data[nesting->start+2] = (len>>16) & 0xFF;
		data->data[nesting->start+3] = (len>>8) & 0xFF;
		data->data[nesting->start+4] = len&0xff;
	} else if (len > 0xFFFF) {
		data->data[nesting->start] = 0x83;
		if (!asn1_write_uint8(data, 0)) return false;
		if (!asn1_write_uint8(data, 0)) return false;
		if (!asn1_write_uint8(data, 0)) return false;
		memmove(data->data+nesting->start+4, data->data+nesting->start+1, len);
		data->data[nesting->start+1] = (len>>16) & 0xFF;
		data->data[nesting->start+2] = (len>>8) & 0xFF;
		data->data[nesting->start+3] = len&0xff;
	} else if (len > 255) {
		data->data[nesting->start] = 0x82;
		if (!asn1_write_uint8(data, 0)) return false;
		if (!asn1_write_uint8(data, 0)) return false;
		memmove(data->data+nesting->start+3, data->data+nesting->start+1, len);
		data->data[nesting->start+1] = len>>8;
		data->data[nesting->start+2] = len&0xff;
	} else if (len > 127) {
		data->data[nesting->start] = 0x81;
		if (!asn1_write_uint8(data, 0)) return false;
		memmove(data->data+nesting->start+2, data->data+nesting->start+1, len);
		data->data[nesting->start+1] = len;
	} else {
		data->data[nesting->start] = len;
	}

	data->nesting = nesting->next;
	talloc_free(nesting);
	return true;
}

/* "i" is the one's complement representation, as is the normal result of an
 * implicit signed->unsigned conversion */

static bool push_int_bigendian(struct asn1_data *data, unsigned int i, bool negative)
{
	uint8_t lowest = i & 0xFF;

	i = i >> 8;
	if (i != 0)
		if (!push_int_bigendian(data, i, negative))
			return false;

	if (data->nesting->start+1 == data->ofs) {

		/* We did not write anything yet, looking at the highest
		 * valued byte */

		if (negative) {
			/* Don't write leading 0xff's */
			if (lowest == 0xFF)
				return true;

			if ((lowest & 0x80) == 0) {
				/* The only exception for a leading 0xff is if
				 * the highest bit is 0, which would indicate
				 * a positive value */
				if (!asn1_write_uint8(data, 0xff))
					return false;
			}
		} else {
			if (lowest & 0x80) {
				/* The highest bit of a positive integer is 1,
				 * this would indicate a negative number. Push
				 * a 0 to indicate a positive one */
				if (!asn1_write_uint8(data, 0))
					return false;
			}
		}
	}

	return asn1_write_uint8(data, lowest);
}

/* write an Integer without the tag framing. Needed for example for the LDAP
 * Abandon Operation */

bool asn1_write_implicit_Integer(struct asn1_data *data, int i)
{
	if (i == -1) {
		/* -1 is special as it consists of all-0xff bytes. In
                    push_int_bigendian this is the only case that is not
                    properly handled, as all 0xff bytes would be handled as
                    leading ones to be ignored. */
		return asn1_write_uint8(data, 0xff);
	} else {
		return push_int_bigendian(data, i, i<0);
	}
}


/* write an integer */
bool asn1_write_Integer(struct asn1_data *data, int i)
{
	if (!asn1_push_tag(data, ASN1_INTEGER)) return false;
	if (!asn1_write_implicit_Integer(data, i)) return false;
	return asn1_pop_tag(data);
}

bool ber_write_OID_String(DATA_BLOB *blob, const char *OID)
{
	uint_t v, v2;
	const char *p = (const char *)OID;
	char *newp;
	int i;

	v = strtoul(p, &newp, 10);
	if (newp[0] != '.') return false;
	p = newp + 1;

	v2 = strtoul(p, &newp, 10);
	if (newp[0] != '.') return false;
	p = newp + 1;

	/*the ber representation can't use more space then the string one */
	*blob = data_blob(NULL, strlen(OID));
	if (!blob->data) return false;

	blob->data[0] = 40*v + v2;

	i = 1;
	while (*p) {
		v = strtoul(p, &newp, 10);
		if (newp[0] == '.') {
			p = newp + 1;
		} else if (newp[0] == '\0') {
			p = newp;
		} else {
			data_blob_free(blob);
			return false;
		}
		if (v >= (1<<28)) blob->data[i++] = (0x80 | ((v>>28)&0x7f));
		if (v >= (1<<21)) blob->data[i++] = (0x80 | ((v>>21)&0x7f));
		if (v >= (1<<14)) blob->data[i++] = (0x80 | ((v>>14)&0x7f));
		if (v >= (1<<7)) blob->data[i++] = (0x80 | ((v>>7)&0x7f));
		blob->data[i++] = (v&0x7f);
	}

	blob->length = i;

	return true;
}

/* write an object ID to a ASN1 buffer */
bool asn1_write_OID(struct asn1_data *data, const char *OID)
{
	DATA_BLOB blob;

	if (!asn1_push_tag(data, ASN1_OID)) return false;

	if (!ber_write_OID_String(&blob, OID)) {
		data->has_error = true;
		return false;
	}

	if (!asn1_write(data, blob.data, blob.length)) {
		data->has_error = true;
		return false;
	}
	data_blob_free(&blob);
	return asn1_pop_tag(data);
}

/* write an octet string */
bool asn1_write_OctetString(struct asn1_data *data, const void *p, size_t length)
{
	asn1_push_tag(data, ASN1_OCTET_STRING);
	asn1_write(data, p, length);
	asn1_pop_tag(data);
	return !data->has_error;
}

/* write a LDAP string */
bool asn1_write_LDAPString(struct asn1_data *data, const char *s)
{
	asn1_write(data, s, strlen(s));
	return !data->has_error;
}

/* write a LDAP string from a DATA_BLOB */
bool asn1_write_DATA_BLOB_LDAPString(struct asn1_data *data, const DATA_BLOB *s)
{
	asn1_write(data, s->data, s->length);
	return !data->has_error;
}

/* write a general string */
bool asn1_write_GeneralString(struct asn1_data *data, const char *s)
{
	asn1_push_tag(data, ASN1_GENERAL_STRING);
	asn1_write_LDAPString(data, s);
	asn1_pop_tag(data);
	return !data->has_error;
}

bool asn1_write_ContextSimple(struct asn1_data *data, uint8_t num, DATA_BLOB *blob)
{
	asn1_push_tag(data, ASN1_CONTEXT_SIMPLE(num));
	asn1_write(data, blob->data, blob->length);
	asn1_pop_tag(data);
	return !data->has_error;
}

/* write a BOOLEAN */
bool asn1_write_BOOLEAN(struct asn1_data *data, bool v)
{
	asn1_push_tag(data, ASN1_BOOLEAN);
	asn1_write_uint8(data, v ? 0xFF : 0);
	asn1_pop_tag(data);
	return !data->has_error;
}

bool asn1_read_BOOLEAN(struct asn1_data *data, bool *v)
{
	uint8_t tmp = 0;
	asn1_start_tag(data, ASN1_BOOLEAN);
	asn1_read_uint8(data, &tmp);
	if (tmp == 0xFF) {
		*v = true;
	} else {
		*v = false;
	}
	asn1_end_tag(data);
	return !data->has_error;
}

/* check a BOOLEAN */
bool asn1_check_BOOLEAN(struct asn1_data *data, bool v)
{
	uint8_t b = 0;

	asn1_read_uint8(data, &b);
	if (b != ASN1_BOOLEAN) {
		data->has_error = true;
		return false;
	}
	asn1_read_uint8(data, &b);
	if (b != v) {
		data->has_error = true;
		return false;
	}
	return !data->has_error;
}


/* load a struct asn1_data structure with a lump of data, ready to be parsed */
bool asn1_load(struct asn1_data *data, DATA_BLOB blob)
{
	ZERO_STRUCTP(data);
	data->data = (uint8_t *)talloc_memdup(data, blob.data, blob.length);
	if (!data->data) {
		data->has_error = true;
		return false;
	}
	data->length = blob.length;
	return true;
}

/* Peek into an ASN1 buffer, not advancing the pointer */
bool asn1_peek(struct asn1_data *data, void *p, int len)
{
	if (data->has_error)
		return false;

	if (len < 0 || data->ofs + len < data->ofs || data->ofs + len < len)
		return false;

	if (data->ofs + len > data->length) {
		/* we need to mark the buffer as consumed, so the caller knows
		   this was an out of data error, and not a decode error */
		data->ofs = data->length;
		return false;
	}

	memcpy(p, data->data + data->ofs, len);
	return true;
}

/* read from a ASN1 buffer, advancing the buffer pointer */
bool asn1_read(struct asn1_data *data, void *p, int len)
{
	if (!asn1_peek(data, p, len)) {
		data->has_error = true;
		return false;
	}

	data->ofs += len;
	return true;
}

/* read a uint8_t from a ASN1 buffer */
bool asn1_read_uint8(struct asn1_data *data, uint8_t *v)
{
	return asn1_read(data, v, 1);
}

bool asn1_peek_uint8(struct asn1_data *data, uint8_t *v)
{
	return asn1_peek(data, v, 1);
}

bool asn1_peek_tag(struct asn1_data *data, uint8_t tag)
{
	uint8_t b;

	if (asn1_tag_remaining(data) <= 0) {
		return false;
	}

	if (!asn1_peek_uint8(data, &b))
		return false;

	return (b == tag);
}

/* start reading a nested asn1 structure */
bool asn1_start_tag(struct asn1_data *data, uint8_t tag)
{
	uint8_t b;
	struct nesting *nesting;
	
	if (!asn1_read_uint8(data, &b))
		return false;

	if (b != tag) {
		data->has_error = true;
		return false;
	}
	nesting = talloc(data, struct nesting);
	if (!nesting) {
		data->has_error = true;
		return false;
	}

	if (!asn1_read_uint8(data, &b)) {
		return false;
	}

	if (b & 0x80) {
		int n = b & 0x7f;
		if (!asn1_read_uint8(data, &b))
			return false;
		nesting->taglen = b;
		while (n > 1) {
			if (!asn1_read_uint8(data, &b)) 
				return false;
			nesting->taglen = (nesting->taglen << 8) | b;
			n--;
		}
	} else {
		nesting->taglen = b;
	}
	nesting->start = data->ofs;
	nesting->next = data->nesting;
	data->nesting = nesting;
	if (asn1_tag_remaining(data) == -1) {
		return false;
	}
	return !data->has_error;
}

/* stop reading a tag */
bool asn1_end_tag(struct asn1_data *data)
{
	struct nesting *nesting;

	/* make sure we read it all */
	if (asn1_tag_remaining(data) != 0) {
		data->has_error = true;
		return false;
	}

	nesting = data->nesting;

	if (!nesting) {
		data->has_error = true;
		return false;
	}

	data->nesting = nesting->next;
	talloc_free(nesting);
	return true;
}

/* work out how many bytes are left in this nested tag */
int asn1_tag_remaining(struct asn1_data *data)
{
	int remaining;
	if (data->has_error) {
		return -1;
	}

	if (!data->nesting) {
		data->has_error = true;
		return -1;
	}
	remaining = data->nesting->taglen - (data->ofs - data->nesting->start);
	if (remaining > (data->length - data->ofs)) {
		data->has_error = true;
		return -1;
	}
	return remaining;
}

/* read an object ID from a data blob */
bool ber_read_OID_String(TALLOC_CTX *mem_ctx, DATA_BLOB blob, const char **OID)
{
	int i;
	uint8_t *b;
	uint_t v;
	char *tmp_oid = NULL;

	if (blob.length < 2) return false;

	b = blob.data;

	tmp_oid = talloc_asprintf(mem_ctx, "%u",  b[0]/40);
	if (!tmp_oid) goto nomem;
	tmp_oid = talloc_asprintf_append_buffer(tmp_oid, ".%u",  b[0]%40);
	if (!tmp_oid) goto nomem;

	for(i = 1, v = 0; i < blob.length; i++) {
		v = (v<<7) | (b[i]&0x7f);
		if ( ! (b[i] & 0x80)) {
			tmp_oid = talloc_asprintf_append_buffer(tmp_oid, ".%u",  v);
			v = 0;
		}
		if (!tmp_oid) goto nomem;
	}

	if (v != 0) {
		talloc_free(tmp_oid);
		return false;
	}

	*OID = tmp_oid;
	return true;

nomem:	
	return false;
}

/* read an object ID from a ASN1 buffer */
bool asn1_read_OID(struct asn1_data *data, TALLOC_CTX *mem_ctx, const char **OID)
{
	DATA_BLOB blob;
	int len;

	if (!asn1_start_tag(data, ASN1_OID)) return false;

	len = asn1_tag_remaining(data);
	if (len < 0) {
		data->has_error = true;
		return false;
	}

	blob = data_blob(NULL, len);
	if (!blob.data) {
		data->has_error = true;
		return false;
	}

	asn1_read(data, blob.data, len);
	asn1_end_tag(data);
	if (data->has_error) {
		data_blob_free(&blob);
		return false;
	}

	if (!ber_read_OID_String(mem_ctx, blob, OID)) {
		data->has_error = true;
		data_blob_free(&blob);
		return false;
	}

	data_blob_free(&blob);
	return true;
}

/* check that the next object ID is correct */
bool asn1_check_OID(struct asn1_data *data, const char *OID)
{
	const char *id;

	if (!asn1_read_OID(data, data, &id)) return false;

	if (strcmp(id, OID) != 0) {
		talloc_free(discard_const(id));
		data->has_error = true;
		return false;
	}
	talloc_free(discard_const(id));
	return true;
}

/* read a LDAPString from a ASN1 buffer */
bool asn1_read_LDAPString(struct asn1_data *data, TALLOC_CTX *mem_ctx, char **s)
{
	int len;
	len = asn1_tag_remaining(data);
	if (len < 0) {
		data->has_error = true;
		return false;
	}
	*s = talloc_array(mem_ctx, char, len+1);
	if (! *s) {
		data->has_error = true;
		return false;
	}
	asn1_read(data, *s, len);
	(*s)[len] = 0;
	return !data->has_error;
}


/* read a GeneralString from a ASN1 buffer */
bool asn1_read_GeneralString(struct asn1_data *data, TALLOC_CTX *mem_ctx, char **s)
{
	if (!asn1_start_tag(data, ASN1_GENERAL_STRING)) return false;
	if (!asn1_read_LDAPString(data, mem_ctx, s)) return false;
	return asn1_end_tag(data);
}


/* read a octet string blob */
bool asn1_read_OctetString(struct asn1_data *data, TALLOC_CTX *mem_ctx, DATA_BLOB *blob)
{
	int len;
	ZERO_STRUCTP(blob);
	if (!asn1_start_tag(data, ASN1_OCTET_STRING)) return false;
	len = asn1_tag_remaining(data);
	if (len < 0) {
		data->has_error = true;
		return false;
	}
	*blob = data_blob_talloc(mem_ctx, NULL, len+1);
	if (!blob->data) {
		data->has_error = true;
		return false;
	}
	asn1_read(data, blob->data, len);
	asn1_end_tag(data);
	blob->length--;
	blob->data[len] = 0;
	
	if (data->has_error) {
		data_blob_free(blob);
		*blob = data_blob_null;
		return false;
	}
	return true;
}

bool asn1_read_ContextSimple(struct asn1_data *data, uint8_t num, DATA_BLOB *blob)
{
	int len;
	ZERO_STRUCTP(blob);
	if (!asn1_start_tag(data, ASN1_CONTEXT_SIMPLE(num))) return false;
	len = asn1_tag_remaining(data);
	if (len < 0) {
		data->has_error = true;
		return false;
	}
	*blob = data_blob(NULL, len);
	if ((len != 0) && (!blob->data)) {
		data->has_error = true;
		return false;
	}
	asn1_read(data, blob->data, len);
	asn1_end_tag(data);
	return !data->has_error;
}

/* read an integer without tag*/
bool asn1_read_implicit_Integer(struct asn1_data *data, int *i)
{
	uint8_t b;
	*i = 0;

	while (!data->has_error && asn1_tag_remaining(data)>0) {
		if (!asn1_read_uint8(data, &b)) return false;
		*i = (*i << 8) + b;
	}
	return !data->has_error;	
	
}

/* read an integer */
bool asn1_read_Integer(struct asn1_data *data, int *i)
{
	*i = 0;

	if (!asn1_start_tag(data, ASN1_INTEGER)) return false;
	if (!asn1_read_implicit_Integer(data, i)) return false;
	return asn1_end_tag(data);	
}

/* read an integer */
bool asn1_read_enumerated(struct asn1_data *data, int *v)
{
	*v = 0;
	
	if (!asn1_start_tag(data, ASN1_ENUMERATED)) return false;
	while (!data->has_error && asn1_tag_remaining(data)>0) {
		uint8_t b;
		asn1_read_uint8(data, &b);
		*v = (*v << 8) + b;
	}
	return asn1_end_tag(data);	
}

/* check a enumerated value is correct */
bool asn1_check_enumerated(struct asn1_data *data, int v)
{
	uint8_t b;
	if (!asn1_start_tag(data, ASN1_ENUMERATED)) return false;
	asn1_read_uint8(data, &b);
	asn1_end_tag(data);

	if (v != b)
		data->has_error = false;

	return !data->has_error;
}

/* write an enumerated value to the stream */
bool asn1_write_enumerated(struct asn1_data *data, uint8_t v)
{
	if (!asn1_push_tag(data, ASN1_ENUMERATED)) return false;
	asn1_write_uint8(data, v);
	asn1_pop_tag(data);
	return !data->has_error;
}

/*
  check if a ASN.1 blob is a full tag
*/
NTSTATUS asn1_full_tag(DATA_BLOB blob, uint8_t tag, size_t *packet_size)
{
	struct asn1_data *asn1 = asn1_init(NULL);
	int size;

	NT_STATUS_HAVE_NO_MEMORY(asn1);

	asn1->data = blob.data;
	asn1->length = blob.length;
	asn1_start_tag(asn1, tag);
	if (asn1->has_error) {
		talloc_free(asn1);
		return STATUS_MORE_ENTRIES;
	}
	size = asn1_tag_remaining(asn1) + asn1->ofs;

	talloc_free(asn1);

	if (size > blob.length) {
		return STATUS_MORE_ENTRIES;
	}		

	*packet_size = size;
	return NT_STATUS_OK;
}