1 /*
2 * X.509 base functions for creating certificates / CSRs
3 *
4 * Copyright The Mbed TLS Contributors
5 * SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
6 */
7
8 #include "common.h"
9
10 #if defined(MBEDTLS_X509_CREATE_C)
11
12 #include "mbedtls/x509.h"
13 #include "mbedtls/asn1write.h"
14 #include "mbedtls/error.h"
15 #include "mbedtls/oid.h"
16
17 #include <string.h>
18
19 #include "mbedtls/platform.h"
20
21 #include "mbedtls/asn1.h"
22
23 /* Structure linking OIDs for X.509 DN AttributeTypes to their
24 * string representations and default string encodings used by Mbed TLS. */
25 typedef struct {
26 const char *name; /* String representation of AttributeType, e.g.
27 * "CN" or "emailAddress". */
28 size_t name_len; /* Length of 'name', without trailing 0 byte. */
29 const char *oid; /* String representation of OID of AttributeType,
30 * as per RFC 5280, Appendix A.1. encoded as per
31 * X.690 */
32 int default_tag; /* The default character encoding used for the
33 * given attribute type, e.g.
34 * MBEDTLS_ASN1_UTF8_STRING for UTF-8. */
35 } x509_attr_descriptor_t;
36
37 #define ADD_STRLEN(s) s, sizeof(s) - 1
38
39 /* X.509 DN attributes from RFC 5280, Appendix A.1. */
40 static const x509_attr_descriptor_t x509_attrs[] =
41 {
42 { ADD_STRLEN("CN"),
43 MBEDTLS_OID_AT_CN, MBEDTLS_ASN1_UTF8_STRING },
44 { ADD_STRLEN("commonName"),
45 MBEDTLS_OID_AT_CN, MBEDTLS_ASN1_UTF8_STRING },
46 { ADD_STRLEN("C"),
47 MBEDTLS_OID_AT_COUNTRY, MBEDTLS_ASN1_PRINTABLE_STRING },
48 { ADD_STRLEN("countryName"),
49 MBEDTLS_OID_AT_COUNTRY, MBEDTLS_ASN1_PRINTABLE_STRING },
50 { ADD_STRLEN("O"),
51 MBEDTLS_OID_AT_ORGANIZATION, MBEDTLS_ASN1_UTF8_STRING },
52 { ADD_STRLEN("organizationName"),
53 MBEDTLS_OID_AT_ORGANIZATION, MBEDTLS_ASN1_UTF8_STRING },
54 { ADD_STRLEN("L"),
55 MBEDTLS_OID_AT_LOCALITY, MBEDTLS_ASN1_UTF8_STRING },
56 { ADD_STRLEN("locality"),
57 MBEDTLS_OID_AT_LOCALITY, MBEDTLS_ASN1_UTF8_STRING },
58 { ADD_STRLEN("R"),
59 MBEDTLS_OID_PKCS9_EMAIL, MBEDTLS_ASN1_IA5_STRING },
60 { ADD_STRLEN("OU"),
61 MBEDTLS_OID_AT_ORG_UNIT, MBEDTLS_ASN1_UTF8_STRING },
62 { ADD_STRLEN("organizationalUnitName"),
63 MBEDTLS_OID_AT_ORG_UNIT, MBEDTLS_ASN1_UTF8_STRING },
64 { ADD_STRLEN("ST"),
65 MBEDTLS_OID_AT_STATE, MBEDTLS_ASN1_UTF8_STRING },
66 { ADD_STRLEN("stateOrProvinceName"),
67 MBEDTLS_OID_AT_STATE, MBEDTLS_ASN1_UTF8_STRING },
68 { ADD_STRLEN("emailAddress"),
69 MBEDTLS_OID_PKCS9_EMAIL, MBEDTLS_ASN1_IA5_STRING },
70 { ADD_STRLEN("serialNumber"),
71 MBEDTLS_OID_AT_SERIAL_NUMBER, MBEDTLS_ASN1_PRINTABLE_STRING },
72 { ADD_STRLEN("postalAddress"),
73 MBEDTLS_OID_AT_POSTAL_ADDRESS, MBEDTLS_ASN1_PRINTABLE_STRING },
74 { ADD_STRLEN("postalCode"),
75 MBEDTLS_OID_AT_POSTAL_CODE, MBEDTLS_ASN1_PRINTABLE_STRING },
76 { ADD_STRLEN("dnQualifier"),
77 MBEDTLS_OID_AT_DN_QUALIFIER, MBEDTLS_ASN1_PRINTABLE_STRING },
78 { ADD_STRLEN("title"),
79 MBEDTLS_OID_AT_TITLE, MBEDTLS_ASN1_UTF8_STRING },
80 { ADD_STRLEN("surName"),
81 MBEDTLS_OID_AT_SUR_NAME, MBEDTLS_ASN1_UTF8_STRING },
82 { ADD_STRLEN("SN"),
83 MBEDTLS_OID_AT_SUR_NAME, MBEDTLS_ASN1_UTF8_STRING },
84 { ADD_STRLEN("givenName"),
85 MBEDTLS_OID_AT_GIVEN_NAME, MBEDTLS_ASN1_UTF8_STRING },
86 { ADD_STRLEN("GN"),
87 MBEDTLS_OID_AT_GIVEN_NAME, MBEDTLS_ASN1_UTF8_STRING },
88 { ADD_STRLEN("initials"),
89 MBEDTLS_OID_AT_INITIALS, MBEDTLS_ASN1_UTF8_STRING },
90 { ADD_STRLEN("pseudonym"),
91 MBEDTLS_OID_AT_PSEUDONYM, MBEDTLS_ASN1_UTF8_STRING },
92 { ADD_STRLEN("generationQualifier"),
93 MBEDTLS_OID_AT_GENERATION_QUALIFIER, MBEDTLS_ASN1_UTF8_STRING },
94 { ADD_STRLEN("domainComponent"),
95 MBEDTLS_OID_DOMAIN_COMPONENT, MBEDTLS_ASN1_IA5_STRING },
96 { ADD_STRLEN("DC"),
97 MBEDTLS_OID_DOMAIN_COMPONENT, MBEDTLS_ASN1_IA5_STRING },
98 { NULL, 0, NULL, MBEDTLS_ASN1_NULL }
99 };
100
x509_attr_descr_from_name(const char * name,size_t name_len)101 static const x509_attr_descriptor_t *x509_attr_descr_from_name(const char *name, size_t name_len)
102 {
103 const x509_attr_descriptor_t *cur;
104
105 for (cur = x509_attrs; cur->name != NULL; cur++) {
106 if (cur->name_len == name_len &&
107 strncmp(cur->name, name, name_len) == 0) {
108 break;
109 }
110 }
111
112 if (cur->name == NULL) {
113 return NULL;
114 }
115
116 return cur;
117 }
118
hex_to_int(char c)119 static int hex_to_int(char c)
120 {
121 return ('0' <= c && c <= '9') ? (c - '0') :
122 ('a' <= c && c <= 'f') ? (c - 'a' + 10) :
123 ('A' <= c && c <= 'F') ? (c - 'A' + 10) : -1;
124 }
125
hexpair_to_int(const char * hexpair)126 static int hexpair_to_int(const char *hexpair)
127 {
128 int n1 = hex_to_int(*hexpair);
129 int n2 = hex_to_int(*(hexpair + 1));
130
131 if (n1 != -1 && n2 != -1) {
132 return (n1 << 4) | n2;
133 } else {
134 return -1;
135 }
136 }
137
parse_attribute_value_string(const char * s,int len,unsigned char * data,size_t * data_len)138 static int parse_attribute_value_string(const char *s,
139 int len,
140 unsigned char *data,
141 size_t *data_len)
142 {
143 const char *c;
144 const char *end = s + len;
145 unsigned char *d = data;
146 int n;
147
148 for (c = s; c < end; c++) {
149 if (*c == '\\') {
150 c++;
151
152 /* Check for valid escaped characters as per RFC 4514 Section 3 */
153 if (c + 1 < end && (n = hexpair_to_int(c)) != -1) {
154 if (n == 0) {
155 return MBEDTLS_ERR_X509_INVALID_NAME;
156 }
157 *(d++) = n;
158 c++;
159 } else if (c < end && strchr(" ,=+<>#;\"\\", *c)) {
160 *(d++) = *c;
161 } else {
162 return MBEDTLS_ERR_X509_INVALID_NAME;
163 }
164 } else {
165 *(d++) = *c;
166 }
167
168 if (d - data == MBEDTLS_X509_MAX_DN_NAME_SIZE) {
169 return MBEDTLS_ERR_X509_INVALID_NAME;
170 }
171 }
172 *data_len = d - data;
173 return 0;
174 }
175
176 /** Parse a hexstring containing a DER-encoded string.
177 *
178 * \param s A string of \p len bytes hexadecimal digits.
179 * \param len Number of bytes to read from \p s.
180 * \param data Output buffer of size \p data_size.
181 * On success, it contains the payload that's DER-encoded
182 * in the input (content without the tag and length).
183 * If the DER tag is a string tag, the payload is guaranteed
184 * not to contain null bytes.
185 * \param data_size Length of the \p data buffer.
186 * \param data_len On success, the length of the parsed string.
187 * It is guaranteed to be less than
188 * #MBEDTLS_X509_MAX_DN_NAME_SIZE.
189 * \param tag The ASN.1 tag that the payload in \p data is encoded in.
190 *
191 * \retval 0 on success.
192 * \retval #MBEDTLS_ERR_X509_INVALID_NAME if \p s does not contain
193 * a valid hexstring,
194 * or if the decoded hexstring is not valid DER,
195 * or if the payload does not fit in \p data,
196 * or if the payload is more than
197 * #MBEDTLS_X509_MAX_DN_NAME_SIZE bytes,
198 * of if \p *tag is an ASN.1 string tag and the payload
199 * contains a null byte.
200 * \retval #MBEDTLS_ERR_X509_ALLOC_FAILED on low memory.
201 */
parse_attribute_value_hex_der_encoded(const char * s,size_t len,unsigned char * data,size_t data_size,size_t * data_len,int * tag)202 static int parse_attribute_value_hex_der_encoded(const char *s,
203 size_t len,
204 unsigned char *data,
205 size_t data_size,
206 size_t *data_len,
207 int *tag)
208 {
209 /* Step 1: preliminary length checks. */
210 /* Each byte is encoded by exactly two hexadecimal digits. */
211 if (len % 2 != 0) {
212 /* Odd number of hex digits */
213 return MBEDTLS_ERR_X509_INVALID_NAME;
214 }
215 size_t const der_length = len / 2;
216 if (der_length > MBEDTLS_X509_MAX_DN_NAME_SIZE + 4) {
217 /* The payload would be more than MBEDTLS_X509_MAX_DN_NAME_SIZE
218 * (after subtracting the ASN.1 tag and length). Reject this early
219 * to avoid allocating a large intermediate buffer. */
220 return MBEDTLS_ERR_X509_INVALID_NAME;
221 }
222 if (der_length < 1) {
223 /* Avoid empty-buffer shenanigans. A valid DER encoding is never
224 * empty. */
225 return MBEDTLS_ERR_X509_INVALID_NAME;
226 }
227
228 /* Step 2: Decode the hex string into an intermediate buffer. */
229 unsigned char *der = mbedtls_calloc(1, der_length);
230 if (der == NULL) {
231 return MBEDTLS_ERR_X509_ALLOC_FAILED;
232 }
233 /* Beyond this point, der needs to be freed on exit. */
234 for (size_t i = 0; i < der_length; i++) {
235 int c = hexpair_to_int(s + 2 * i);
236 if (c < 0) {
237 goto error;
238 }
239 der[i] = c;
240 }
241
242 /* Step 3: decode the DER. */
243 /* We've checked that der_length >= 1 above. */
244 *tag = der[0];
245 unsigned char *p = der + 1;
246 if (mbedtls_asn1_get_len(&p, der + der_length, data_len) != 0) {
247 goto error;
248 }
249 /* Now p points to the first byte of the payload inside der,
250 * and *data_len is the length of the payload. */
251
252 /* Step 4: payload validation */
253 if (*data_len > MBEDTLS_X509_MAX_DN_NAME_SIZE) {
254 goto error;
255 }
256 /* Strings must not contain null bytes. */
257 if (MBEDTLS_ASN1_IS_STRING_TAG(*tag)) {
258 for (size_t i = 0; i < *data_len; i++) {
259 if (p[i] == 0) {
260 goto error;
261 }
262 }
263 }
264
265 /* Step 5: output the payload. */
266 if (*data_len > data_size) {
267 goto error;
268 }
269 memcpy(data, p, *data_len);
270 mbedtls_free(der);
271
272 return 0;
273
274 error:
275 mbedtls_free(der);
276 return MBEDTLS_ERR_X509_INVALID_NAME;
277 }
278
mbedtls_x509_string_to_names(mbedtls_asn1_named_data ** head,const char * name)279 int mbedtls_x509_string_to_names(mbedtls_asn1_named_data **head, const char *name)
280 {
281 int ret = MBEDTLS_ERR_X509_INVALID_NAME;
282 int parse_ret = 0;
283 const char *s = name, *c = s;
284 const char *end = s + strlen(s);
285 mbedtls_asn1_buf oid = { .p = NULL, .len = 0, .tag = MBEDTLS_ASN1_NULL };
286 const x509_attr_descriptor_t *attr_descr = NULL;
287 int in_attr_type = 1;
288 int tag;
289 int numericoid = 0;
290 unsigned char data[MBEDTLS_X509_MAX_DN_NAME_SIZE];
291 size_t data_len = 0;
292
293 /* Clear existing chain if present */
294 mbedtls_asn1_free_named_data_list(head);
295
296 while (c <= end) {
297 if (in_attr_type && *c == '=') {
298 if ((attr_descr = x509_attr_descr_from_name(s, c - s)) == NULL) {
299 if ((mbedtls_oid_from_numeric_string(&oid, s, c - s)) != 0) {
300 return MBEDTLS_ERR_X509_INVALID_NAME;
301 } else {
302 numericoid = 1;
303 }
304 } else {
305 oid.len = strlen(attr_descr->oid);
306 oid.p = mbedtls_calloc(1, oid.len);
307 memcpy(oid.p, attr_descr->oid, oid.len);
308 numericoid = 0;
309 }
310
311 s = c + 1;
312 in_attr_type = 0;
313 }
314
315 if (!in_attr_type && ((*c == ',' && *(c-1) != '\\') || c == end)) {
316 if (s == c) {
317 mbedtls_free(oid.p);
318 return MBEDTLS_ERR_X509_INVALID_NAME;
319 } else if (*s == '#') {
320 /* We know that c >= s (loop invariant) and c != s (in this
321 * else branch), hence c - s - 1 >= 0. */
322 parse_ret = parse_attribute_value_hex_der_encoded(
323 s + 1, c - s - 1,
324 data, sizeof(data), &data_len, &tag);
325 if (parse_ret != 0) {
326 mbedtls_free(oid.p);
327 return parse_ret;
328 }
329 } else {
330 if (numericoid) {
331 mbedtls_free(oid.p);
332 return MBEDTLS_ERR_X509_INVALID_NAME;
333 } else {
334 if ((parse_ret =
335 parse_attribute_value_string(s, (int) (c - s), data,
336 &data_len)) != 0) {
337 mbedtls_free(oid.p);
338 return parse_ret;
339 }
340 tag = attr_descr->default_tag;
341 }
342 }
343
344 mbedtls_asn1_named_data *cur =
345 mbedtls_asn1_store_named_data(head, (char *) oid.p, oid.len,
346 (unsigned char *) data,
347 data_len);
348 mbedtls_free(oid.p);
349 oid.p = NULL;
350 if (cur == NULL) {
351 return MBEDTLS_ERR_X509_ALLOC_FAILED;
352 }
353
354 // set tagType
355 cur->val.tag = tag;
356
357 while (c < end && *(c + 1) == ' ') {
358 c++;
359 }
360
361 s = c + 1;
362 in_attr_type = 1;
363
364 /* Successfully parsed one name, update ret to success */
365 ret = 0;
366 }
367 c++;
368 }
369 if (oid.p != NULL) {
370 mbedtls_free(oid.p);
371 }
372 return ret;
373 }
374
375 /* The first byte of the value in the mbedtls_asn1_named_data structure is reserved
376 * to store the critical boolean for us
377 */
mbedtls_x509_set_extension(mbedtls_asn1_named_data ** head,const char * oid,size_t oid_len,int critical,const unsigned char * val,size_t val_len)378 int mbedtls_x509_set_extension(mbedtls_asn1_named_data **head, const char *oid, size_t oid_len,
379 int critical, const unsigned char *val, size_t val_len)
380 {
381 mbedtls_asn1_named_data *cur;
382
383 if (val_len > (SIZE_MAX - 1)) {
384 return MBEDTLS_ERR_X509_BAD_INPUT_DATA;
385 }
386
387 if ((cur = mbedtls_asn1_store_named_data(head, oid, oid_len,
388 NULL, val_len + 1)) == NULL) {
389 return MBEDTLS_ERR_X509_ALLOC_FAILED;
390 }
391
392 cur->val.p[0] = critical;
393 memcpy(cur->val.p + 1, val, val_len);
394
395 return 0;
396 }
397
398 /*
399 * RelativeDistinguishedName ::=
400 * SET OF AttributeTypeAndValue
401 *
402 * AttributeTypeAndValue ::= SEQUENCE {
403 * type AttributeType,
404 * value AttributeValue }
405 *
406 * AttributeType ::= OBJECT IDENTIFIER
407 *
408 * AttributeValue ::= ANY DEFINED BY AttributeType
409 */
x509_write_name(unsigned char ** p,unsigned char * start,mbedtls_asn1_named_data * cur_name)410 static int x509_write_name(unsigned char **p,
411 unsigned char *start,
412 mbedtls_asn1_named_data *cur_name)
413 {
414 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
415 size_t len = 0;
416 const char *oid = (const char *) cur_name->oid.p;
417 size_t oid_len = cur_name->oid.len;
418 const unsigned char *name = cur_name->val.p;
419 size_t name_len = cur_name->val.len;
420
421 // Write correct string tag and value
422 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tagged_string(p, start,
423 cur_name->val.tag,
424 (const char *) name,
425 name_len));
426 // Write OID
427 //
428 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_oid(p, start, oid,
429 oid_len));
430
431 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
432 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start,
433 MBEDTLS_ASN1_CONSTRUCTED |
434 MBEDTLS_ASN1_SEQUENCE));
435
436 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
437 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start,
438 MBEDTLS_ASN1_CONSTRUCTED |
439 MBEDTLS_ASN1_SET));
440
441 return (int) len;
442 }
443
mbedtls_x509_write_names(unsigned char ** p,unsigned char * start,mbedtls_asn1_named_data * first)444 int mbedtls_x509_write_names(unsigned char **p, unsigned char *start,
445 mbedtls_asn1_named_data *first)
446 {
447 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
448 size_t len = 0;
449 mbedtls_asn1_named_data *cur = first;
450
451 while (cur != NULL) {
452 MBEDTLS_ASN1_CHK_ADD(len, x509_write_name(p, start, cur));
453 cur = cur->next;
454 }
455
456 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
457 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_CONSTRUCTED |
458 MBEDTLS_ASN1_SEQUENCE));
459
460 return (int) len;
461 }
462
mbedtls_x509_write_sig(unsigned char ** p,unsigned char * start,const char * oid,size_t oid_len,unsigned char * sig,size_t size,mbedtls_pk_type_t pk_alg)463 int mbedtls_x509_write_sig(unsigned char **p, unsigned char *start,
464 const char *oid, size_t oid_len,
465 unsigned char *sig, size_t size,
466 mbedtls_pk_type_t pk_alg)
467 {
468 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
469 int write_null_par;
470 size_t len = 0;
471
472 if (*p < start || (size_t) (*p - start) < size) {
473 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
474 }
475
476 len = size;
477 (*p) -= len;
478 memcpy(*p, sig, len);
479
480 if (*p - start < 1) {
481 return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
482 }
483
484 *--(*p) = 0;
485 len += 1;
486
487 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
488 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_BIT_STRING));
489
490 // Write OID
491 //
492 if (pk_alg == MBEDTLS_PK_ECDSA) {
493 /*
494 * The AlgorithmIdentifier's parameters field must be absent for DSA/ECDSA signature
495 * algorithms, see https://www.rfc-editor.org/rfc/rfc5480#page-17 and
496 * https://www.rfc-editor.org/rfc/rfc5758#section-3.
497 */
498 write_null_par = 0;
499 } else {
500 write_null_par = 1;
501 }
502 MBEDTLS_ASN1_CHK_ADD(len,
503 mbedtls_asn1_write_algorithm_identifier_ext(p, start, oid, oid_len,
504 0, write_null_par));
505
506 return (int) len;
507 }
508
x509_write_extension(unsigned char ** p,unsigned char * start,mbedtls_asn1_named_data * ext)509 static int x509_write_extension(unsigned char **p, unsigned char *start,
510 mbedtls_asn1_named_data *ext)
511 {
512 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
513 size_t len = 0;
514
515 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_raw_buffer(p, start, ext->val.p + 1,
516 ext->val.len - 1));
517 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, ext->val.len - 1));
518 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_OCTET_STRING));
519
520 if (ext->val.p[0] != 0) {
521 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_bool(p, start, 1));
522 }
523
524 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_raw_buffer(p, start, ext->oid.p,
525 ext->oid.len));
526 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, ext->oid.len));
527 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_OID));
528
529 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_len(p, start, len));
530 MBEDTLS_ASN1_CHK_ADD(len, mbedtls_asn1_write_tag(p, start, MBEDTLS_ASN1_CONSTRUCTED |
531 MBEDTLS_ASN1_SEQUENCE));
532
533 return (int) len;
534 }
535
536 /*
537 * Extension ::= SEQUENCE {
538 * extnID OBJECT IDENTIFIER,
539 * critical BOOLEAN DEFAULT FALSE,
540 * extnValue OCTET STRING
541 * -- contains the DER encoding of an ASN.1 value
542 * -- corresponding to the extension type identified
543 * -- by extnID
544 * }
545 */
mbedtls_x509_write_extensions(unsigned char ** p,unsigned char * start,mbedtls_asn1_named_data * first)546 int mbedtls_x509_write_extensions(unsigned char **p, unsigned char *start,
547 mbedtls_asn1_named_data *first)
548 {
549 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
550 size_t len = 0;
551 mbedtls_asn1_named_data *cur_ext = first;
552
553 while (cur_ext != NULL) {
554 MBEDTLS_ASN1_CHK_ADD(len, x509_write_extension(p, start, cur_ext));
555 cur_ext = cur_ext->next;
556 }
557
558 return (int) len;
559 }
560
561 #endif /* MBEDTLS_X509_CREATE_C */
562
