d41d2e0c4b56ff5253a3f5f01692b55609c7274c
[openssl.git] / doc / man3 / d2i_X509.pod
1 =pod
2
3 =head1 NAME
4
5 d2i_ACCESS_DESCRIPTION,
6 d2i_ADMISSIONS,
7 d2i_ADMISSION_SYNTAX,
8 d2i_ASIdOrRange,
9 d2i_ASIdentifierChoice,
10 d2i_ASIdentifiers,
11 d2i_ASN1_BIT_STRING,
12 d2i_ASN1_BMPSTRING,
13 d2i_ASN1_ENUMERATED,
14 d2i_ASN1_GENERALIZEDTIME,
15 d2i_ASN1_GENERALSTRING,
16 d2i_ASN1_IA5STRING,
17 d2i_ASN1_INTEGER,
18 d2i_ASN1_NULL,
19 d2i_ASN1_OBJECT,
20 d2i_ASN1_OCTET_STRING,
21 d2i_ASN1_PRINTABLE,
22 d2i_ASN1_PRINTABLESTRING,
23 d2i_ASN1_SEQUENCE_ANY,
24 d2i_ASN1_SET_ANY,
25 d2i_ASN1_T61STRING,
26 d2i_ASN1_TIME,
27 d2i_ASN1_TYPE,
28 d2i_ASN1_UINTEGER,
29 d2i_ASN1_UNIVERSALSTRING,
30 d2i_ASN1_UTCTIME,
31 d2i_ASN1_UTF8STRING,
32 d2i_ASN1_VISIBLESTRING,
33 d2i_ASRange,
34 d2i_AUTHORITY_INFO_ACCESS,
35 d2i_AUTHORITY_KEYID,
36 d2i_BASIC_CONSTRAINTS,
37 d2i_CERTIFICATEPOLICIES,
38 d2i_CMS_ContentInfo,
39 d2i_CMS_ReceiptRequest,
40 d2i_CMS_bio,
41 d2i_CRL_DIST_POINTS,
42 d2i_DHxparams,
43 d2i_DIRECTORYSTRING,
44 d2i_DISPLAYTEXT,
45 d2i_DIST_POINT,
46 d2i_DIST_POINT_NAME,
47 d2i_DSAPrivateKey,
48 d2i_DSAPrivateKey_bio,
49 d2i_DSAPrivateKey_fp,
50 d2i_DSAPublicKey,
51 d2i_DSA_PUBKEY,
52 d2i_DSA_PUBKEY_bio,
53 d2i_DSA_PUBKEY_fp,
54 d2i_DSA_SIG,
55 d2i_DSAparams,
56 d2i_ECDSA_SIG,
57 d2i_ECPKParameters,
58 d2i_ECParameters,
59 d2i_ECPrivateKey,
60 d2i_ECPrivateKey_bio,
61 d2i_ECPrivateKey_fp,
62 d2i_EC_PUBKEY,
63 d2i_EC_PUBKEY_bio,
64 d2i_EC_PUBKEY_fp,
65 d2i_EDIPARTYNAME,
66 d2i_ESS_CERT_ID,
67 d2i_ESS_CERT_ID_V2,
68 d2i_ESS_ISSUER_SERIAL,
69 d2i_ESS_SIGNING_CERT,
70 d2i_ESS_SIGNING_CERT_V2,
71 d2i_EXTENDED_KEY_USAGE,
72 d2i_GENERAL_NAME,
73 d2i_GENERAL_NAMES,
74 d2i_IPAddressChoice,
75 d2i_IPAddressFamily,
76 d2i_IPAddressOrRange,
77 d2i_IPAddressRange,
78 d2i_ISSUING_DIST_POINT,
79 d2i_NAMING_AUTHORITY,
80 d2i_NETSCAPE_CERT_SEQUENCE,
81 d2i_NETSCAPE_SPKAC,
82 d2i_NETSCAPE_SPKI,
83 d2i_NOTICEREF,
84 d2i_OCSP_BASICRESP,
85 d2i_OCSP_CERTID,
86 d2i_OCSP_CERTSTATUS,
87 d2i_OCSP_CRLID,
88 d2i_OCSP_ONEREQ,
89 d2i_OCSP_REQINFO,
90 d2i_OCSP_REQUEST,
91 d2i_OCSP_RESPBYTES,
92 d2i_OCSP_RESPDATA,
93 d2i_OCSP_RESPID,
94 d2i_OCSP_RESPONSE,
95 d2i_OCSP_REVOKEDINFO,
96 d2i_OCSP_SERVICELOC,
97 d2i_OCSP_SIGNATURE,
98 d2i_OCSP_SINGLERESP,
99 d2i_OSSL_CMP_MSG,
100 d2i_OSSL_CMP_PKIHEADER,
101 d2i_OSSL_CRMF_CERTID,
102 d2i_OSSL_CRMF_CERTTEMPLATE,
103 d2i_OSSL_CRMF_ENCRYPTEDVALUE,
104 d2i_OSSL_CRMF_MSG,
105 d2i_OSSL_CRMF_MSGS,
106 d2i_OSSL_CRMF_PBMPARAMETER,
107 d2i_OSSL_CRMF_PKIPUBLICATIONINFO,
108 d2i_OSSL_CRMF_SINGLEPUBINFO,
109 d2i_OTHERNAME,
110 d2i_PBE2PARAM,
111 d2i_PBEPARAM,
112 d2i_PBKDF2PARAM,
113 d2i_PKCS12,
114 d2i_PKCS12_BAGS,
115 d2i_PKCS12_MAC_DATA,
116 d2i_PKCS12_SAFEBAG,
117 d2i_PKCS12_bio,
118 d2i_PKCS12_fp,
119 d2i_PKCS7,
120 d2i_PKCS7_DIGEST,
121 d2i_PKCS7_ENCRYPT,
122 d2i_PKCS7_ENC_CONTENT,
123 d2i_PKCS7_ENVELOPE,
124 d2i_PKCS7_ISSUER_AND_SERIAL,
125 d2i_PKCS7_RECIP_INFO,
126 d2i_PKCS7_SIGNED,
127 d2i_PKCS7_SIGNER_INFO,
128 d2i_PKCS7_SIGN_ENVELOPE,
129 d2i_PKCS7_bio,
130 d2i_PKCS7_fp,
131 d2i_PKCS8_PRIV_KEY_INFO,
132 d2i_PKCS8_PRIV_KEY_INFO_bio,
133 d2i_PKCS8_PRIV_KEY_INFO_fp,
134 d2i_PKCS8_bio,
135 d2i_PKCS8_fp,
136 d2i_PKEY_USAGE_PERIOD,
137 d2i_POLICYINFO,
138 d2i_POLICYQUALINFO,
139 d2i_PROFESSION_INFO,
140 d2i_PROXY_CERT_INFO_EXTENSION,
141 d2i_PROXY_POLICY,
142 d2i_RSAPrivateKey,
143 d2i_RSAPrivateKey_bio,
144 d2i_RSAPrivateKey_fp,
145 d2i_RSAPublicKey,
146 d2i_RSAPublicKey_bio,
147 d2i_RSAPublicKey_fp,
148 d2i_RSA_OAEP_PARAMS,
149 d2i_RSA_PSS_PARAMS,
150 d2i_RSA_PUBKEY,
151 d2i_RSA_PUBKEY_bio,
152 d2i_RSA_PUBKEY_fp,
153 d2i_SCRYPT_PARAMS,
154 d2i_SCT_LIST,
155 d2i_SXNET,
156 d2i_SXNETID,
157 d2i_TS_ACCURACY,
158 d2i_TS_MSG_IMPRINT,
159 d2i_TS_MSG_IMPRINT_bio,
160 d2i_TS_MSG_IMPRINT_fp,
161 d2i_TS_REQ,
162 d2i_TS_REQ_bio,
163 d2i_TS_REQ_fp,
164 d2i_TS_RESP,
165 d2i_TS_RESP_bio,
166 d2i_TS_RESP_fp,
167 d2i_TS_STATUS_INFO,
168 d2i_TS_TST_INFO,
169 d2i_TS_TST_INFO_bio,
170 d2i_TS_TST_INFO_fp,
171 d2i_USERNOTICE,
172 d2i_X509,
173 d2i_X509_ALGOR,
174 d2i_X509_ALGORS,
175 d2i_X509_ATTRIBUTE,
176 d2i_X509_CERT_AUX,
177 d2i_X509_CINF,
178 d2i_X509_CRL,
179 d2i_X509_CRL_INFO,
180 d2i_X509_CRL_bio,
181 d2i_X509_CRL_fp,
182 d2i_X509_EXTENSION,
183 d2i_X509_EXTENSIONS,
184 d2i_X509_NAME,
185 d2i_X509_NAME_ENTRY,
186 d2i_X509_PUBKEY,
187 d2i_X509_PUBKEY_bio,
188 d2i_X509_PUBKEY_fp,
189 d2i_X509_REQ,
190 d2i_X509_REQ_INFO,
191 d2i_X509_REQ_bio,
192 d2i_X509_REQ_fp,
193 d2i_X509_REVOKED,
194 d2i_X509_SIG,
195 d2i_X509_VAL,
196 i2d_ACCESS_DESCRIPTION,
197 i2d_ADMISSIONS,
198 i2d_ADMISSION_SYNTAX,
199 i2d_ASIdOrRange,
200 i2d_ASIdentifierChoice,
201 i2d_ASIdentifiers,
202 i2d_ASN1_BIT_STRING,
203 i2d_ASN1_BMPSTRING,
204 i2d_ASN1_ENUMERATED,
205 i2d_ASN1_GENERALIZEDTIME,
206 i2d_ASN1_GENERALSTRING,
207 i2d_ASN1_IA5STRING,
208 i2d_ASN1_INTEGER,
209 i2d_ASN1_NULL,
210 i2d_ASN1_OBJECT,
211 i2d_ASN1_OCTET_STRING,
212 i2d_ASN1_PRINTABLE,
213 i2d_ASN1_PRINTABLESTRING,
214 i2d_ASN1_SEQUENCE_ANY,
215 i2d_ASN1_SET_ANY,
216 i2d_ASN1_T61STRING,
217 i2d_ASN1_TIME,
218 i2d_ASN1_TYPE,
219 i2d_ASN1_UNIVERSALSTRING,
220 i2d_ASN1_UTCTIME,
221 i2d_ASN1_UTF8STRING,
222 i2d_ASN1_VISIBLESTRING,
223 i2d_ASN1_bio_stream,
224 i2d_ASRange,
225 i2d_AUTHORITY_INFO_ACCESS,
226 i2d_AUTHORITY_KEYID,
227 i2d_BASIC_CONSTRAINTS,
228 i2d_CERTIFICATEPOLICIES,
229 i2d_CMS_ContentInfo,
230 i2d_CMS_ReceiptRequest,
231 i2d_CMS_bio,
232 i2d_CRL_DIST_POINTS,
233 i2d_DHxparams,
234 i2d_DIRECTORYSTRING,
235 i2d_DISPLAYTEXT,
236 i2d_DIST_POINT,
237 i2d_DIST_POINT_NAME,
238 i2d_DSAPrivateKey,
239 i2d_DSAPrivateKey_bio,
240 i2d_DSAPrivateKey_fp,
241 i2d_DSAPublicKey,
242 i2d_DSA_PUBKEY,
243 i2d_DSA_PUBKEY_bio,
244 i2d_DSA_PUBKEY_fp,
245 i2d_DSA_SIG,
246 i2d_DSAparams,
247 i2d_ECDSA_SIG,
248 i2d_ECPKParameters,
249 i2d_ECParameters,
250 i2d_ECPrivateKey,
251 i2d_ECPrivateKey_bio,
252 i2d_ECPrivateKey_fp,
253 i2d_EC_PUBKEY,
254 i2d_EC_PUBKEY_bio,
255 i2d_EC_PUBKEY_fp,
256 i2d_EDIPARTYNAME,
257 i2d_ESS_CERT_ID,
258 i2d_ESS_CERT_ID_V2,
259 i2d_ESS_ISSUER_SERIAL,
260 i2d_ESS_SIGNING_CERT,
261 i2d_ESS_SIGNING_CERT_V2,
262 i2d_EXTENDED_KEY_USAGE,
263 i2d_GENERAL_NAME,
264 i2d_GENERAL_NAMES,
265 i2d_IPAddressChoice,
266 i2d_IPAddressFamily,
267 i2d_IPAddressOrRange,
268 i2d_IPAddressRange,
269 i2d_ISSUING_DIST_POINT,
270 i2d_NAMING_AUTHORITY,
271 i2d_NETSCAPE_CERT_SEQUENCE,
272 i2d_NETSCAPE_SPKAC,
273 i2d_NETSCAPE_SPKI,
274 i2d_NOTICEREF,
275 i2d_OCSP_BASICRESP,
276 i2d_OCSP_CERTID,
277 i2d_OCSP_CERTSTATUS,
278 i2d_OCSP_CRLID,
279 i2d_OCSP_ONEREQ,
280 i2d_OCSP_REQINFO,
281 i2d_OCSP_REQUEST,
282 i2d_OCSP_RESPBYTES,
283 i2d_OCSP_RESPDATA,
284 i2d_OCSP_RESPID,
285 i2d_OCSP_RESPONSE,
286 i2d_OCSP_REVOKEDINFO,
287 i2d_OCSP_SERVICELOC,
288 i2d_OCSP_SIGNATURE,
289 i2d_OCSP_SINGLERESP,
290 i2d_OSSL_CMP_MSG,
291 i2d_OSSL_CMP_PKIHEADER,
292 i2d_OSSL_CRMF_CERTID,
293 i2d_OSSL_CRMF_CERTTEMPLATE,
294 i2d_OSSL_CRMF_ENCRYPTEDVALUE,
295 i2d_OSSL_CRMF_MSG,
296 i2d_OSSL_CRMF_MSGS,
297 i2d_OSSL_CRMF_PBMPARAMETER,
298 i2d_OSSL_CRMF_PKIPUBLICATIONINFO,
299 i2d_OSSL_CRMF_SINGLEPUBINFO,
300 i2d_OTHERNAME,
301 i2d_PBE2PARAM,
302 i2d_PBEPARAM,
303 i2d_PBKDF2PARAM,
304 i2d_PKCS12,
305 i2d_PKCS12_BAGS,
306 i2d_PKCS12_MAC_DATA,
307 i2d_PKCS12_SAFEBAG,
308 i2d_PKCS12_bio,
309 i2d_PKCS12_fp,
310 i2d_PKCS7,
311 i2d_PKCS7_DIGEST,
312 i2d_PKCS7_ENCRYPT,
313 i2d_PKCS7_ENC_CONTENT,
314 i2d_PKCS7_ENVELOPE,
315 i2d_PKCS7_ISSUER_AND_SERIAL,
316 i2d_PKCS7_NDEF,
317 i2d_PKCS7_RECIP_INFO,
318 i2d_PKCS7_SIGNED,
319 i2d_PKCS7_SIGNER_INFO,
320 i2d_PKCS7_SIGN_ENVELOPE,
321 i2d_PKCS7_bio,
322 i2d_PKCS7_fp,
323 i2d_PKCS8PrivateKeyInfo_bio,
324 i2d_PKCS8PrivateKeyInfo_fp,
325 i2d_PKCS8_PRIV_KEY_INFO,
326 i2d_PKCS8_PRIV_KEY_INFO_bio,
327 i2d_PKCS8_PRIV_KEY_INFO_fp,
328 i2d_PKCS8_bio,
329 i2d_PKCS8_fp,
330 i2d_PKEY_USAGE_PERIOD,
331 i2d_POLICYINFO,
332 i2d_POLICYQUALINFO,
333 i2d_PROFESSION_INFO,
334 i2d_PROXY_CERT_INFO_EXTENSION,
335 i2d_PROXY_POLICY,
336 i2d_RSAPrivateKey,
337 i2d_RSAPrivateKey_bio,
338 i2d_RSAPrivateKey_fp,
339 i2d_RSAPublicKey,
340 i2d_RSAPublicKey_bio,
341 i2d_RSAPublicKey_fp,
342 i2d_RSA_OAEP_PARAMS,
343 i2d_RSA_PSS_PARAMS,
344 i2d_RSA_PUBKEY,
345 i2d_RSA_PUBKEY_bio,
346 i2d_RSA_PUBKEY_fp,
347 i2d_SCRYPT_PARAMS,
348 i2d_SCT_LIST,
349 i2d_SXNET,
350 i2d_SXNETID,
351 i2d_TS_ACCURACY,
352 i2d_TS_MSG_IMPRINT,
353 i2d_TS_MSG_IMPRINT_bio,
354 i2d_TS_MSG_IMPRINT_fp,
355 i2d_TS_REQ,
356 i2d_TS_REQ_bio,
357 i2d_TS_REQ_fp,
358 i2d_TS_RESP,
359 i2d_TS_RESP_bio,
360 i2d_TS_RESP_fp,
361 i2d_TS_STATUS_INFO,
362 i2d_TS_TST_INFO,
363 i2d_TS_TST_INFO_bio,
364 i2d_TS_TST_INFO_fp,
365 i2d_USERNOTICE,
366 i2d_X509,
367 i2d_X509_ALGOR,
368 i2d_X509_ALGORS,
369 i2d_X509_ATTRIBUTE,
370 i2d_X509_CERT_AUX,
371 i2d_X509_CINF,
372 i2d_X509_CRL,
373 i2d_X509_CRL_INFO,
374 i2d_X509_CRL_bio,
375 i2d_X509_CRL_fp,
376 i2d_X509_EXTENSION,
377 i2d_X509_EXTENSIONS,
378 i2d_X509_NAME,
379 i2d_X509_NAME_ENTRY,
380 i2d_X509_PUBKEY,
381 i2d_X509_PUBKEY_bio,
382 i2d_X509_PUBKEY_fp,
383 i2d_X509_REQ,
384 i2d_X509_REQ_INFO,
385 i2d_X509_REQ_bio,
386 i2d_X509_REQ_fp,
387 i2d_X509_REVOKED,
388 i2d_X509_SIG,
389 i2d_X509_VAL,
390 - convert objects from/to ASN.1/DER representation
391
392 =head1 SYNOPSIS
393
394 =for openssl generic
395
396  TYPE *d2i_TYPE(TYPE **a, unsigned char **ppin, long length);
397  TYPE *d2i_TYPE_bio(BIO *bp, TYPE **a);
398  TYPE *d2i_TYPE_fp(FILE *fp, TYPE **a);
399
400  int i2d_TYPE(const TYPE *a, unsigned char **ppout);
401  int i2d_TYPE(TYPE *a, unsigned char **ppout);
402  int i2d_TYPE_fp(FILE *fp, const TYPE *a);
403  int i2d_TYPE_fp(FILE *fp, TYPE *a);
404  int i2d_TYPE_bio(BIO *bp, const TYPE *a);
405  int i2d_TYPE_bio(BIO *bp, TYPE *a);
406
407 =head1 DESCRIPTION
408
409 In the description here, B<I<TYPE>> is used a placeholder
410 for any of the OpenSSL datatypes, such as I<X509_CRL>.
411 The function parameters I<ppin> and I<ppout> are generally
412 either both named I<pp> in the headers, or I<in> and I<out>.
413
414 These functions convert OpenSSL objects to and from their ASN.1/DER
415 encoding.  Unlike the C structures which can have pointers to sub-objects
416 within, the DER is a serialized encoding, suitable for sending over the
417 network, writing to a file, and so on.
418
419 B<d2i_I<TYPE>>() attempts to decode I<len> bytes at I<*ppin>. If successful a
420 pointer to the B<I<TYPE>> structure is returned and I<*ppin> is incremented to
421 the byte following the parsed data.  If I<a> is not NULL then a pointer
422 to the returned structure is also written to I<*a>.  If an error occurred
423 then NULL is returned.
424
425 On a successful return, if I<*a> is not NULL then it is assumed that I<*a>
426 contains a valid B<I<TYPE>> structure and an attempt is made to reuse it. This
427 "reuse" capability is present for historical compatibility but its use is
428 B<strongly discouraged> (see BUGS below, and the discussion in the RETURN
429 VALUES section).
430
431 B<d2i_I<TYPE>_bio>() is similar to B<d2i_I<TYPE>>() except it attempts
432 to parse data from BIO I<bp>.
433
434 B<d2i_I<TYPE>_fp>() is similar to B<d2i_I<TYPE>>() except it attempts
435 to parse data from FILE pointer I<fp>.
436
437 B<i2d_I<TYPE>>() encodes the structure pointed to by I<a> into DER format.
438 If I<ppout> is not NULL, it writes the DER encoded data to the buffer
439 at I<*ppout>, and increments it to point after the data just written.
440 If the return value is negative an error occurred, otherwise it
441 returns the length of the encoded data.
442
443 If I<*ppout> is NULL memory will be allocated for a buffer and the encoded
444 data written to it. In this case I<*ppout> is not incremented and it points
445 to the start of the data just written.
446
447 B<i2d_I<TYPE>_bio>() is similar to B<i2d_I<TYPE>>() except it writes
448 the encoding of the structure I<a> to BIO I<bp> and it
449 returns 1 for success and 0 for failure.
450
451 B<i2d_I<TYPE>_fp>() is similar to B<i2d_I<TYPE>>() except it writes
452 the encoding of the structure I<a> to BIO I<bp> and it
453 returns 1 for success and 0 for failure.
454
455 These routines do not encrypt private keys and therefore offer no
456 security; use L<PEM_write_PrivateKey(3)> or similar for writing to files.
457
458 =head1 NOTES
459
460 The letters B<i> and B<d> in B<i2d_I<TYPE>>() stand for
461 "internal" (that is, an internal C structure) and "DER" respectively.
462 So B<i2d_I<TYPE>>() converts from internal to DER.
463
464 The functions can also understand B<BER> forms.
465
466 The actual TYPE structure passed to B<i2d_I<TYPE>>() must be a valid
467 populated B<I<TYPE>> structure -- it B<cannot> simply be fed with an
468 empty structure such as that returned by TYPE_new().
469
470 The encoded data is in binary form and may contain embedded zeros.
471 Therefore any FILE pointers or BIOs should be opened in binary mode.
472 Functions such as strlen() will B<not> return the correct length
473 of the encoded structure.
474
475 The ways that I<*ppin> and I<*ppout> are incremented after the operation
476 can trap the unwary. See the B<WARNINGS> section for some common
477 errors.
478 The reason for this-auto increment behaviour is to reflect a typical
479 usage of ASN1 functions: after one structure is encoded or decoded
480 another will be processed after it.
481
482 The following points about the data types might be useful:
483
484 =over 4
485
486 =item B<ASN1_OBJECT>
487
488 Represents an ASN1 OBJECT IDENTIFIER.
489
490 =item B<DHparams>
491
492 Represents a PKCS#3 DH parameters structure.
493
494 =item B<DHxparams>
495
496 Represents an ANSI X9.42 DH parameters structure.
497
498 =item B<DSA_PUBKEY>
499
500 Represents a DSA public key using a B<SubjectPublicKeyInfo> structure.
501
502 =item B<DSAPublicKey>, B<DSAPrivateKey>
503
504 Use a non-standard OpenSSL format and should be avoided; use B<DSA_PUBKEY>,
505 L<PEM_write_PrivateKey(3)>, or similar instead.
506
507 =item B<ECDSA_SIG>
508
509 Represents an ECDSA signature.
510
511 =item B<RSAPublicKey>
512
513 Represents a PKCS#1 RSA public key structure.
514
515 =item B<X509_ALGOR>
516
517 Represents an B<AlgorithmIdentifier> structure as used in IETF RFC 6960 and
518 elsewhere.
519
520 =item B<X509_Name>
521
522 Represents a B<Name> type as used for subject and issuer names in
523 IETF RFC 6960 and elsewhere.
524
525 =item B<X509_REQ>
526
527 Represents a PKCS#10 certificate request.
528
529 =item B<X509_SIG>
530
531 Represents the B<DigestInfo> structure defined in PKCS#1 and PKCS#7.
532
533 =back
534
535 =head1 RETURN VALUES
536
537 B<d2i_I<TYPE>>(), B<d2i_I<TYPE>_bio>() and B<d2i_I<TYPE>_fp>() return a valid
538 B<I<TYPE>> structure or NULL if an error occurs.  If the "reuse" capability has
539 been used with a valid structure being passed in via I<a>, then the object is
540 freed in the event of error and I<*a> is set to NULL.
541
542 B<i2d_I<TYPE>>() returns the number of bytes successfully encoded or a negative
543 value if an error occurs.
544
545 B<i2d_I<TYPE>_bio>() and B<i2d_I<TYPE>_fp>() return 1 for success and 0 if an
546 error occurs.
547
548 =head1 EXAMPLES
549
550 Allocate and encode the DER encoding of an X509 structure:
551
552  int len;
553  unsigned char *buf;
554
555  buf = NULL;
556  len = i2d_X509(x, &buf);
557  if (len < 0)
558      /* error */
559
560 Attempt to decode a buffer:
561
562  X509 *x;
563  unsigned char *buf, *p;
564  int len;
565
566  /* Set up buf and len to point to the input buffer. */
567  p = buf;
568  x = d2i_X509(NULL, &p, len);
569  if (x == NULL)
570      /* error */
571
572 Alternative technique:
573
574  X509 *x;
575  unsigned char *buf, *p;
576  int len;
577
578  /* Set up buf and len to point to the input buffer. */
579  p = buf;
580  x = NULL;
581
582  if (d2i_X509(&x, &p, len) == NULL)
583      /* error */
584
585 =head1 WARNINGS
586
587 Using a temporary variable is mandatory. A common
588 mistake is to attempt to use a buffer directly as follows:
589
590  int len;
591  unsigned char *buf;
592
593  len = i2d_X509(x, NULL);
594  buf = OPENSSL_malloc(len);
595  ...
596  i2d_X509(x, &buf);
597  ...
598  OPENSSL_free(buf);
599
600 This code will result in I<buf> apparently containing garbage because
601 it was incremented after the call to point after the data just written.
602 Also I<buf> will no longer contain the pointer allocated by OPENSSL_malloc()
603 and the subsequent call to OPENSSL_free() is likely to crash.
604
605 Another trap to avoid is misuse of the I<a> argument to B<d2i_I<TYPE>>():
606
607  X509 *x;
608
609  if (d2i_X509(&x, &p, len) == NULL)
610      /* error */
611
612 This will probably crash somewhere in d2i_X509(). The reason for this
613 is that the variable I<x> is uninitialized and an attempt will be made to
614 interpret its (invalid) value as an B<X509> structure, typically causing
615 a segmentation violation. If I<x> is set to NULL first then this will not
616 happen.
617
618 =head1 BUGS
619
620 In some versions of OpenSSL the "reuse" behaviour of B<d2i_I<TYPE>>() when
621 I<*a> is valid is broken and some parts of the reused structure may
622 persist if they are not present in the new one. Additionally, in versions of
623 OpenSSL prior to 1.1.0, when the "reuse" behaviour is used and an error occurs
624 the behaviour is inconsistent. Some functions behaved as described here, while
625 some did not free I<*a> on error and did not set I<*a> to NULL.
626
627 As a result of the above issues the "reuse" behaviour is strongly discouraged.
628
629 B<i2d_I<TYPE>>() will not return an error in many versions of OpenSSL,
630 if mandatory fields are not initialized due to a programming error
631 then the encoded structure may contain invalid data or omit the
632 fields entirely and will not be parsed by B<d2i_I<TYPE>>(). This may be
633 fixed in future so code should not assume that B<i2d_I<TYPE>>() will
634 always succeed.
635
636 Any function which encodes a structure (B<i2d_I<TYPE>>(),
637 B<i2d_I<TYPE>>() or B<i2d_I<TYPE>>()) may return a stale encoding if the
638 structure has been modified after deserialization or previous
639 serialization. This is because some objects cache the encoding for
640 efficiency reasons.
641
642 =head1 COPYRIGHT
643
644 Copyright 1998-2018 The OpenSSL Project Authors. All Rights Reserved.
645
646 Licensed under the Apache License 2.0 (the "License").  You may not use
647 this file except in compliance with the License.  You can obtain a copy
648 in the file LICENSE in the source distribution or at
649 L<https://www.openssl.org/source/license.html>.
650
651 =cut