Update the d2i docs to reflect reality
[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_ECPKParameters,
57 d2i_ECParameters,
58 d2i_ECPrivateKey,
59 d2i_ECPrivateKey_bio,
60 d2i_ECPrivateKey_fp,
61 d2i_EC_PUBKEY,
62 d2i_EC_PUBKEY_bio,
63 d2i_EC_PUBKEY_fp,
64 d2i_EDIPARTYNAME,
65 d2i_ESS_CERT_ID,
66 d2i_ESS_ISSUER_SERIAL,
67 d2i_ESS_SIGNING_CERT,
68 d2i_EXTENDED_KEY_USAGE,
69 d2i_GENERAL_NAME,
70 d2i_GENERAL_NAMES,
71 d2i_IPAddressChoice,
72 d2i_IPAddressFamily,
73 d2i_IPAddressOrRange,
74 d2i_IPAddressRange,
75 d2i_ISSUING_DIST_POINT,
76 d2i_NAMING_AUTHORITY,
77 d2i_NETSCAPE_CERT_SEQUENCE,
78 d2i_NETSCAPE_SPKAC,
79 d2i_NETSCAPE_SPKI,
80 d2i_NOTICEREF,
81 d2i_OCSP_BASICRESP,
82 d2i_OCSP_CERTID,
83 d2i_OCSP_CERTSTATUS,
84 d2i_OCSP_CRLID,
85 d2i_OCSP_ONEREQ,
86 d2i_OCSP_REQINFO,
87 d2i_OCSP_REQUEST,
88 d2i_OCSP_RESPBYTES,
89 d2i_OCSP_RESPDATA,
90 d2i_OCSP_RESPID,
91 d2i_OCSP_RESPONSE,
92 d2i_OCSP_REVOKEDINFO,
93 d2i_OCSP_SERVICELOC,
94 d2i_OCSP_SIGNATURE,
95 d2i_OCSP_SINGLERESP,
96 d2i_OSSL_CMP_MSG,
97 d2i_OSSL_CMP_PKIHEADER,
98 d2i_OSSL_CRMF_CERTID,
99 d2i_OSSL_CRMF_CERTTEMPLATE,
100 d2i_OSSL_CRMF_ENCRYPTEDVALUE,
101 d2i_OSSL_CRMF_MSG,
102 d2i_OSSL_CRMF_MSGS,
103 d2i_OSSL_CRMF_PBMPARAMETER,
104 d2i_OSSL_CRMF_PKIPUBLICATIONINFO,
105 d2i_OSSL_CRMF_SINGLEPUBINFO,
106 d2i_OTHERNAME,
107 d2i_PBE2PARAM,
108 d2i_PBEPARAM,
109 d2i_PBKDF2PARAM,
110 d2i_PKCS12,
111 d2i_PKCS12_BAGS,
112 d2i_PKCS12_MAC_DATA,
113 d2i_PKCS12_SAFEBAG,
114 d2i_PKCS12_bio,
115 d2i_PKCS12_fp,
116 d2i_PKCS7,
117 d2i_PKCS7_DIGEST,
118 d2i_PKCS7_ENCRYPT,
119 d2i_PKCS7_ENC_CONTENT,
120 d2i_PKCS7_ENVELOPE,
121 d2i_PKCS7_ISSUER_AND_SERIAL,
122 d2i_PKCS7_RECIP_INFO,
123 d2i_PKCS7_SIGNED,
124 d2i_PKCS7_SIGNER_INFO,
125 d2i_PKCS7_SIGN_ENVELOPE,
126 d2i_PKCS7_bio,
127 d2i_PKCS7_fp,
128 d2i_PKCS8_PRIV_KEY_INFO,
129 d2i_PKCS8_PRIV_KEY_INFO_bio,
130 d2i_PKCS8_PRIV_KEY_INFO_fp,
131 d2i_PKCS8_bio,
132 d2i_PKCS8_fp,
133 d2i_PKEY_USAGE_PERIOD,
134 d2i_POLICYINFO,
135 d2i_POLICYQUALINFO,
136 d2i_PROFESSION_INFO,
137 d2i_PROXY_CERT_INFO_EXTENSION,
138 d2i_PROXY_POLICY,
139 d2i_RSAPrivateKey,
140 d2i_RSAPrivateKey_bio,
141 d2i_RSAPrivateKey_fp,
142 d2i_RSAPublicKey,
143 d2i_RSAPublicKey_bio,
144 d2i_RSAPublicKey_fp,
145 d2i_RSA_OAEP_PARAMS,
146 d2i_RSA_PSS_PARAMS,
147 d2i_RSA_PUBKEY,
148 d2i_RSA_PUBKEY_bio,
149 d2i_RSA_PUBKEY_fp,
150 d2i_SCRYPT_PARAMS,
151 d2i_SCT_LIST,
152 d2i_SXNET,
153 d2i_SXNETID,
154 d2i_TS_ACCURACY,
155 d2i_TS_MSG_IMPRINT,
156 d2i_TS_MSG_IMPRINT_bio,
157 d2i_TS_MSG_IMPRINT_fp,
158 d2i_TS_REQ,
159 d2i_TS_REQ_bio,
160 d2i_TS_REQ_fp,
161 d2i_TS_RESP,
162 d2i_TS_RESP_bio,
163 d2i_TS_RESP_fp,
164 d2i_TS_STATUS_INFO,
165 d2i_TS_TST_INFO,
166 d2i_TS_TST_INFO_bio,
167 d2i_TS_TST_INFO_fp,
168 d2i_USERNOTICE,
169 d2i_X509,
170 d2i_X509_ALGOR,
171 d2i_X509_ALGORS,
172 d2i_X509_ATTRIBUTE,
173 d2i_X509_CERT_AUX,
174 d2i_X509_CINF,
175 d2i_X509_CRL,
176 d2i_X509_CRL_INFO,
177 d2i_X509_CRL_bio,
178 d2i_X509_CRL_fp,
179 d2i_X509_EXTENSION,
180 d2i_X509_EXTENSIONS,
181 d2i_X509_NAME,
182 d2i_X509_NAME_ENTRY,
183 d2i_X509_PUBKEY,
184 d2i_X509_REQ,
185 d2i_X509_REQ_INFO,
186 d2i_X509_REQ_bio,
187 d2i_X509_REQ_fp,
188 d2i_X509_REVOKED,
189 d2i_X509_SIG,
190 d2i_X509_VAL,
191 i2d_ACCESS_DESCRIPTION,
192 i2d_ADMISSIONS,
193 i2d_ADMISSION_SYNTAX,
194 i2d_ASIdOrRange,
195 i2d_ASIdentifierChoice,
196 i2d_ASIdentifiers,
197 i2d_ASN1_BIT_STRING,
198 i2d_ASN1_BMPSTRING,
199 i2d_ASN1_ENUMERATED,
200 i2d_ASN1_GENERALIZEDTIME,
201 i2d_ASN1_GENERALSTRING,
202 i2d_ASN1_IA5STRING,
203 i2d_ASN1_INTEGER,
204 i2d_ASN1_NULL,
205 i2d_ASN1_OBJECT,
206 i2d_ASN1_OCTET_STRING,
207 i2d_ASN1_PRINTABLE,
208 i2d_ASN1_PRINTABLESTRING,
209 i2d_ASN1_SEQUENCE_ANY,
210 i2d_ASN1_SET_ANY,
211 i2d_ASN1_T61STRING,
212 i2d_ASN1_TIME,
213 i2d_ASN1_TYPE,
214 i2d_ASN1_UNIVERSALSTRING,
215 i2d_ASN1_UTCTIME,
216 i2d_ASN1_UTF8STRING,
217 i2d_ASN1_VISIBLESTRING,
218 i2d_ASN1_bio_stream,
219 i2d_ASRange,
220 i2d_AUTHORITY_INFO_ACCESS,
221 i2d_AUTHORITY_KEYID,
222 i2d_BASIC_CONSTRAINTS,
223 i2d_CERTIFICATEPOLICIES,
224 i2d_CMS_ContentInfo,
225 i2d_CMS_ReceiptRequest,
226 i2d_CMS_bio,
227 i2d_CRL_DIST_POINTS,
228 i2d_DHxparams,
229 i2d_DIRECTORYSTRING,
230 i2d_DISPLAYTEXT,
231 i2d_DIST_POINT,
232 i2d_DIST_POINT_NAME,
233 i2d_DSAPrivateKey,
234 i2d_DSAPrivateKey_bio,
235 i2d_DSAPrivateKey_fp,
236 i2d_DSAPublicKey,
237 i2d_DSA_PUBKEY,
238 i2d_DSA_PUBKEY_bio,
239 i2d_DSA_PUBKEY_fp,
240 i2d_DSA_SIG,
241 i2d_DSAparams,
242 i2d_ECPKParameters,
243 i2d_ECParameters,
244 i2d_ECPrivateKey,
245 i2d_ECPrivateKey_bio,
246 i2d_ECPrivateKey_fp,
247 i2d_EC_PUBKEY,
248 i2d_EC_PUBKEY_bio,
249 i2d_EC_PUBKEY_fp,
250 i2d_EDIPARTYNAME,
251 i2d_ESS_CERT_ID,
252 i2d_ESS_ISSUER_SERIAL,
253 i2d_ESS_SIGNING_CERT,
254 i2d_EXTENDED_KEY_USAGE,
255 i2d_GENERAL_NAME,
256 i2d_GENERAL_NAMES,
257 i2d_IPAddressChoice,
258 i2d_IPAddressFamily,
259 i2d_IPAddressOrRange,
260 i2d_IPAddressRange,
261 i2d_ISSUING_DIST_POINT,
262 i2d_NAMING_AUTHORITY,
263 i2d_NETSCAPE_CERT_SEQUENCE,
264 i2d_NETSCAPE_SPKAC,
265 i2d_NETSCAPE_SPKI,
266 i2d_NOTICEREF,
267 i2d_OCSP_BASICRESP,
268 i2d_OCSP_CERTID,
269 i2d_OCSP_CERTSTATUS,
270 i2d_OCSP_CRLID,
271 i2d_OCSP_ONEREQ,
272 i2d_OCSP_REQINFO,
273 i2d_OCSP_REQUEST,
274 i2d_OCSP_RESPBYTES,
275 i2d_OCSP_RESPDATA,
276 i2d_OCSP_RESPID,
277 i2d_OCSP_RESPONSE,
278 i2d_OCSP_REVOKEDINFO,
279 i2d_OCSP_SERVICELOC,
280 i2d_OCSP_SIGNATURE,
281 i2d_OCSP_SINGLERESP,
282 i2d_OSSL_CMP_MSG,
283 i2d_OSSL_CMP_PKIHEADER,
284 i2d_OSSL_CRMF_CERTID,
285 i2d_OSSL_CRMF_CERTTEMPLATE,
286 i2d_OSSL_CRMF_ENCRYPTEDVALUE,
287 i2d_OSSL_CRMF_MSG,
288 i2d_OSSL_CRMF_MSGS,
289 i2d_OSSL_CRMF_PBMPARAMETER,
290 i2d_OSSL_CRMF_PKIPUBLICATIONINFO,
291 i2d_OSSL_CRMF_SINGLEPUBINFO,
292 i2d_OTHERNAME,
293 i2d_PBE2PARAM,
294 i2d_PBEPARAM,
295 i2d_PBKDF2PARAM,
296 i2d_PKCS12,
297 i2d_PKCS12_BAGS,
298 i2d_PKCS12_MAC_DATA,
299 i2d_PKCS12_SAFEBAG,
300 i2d_PKCS12_bio,
301 i2d_PKCS12_fp,
302 i2d_PKCS7,
303 i2d_PKCS7_DIGEST,
304 i2d_PKCS7_ENCRYPT,
305 i2d_PKCS7_ENC_CONTENT,
306 i2d_PKCS7_ENVELOPE,
307 i2d_PKCS7_ISSUER_AND_SERIAL,
308 i2d_PKCS7_NDEF,
309 i2d_PKCS7_RECIP_INFO,
310 i2d_PKCS7_SIGNED,
311 i2d_PKCS7_SIGNER_INFO,
312 i2d_PKCS7_SIGN_ENVELOPE,
313 i2d_PKCS7_bio,
314 i2d_PKCS7_fp,
315 i2d_PKCS8PrivateKeyInfo_bio,
316 i2d_PKCS8PrivateKeyInfo_fp,
317 i2d_PKCS8_PRIV_KEY_INFO,
318 i2d_PKCS8_PRIV_KEY_INFO_bio,
319 i2d_PKCS8_PRIV_KEY_INFO_fp,
320 i2d_PKCS8_bio,
321 i2d_PKCS8_fp,
322 i2d_PKEY_USAGE_PERIOD,
323 i2d_POLICYINFO,
324 i2d_POLICYQUALINFO,
325 i2d_PROFESSION_INFO,
326 i2d_PROXY_CERT_INFO_EXTENSION,
327 i2d_PROXY_POLICY,
328 i2d_RSAPrivateKey,
329 i2d_RSAPrivateKey_bio,
330 i2d_RSAPrivateKey_fp,
331 i2d_RSAPublicKey,
332 i2d_RSAPublicKey_bio,
333 i2d_RSAPublicKey_fp,
334 i2d_RSA_OAEP_PARAMS,
335 i2d_RSA_PSS_PARAMS,
336 i2d_RSA_PUBKEY,
337 i2d_RSA_PUBKEY_bio,
338 i2d_RSA_PUBKEY_fp,
339 i2d_SCRYPT_PARAMS,
340 i2d_SCT_LIST,
341 i2d_SXNET,
342 i2d_SXNETID,
343 i2d_TS_ACCURACY,
344 i2d_TS_MSG_IMPRINT,
345 i2d_TS_MSG_IMPRINT_bio,
346 i2d_TS_MSG_IMPRINT_fp,
347 i2d_TS_REQ,
348 i2d_TS_REQ_bio,
349 i2d_TS_REQ_fp,
350 i2d_TS_RESP,
351 i2d_TS_RESP_bio,
352 i2d_TS_RESP_fp,
353 i2d_TS_STATUS_INFO,
354 i2d_TS_TST_INFO,
355 i2d_TS_TST_INFO_bio,
356 i2d_TS_TST_INFO_fp,
357 i2d_USERNOTICE,
358 i2d_X509,
359 i2d_X509_ALGOR,
360 i2d_X509_ALGORS,
361 i2d_X509_ATTRIBUTE,
362 i2d_X509_CERT_AUX,
363 i2d_X509_CINF,
364 i2d_X509_CRL,
365 i2d_X509_CRL_INFO,
366 i2d_X509_CRL_bio,
367 i2d_X509_CRL_fp,
368 i2d_X509_EXTENSION,
369 i2d_X509_EXTENSIONS,
370 i2d_X509_NAME,
371 i2d_X509_NAME_ENTRY,
372 i2d_X509_PUBKEY,
373 i2d_X509_REQ,
374 i2d_X509_REQ_INFO,
375 i2d_X509_REQ_bio,
376 i2d_X509_REQ_fp,
377 i2d_X509_REVOKED,
378 i2d_X509_SIG,
379 i2d_X509_VAL,
380 - convert objects from/to ASN.1/DER representation
381
382 =head1 SYNOPSIS
383
384 =for comment generic
385
386  TYPE *d2i_TYPE(TYPE **a, unsigned char **ppin, long length);
387  TYPE *d2i_TYPE_bio(BIO *bp, TYPE **a);
388  TYPE *d2i_TYPE_fp(FILE *fp, TYPE **a);
389
390  int i2d_TYPE(const TYPE *a, unsigned char **ppout);
391  int i2d_TYPE(TYPE *a, unsigned char **ppout);
392  int i2d_TYPE_fp(FILE *fp, const TYPE *a);
393  int i2d_TYPE_fp(FILE *fp, TYPE *a);
394  int i2d_TYPE_bio(BIO *bp, const TYPE *a);
395  int i2d_TYPE_bio(BIO *bp, TYPE *a);
396
397 =head1 DESCRIPTION
398
399 In the description here, I<TYPE> is used a placeholder
400 for any of the OpenSSL datatypes, such as I<X509_CRL>.
401 The function parameters I<ppin> and I<ppout> are generally
402 either both named I<pp> in the headers, or I<in> and I<out>.
403
404 These functions convert OpenSSL objects to and from their ASN.1/DER
405 encoding.  Unlike the C structures which can have pointers to sub-objects
406 within, the DER is a serialized encoding, suitable for sending over the
407 network, writing to a file, and so on.
408
409 d2i_TYPE() attempts to decode B<len> bytes at B<*ppin>. If successful a
410 pointer to the B<TYPE> structure is returned and B<*ppin> is incremented to
411 the byte following the parsed data.  If B<a> is not B<NULL> then a pointer
412 to the returned structure is also written to B<*a>.  If an error occurred
413 then B<NULL> is returned.
414
415 On a successful return, if B<*a> is not B<NULL> then it is assumed that B<*a>
416 contains a valid B<TYPE> structure and an attempt is made to reuse it. This
417 "reuse" capability is present for historical compatibility but its use is
418 B<strongly discouraged> (see BUGS below, and the discussion in the RETURN
419 VALUES section).
420
421 d2i_TYPE_bio() is similar to d2i_TYPE() except it attempts
422 to parse data from BIO B<bp>.
423
424 d2i_TYPE_fp() is similar to d2i_TYPE() except it attempts
425 to parse data from FILE pointer B<fp>.
426
427 i2d_TYPE() encodes the structure pointed to by B<a> into DER format.
428 If B<ppout> is not B<NULL>, it writes the DER encoded data to the buffer
429 at B<*ppout>, and increments it to point after the data just written.
430 If the return value is negative an error occurred, otherwise it
431 returns the length of the encoded data.
432
433 If B<*ppout> is B<NULL> memory will be allocated for a buffer and the encoded
434 data written to it. In this case B<*ppout> is not incremented and it points
435 to the start of the data just written.
436
437 i2d_TYPE_bio() is similar to i2d_TYPE() except it writes
438 the encoding of the structure B<a> to BIO B<bp> and it
439 returns 1 for success and 0 for failure.
440
441 i2d_TYPE_fp() is similar to i2d_TYPE() except it writes
442 the encoding of the structure B<a> to BIO B<bp> and it
443 returns 1 for success and 0 for failure.
444
445 These routines do not encrypt private keys and therefore offer no
446 security; use L<PEM_write_PrivateKey(3)> or similar for writing to files.
447
448 =head1 NOTES
449
450 The letters B<i> and B<d> in B<i2d_TYPE> stand for
451 "internal" (that is, an internal C structure) and "DER" respectively.
452 So B<i2d_TYPE> converts from internal to DER.
453
454 The functions can also understand B<BER> forms.
455
456 The actual TYPE structure passed to i2d_TYPE() must be a valid
457 populated B<TYPE> structure -- it B<cannot> simply be fed with an
458 empty structure such as that returned by TYPE_new().
459
460 The encoded data is in binary form and may contain embedded zeroes.
461 Therefore any FILE pointers or BIOs should be opened in binary mode.
462 Functions such as strlen() will B<not> return the correct length
463 of the encoded structure.
464
465 The ways that B<*ppin> and B<*ppout> are incremented after the operation
466 can trap the unwary. See the B<WARNINGS> section for some common
467 errors.
468 The reason for this-auto increment behaviour is to reflect a typical
469 usage of ASN1 functions: after one structure is encoded or decoded
470 another will be processed after it.
471
472 The following points about the data types might be useful:
473
474 =over 4
475
476 =item B<ASN1_OBJECT>
477
478 Represents an ASN1 OBJECT IDENTIFIER.
479
480 =item B<DHparams>
481
482 Represents a PKCS#3 DH parameters structure.
483
484 =item B<DHparamx>
485
486 Represents an ANSI X9.42 DH parameters structure.
487
488 =item B<DSA_PUBKEY>
489
490 Represents a DSA public key using a B<SubjectPublicKeyInfo> structure.
491
492 =item B<DSAPublicKey, DSAPrivateKey>
493
494 Use a non-standard OpenSSL format and should be avoided; use B<DSA_PUBKEY>,
495 B<PEM_write_PrivateKey(3)>, or similar instead.
496
497 =item B<RSAPublicKey>
498
499 Represents a PKCS#1 RSA public key structure.
500
501 =item B<X509_ALGOR>
502
503 Represents an B<AlgorithmIdentifier> structure as used in IETF RFC 6960 and
504 elsewhere.
505
506 =item B<X509_Name>
507
508 Represents a B<Name> type as used for subject and issuer names in
509 IETF RFC 6960 and elsewhere.
510
511 =item B<X509_REQ>
512
513 Represents a PKCS#10 certificate request.
514
515 =item B<X509_SIG>
516
517 Represents the B<DigestInfo> structure defined in PKCS#1 and PKCS#7.
518
519 =back
520
521 =head1 RETURN VALUES
522
523 d2i_TYPE(), d2i_TYPE_bio() and d2i_TYPE_fp() return a valid B<TYPE> structure
524 or B<NULL> if an error occurs.  If the "reuse" capability has been used with
525 a valid structure being passed in via B<a>, then the object is freed in
526 the event of error and B<*a> is set to NULL.
527
528 i2d_TYPE() returns the number of bytes successfully encoded or a negative
529 value if an error occurs.
530
531 i2d_TYPE_bio() and i2d_TYPE_fp() return 1 for success and 0 if an error
532 occurs.
533
534 =head1 EXAMPLES
535
536 Allocate and encode the DER encoding of an X509 structure:
537
538  int len;
539  unsigned char *buf;
540
541  buf = NULL;
542  len = i2d_X509(x, &buf);
543  if (len < 0)
544      /* error */
545
546 Attempt to decode a buffer:
547
548  X509 *x;
549  unsigned char *buf, *p;
550  int len;
551
552  /* Set up buf and len to point to the input buffer. */
553  p = buf;
554  x = d2i_X509(NULL, &p, len);
555  if (x == NULL)
556      /* error */
557
558 Alternative technique:
559
560  X509 *x;
561  unsigned char *buf, *p;
562  int len;
563
564  /* Set up buf and len to point to the input buffer. */
565  p = buf;
566  x = NULL;
567
568  if (d2i_X509(&x, &p, len) == NULL)
569      /* error */
570
571 =head1 WARNINGS
572
573 Using a temporary variable is mandatory. A common
574 mistake is to attempt to use a buffer directly as follows:
575
576  int len;
577  unsigned char *buf;
578
579  len = i2d_X509(x, NULL);
580  buf = OPENSSL_malloc(len);
581  ...
582  i2d_X509(x, &buf);
583  ...
584  OPENSSL_free(buf);
585
586 This code will result in B<buf> apparently containing garbage because
587 it was incremented after the call to point after the data just written.
588 Also B<buf> will no longer contain the pointer allocated by OPENSSL_malloc()
589 and the subsequent call to OPENSSL_free() is likely to crash.
590
591 Another trap to avoid is misuse of the B<a> argument to d2i_TYPE():
592
593  X509 *x;
594
595  if (d2i_X509(&x, &p, len) == NULL)
596      /* error */
597
598 This will probably crash somewhere in d2i_X509(). The reason for this
599 is that the variable B<x> is uninitialized and an attempt will be made to
600 interpret its (invalid) value as an B<X509> structure, typically causing
601 a segmentation violation. If B<x> is set to NULL first then this will not
602 happen.
603
604 =head1 BUGS
605
606 In some versions of OpenSSL the "reuse" behaviour of d2i_TYPE() when
607 B<*a> is valid is broken and some parts of the reused structure may
608 persist if they are not present in the new one. Additionally, in versions of
609 OpenSSL prior to 1.1.0, when the "reuse" behaviour is used and an error occurs
610 the behaviour is inconsistent. Some functions behaved as described here, while
611 some did not free B<*a> on error and did not set B<*a> to NULL.
612
613 As a result of the above issues the "reuse" behaviour is strongly discouraged.
614
615 i2d_TYPE() will not return an error in many versions of OpenSSL,
616 if mandatory fields are not initialized due to a programming error
617 then the encoded structure may contain invalid data or omit the
618 fields entirely and will not be parsed by d2i_TYPE(). This may be
619 fixed in future so code should not assume that i2d_TYPE() will
620 always succeed.
621
622 Any function which encodes a structure (i2d_TYPE(),
623 i2d_TYPE() or i2d_TYPE()) may return a stale encoding if the
624 structure has been modified after deserialization or previous
625 serialization. This is because some objects cache the encoding for
626 efficiency reasons.
627
628 =head1 COPYRIGHT
629
630 Copyright 1998-2018 The OpenSSL Project Authors. All Rights Reserved.
631
632 Licensed under the Apache License 2.0 (the "License").  You may not use
633 this file except in compliance with the License.  You can obtain a copy
634 in the file LICENSE in the source distribution or at
635 L<https://www.openssl.org/source/license.html>.
636
637 =cut