doc/man3/d2i_X509.pod

   1 =pod
   2
   3 =begin comment
   4
   5 Any keypair function here that gets deprecated should be moved to
   6 d2i_RSAPrivateKey.pod.
   7
   8 =end comment
   9
  10 =head1 NAME
  11
  12 d2i_ACCESS_DESCRIPTION,
  13 d2i_ADMISSIONS,
  14 d2i_ADMISSION_SYNTAX,
  15 d2i_ASIdOrRange,
  16 d2i_ASIdentifierChoice,
  17 d2i_ASIdentifiers,
  18 d2i_ASN1_BIT_STRING,
  19 d2i_ASN1_BMPSTRING,
  20 d2i_ASN1_ENUMERATED,
  21 d2i_ASN1_GENERALIZEDTIME,
  22 d2i_ASN1_GENERALSTRING,
  23 d2i_ASN1_IA5STRING,
  24 d2i_ASN1_INTEGER,
  25 d2i_ASN1_NULL,
  26 d2i_ASN1_OBJECT,
  27 d2i_ASN1_OCTET_STRING,
  28 d2i_ASN1_PRINTABLE,
  29 d2i_ASN1_PRINTABLESTRING,
  30 d2i_ASN1_SEQUENCE_ANY,
  31 d2i_ASN1_SET_ANY,
  32 d2i_ASN1_T61STRING,
  33 d2i_ASN1_TIME,
  34 d2i_ASN1_TYPE,
  35 d2i_ASN1_UINTEGER,
  36 d2i_ASN1_UNIVERSALSTRING,
  37 d2i_ASN1_UTCTIME,
  38 d2i_ASN1_UTF8STRING,
  39 d2i_ASN1_VISIBLESTRING,
  40 d2i_ASRange,
  41 d2i_AUTHORITY_INFO_ACCESS,
  42 d2i_AUTHORITY_KEYID,
  43 d2i_BASIC_CONSTRAINTS,
  44 d2i_CERTIFICATEPOLICIES,
  45 d2i_CMS_ContentInfo,
  46 d2i_CMS_ReceiptRequest,
  47 d2i_CMS_bio,
  48 d2i_CRL_DIST_POINTS,
  49 d2i_DHxparams,
  50 d2i_DIRECTORYSTRING,
  51 d2i_DISPLAYTEXT,
  52 d2i_DIST_POINT,
  53 d2i_DIST_POINT_NAME,
  54 d2i_DSA_SIG,
  55 d2i_ECDSA_SIG,
  56 d2i_EDIPARTYNAME,
  57 d2i_ESS_CERT_ID,
  58 d2i_ESS_CERT_ID_V2,
  59 d2i_ESS_ISSUER_SERIAL,
  60 d2i_ESS_SIGNING_CERT,
  61 d2i_ESS_SIGNING_CERT_V2,
  62 d2i_EXTENDED_KEY_USAGE,
  63 d2i_GENERAL_NAME,
  64 d2i_GENERAL_NAMES,
  65 d2i_IPAddressChoice,
  66 d2i_IPAddressFamily,
  67 d2i_IPAddressOrRange,
  68 d2i_IPAddressRange,
  69 d2i_ISSUER_SIGN_TOOL,
  70 d2i_ISSUING_DIST_POINT,
  71 d2i_NAMING_AUTHORITY,
  72 d2i_NETSCAPE_CERT_SEQUENCE,
  73 d2i_NETSCAPE_SPKAC,
  74 d2i_NETSCAPE_SPKI,
  75 d2i_NOTICEREF,
  76 d2i_OCSP_BASICRESP,
  77 d2i_OCSP_CERTID,
  78 d2i_OCSP_CERTSTATUS,
  79 d2i_OCSP_CRLID,
  80 d2i_OCSP_ONEREQ,
  81 d2i_OCSP_REQINFO,
  82 d2i_OCSP_REQUEST,
  83 d2i_OCSP_RESPBYTES,
  84 d2i_OCSP_RESPDATA,
  85 d2i_OCSP_RESPID,
  86 d2i_OCSP_RESPONSE,
  87 d2i_OCSP_REVOKEDINFO,
  88 d2i_OCSP_SERVICELOC,
  89 d2i_OCSP_SIGNATURE,
  90 d2i_OCSP_SINGLERESP,
  91 d2i_OSSL_CMP_MSG,
  92 d2i_OSSL_CMP_PKIHEADER,
  93 d2i_OSSL_CMP_PKISI,
  94 d2i_OSSL_CRMF_CERTID,
  95 d2i_OSSL_CRMF_CERTTEMPLATE,
  96 d2i_OSSL_CRMF_ENCRYPTEDVALUE,
  97 d2i_OSSL_CRMF_MSG,
  98 d2i_OSSL_CRMF_MSGS,
  99 d2i_OSSL_CRMF_PBMPARAMETER,
 100 d2i_OSSL_CRMF_PKIPUBLICATIONINFO,
 101 d2i_OSSL_CRMF_SINGLEPUBINFO,
 102 d2i_OTHERNAME,
 103 d2i_PBE2PARAM,
 104 d2i_PBEPARAM,
 105 d2i_PBKDF2PARAM,
 106 d2i_PKCS12,
 107 d2i_PKCS12_BAGS,
 108 d2i_PKCS12_MAC_DATA,
 109 d2i_PKCS12_SAFEBAG,
 110 d2i_PKCS12_bio,
 111 d2i_PKCS12_fp,
 112 d2i_PKCS7,
 113 d2i_PKCS7_DIGEST,
 114 d2i_PKCS7_ENCRYPT,
 115 d2i_PKCS7_ENC_CONTENT,
 116 d2i_PKCS7_ENVELOPE,
 117 d2i_PKCS7_ISSUER_AND_SERIAL,
 118 d2i_PKCS7_RECIP_INFO,
 119 d2i_PKCS7_SIGNED,
 120 d2i_PKCS7_SIGNER_INFO,
 121 d2i_PKCS7_SIGN_ENVELOPE,
 122 d2i_PKCS7_bio,
 123 d2i_PKCS7_fp,
 124 d2i_PKCS8_PRIV_KEY_INFO,
 125 d2i_PKCS8_PRIV_KEY_INFO_bio,
 126 d2i_PKCS8_PRIV_KEY_INFO_fp,
 127 d2i_PKCS8_bio,
 128 d2i_PKCS8_fp,
 129 d2i_PKEY_USAGE_PERIOD,
 130 d2i_POLICYINFO,
 131 d2i_POLICYQUALINFO,
 132 d2i_PROFESSION_INFO,
 133 d2i_PROXY_CERT_INFO_EXTENSION,
 134 d2i_PROXY_POLICY,
 135 d2i_RSA_OAEP_PARAMS,
 136 d2i_RSA_PSS_PARAMS,
 137 d2i_SCRYPT_PARAMS,
 138 d2i_SCT_LIST,
 139 d2i_SXNET,
 140 d2i_SXNETID,
 141 d2i_TS_ACCURACY,
 142 d2i_TS_MSG_IMPRINT,
 143 d2i_TS_MSG_IMPRINT_bio,
 144 d2i_TS_MSG_IMPRINT_fp,
 145 d2i_TS_REQ,
 146 d2i_TS_REQ_bio,
 147 d2i_TS_REQ_fp,
 148 d2i_TS_RESP,
 149 d2i_TS_RESP_bio,
 150 d2i_TS_RESP_fp,
 151 d2i_TS_STATUS_INFO,
 152 d2i_TS_TST_INFO,
 153 d2i_TS_TST_INFO_bio,
 154 d2i_TS_TST_INFO_fp,
 155 d2i_USERNOTICE,
 156 d2i_X509,
 157 d2i_X509_ALGOR,
 158 d2i_X509_ALGORS,
 159 d2i_X509_ATTRIBUTE,
 160 d2i_X509_CERT_AUX,
 161 d2i_X509_CINF,
 162 d2i_X509_CRL,
 163 d2i_X509_CRL_INFO,
 164 d2i_X509_CRL_bio,
 165 d2i_X509_CRL_fp,
 166 d2i_X509_EXTENSION,
 167 d2i_X509_EXTENSIONS,
 168 d2i_X509_NAME,
 169 d2i_X509_NAME_ENTRY,
 170 d2i_X509_PUBKEY,
 171 d2i_X509_PUBKEY_bio,
 172 d2i_X509_PUBKEY_fp,
 173 d2i_X509_REQ,
 174 d2i_X509_REQ_INFO,
 175 d2i_X509_REQ_bio,
 176 d2i_X509_REQ_fp,
 177 d2i_X509_REVOKED,
 178 d2i_X509_SIG,
 179 d2i_X509_VAL,
 180 i2d_ACCESS_DESCRIPTION,
 181 i2d_ADMISSIONS,
 182 i2d_ADMISSION_SYNTAX,
 183 i2d_ASIdOrRange,
 184 i2d_ASIdentifierChoice,
 185 i2d_ASIdentifiers,
 186 i2d_ASN1_BIT_STRING,
 187 i2d_ASN1_BMPSTRING,
 188 i2d_ASN1_ENUMERATED,
 189 i2d_ASN1_GENERALIZEDTIME,
 190 i2d_ASN1_GENERALSTRING,
 191 i2d_ASN1_IA5STRING,
 192 i2d_ASN1_INTEGER,
 193 i2d_ASN1_NULL,
 194 i2d_ASN1_OBJECT,
 195 i2d_ASN1_OCTET_STRING,
 196 i2d_ASN1_PRINTABLE,
 197 i2d_ASN1_PRINTABLESTRING,
 198 i2d_ASN1_SEQUENCE_ANY,
 199 i2d_ASN1_SET_ANY,
 200 i2d_ASN1_T61STRING,
 201 i2d_ASN1_TIME,
 202 i2d_ASN1_TYPE,
 203 i2d_ASN1_UNIVERSALSTRING,
 204 i2d_ASN1_UTCTIME,
 205 i2d_ASN1_UTF8STRING,
 206 i2d_ASN1_VISIBLESTRING,
 207 i2d_ASN1_bio_stream,
 208 i2d_ASRange,
 209 i2d_AUTHORITY_INFO_ACCESS,
 210 i2d_AUTHORITY_KEYID,
 211 i2d_BASIC_CONSTRAINTS,
 212 i2d_CERTIFICATEPOLICIES,
 213 i2d_CMS_ContentInfo,
 214 i2d_CMS_ReceiptRequest,
 215 i2d_CMS_bio,
 216 i2d_CRL_DIST_POINTS,
 217 i2d_DHxparams,
 218 i2d_DIRECTORYSTRING,
 219 i2d_DISPLAYTEXT,
 220 i2d_DIST_POINT,
 221 i2d_DIST_POINT_NAME,
 222 i2d_DSA_SIG,
 223 i2d_ECDSA_SIG,
 224 i2d_EDIPARTYNAME,
 225 i2d_ESS_CERT_ID,
 226 i2d_ESS_CERT_ID_V2,
 227 i2d_ESS_ISSUER_SERIAL,
 228 i2d_ESS_SIGNING_CERT,
 229 i2d_ESS_SIGNING_CERT_V2,
 230 i2d_EXTENDED_KEY_USAGE,
 231 i2d_GENERAL_NAME,
 232 i2d_GENERAL_NAMES,
 233 i2d_IPAddressChoice,
 234 i2d_IPAddressFamily,
 235 i2d_IPAddressOrRange,
 236 i2d_IPAddressRange,
 237 i2d_ISSUER_SIGN_TOOL,
 238 i2d_ISSUING_DIST_POINT,
 239 i2d_NAMING_AUTHORITY,
 240 i2d_NETSCAPE_CERT_SEQUENCE,
 241 i2d_NETSCAPE_SPKAC,
 242 i2d_NETSCAPE_SPKI,
 243 i2d_NOTICEREF,
 244 i2d_OCSP_BASICRESP,
 245 i2d_OCSP_CERTID,
 246 i2d_OCSP_CERTSTATUS,
 247 i2d_OCSP_CRLID,
 248 i2d_OCSP_ONEREQ,
 249 i2d_OCSP_REQINFO,
 250 i2d_OCSP_REQUEST,
 251 i2d_OCSP_RESPBYTES,
 252 i2d_OCSP_RESPDATA,
 253 i2d_OCSP_RESPID,
 254 i2d_OCSP_RESPONSE,
 255 i2d_OCSP_REVOKEDINFO,
 256 i2d_OCSP_SERVICELOC,
 257 i2d_OCSP_SIGNATURE,
 258 i2d_OCSP_SINGLERESP,
 259 i2d_OSSL_CMP_MSG,
 260 i2d_OSSL_CMP_PKIHEADER,
 261 i2d_OSSL_CMP_PKISI,
 262 i2d_OSSL_CRMF_CERTID,
 263 i2d_OSSL_CRMF_CERTTEMPLATE,
 264 i2d_OSSL_CRMF_ENCRYPTEDVALUE,
 265 i2d_OSSL_CRMF_MSG,
 266 i2d_OSSL_CRMF_MSGS,
 267 i2d_OSSL_CRMF_PBMPARAMETER,
 268 i2d_OSSL_CRMF_PKIPUBLICATIONINFO,
 269 i2d_OSSL_CRMF_SINGLEPUBINFO,
 270 i2d_OTHERNAME,
 271 i2d_PBE2PARAM,
 272 i2d_PBEPARAM,
 273 i2d_PBKDF2PARAM,
 274 i2d_PKCS12,
 275 i2d_PKCS12_BAGS,
 276 i2d_PKCS12_MAC_DATA,
 277 i2d_PKCS12_SAFEBAG,
 278 i2d_PKCS12_bio,
 279 i2d_PKCS12_fp,
 280 i2d_PKCS7,
 281 i2d_PKCS7_DIGEST,
 282 i2d_PKCS7_ENCRYPT,
 283 i2d_PKCS7_ENC_CONTENT,
 284 i2d_PKCS7_ENVELOPE,
 285 i2d_PKCS7_ISSUER_AND_SERIAL,
 286 i2d_PKCS7_NDEF,
 287 i2d_PKCS7_RECIP_INFO,
 288 i2d_PKCS7_SIGNED,
 289 i2d_PKCS7_SIGNER_INFO,
 290 i2d_PKCS7_SIGN_ENVELOPE,
 291 i2d_PKCS7_bio,
 292 i2d_PKCS7_fp,
 293 i2d_PKCS8PrivateKeyInfo_bio,
 294 i2d_PKCS8PrivateKeyInfo_fp,
 295 i2d_PKCS8_PRIV_KEY_INFO,
 296 i2d_PKCS8_PRIV_KEY_INFO_bio,
 297 i2d_PKCS8_PRIV_KEY_INFO_fp,
 298 i2d_PKCS8_bio,
 299 i2d_PKCS8_fp,
 300 i2d_PKEY_USAGE_PERIOD,
 301 i2d_POLICYINFO,
 302 i2d_POLICYQUALINFO,
 303 i2d_PROFESSION_INFO,
 304 i2d_PROXY_CERT_INFO_EXTENSION,
 305 i2d_PROXY_POLICY,
 306 i2d_RSA_OAEP_PARAMS,
 307 i2d_RSA_PSS_PARAMS,
 308 i2d_SCRYPT_PARAMS,
 309 i2d_SCT_LIST,
 310 i2d_SXNET,
 311 i2d_SXNETID,
 312 i2d_TS_ACCURACY,
 313 i2d_TS_MSG_IMPRINT,
 314 i2d_TS_MSG_IMPRINT_bio,
 315 i2d_TS_MSG_IMPRINT_fp,
 316 i2d_TS_REQ,
 317 i2d_TS_REQ_bio,
 318 i2d_TS_REQ_fp,
 319 i2d_TS_RESP,
 320 i2d_TS_RESP_bio,
 321 i2d_TS_RESP_fp,
 322 i2d_TS_STATUS_INFO,
 323 i2d_TS_TST_INFO,
 324 i2d_TS_TST_INFO_bio,
 325 i2d_TS_TST_INFO_fp,
 326 i2d_USERNOTICE,
 327 i2d_X509,
 328 i2d_X509_ALGOR,
 329 i2d_X509_ALGORS,
 330 i2d_X509_ATTRIBUTE,
 331 i2d_X509_CERT_AUX,
 332 i2d_X509_CINF,
 333 i2d_X509_CRL,
 334 i2d_X509_CRL_INFO,
 335 i2d_X509_CRL_bio,
 336 i2d_X509_CRL_fp,
 337 i2d_X509_EXTENSION,
 338 i2d_X509_EXTENSIONS,
 339 i2d_X509_NAME,
 340 i2d_X509_NAME_ENTRY,
 341 i2d_X509_PUBKEY,
 342 i2d_X509_PUBKEY_bio,
 343 i2d_X509_PUBKEY_fp,
 344 i2d_X509_REQ,
 345 i2d_X509_REQ_INFO,
 346 i2d_X509_REQ_bio,
 347 i2d_X509_REQ_fp,
 348 i2d_X509_REVOKED,
 349 i2d_X509_SIG,
 350 i2d_X509_VAL,
 351 - convert objects from/to ASN.1/DER representation
 352
 353 =head1 SYNOPSIS
 354
 355 =for openssl generic
 356
 357  TYPE *d2i_TYPE(TYPE **a, const unsigned char **ppin, long length);
 358  TYPE *d2i_TYPE_bio(BIO *bp, TYPE **a);
 359  TYPE *d2i_TYPE_fp(FILE *fp, TYPE **a);
 360
 361  int i2d_TYPE(const TYPE *a, unsigned char **ppout);
 362  int i2d_TYPE(TYPE *a, unsigned char **ppout);
 363  int i2d_TYPE_fp(FILE *fp, const TYPE *a);
 364  int i2d_TYPE_fp(FILE *fp, TYPE *a);
 365  int i2d_TYPE_bio(BIO *bp, const TYPE *a);
 366  int i2d_TYPE_bio(BIO *bp, TYPE *a);
 367
 368 =head1 DESCRIPTION
 369
 370 In the description here, B<I<TYPE>> is used a placeholder
 371 for any of the OpenSSL datatypes, such as B<X509_CRL>.
 372 The function parameters I<ppin> and I<ppout> are generally
 373 either both named I<pp> in the headers, or I<in> and I<out>.
 374
 375 These functions convert OpenSSL objects to and from their ASN.1/DER
 376 encoding.  Unlike the C structures which can have pointers to sub-objects
 377 within, the DER is a serialized encoding, suitable for sending over the
 378 network, writing to a file, and so on.
 379
 380 B<d2i_I<TYPE>>() attempts to decode I<len> bytes at I<*ppin>. If successful a
 381 pointer to the B<I<TYPE>> structure is returned and I<*ppin> is incremented to
 382 the byte following the parsed data.  If I<a> is not NULL then a pointer
 383 to the returned structure is also written to I<*a>.  If an error occurred
 384 then NULL is returned.
 385
 386 On a successful return, if I<*a> is not NULL then it is assumed that I<*a>
 387 contains a valid B<I<TYPE>> structure and an attempt is made to reuse it. This
 388 "reuse" capability is present for historical compatibility but its use is
 389 B<strongly discouraged> (see BUGS below, and the discussion in the RETURN
 390 VALUES section).
 391
 392 B<d2i_I<TYPE>_bio>() is similar to B<d2i_I<TYPE>>() except it attempts
 393 to parse data from BIO I<bp>.
 394
 395 B<d2i_I<TYPE>_fp>() is similar to B<d2i_I<TYPE>>() except it attempts
 396 to parse data from FILE pointer I<fp>.
 397
 398 B<i2d_I<TYPE>>() encodes the structure pointed to by I<a> into DER format.
 399 If I<ppout> is not NULL, it writes the DER encoded data to the buffer
 400 at I<*ppout>, and increments it to point after the data just written.
 401 If the return value is negative an error occurred, otherwise it
 402 returns the length of the encoded data.
 403
 404 If I<*ppout> is NULL memory will be allocated for a buffer and the encoded
 405 data written to it. In this case I<*ppout> is not incremented and it points
 406 to the start of the data just written.
 407
 408 B<i2d_I<TYPE>_bio>() is similar to B<i2d_I<TYPE>>() except it writes
 409 the encoding of the structure I<a> to BIO I<bp> and it
 410 returns 1 for success and 0 for failure.
 411
 412 B<i2d_I<TYPE>_fp>() is similar to B<i2d_I<TYPE>>() except it writes
 413 the encoding of the structure I<a> to FILE pointer I<fp> and it
 414 returns 1 for success and 0 for failure.
 415
 416 These routines do not encrypt private keys and therefore offer no
 417 security; use L<PEM_write_PrivateKey(3)> or similar for writing to files.
 418
 419 =head1 NOTES
 420
 421 The letters B<i> and B<d> in B<i2d_I<TYPE>>() stand for
 422 "internal" (that is, an internal C structure) and "DER" respectively.
 423 So B<i2d_I<TYPE>>() converts from internal to DER.
 424
 425 The functions can also understand B<BER> forms.
 426
 427 The actual TYPE structure passed to B<i2d_I<TYPE>>() must be a valid
 428 populated B<I<TYPE>> structure -- it B<cannot> simply be fed with an
 429 empty structure such as that returned by TYPE_new().
 430
 431 The encoded data is in binary form and may contain embedded zeros.
 432 Therefore, any FILE pointers or BIOs should be opened in binary mode.
 433 Functions such as strlen() will B<not> return the correct length
 434 of the encoded structure.
 435
 436 The ways that I<*ppin> and I<*ppout> are incremented after the operation
 437 can trap the unwary. See the B<WARNINGS> section for some common
 438 errors.
 439 The reason for this-auto increment behaviour is to reflect a typical
 440 usage of ASN1 functions: after one structure is encoded or decoded
 441 another will be processed after it.
 442
 443 The following points about the data types might be useful:
 444
 445 =over 4
 446
 447 =item B<ASN1_OBJECT>
 448
 449 Represents an ASN1 OBJECT IDENTIFIER.
 450
 451 =item B<DHparams>
 452
 453 Represents a PKCS#3 DH parameters structure.
 454
 455 =item B<DHxparams>
 456
 457 Represents an ANSI X9.42 DH parameters structure.
 458
 459 =item B<ECDSA_SIG>
 460
 461 Represents an ECDSA signature.
 462
 463 =item B<X509_ALGOR>
 464
 465 Represents an B<AlgorithmIdentifier> structure as used in IETF RFC 6960 and
 466 elsewhere.
 467
 468 =item B<X509_Name>
 469
 470 Represents a B<Name> type as used for subject and issuer names in
 471 IETF RFC 6960 and elsewhere.
 472
 473 =item B<X509_REQ>
 474
 475 Represents a PKCS#10 certificate request.
 476
 477 =item B<X509_SIG>
 478
 479 Represents the B<DigestInfo> structure defined in PKCS#1 and PKCS#7.
 480
 481 =back
 482
 483 =head1 RETURN VALUES
 484
 485 B<d2i_I<TYPE>>(), B<d2i_I<TYPE>_bio>() and B<d2i_I<TYPE>_fp>() return a valid
 486 B<I<TYPE>> structure or NULL if an error occurs.  If the "reuse" capability has
 487 been used with a valid structure being passed in via I<a>, then the object is
 488 freed in the event of error and I<*a> is set to NULL.
 489
 490 B<i2d_I<TYPE>>() returns the number of bytes successfully encoded or a negative
 491 value if an error occurs.
 492
 493 B<i2d_I<TYPE>_bio>() and B<i2d_I<TYPE>_fp>() return 1 for success and 0 if an
 494 error occurs.
 495
 496 =head1 EXAMPLES
 497
 498 Allocate and encode the DER encoding of an X509 structure:
 499
 500  int len;
 501  unsigned char *buf;
 502
 503  buf = NULL;
 504  len = i2d_X509(x, &buf);
 505  if (len < 0)
 506      /* error */
 507
 508 Attempt to decode a buffer:
 509
 510  X509 *x;
 511  unsigned char *buf;
 512  const unsigned char *p;
 513  int len;
 514
 515  /* Set up buf and len to point to the input buffer. */
 516  p = buf;
 517  x = d2i_X509(NULL, &p, len);
 518  if (x == NULL)
 519      /* error */
 520
 521 Alternative technique:
 522
 523  X509 *x;
 524  unsigned char *buf;
 525  const unsigned char *p;
 526  int len;
 527
 528  /* Set up buf and len to point to the input buffer. */
 529  p = buf;
 530  x = NULL;
 531
 532  if (d2i_X509(&x, &p, len) == NULL)
 533      /* error */
 534
 535 =head1 WARNINGS
 536
 537 Using a temporary variable is mandatory. A common
 538 mistake is to attempt to use a buffer directly as follows:
 539
 540  int len;
 541  unsigned char *buf;
 542
 543  len = i2d_X509(x, NULL);
 544  buf = OPENSSL_malloc(len);
 545  ...
 546  i2d_X509(x, &buf);
 547  ...
 548  OPENSSL_free(buf);
 549
 550 This code will result in I<buf> apparently containing garbage because
 551 it was incremented after the call to point after the data just written.
 552 Also I<buf> will no longer contain the pointer allocated by OPENSSL_malloc()
 553 and the subsequent call to OPENSSL_free() is likely to crash.
 554
 555 Another trap to avoid is misuse of the I<a> argument to B<d2i_I<TYPE>>():
 556
 557  X509 *x;
 558
 559  if (d2i_X509(&x, &p, len) == NULL)
 560      /* error */
 561
 562 This will probably crash somewhere in d2i_X509(). The reason for this
 563 is that the variable I<x> is uninitialized and an attempt will be made to
 564 interpret its (invalid) value as an B<X509> structure, typically causing
 565 a segmentation violation. If I<x> is set to NULL first then this will not
 566 happen.
 567
 568 =head1 BUGS
 569
 570 In some versions of OpenSSL the "reuse" behaviour of B<d2i_I<TYPE>>() when
 571 I<*a> is valid is broken and some parts of the reused structure may
 572 persist if they are not present in the new one. Additionally, in versions of
 573 OpenSSL prior to 1.1.0, when the "reuse" behaviour is used and an error occurs
 574 the behaviour is inconsistent. Some functions behaved as described here, while
 575 some did not free I<*a> on error and did not set I<*a> to NULL.
 576
 577 As a result of the above issues the "reuse" behaviour is strongly discouraged.
 578
 579 B<i2d_I<TYPE>>() will not return an error in many versions of OpenSSL,
 580 if mandatory fields are not initialized due to a programming error
 581 then the encoded structure may contain invalid data or omit the
 582 fields entirely and will not be parsed by B<d2i_I<TYPE>>(). This may be
 583 fixed in future so code should not assume that B<i2d_I<TYPE>>() will
 584 always succeed.
 585
 586 Any function which encodes a structure (B<i2d_I<TYPE>>(),
 587 B<i2d_I<TYPE>>() or B<i2d_I<TYPE>>()) may return a stale encoding if the
 588 structure has been modified after deserialization or previous
 589 serialization. This is because some objects cache the encoding for
 590 efficiency reasons.
 591
 592 =head1 COPYRIGHT
 593
 594 Copyright 1998-2021 The OpenSSL Project Authors. All Rights Reserved.
 595
 596 Licensed under the Apache License 2.0 (the "License").  You may not use
 597 this file except in compliance with the License.  You can obtain a copy
 598 in the file LICENSE in the source distribution or at
 599 L<https://www.openssl.org/source/license.html>.
 600
 601 =cut