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_ISSUER_SERIAL,
  68 d2i_ESS_SIGNING_CERT,
  69 d2i_EXTENDED_KEY_USAGE,
  70 d2i_GENERAL_NAME,
  71 d2i_GENERAL_NAMES,
  72 d2i_IPAddressChoice,
  73 d2i_IPAddressFamily,
  74 d2i_IPAddressOrRange,
  75 d2i_IPAddressRange,
  76 d2i_ISSUING_DIST_POINT,
  77 d2i_NAMING_AUTHORITY,
  78 d2i_NETSCAPE_CERT_SEQUENCE,
  79 d2i_NETSCAPE_SPKAC,
  80 d2i_NETSCAPE_SPKI,
  81 d2i_NOTICEREF,
  82 d2i_OCSP_BASICRESP,
  83 d2i_OCSP_CERTID,
  84 d2i_OCSP_CERTSTATUS,
  85 d2i_OCSP_CRLID,
  86 d2i_OCSP_ONEREQ,
  87 d2i_OCSP_REQINFO,
  88 d2i_OCSP_REQUEST,
  89 d2i_OCSP_RESPBYTES,
  90 d2i_OCSP_RESPDATA,
  91 d2i_OCSP_RESPID,
  92 d2i_OCSP_RESPONSE,
  93 d2i_OCSP_REVOKEDINFO,
  94 d2i_OCSP_SERVICELOC,
  95 d2i_OCSP_SIGNATURE,
  96 d2i_OCSP_SINGLERESP,
  97 d2i_OTHERNAME,
  98 d2i_PBE2PARAM,
  99 d2i_PBEPARAM,
 100 d2i_PBKDF2PARAM,
 101 d2i_PKCS12,
 102 d2i_PKCS12_BAGS,
 103 d2i_PKCS12_MAC_DATA,
 104 d2i_PKCS12_SAFEBAG,
 105 d2i_PKCS12_bio,
 106 d2i_PKCS12_fp,
 107 d2i_PKCS7,
 108 d2i_PKCS7_DIGEST,
 109 d2i_PKCS7_ENCRYPT,
 110 d2i_PKCS7_ENC_CONTENT,
 111 d2i_PKCS7_ENVELOPE,
 112 d2i_PKCS7_ISSUER_AND_SERIAL,
 113 d2i_PKCS7_RECIP_INFO,
 114 d2i_PKCS7_SIGNED,
 115 d2i_PKCS7_SIGNER_INFO,
 116 d2i_PKCS7_SIGN_ENVELOPE,
 117 d2i_PKCS7_bio,
 118 d2i_PKCS7_fp,
 119 d2i_PKCS8_PRIV_KEY_INFO,
 120 d2i_PKCS8_PRIV_KEY_INFO_bio,
 121 d2i_PKCS8_PRIV_KEY_INFO_fp,
 122 d2i_PKCS8_bio,
 123 d2i_PKCS8_fp,
 124 d2i_PKEY_USAGE_PERIOD,
 125 d2i_POLICYINFO,
 126 d2i_POLICYQUALINFO,
 127 d2i_PROFESSION_INFO,
 128 d2i_PROXY_CERT_INFO_EXTENSION,
 129 d2i_PROXY_POLICY,
 130 d2i_RSAPrivateKey,
 131 d2i_RSAPrivateKey_bio,
 132 d2i_RSAPrivateKey_fp,
 133 d2i_RSAPublicKey,
 134 d2i_RSAPublicKey_bio,
 135 d2i_RSAPublicKey_fp,
 136 d2i_RSA_OAEP_PARAMS,
 137 d2i_RSA_PSS_PARAMS,
 138 d2i_RSA_PUBKEY,
 139 d2i_RSA_PUBKEY_bio,
 140 d2i_RSA_PUBKEY_fp,
 141 d2i_SCRYPT_PARAMS,
 142 d2i_SCT_LIST,
 143 d2i_SXNET,
 144 d2i_SXNETID,
 145 d2i_TS_ACCURACY,
 146 d2i_TS_MSG_IMPRINT,
 147 d2i_TS_MSG_IMPRINT_bio,
 148 d2i_TS_MSG_IMPRINT_fp,
 149 d2i_TS_REQ,
 150 d2i_TS_REQ_bio,
 151 d2i_TS_REQ_fp,
 152 d2i_TS_RESP,
 153 d2i_TS_RESP_bio,
 154 d2i_TS_RESP_fp,
 155 d2i_TS_STATUS_INFO,
 156 d2i_TS_TST_INFO,
 157 d2i_TS_TST_INFO_bio,
 158 d2i_TS_TST_INFO_fp,
 159 d2i_USERNOTICE,
 160 d2i_X509,
 161 d2i_X509_ALGOR,
 162 d2i_X509_ALGORS,
 163 d2i_X509_ATTRIBUTE,
 164 d2i_X509_CERT_AUX,
 165 d2i_X509_CINF,
 166 d2i_X509_CRL,
 167 d2i_X509_CRL_INFO,
 168 d2i_X509_CRL_bio,
 169 d2i_X509_CRL_fp,
 170 d2i_X509_EXTENSION,
 171 d2i_X509_EXTENSIONS,
 172 d2i_X509_NAME,
 173 d2i_X509_NAME_ENTRY,
 174 d2i_X509_PUBKEY,
 175 d2i_X509_REQ,
 176 d2i_X509_REQ_INFO,
 177 d2i_X509_REQ_bio,
 178 d2i_X509_REQ_fp,
 179 d2i_X509_REVOKED,
 180 d2i_X509_SIG,
 181 d2i_X509_VAL,
 182 i2d_ACCESS_DESCRIPTION,
 183 i2d_ADMISSIONS,
 184 i2d_ADMISSION_SYNTAX,
 185 i2d_ASIdOrRange,
 186 i2d_ASIdentifierChoice,
 187 i2d_ASIdentifiers,
 188 i2d_ASN1_BIT_STRING,
 189 i2d_ASN1_BMPSTRING,
 190 i2d_ASN1_ENUMERATED,
 191 i2d_ASN1_GENERALIZEDTIME,
 192 i2d_ASN1_GENERALSTRING,
 193 i2d_ASN1_IA5STRING,
 194 i2d_ASN1_INTEGER,
 195 i2d_ASN1_NULL,
 196 i2d_ASN1_OBJECT,
 197 i2d_ASN1_OCTET_STRING,
 198 i2d_ASN1_PRINTABLE,
 199 i2d_ASN1_PRINTABLESTRING,
 200 i2d_ASN1_SEQUENCE_ANY,
 201 i2d_ASN1_SET_ANY,
 202 i2d_ASN1_T61STRING,
 203 i2d_ASN1_TIME,
 204 i2d_ASN1_TYPE,
 205 i2d_ASN1_UNIVERSALSTRING,
 206 i2d_ASN1_UTCTIME,
 207 i2d_ASN1_UTF8STRING,
 208 i2d_ASN1_VISIBLESTRING,
 209 i2d_ASN1_bio_stream,
 210 i2d_ASRange,
 211 i2d_AUTHORITY_INFO_ACCESS,
 212 i2d_AUTHORITY_KEYID,
 213 i2d_BASIC_CONSTRAINTS,
 214 i2d_CERTIFICATEPOLICIES,
 215 i2d_CMS_ContentInfo,
 216 i2d_CMS_ReceiptRequest,
 217 i2d_CMS_bio,
 218 i2d_CRL_DIST_POINTS,
 219 i2d_DHxparams,
 220 i2d_DIRECTORYSTRING,
 221 i2d_DISPLAYTEXT,
 222 i2d_DIST_POINT,
 223 i2d_DIST_POINT_NAME,
 224 i2d_DSAPrivateKey,
 225 i2d_DSAPrivateKey_bio,
 226 i2d_DSAPrivateKey_fp,
 227 i2d_DSAPublicKey,
 228 i2d_DSA_PUBKEY,
 229 i2d_DSA_PUBKEY_bio,
 230 i2d_DSA_PUBKEY_fp,
 231 i2d_DSA_SIG,
 232 i2d_DSAparams,
 233 i2d_ECDSA_SIG,
 234 i2d_ECPKParameters,
 235 i2d_ECParameters,
 236 i2d_ECPrivateKey,
 237 i2d_ECPrivateKey_bio,
 238 i2d_ECPrivateKey_fp,
 239 i2d_EC_PUBKEY,
 240 i2d_EC_PUBKEY_bio,
 241 i2d_EC_PUBKEY_fp,
 242 i2d_EDIPARTYNAME,
 243 i2d_ESS_CERT_ID,
 244 i2d_ESS_ISSUER_SERIAL,
 245 i2d_ESS_SIGNING_CERT,
 246 i2d_EXTENDED_KEY_USAGE,
 247 i2d_GENERAL_NAME,
 248 i2d_GENERAL_NAMES,
 249 i2d_IPAddressChoice,
 250 i2d_IPAddressFamily,
 251 i2d_IPAddressOrRange,
 252 i2d_IPAddressRange,
 253 i2d_ISSUING_DIST_POINT,
 254 i2d_NAMING_AUTHORITY,
 255 i2d_NETSCAPE_CERT_SEQUENCE,
 256 i2d_NETSCAPE_SPKAC,
 257 i2d_NETSCAPE_SPKI,
 258 i2d_NOTICEREF,
 259 i2d_OCSP_BASICRESP,
 260 i2d_OCSP_CERTID,
 261 i2d_OCSP_CERTSTATUS,
 262 i2d_OCSP_CRLID,
 263 i2d_OCSP_ONEREQ,
 264 i2d_OCSP_REQINFO,
 265 i2d_OCSP_REQUEST,
 266 i2d_OCSP_RESPBYTES,
 267 i2d_OCSP_RESPDATA,
 268 i2d_OCSP_RESPID,
 269 i2d_OCSP_RESPONSE,
 270 i2d_OCSP_REVOKEDINFO,
 271 i2d_OCSP_SERVICELOC,
 272 i2d_OCSP_SIGNATURE,
 273 i2d_OCSP_SINGLERESP,
 274 i2d_OTHERNAME,
 275 i2d_PBE2PARAM,
 276 i2d_PBEPARAM,
 277 i2d_PBKDF2PARAM,
 278 i2d_PKCS12,
 279 i2d_PKCS12_BAGS,
 280 i2d_PKCS12_MAC_DATA,
 281 i2d_PKCS12_SAFEBAG,
 282 i2d_PKCS12_bio,
 283 i2d_PKCS12_fp,
 284 i2d_PKCS7,
 285 i2d_PKCS7_DIGEST,
 286 i2d_PKCS7_ENCRYPT,
 287 i2d_PKCS7_ENC_CONTENT,
 288 i2d_PKCS7_ENVELOPE,
 289 i2d_PKCS7_ISSUER_AND_SERIAL,
 290 i2d_PKCS7_NDEF,
 291 i2d_PKCS7_RECIP_INFO,
 292 i2d_PKCS7_SIGNED,
 293 i2d_PKCS7_SIGNER_INFO,
 294 i2d_PKCS7_SIGN_ENVELOPE,
 295 i2d_PKCS7_bio,
 296 i2d_PKCS7_fp,
 297 i2d_PKCS8PrivateKeyInfo_bio,
 298 i2d_PKCS8PrivateKeyInfo_fp,
 299 i2d_PKCS8_PRIV_KEY_INFO,
 300 i2d_PKCS8_PRIV_KEY_INFO_bio,
 301 i2d_PKCS8_PRIV_KEY_INFO_fp,
 302 i2d_PKCS8_bio,
 303 i2d_PKCS8_fp,
 304 i2d_PKEY_USAGE_PERIOD,
 305 i2d_POLICYINFO,
 306 i2d_POLICYQUALINFO,
 307 i2d_PROFESSION_INFO,
 308 i2d_PROXY_CERT_INFO_EXTENSION,
 309 i2d_PROXY_POLICY,
 310 i2d_RSAPrivateKey,
 311 i2d_RSAPrivateKey_bio,
 312 i2d_RSAPrivateKey_fp,
 313 i2d_RSAPublicKey,
 314 i2d_RSAPublicKey_bio,
 315 i2d_RSAPublicKey_fp,
 316 i2d_RSA_OAEP_PARAMS,
 317 i2d_RSA_PSS_PARAMS,
 318 i2d_RSA_PUBKEY,
 319 i2d_RSA_PUBKEY_bio,
 320 i2d_RSA_PUBKEY_fp,
 321 i2d_SCRYPT_PARAMS,
 322 i2d_SCT_LIST,
 323 i2d_SXNET,
 324 i2d_SXNETID,
 325 i2d_TS_ACCURACY,
 326 i2d_TS_MSG_IMPRINT,
 327 i2d_TS_MSG_IMPRINT_bio,
 328 i2d_TS_MSG_IMPRINT_fp,
 329 i2d_TS_REQ,
 330 i2d_TS_REQ_bio,
 331 i2d_TS_REQ_fp,
 332 i2d_TS_RESP,
 333 i2d_TS_RESP_bio,
 334 i2d_TS_RESP_fp,
 335 i2d_TS_STATUS_INFO,
 336 i2d_TS_TST_INFO,
 337 i2d_TS_TST_INFO_bio,
 338 i2d_TS_TST_INFO_fp,
 339 i2d_USERNOTICE,
 340 i2d_X509,
 341 i2d_X509_ALGOR,
 342 i2d_X509_ALGORS,
 343 i2d_X509_ATTRIBUTE,
 344 i2d_X509_CERT_AUX,
 345 i2d_X509_CINF,
 346 i2d_X509_CRL,
 347 i2d_X509_CRL_INFO,
 348 i2d_X509_CRL_bio,
 349 i2d_X509_CRL_fp,
 350 i2d_X509_EXTENSION,
 351 i2d_X509_EXTENSIONS,
 352 i2d_X509_NAME,
 353 i2d_X509_NAME_ENTRY,
 354 i2d_X509_PUBKEY,
 355 i2d_X509_REQ,
 356 i2d_X509_REQ_INFO,
 357 i2d_X509_REQ_bio,
 358 i2d_X509_REQ_fp,
 359 i2d_X509_REVOKED,
 360 i2d_X509_SIG,
 361 i2d_X509_VAL,
 362 - convert objects from/to ASN.1/DER representation
 363
 364 =head1 SYNOPSIS
 365
 366 =for comment generic
 367
 368  TYPE *d2i_TYPE(TYPE **a, unsigned char **ppin, long length);
 369  TYPE *d2i_TYPE_bio(BIO *bp, TYPE **a);
 370  TYPE *d2i_TYPE_fp(FILE *fp, TYPE **a);
 371
 372  int i2d_TYPE(TYPE *a, unsigned char **ppout);
 373  int i2d_TYPE_fp(FILE *fp, TYPE *a);
 374  int i2d_TYPE_bio(BIO *bp, TYPE *a);
 375
 376 =head1 DESCRIPTION
 377
 378 In the description here, I<TYPE> is used a placeholder
 379 for any of the OpenSSL datatypes, such as I<X509_CRL>.
 380 The function parameters I<ppin> and I<ppout> are generally
 381 either both named I<pp> in the headers, or I<in> and I<out>.
 382
 383 These functions convert OpenSSL objects to and from their ASN.1/DER
 384 encoding.  Unlike the C structures which can have pointers to sub-objects
 385 within, the DER is a serialized encoding, suitable for sending over the
 386 network, writing to a file, and so on.
 387
 388 d2i_TYPE() attempts to decode B<len> bytes at B<*ppin>. If successful a
 389 pointer to the B<TYPE> structure is returned and B<*ppin> is incremented to
 390 the byte following the parsed data.  If B<a> is not B<NULL> then a pointer
 391 to the returned structure is also written to B<*a>.  If an error occurred
 392 then B<NULL> is returned.
 393
 394 On a successful return, if B<*a> is not B<NULL> then it is assumed that B<*a>
 395 contains a valid B<TYPE> structure and an attempt is made to reuse it. This
 396 "reuse" capability is present for historical compatibility but its use is
 397 B<strongly discouraged> (see BUGS below, and the discussion in the RETURN
 398 VALUES section).
 399
 400 d2i_TYPE_bio() is similar to d2i_TYPE() except it attempts
 401 to parse data from BIO B<bp>.
 402
 403 d2i_TYPE_fp() is similar to d2i_TYPE() except it attempts
 404 to parse data from FILE pointer B<fp>.
 405
 406 i2d_TYPE() encodes the structure pointed to by B<a> into DER format.
 407 If B<ppout> is not B<NULL>, it writes the DER encoded data to the buffer
 408 at B<*ppout>, and increments it to point after the data just written.
 409 If the return value is negative an error occurred, otherwise it
 410 returns the length of the encoded data.
 411
 412 If B<*ppout> is B<NULL> memory will be allocated for a buffer and the encoded
 413 data written to it. In this case B<*ppout> is not incremented and it points
 414 to the start of the data just written.
 415
 416 i2d_TYPE_bio() is similar to i2d_TYPE() except it writes
 417 the encoding of the structure B<a> to BIO B<bp> and it
 418 returns 1 for success and 0 for failure.
 419
 420 i2d_TYPE_fp() is similar to i2d_TYPE() except it writes
 421 the encoding of the structure B<a> to BIO B<bp> and it
 422 returns 1 for success and 0 for failure.
 423
 424 These routines do not encrypt private keys and therefore offer no
 425 security; use L<PEM_write_PrivateKey(3)> or similar for writing to files.
 426
 427 =head1 NOTES
 428
 429 The letters B<i> and B<d> in B<i2d_TYPE> stand for
 430 "internal" (that is, an internal C structure) and "DER" respectively.
 431 So B<i2d_TYPE> converts from internal to DER.
 432
 433 The functions can also understand B<BER> forms.
 434
 435 The actual TYPE structure passed to i2d_TYPE() must be a valid
 436 populated B<TYPE> structure -- it B<cannot> simply be fed with an
 437 empty structure such as that returned by TYPE_new().
 438
 439 The encoded data is in binary form and may contain embedded zeroes.
 440 Therefore any FILE pointers or BIOs should be opened in binary mode.
 441 Functions such as strlen() will B<not> return the correct length
 442 of the encoded structure.
 443
 444 The ways that B<*ppin> and B<*ppout> are incremented after the operation
 445 can trap the unwary. See the B<WARNINGS> section for some common
 446 errors.
 447 The reason for this-auto increment behaviour is to reflect a typical
 448 usage of ASN1 functions: after one structure is encoded or decoded
 449 another will be processed after it.
 450
 451 The following points about the data types might be useful:
 452
 453 =over 4
 454
 455 =item B<ASN1_OBJECT>
 456
 457 Represents an ASN1 OBJECT IDENTIFIER.
 458
 459 =item B<DHparams>
 460
 461 Represents a PKCS#3 DH parameters structure.
 462
 463 =item B<DHxparams>
 464
 465 Represents an ANSI X9.42 DH parameters structure.
 466
 467 =item B<DSA_PUBKEY>
 468
 469 Represents a DSA public key using a B<SubjectPublicKeyInfo> structure.
 470
 471 =item B<DSAPublicKey, DSAPrivateKey>
 472
 473 Use a non-standard OpenSSL format and should be avoided; use B<DSA_PUBKEY>,
 474 B<PEM_write_PrivateKey(3)>, or similar instead.
 475
 476 =item B<ECDSA_SIG>
 477
 478 Represents an ECDSA signature.
 479
 480 =item B<RSAPublicKey>
 481
 482 Represents a PKCS#1 RSA public key structure.
 483
 484 =item B<X509_ALGOR>
 485
 486 Represents an B<AlgorithmIdentifier> structure as used in IETF RFC 6960 and
 487 elsewhere.
 488
 489 =item B<X509_Name>
 490
 491 Represents a B<Name> type as used for subject and issuer names in
 492 IETF RFC 6960 and elsewhere.
 493
 494 =item B<X509_REQ>
 495
 496 Represents a PKCS#10 certificate request.
 497
 498 =item B<X509_SIG>
 499
 500 Represents the B<DigestInfo> structure defined in PKCS#1 and PKCS#7.
 501
 502 =back
 503
 504 =head1 RETURN VALUES
 505
 506 d2i_TYPE(), d2i_TYPE_bio() and d2i_TYPE_fp() return a valid B<TYPE> structure
 507 or B<NULL> if an error occurs.  If the "reuse" capability has been used with
 508 a valid structure being passed in via B<a>, then the object is freed in
 509 the event of error and B<*a> is set to NULL.
 510
 511 i2d_TYPE() returns the number of bytes successfully encoded or a negative
 512 value if an error occurs.
 513
 514 i2d_TYPE_bio() and i2d_TYPE_fp() return 1 for success and 0 if an error
 515 occurs.
 516
 517 =head1 EXAMPLES
 518
 519 Allocate and encode the DER encoding of an X509 structure:
 520
 521  int len;
 522  unsigned char *buf;
 523
 524  buf = NULL;
 525  len = i2d_X509(x, &buf);
 526  if (len < 0)
 527      /* error */
 528
 529 Attempt to decode a buffer:
 530
 531  X509 *x;
 532  unsigned char *buf, *p;
 533  int len;
 534
 535  /* Set up buf and len to point to the input buffer. */
 536  p = buf;
 537  x = d2i_X509(NULL, &p, len);
 538  if (x == NULL)
 539      /* error */
 540
 541 Alternative technique:
 542
 543  X509 *x;
 544  unsigned char *buf, *p;
 545  int len;
 546
 547  /* Set up buf and len to point to the input buffer. */
 548  p = buf;
 549  x = NULL;
 550
 551  if (d2i_X509(&x, &p, len) == NULL)
 552      /* error */
 553
 554 =head1 WARNINGS
 555
 556 Using a temporary variable is mandatory. A common
 557 mistake is to attempt to use a buffer directly as follows:
 558
 559  int len;
 560  unsigned char *buf;
 561
 562  len = i2d_X509(x, NULL);
 563  buf = OPENSSL_malloc(len);
 564  ...
 565  i2d_X509(x, &buf);
 566  ...
 567  OPENSSL_free(buf);
 568
 569 This code will result in B<buf> apparently containing garbage because
 570 it was incremented after the call to point after the data just written.
 571 Also B<buf> will no longer contain the pointer allocated by OPENSSL_malloc()
 572 and the subsequent call to OPENSSL_free() is likely to crash.
 573
 574 Another trap to avoid is misuse of the B<a> argument to d2i_TYPE():
 575
 576  X509 *x;
 577
 578  if (d2i_X509(&x, &p, len) == NULL)
 579      /* error */
 580
 581 This will probably crash somewhere in d2i_X509(). The reason for this
 582 is that the variable B<x> is uninitialized and an attempt will be made to
 583 interpret its (invalid) value as an B<X509> structure, typically causing
 584 a segmentation violation. If B<x> is set to NULL first then this will not
 585 happen.
 586
 587 =head1 BUGS
 588
 589 In some versions of OpenSSL the "reuse" behaviour of d2i_TYPE() when
 590 B<*a> is valid is broken and some parts of the reused structure may
 591 persist if they are not present in the new one. Additionally, in versions of
 592 OpenSSL prior to 1.1.0, when the "reuse" behaviour is used and an error occurs
 593 the behaviour is inconsistent. Some functions behaved as described here, while
 594 some did not free B<*a> on error and did not set B<*a> to NULL.
 595
 596 As a result of the above issues the "reuse" behaviour is strongly discouraged.
 597
 598 i2d_TYPE() will not return an error in many versions of OpenSSL,
 599 if mandatory fields are not initialized due to a programming error
 600 then the encoded structure may contain invalid data or omit the
 601 fields entirely and will not be parsed by d2i_TYPE(). This may be
 602 fixed in future so code should not assume that i2d_TYPE() will
 603 always succeed.
 604
 605 Any function which encodes a structure (i2d_TYPE(),
 606 i2d_TYPE() or i2d_TYPE()) may return a stale encoding if the
 607 structure has been modified after deserialization or previous
 608 serialization. This is because some objects cache the encoding for
 609 efficiency reasons.
 610
 611 =head1 COPYRIGHT
 612
 613 Copyright 1998-2019 The OpenSSL Project Authors. All Rights Reserved.
 614
 615 Licensed under the OpenSSL license (the "License").  You may not use
 616 this file except in compliance with the License.  You can obtain a copy
 617 in the file LICENSE in the source distribution or at
 618 L<https://www.openssl.org/source/license.html>.
 619
 620 =cut