d2i_ACCESS_DESCRIPTION, d2i_ADMISSIONS, d2i_ADMISSION_SYNTAX, d2i_ASIdOrRange,
  d2i_ASIdentifierChoice, d2i_ASIdentifiers, d2i_ASN1_BIT_STRING,
  d2i_ASN1_BMPSTRING, d2i_ASN1_ENUMERATED, d2i_ASN1_GENERALIZEDTIME,
  d2i_ASN1_GENERALSTRING, d2i_ASN1_IA5STRING, d2i_ASN1_INTEGER, d2i_ASN1_NULL,
  d2i_ASN1_OBJECT, d2i_ASN1_OCTET_STRING, d2i_ASN1_PRINTABLE,
  d2i_ASN1_PRINTABLESTRING, d2i_ASN1_SEQUENCE_ANY, d2i_ASN1_SET_ANY,
  d2i_ASN1_T61STRING, d2i_ASN1_TIME, d2i_ASN1_TYPE, d2i_ASN1_UINTEGER,
  d2i_ASN1_UNIVERSALSTRING, d2i_ASN1_UTCTIME, d2i_ASN1_UTF8STRING,
  d2i_ASN1_VISIBLESTRING, d2i_ASRange, d2i_AUTHORITY_INFO_ACCESS,
  d2i_AUTHORITY_KEYID, d2i_BASIC_CONSTRAINTS, d2i_CERTIFICATEPOLICIES,
  d2i_CMS_ContentInfo, d2i_CMS_ReceiptRequest, d2i_CMS_bio, d2i_CRL_DIST_POINTS,
  d2i_DHxparams, d2i_DIRECTORYSTRING, d2i_DISPLAYTEXT, d2i_DIST_POINT,
  d2i_DIST_POINT_NAME, d2i_DSAPrivateKey, d2i_DSAPrivateKey_bio,
  d2i_DSAPrivateKey_fp, d2i_DSAPublicKey, d2i_DSA_PUBKEY, d2i_DSA_PUBKEY_bio,
  d2i_DSA_PUBKEY_fp, d2i_DSA_SIG, d2i_DSAparams, d2i_ECDSA_SIG,
  d2i_ECPKParameters, d2i_ECParameters, d2i_ECPrivateKey, d2i_ECPrivateKey_bio,
  d2i_ECPrivateKey_fp, d2i_EC_PUBKEY, d2i_EC_PUBKEY_bio, d2i_EC_PUBKEY_fp,
  d2i_EDIPARTYNAME, d2i_ESS_CERT_ID, d2i_ESS_ISSUER_SERIAL,
  d2i_ESS_SIGNING_CERT, d2i_EXTENDED_KEY_USAGE, d2i_GENERAL_NAME,
  d2i_GENERAL_NAMES, d2i_IPAddressChoice, d2i_IPAddressFamily,
  d2i_IPAddressOrRange, d2i_IPAddressRange, d2i_ISSUING_DIST_POINT,
  d2i_NAMING_AUTHORITY, d2i_NETSCAPE_CERT_SEQUENCE, d2i_NETSCAPE_SPKAC,
  d2i_NETSCAPE_SPKI, d2i_NOTICEREF, d2i_OCSP_BASICRESP, d2i_OCSP_CERTID,
  d2i_OCSP_CERTSTATUS, d2i_OCSP_CRLID, d2i_OCSP_ONEREQ, d2i_OCSP_REQINFO,
  d2i_OCSP_REQUEST, d2i_OCSP_RESPBYTES, d2i_OCSP_RESPDATA, d2i_OCSP_RESPID,
  d2i_OCSP_RESPONSE, d2i_OCSP_REVOKEDINFO, d2i_OCSP_SERVICELOC,
  d2i_OCSP_SIGNATURE, d2i_OCSP_SINGLERESP, d2i_OTHERNAME, d2i_PBE2PARAM,
  d2i_PBEPARAM, d2i_PBKDF2PARAM, d2i_PKCS12, d2i_PKCS12_BAGS,
  d2i_PKCS12_MAC_DATA, d2i_PKCS12_SAFEBAG, d2i_PKCS12_bio, d2i_PKCS12_fp,
  d2i_PKCS7, d2i_PKCS7_DIGEST, d2i_PKCS7_ENCRYPT, d2i_PKCS7_ENC_CONTENT,
  d2i_PKCS7_ENVELOPE, d2i_PKCS7_ISSUER_AND_SERIAL, d2i_PKCS7_RECIP_INFO,
  d2i_PKCS7_SIGNED, d2i_PKCS7_SIGNER_INFO, d2i_PKCS7_SIGN_ENVELOPE,
  d2i_PKCS7_bio, d2i_PKCS7_fp, d2i_PKCS8_PRIV_KEY_INFO,
  d2i_PKCS8_PRIV_KEY_INFO_bio, d2i_PKCS8_PRIV_KEY_INFO_fp, d2i_PKCS8_bio,
  d2i_PKCS8_fp, d2i_PKEY_USAGE_PERIOD, d2i_POLICYINFO, d2i_POLICYQUALINFO,
  d2i_PROFESSION_INFO, d2i_PROXY_CERT_INFO_EXTENSION, d2i_PROXY_POLICY,
  d2i_RSAPrivateKey, d2i_RSAPrivateKey_bio, d2i_RSAPrivateKey_fp,
  d2i_RSAPublicKey, d2i_RSAPublicKey_bio, d2i_RSAPublicKey_fp,
  d2i_RSA_OAEP_PARAMS, d2i_RSA_PSS_PARAMS, d2i_RSA_PUBKEY, d2i_RSA_PUBKEY_bio,
  d2i_RSA_PUBKEY_fp, d2i_SCRYPT_PARAMS, d2i_SCT_LIST, d2i_SXNET, d2i_SXNETID,
  d2i_TS_ACCURACY, d2i_TS_MSG_IMPRINT, d2i_TS_MSG_IMPRINT_bio,
  d2i_TS_MSG_IMPRINT_fp, d2i_TS_REQ, d2i_TS_REQ_bio, d2i_TS_REQ_fp, d2i_TS_RESP,
  d2i_TS_RESP_bio, d2i_TS_RESP_fp, d2i_TS_STATUS_INFO, d2i_TS_TST_INFO,
  d2i_TS_TST_INFO_bio, d2i_TS_TST_INFO_fp, d2i_USERNOTICE, d2i_X509,
  d2i_X509_ALGOR, d2i_X509_ALGORS, d2i_X509_ATTRIBUTE, d2i_X509_CERT_AUX,
  d2i_X509_CINF, d2i_X509_CRL, d2i_X509_CRL_INFO, d2i_X509_CRL_bio,
  d2i_X509_CRL_fp, d2i_X509_EXTENSION, d2i_X509_EXTENSIONS, d2i_X509_NAME,
  d2i_X509_NAME_ENTRY, d2i_X509_PUBKEY, d2i_X509_REQ, d2i_X509_REQ_INFO,
  d2i_X509_REQ_bio, d2i_X509_REQ_fp, d2i_X509_REVOKED, d2i_X509_SIG,
  d2i_X509_VAL, i2d_ACCESS_DESCRIPTION, i2d_ADMISSIONS, i2d_ADMISSION_SYNTAX,
  i2d_ASIdOrRange, i2d_ASIdentifierChoice, i2d_ASIdentifiers,
  i2d_ASN1_BIT_STRING, i2d_ASN1_BMPSTRING, i2d_ASN1_ENUMERATED,
  i2d_ASN1_GENERALIZEDTIME, i2d_ASN1_GENERALSTRING, i2d_ASN1_IA5STRING,
  i2d_ASN1_INTEGER, i2d_ASN1_NULL, i2d_ASN1_OBJECT, i2d_ASN1_OCTET_STRING,
  i2d_ASN1_PRINTABLE, i2d_ASN1_PRINTABLESTRING, i2d_ASN1_SEQUENCE_ANY,
  i2d_ASN1_SET_ANY, i2d_ASN1_T61STRING, i2d_ASN1_TIME, i2d_ASN1_TYPE,
  i2d_ASN1_UNIVERSALSTRING, i2d_ASN1_UTCTIME, i2d_ASN1_UTF8STRING,
  i2d_ASN1_VISIBLESTRING, i2d_ASN1_bio_stream, i2d_ASRange,
  i2d_AUTHORITY_INFO_ACCESS, i2d_AUTHORITY_KEYID, i2d_BASIC_CONSTRAINTS,
  i2d_CERTIFICATEPOLICIES, i2d_CMS_ContentInfo, i2d_CMS_ReceiptRequest,
  i2d_CMS_bio, i2d_CRL_DIST_POINTS, i2d_DHxparams, i2d_DIRECTORYSTRING,
  i2d_DISPLAYTEXT, i2d_DIST_POINT, i2d_DIST_POINT_NAME, i2d_DSAPrivateKey,
  i2d_DSAPrivateKey_bio, i2d_DSAPrivateKey_fp, i2d_DSAPublicKey, i2d_DSA_PUBKEY,
  i2d_DSA_PUBKEY_bio, i2d_DSA_PUBKEY_fp, i2d_DSA_SIG, i2d_DSAparams,
  i2d_ECDSA_SIG, i2d_ECPKParameters, i2d_ECParameters, i2d_ECPrivateKey,
  i2d_ECPrivateKey_bio, i2d_ECPrivateKey_fp, i2d_EC_PUBKEY, i2d_EC_PUBKEY_bio,
  i2d_EC_PUBKEY_fp, i2d_EDIPARTYNAME, i2d_ESS_CERT_ID, i2d_ESS_ISSUER_SERIAL,
  i2d_ESS_SIGNING_CERT, i2d_EXTENDED_KEY_USAGE, i2d_GENERAL_NAME,
  i2d_GENERAL_NAMES, i2d_IPAddressChoice, i2d_IPAddressFamily,
  i2d_IPAddressOrRange, i2d_IPAddressRange, i2d_ISSUING_DIST_POINT,
  i2d_NAMING_AUTHORITY, i2d_NETSCAPE_CERT_SEQUENCE, i2d_NETSCAPE_SPKAC,
  i2d_NETSCAPE_SPKI, i2d_NOTICEREF, i2d_OCSP_BASICRESP, i2d_OCSP_CERTID,
  i2d_OCSP_CERTSTATUS, i2d_OCSP_CRLID, i2d_OCSP_ONEREQ, i2d_OCSP_REQINFO,
  i2d_OCSP_REQUEST, i2d_OCSP_RESPBYTES, i2d_OCSP_RESPDATA, i2d_OCSP_RESPID,
  i2d_OCSP_RESPONSE, i2d_OCSP_REVOKEDINFO, i2d_OCSP_SERVICELOC,
  i2d_OCSP_SIGNATURE, i2d_OCSP_SINGLERESP, i2d_OTHERNAME, i2d_PBE2PARAM,
  i2d_PBEPARAM, i2d_PBKDF2PARAM, i2d_PKCS12, i2d_PKCS12_BAGS,
  i2d_PKCS12_MAC_DATA, i2d_PKCS12_SAFEBAG, i2d_PKCS12_bio, i2d_PKCS12_fp,
  i2d_PKCS7, i2d_PKCS7_DIGEST, i2d_PKCS7_ENCRYPT, i2d_PKCS7_ENC_CONTENT,
  i2d_PKCS7_ENVELOPE, i2d_PKCS7_ISSUER_AND_SERIAL, i2d_PKCS7_NDEF,
  i2d_PKCS7_RECIP_INFO, i2d_PKCS7_SIGNED, i2d_PKCS7_SIGNER_INFO,
  i2d_PKCS7_SIGN_ENVELOPE, i2d_PKCS7_bio, i2d_PKCS7_fp,
  i2d_PKCS8PrivateKeyInfo_bio, i2d_PKCS8PrivateKeyInfo_fp,
  i2d_PKCS8_PRIV_KEY_INFO, i2d_PKCS8_PRIV_KEY_INFO_bio,
  i2d_PKCS8_PRIV_KEY_INFO_fp, i2d_PKCS8_bio, i2d_PKCS8_fp,
  i2d_PKEY_USAGE_PERIOD, i2d_POLICYINFO, i2d_POLICYQUALINFO,
  i2d_PROFESSION_INFO, i2d_PROXY_CERT_INFO_EXTENSION, i2d_PROXY_POLICY,
  i2d_RSAPrivateKey, i2d_RSAPrivateKey_bio, i2d_RSAPrivateKey_fp,
  i2d_RSAPublicKey, i2d_RSAPublicKey_bio, i2d_RSAPublicKey_fp,
  i2d_RSA_OAEP_PARAMS, i2d_RSA_PSS_PARAMS, i2d_RSA_PUBKEY, i2d_RSA_PUBKEY_bio,
  i2d_RSA_PUBKEY_fp, i2d_SCRYPT_PARAMS, i2d_SCT_LIST, i2d_SXNET, i2d_SXNETID,
  i2d_TS_ACCURACY, i2d_TS_MSG_IMPRINT, i2d_TS_MSG_IMPRINT_bio,
  i2d_TS_MSG_IMPRINT_fp, i2d_TS_REQ, i2d_TS_REQ_bio, i2d_TS_REQ_fp, i2d_TS_RESP,
  i2d_TS_RESP_bio, i2d_TS_RESP_fp, i2d_TS_STATUS_INFO, i2d_TS_TST_INFO,
  i2d_TS_TST_INFO_bio, i2d_TS_TST_INFO_fp, i2d_USERNOTICE, i2d_X509,
  i2d_X509_ALGOR, i2d_X509_ALGORS, i2d_X509_ATTRIBUTE, i2d_X509_CERT_AUX,
  i2d_X509_CINF, i2d_X509_CRL, i2d_X509_CRL_INFO, i2d_X509_CRL_bio,
  i2d_X509_CRL_fp, i2d_X509_EXTENSION, i2d_X509_EXTENSIONS, i2d_X509_NAME,
  i2d_X509_NAME_ENTRY, i2d_X509_PUBKEY, i2d_X509_REQ, i2d_X509_REQ_INFO,
  i2d_X509_REQ_bio, i2d_X509_REQ_fp, i2d_X509_REVOKED, i2d_X509_SIG,
  i2d_X509_VAL, - convert objects from/to ASN.1/DER representation
 TYPE *d2i_TYPE(TYPE **a, const unsigned char **ppin, long length);
 TYPE *d2i_TYPE_bio(BIO *bp, TYPE **a);
 TYPE *d2i_TYPE_fp(FILE *fp, TYPE **a);
 int i2d_TYPE(TYPE *a, unsigned char **ppout);
 int i2d_TYPE_fp(FILE *fp, TYPE *a);
 int i2d_TYPE_bio(BIO *bp, TYPE *a);
In the description here, TYPE is used a placeholder for any of the
  OpenSSL datatypes, such as X509_CRL. The function parameters
  ppin and ppout are generally either both named pp in the
  headers, or in and out.
These functions convert OpenSSL objects to and from their
    ASN.1/DER encoding. Unlike the C structures which can have pointers to
    sub-objects within, the DER is a serialized encoding, suitable for sending
    over the network, writing to a file, and so on.
d2i_TYPE() attempts to decode len bytes at
    *ppin. If successful a pointer to the TYPE structure is
    returned and *ppin is incremented to the byte following the parsed
    data. If a is not NULL then a pointer to the returned
    structure is also written to *a. If an error occurred then
    NULL is returned.
On a successful return, if *a is not NULL then it is
    assumed that *a contains a valid TYPE structure and an attempt
    is made to reuse it. This "reuse" capability is present for
    historical compatibility but its use is strongly discouraged (see
    BUGS below, and the discussion in the RETURN VALUES section).
d2i_TYPE_bio() is similar to d2i_TYPE() except it
    attempts to parse data from BIO bp.
d2i_TYPE_fp() is similar to d2i_TYPE() except it
    attempts to parse data from FILE pointer fp.
i2d_TYPE() encodes the structure pointed to by a
    into DER format. If ppout is not NULL, it writes the DER
    encoded data to the buffer at *ppout, and increments it to point
    after the data just written. If the return value is negative an error
    occurred, otherwise it returns the length of the encoded data.
If *ppout is NULL memory will be allocated for a
    buffer and the encoded data written to it. In this case *ppout is not
    incremented and it points to the start of the data just written.
i2d_TYPE_bio() is similar to i2d_TYPE() except it
    writes the encoding of the structure a to BIO bp and it
    returns 1 for success and 0 for failure.
i2d_TYPE_fp() is similar to i2d_TYPE() except it
    writes the encoding of the structure a to BIO bp and it
    returns 1 for success and 0 for failure.
These routines do not encrypt private keys and therefore offer no
    security; use PEM_write_PrivateKey(3) or similar for writing to
    files.
The letters i and d in i2d_TYPE stand for
  "internal" (that is, an internal C structure) and "DER"
  respectively. So i2d_TYPE converts from internal to DER.
The functions can also understand BER forms.
The actual TYPE structure passed to i2d_TYPE() must be a
    valid populated TYPE structure -- it cannot simply be fed with
    an empty structure such as that returned by TYPE_new().
The encoded data is in binary form and may contain embedded zeros.
    Therefore, any FILE pointers or BIOs should be opened in binary mode.
    Functions such as strlen() will not return the correct length
    of the encoded structure.
The ways that *ppin and *ppout are incremented after
    the operation can trap the unwary. See the WARNINGS section for some
    common errors. The reason for this-auto increment behaviour is to reflect a
    typical usage of ASN1 functions: after one structure is encoded or decoded
    another will be processed after it.
The following points about the data types might be useful:
  - ASN1_OBJECT
- Represents an ASN1 OBJECT IDENTIFIER.
- DHparams
- Represents a PKCS#3 DH parameters structure.
- DHxparams
- Represents an ANSI X9.42 DH parameters structure.
- DSA_PUBKEY
- Represents a DSA public key using a SubjectPublicKeyInfo
    structure.
- DSAPublicKey, DSAPrivateKey
- Use a non-standard OpenSSL format and should be avoided; use
      DSA_PUBKEY, PEM_write_PrivateKey(3), or
      similar instead.
- ECDSA_SIG
- Represents an ECDSA signature.
- RSAPublicKey
- Represents a PKCS#1 RSA public key structure.
- X509_ALGOR
- Represents an AlgorithmIdentifier structure as used in IETF RFC
      6960 and elsewhere.
- X509_Name
- Represents a Name type as used for subject and issuer names in IETF
      RFC 6960 and elsewhere.
- X509_REQ
- Represents a PKCS#10 certificate request.
- X509_SIG
- Represents the DigestInfo structure defined in PKCS#1 and
    PKCS#7.
d2i_TYPE(), d2i_TYPE_bio() and d2i_TYPE_fp() return a valid
  TYPE structure or NULL if an error occurs. If the
  "reuse" capability has been used with a valid structure being passed
  in via a, then the object is freed in the event of error and *a
  is set to NULL.i2d_TYPE() returns the number of bytes successfully encoded
    or a negative value if an error occurs.
i2d_TYPE_bio() and i2d_TYPE_fp() return 1 for
    success and 0 if an error occurs.
Allocate and encode the DER encoding of an X509 structure:
 int len;
 unsigned char *buf;
 buf = NULL;
 len = i2d_X509(x, &buf);
 if (len < 0)
     /* error */
Attempt to decode a buffer:
 X509 *x;
 unsigned char *buf;
 const unsigned char *p;
 int len;
 /* Set up buf and len to point to the input buffer. */
 p = buf;
 x = d2i_X509(NULL, &p, len);
 if (x == NULL)
     /* error */
Alternative technique:
 X509 *x;
 unsigned char *buf;
 const unsigned char *p;
 int len;
 /* Set up buf and len to point to the input buffer. */
 p = buf;
 x = NULL;
 if (d2i_X509(&x, &p, len) == NULL)
     /* error */
Using a temporary variable is mandatory. A common mistake is to attempt to use a
  buffer directly as follows:
 int len;
 unsigned char *buf;
 len = i2d_X509(x, NULL);
 buf = OPENSSL_malloc(len);
 ...
 i2d_X509(x, &buf);
 ...
 OPENSSL_free(buf);
This code will result in buf apparently containing garbage
    because it was incremented after the call to point after the data just
    written. Also buf will no longer contain the pointer allocated by
    OPENSSL_malloc() and the subsequent call to OPENSSL_free() is
    likely to crash.
Another trap to avoid is misuse of the a argument to
    d2i_TYPE():
 X509 *x;
 if (d2i_X509(&x, &p, len) == NULL)
     /* error */
This will probably crash somewhere in d2i_X509(). The
    reason for this is that the variable x is uninitialized and an
    attempt will be made to interpret its (invalid) value as an X509
    structure, typically causing a segmentation violation. If x is set to
    NULL first then this will not happen.
In some versions of OpenSSL the "reuse" behaviour of d2i_TYPE()
  when *a is valid is broken and some parts of the reused structure may
  persist if they are not present in the new one. Additionally, in versions of
  OpenSSL prior to 1.1.0, when the "reuse" behaviour is used and an
  error occurs the behaviour is inconsistent. Some functions behaved as
  described here, while some did not free *a on error and did not set
  *a to NULL.
As a result of the above issues the "reuse" behaviour is
    strongly discouraged.
i2d_TYPE() will not return an error in many versions of
    OpenSSL, if mandatory fields are not initialized due to a programming error
    then the encoded structure may contain invalid data or omit the fields
    entirely and will not be parsed by d2i_TYPE(). This may be fixed in
    future so code should not assume that i2d_TYPE() will always
  succeed.
Any function which encodes a structure (i2d_TYPE(),
    i2d_TYPE() or i2d_TYPE()) may return a stale encoding if the
    structure has been modified after deserialization or previous serialization.
    This is because some objects cache the encoding for efficiency reasons.
Copyright 1998-2020 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You
    may not use this file except in compliance with the License. You can obtain
    a copy in the file LICENSE in the source distribution or at
    <https://www.openssl.org/source/license.html>.