=pod

=head1 NAME

X509V3_get_d2i, X509V3_add1_i2d, X509V3_EXT_d2i, X509V3_EXT_i2d,
X509_get_ext_d2i, X509_add1_ext_i2d,
X509_ACERT_get_ext_d2i, X509_ACERT_add1_ext_i2d,
X509_CRL_get_ext_d2i, X509_CRL_add1_ext_i2d,
X509_REVOKED_get_ext_d2i, X509_REVOKED_add1_ext_i2d,
X509_get0_extensions, X509_ACERT_get0_extensions, X509_CRL_get0_extensions,
X509_REVOKED_get0_extensions - X509 extension decode and encode functions

=head1 SYNOPSIS

 #include <openssl/x509v3.h>

 void *X509V3_get_d2i(const STACK_OF(X509_EXTENSION) *x, int nid, int *crit,
                      int *idx);
 int X509V3_add1_i2d(STACK_OF(X509_EXTENSION) **x, int nid, void *value,
                     int crit, unsigned long flags);

 void *X509V3_EXT_d2i(X509_EXTENSION *ext);
 X509_EXTENSION *X509V3_EXT_i2d(int ext_nid, int crit, void *ext_struc);

 void *X509_get_ext_d2i(const X509 *x, int nid, int *crit, int *idx);
 int X509_add1_ext_i2d(X509 *x, int nid, void *value, int crit,
                       unsigned long flags);

 void *X509_ACERT_get_ext_d2i(const X509_ACERT *x, int nid, int *crit, int *idx);
 int X509_ACERT_add1_ext_i2d(X509_ACERT *x, int nid, void *value, int crit,
                             unsigned long flags);

 void *X509_CRL_get_ext_d2i(const X509_CRL *crl, int nid, int *crit, int *idx);
 int X509_CRL_add1_ext_i2d(X509_CRL *crl, int nid, void *value, int crit,
                           unsigned long flags);

 void *X509_REVOKED_get_ext_d2i(const X509_REVOKED *r, int nid, int *crit, int *idx);
 int X509_REVOKED_add1_ext_i2d(X509_REVOKED *r, int nid, void *value, int crit,
                               unsigned long flags);

 const STACK_OF(X509_EXTENSION) *X509_get0_extensions(const X509 *x);
 const STACK_OF(X509_EXTENSION) *X509_ACERT_get0_extensions(const X509 *x);
 const STACK_OF(X509_EXTENSION) *X509_CRL_get0_extensions(const X509_CRL *crl);
 const STACK_OF(X509_EXTENSION) *X509_REVOKED_get0_extensions(const X509_REVOKED *r);

=head1 DESCRIPTION

X509V3_get_d2i() looks for an extension with OID I<nid> in the extensions
I<x> and, if found, decodes it. If I<idx> is NULL then only one
occurrence of an extension is permissible, otherwise the first extension after
index I<*idx> is returned and I<*idx> updated to the location of the extension.
If I<crit> is not NULL then I<*crit> is set to a status value: -2 if the
extension occurs multiple times (this is only returned if I<idx> is NULL),
-1 if the extension could not be found, 0 if the extension is found and is
not critical and 1 if critical. A pointer to an extension specific structure
or NULL is returned.

X509V3_add1_i2d() adds extension I<value> to STACK I<*x> (allocating a new
STACK if necessary) using OID I<nid> and criticality I<crit> according
to I<flags>.

X509V3_EXT_d2i() attempts to decode the ASN.1 data contained in extension
I<ext> and returns a pointer to an extension specific structure or NULL
if the extension could not be decoded (invalid syntax or not supported).

X509V3_EXT_i2d() encodes the extension specific structure I<ext_struc>
with OID I<ext_nid> and criticality I<crit>.

X509_get_ext_d2i() and X509_add1_ext_i2d() operate on the extensions of
certificate I<x>. They are otherwise identical to X509V3_get_d2i() and
X509V3_add1_i2d().

X509_ACERT_get_ext_d2i() and X509_ACERT_add1_ext_i2d() operate on the extensions
of B<X509_ACERT> structure I<x>. They are otherwise identical to X509V3_get_d2i()
and X509V3_add1_i2d().

X509_CRL_get_ext_d2i() and X509_CRL_add1_ext_i2d() operate on the extensions
of CRL I<crl>. They are otherwise identical to X509V3_get_d2i() and
X509V3_add1_i2d().

X509_REVOKED_get_ext_d2i() and X509_REVOKED_add1_ext_i2d() operate on the
extensions of B<X509_REVOKED> structure I<r> (i.e for CRL entry extensions).
They are otherwise identical to X509V3_get_d2i() and X509V3_add1_i2d().

X509_get0_extensions(), X509_ACERT_get0_extensions(),
X509_CRL_get0_extensions() and X509_REVOKED_get0_extensions() return a
STACK of all the extensions of a certificate, an attribute certificate,
a CRL or a CRL entry respectively.

=head1 NOTES

In almost all cases an extension can occur at most once and multiple
occurrences is an error. Therefore, the I<idx> parameter is usually NULL.

The I<flags> parameter may be one of the following values.

B<X509V3_ADD_DEFAULT> appends a new extension only if the extension does
not exist. An error is returned if the extension exists.

B<X509V3_ADD_APPEND> appends a new extension, ignoring whether the extension
exists.

B<X509V3_ADD_REPLACE> replaces an existing extension. If the extension does
not exist, appends a new extension.

B<X509V3_ADD_REPLACE_EXISTING> replaces an existing extension. If the
extension does not exist, returns an error.

B<X509V3_ADD_KEEP_EXISTING> appends a new extension only if the extension does
not exist. An error is B<not> returned if the extension exists.

B<X509V3_ADD_DELETE> deletes and frees an existing extension. If the extension
does not exist, returns an error. No new extension is added.

If B<X509V3_ADD_SILENT> is bitwise ORed with I<flags>: any error returned
will not be added to the error queue.

The function X509V3_get_d2i() and its variants
will return NULL if the extension is not
found, occurs multiple times or cannot be decoded. It is possible to
determine the precise reason by checking the value of I<*crit>.
The returned pointer must be explicitly freed.

The function X509V3_add1_i2d() and its variants allocate B<X509_EXTENSION>
objects on STACK I<*x> depending on I<flags>. The B<X509_EXTENSION> objects
must be explicitly freed using X509_EXTENSION_free().

=head1 SUPPORTED EXTENSIONS

The following sections contain a list of all supported extensions
including their name and NID.

=head2 PKIX Certificate Extensions

The following certificate extensions are defined in PKIX standards such as
RFC5280.

 Basic Constraints                  NID_basic_constraints
 Key Usage                          NID_key_usage
 Extended Key Usage                 NID_ext_key_usage

 Subject Key Identifier             NID_subject_key_identifier
 Authority Key Identifier           NID_authority_key_identifier

 Private Key Usage Period           NID_private_key_usage_period

 Subject Alternative Name           NID_subject_alt_name
 Issuer Alternative Name            NID_issuer_alt_name

 Authority Information Access       NID_info_access
 Subject Information Access         NID_sinfo_access

 Name Constraints                   NID_name_constraints

 Certificate Policies               NID_certificate_policies
 Policy Mappings                    NID_policy_mappings
 Policy Constraints                 NID_policy_constraints
 Inhibit Any Policy                 NID_inhibit_any_policy

 TLS Feature                        NID_tlsfeature

=head2 Netscape Certificate Extensions

The following are (largely obsolete) Netscape certificate extensions.

 Netscape Cert Type                 NID_netscape_cert_type
 Netscape Base Url                  NID_netscape_base_url
 Netscape Revocation Url            NID_netscape_revocation_url
 Netscape CA Revocation Url         NID_netscape_ca_revocation_url
 Netscape Renewal Url               NID_netscape_renewal_url
 Netscape CA Policy Url             NID_netscape_ca_policy_url
 Netscape SSL Server Name           NID_netscape_ssl_server_name
 Netscape Comment                   NID_netscape_comment

=head2 Miscellaneous Certificate Extensions

 Strong Extranet ID                 NID_sxnet
 Proxy Certificate Information      NID_proxyCertInfo

=head2 PKIX CRL Extensions

The following are CRL extensions from PKIX standards such as RFC5280.

 CRL Number                         NID_crl_number
 CRL Distribution Points            NID_crl_distribution_points
 Delta CRL Indicator                NID_delta_crl
 Freshest CRL                       NID_freshest_crl
 Invalidity Date                    NID_invalidity_date
 Issuing Distribution Point         NID_issuing_distribution_point

The following are CRL entry extensions from PKIX standards such as RFC5280.

 CRL Reason Code                    NID_crl_reason
 Certificate Issuer                 NID_certificate_issuer

=head2 OCSP Extensions

 OCSP Nonce                         NID_id_pkix_OCSP_Nonce
 OCSP CRL ID                        NID_id_pkix_OCSP_CrlID
 Acceptable OCSP Responses          NID_id_pkix_OCSP_acceptableResponses
 OCSP No Check                      NID_id_pkix_OCSP_noCheck
 OCSP Archive Cutoff                NID_id_pkix_OCSP_archiveCutoff
 OCSP Service Locator               NID_id_pkix_OCSP_serviceLocator
 Hold Instruction Code              NID_hold_instruction_code

=head2 Certificate Transparency Extensions

The following extensions are used by certificate transparency, RFC6962

 CT Precertificate SCTs             NID_ct_precert_scts
 CT Certificate SCTs                NID_ct_cert_scts

=head1 RETURN VALUES

X509V3_get_d2i(), its variants, and X509V3_EXT_d2i() return
a pointer to an extension specific structure or NULL if an error occurs.

X509V3_add1_i2d() and its variants return 1 if the operation is successful
and 0 if it fails due to a non-fatal error (extension not found, already exists,
cannot be encoded) or -1 due to a fatal error such as a memory allocation
failure.

X509V3_EXT_i2d() returns a pointer to an B<X509_EXTENSION> structure
or NULL if an error occurs.

X509_get0_extensions(), X509_CRL_get0_extensions() and
X509_REVOKED_get0_extensions() return a stack of extensions. They return
NULL if no extensions are present.

=head1 SEE ALSO

L<d2i_X509(3)>,
L<ERR_get_error(3)>,
L<X509_CRL_get0_by_serial(3)>,
L<X509_get0_signature(3)>,
L<X509_get_ext_d2i(3)>,
L<X509_get_extension_flags(3)>,
L<X509_get_pubkey(3)>,
L<X509_get_subject_name(3)>,
L<X509_get_version(3)>,
L<X509_NAME_add_entry_by_txt(3)>,
L<X509_NAME_ENTRY_get_object(3)>,
L<X509_NAME_get_index_by_NID(3)>,
L<X509_NAME_print_ex(3)>,
L<X509_new(3)>,
L<X509_sign(3)>,
L<X509_verify_cert(3)>

=head1 HISTORY

X509_ACERT_get_ext_d2i(), X509_ACERT_add1_ext_i2d(),
X509_ACERT_get0_extensions() were added in OpenSSL 3.4.

=head1 COPYRIGHT

Copyright 2015-2024 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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
L<https://www.openssl.org/source/license.html>.

=cut
