X509V3_GET_D2I(3ossl)

📦
version 3.5.9 · 8 versions
, in fedora 43, fedora 44

💖 X509V3_GET_D2I — X509 extension decode and encode functions 💖

okay bestie, welcome to the 3ossl manual page, aka the group chat where all your certificate extensions come to get decoded and re-encoded. pull up a chair, grab a strawberry 🍓, and let's get into it.

🌸 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 — these are the X509 extension decode and encode functions, and yes that is a lot of them, it's giving extended universe 💅

✨ 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);

🦋 DESCRIPTION 🦋

X509V3_get_d2i() goes looking for an extension with OID nid inside the extensions x, and if it actually finds one, it decodes it. now here's the tea on idx: if idx is NULL, then only one occurrence of the extension is allowed. but if idx isn't NULL, you get the first extension after index *idx, and *idx gets updated to point at wherever that extension is living. ✨

if crit isn't NULL, then *crit gets set to a status value, and bestie, memorise these:

  • -2 — the extension shows up multiple times (and heads up, this one is only returned when idx is NULL)
  • -1 — the extension could not be found, tragic 😭
  • 0 — found it, and it's not critical
  • 1 — found it, and it IS critical

a pointer to an extension specific structure gets returned, or NULL. that's the deal.

X509V3_add1_i2d() adds extension value to STACK *x (allocating a fresh new STACK if one is needed), using OID nid and criticality crit, all according to flags.

X509V3_EXT_d2i() tries to decode the ASN.1 data chillin' inside extension ext, and hands you back a pointer to an extension specific structure — or NULL if it couldn't decode it (either the syntax was invalid or that thing just isn't supported 🙈).

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

X509_get_ext_d2i() and X509_add1_ext_i2d() operate on the extensions of certificate x. otherwise they're 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 an X509_ACERT structure x. otherwise they're 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 crl. otherwise they're 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 an X509_REVOKED structure r (so, CRL entry extensions, iykyk). otherwise they're 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. one STACK to hold them all 💫

🎀 NOTES 🎀

in almost every case, an extension can only occur at most once, and multiple occurrences is an error. so basically, idx is usually NULL. periodt.

the flags parameter can be one of these values:

  • X509V3_ADD_DEFAULT — appends a new extension only if the extension doesn't already exist. if it does exist, you get an error back.
  • X509V3_ADD_APPEND — appends a new extension, and does not care even a little whether the extension exists.
  • X509V3_ADD_REPLACE — replaces an existing extension. if the extension doesn't exist, it appends a new one instead.
  • X509V3_ADD_REPLACE_EXISTING — replaces an existing extension. if the extension doesn't exist, it returns an error.
  • X509V3_ADD_KEEP_EXISTING — appends a new extension only if the extension doesn't exist. and if it does exist, no error is returned. chill vibes.
  • X509V3_ADD_DELETE — deletes and frees an existing extension. if the extension doesn't exist, it returns an error. no new extension gets added.

if X509V3_ADD_SILENT is bitwise ORed with flags: any error that gets returned will not be added to the error queue. 🤫

the function X509V3_get_d2i() and its variants will return NULL if the extension isn't found, occurs multiple times, or cannot be decoded. you can figure out the precise reason by checking the value of *crit. and the returned pointer must be explicitly freed. not me letting you leak memory, absolutely not 💀

the function X509V3_add1_i2d() and its variants allocate X509_EXTENSION objects on STACK *x depending on flags. those X509_EXTENSION objects must be explicitly freed using X509_EXTENSION_free().

🌈 SUPPORTED EXTENSIONS 🌈

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

👑 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

🧚 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

⭐ Miscellaneous Certificate Extensions

  • Strong Extranet ID — NID_sxnet
  • Proxy Certificate Information — NID_proxyCertInfo

💜 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

🫶 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

🔥 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

💅 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, like a memory allocation failure. 😭

X509V3_EXT_i2d() returns a pointer to an 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.

🌟 SEE ALSO 🌟

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

📜 HISTORY 📜

X509_ACERT_get_ext_d2i(), X509_ACERT_add1_ext_i2d(), X509_ACERT_get0_extensions() were added in OpenSSL 3.4. the glow-up is real ✨

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 <https://www.openssl.org/source/license.html>.

and that's the whole page bestie, no cap 🫶 this was OpenSSL 3.5.9, dated 2026-09-29 — thanks for reading my X509V3_GET_D2I(3ossl) brain dump, you ate that 💅💖🌈

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