X509V3_GET_D2I(3)

📦 version 4.4.0, in alpine 3.24, arch rolling

💖 X509V3_GET_D2I(3) — X509 extension decode and encode functions 💖

okay bestie, this is the X509V3_GET_D2I(3) page from the Library Functions Manual, and it’s the whole group chat for X509 extension decode/encode functions. No cap, there are a lot of function names, but we’re gonna get through it together. 💅

✨ NAME ✨

This page covers the whole squad: X509V3_get_d2i, X509V3_add1_i2d, X509V3_EXT_d2i, X509V3_EXT_i2d, X509_get_ext_d2i, X509_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_CRL_get0_extensions, X509_REVOKED_get0_extensions, and X509_get0_uids — X509 extension decode and encode functions.

🌈 SYNOPSIS 🌈

library “libcrypto” #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);

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_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_CRL_get0_extensions(const X509_CRL *crl);

const STACK_OF(X509_EXTENSION) *
X509_REVOKED_get0_extensions(const X509_REVOKED *r);

void
X509_get0_uids(const X509 *x, const ASN1_BIT_STRING **issuerUID,
    const ASN1_BIT_STRING **subjectUID);

🧠 DESCRIPTION 🧠

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

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

X509V3_EXT_d2i() attempts to decode the ASN.1 data contained in extension 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 ext with OID ext_nid and criticality crit.

X509_get_ext_d2i() and X509_add1_ext_i2d() operate on the extensions of certificate x, and 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 crl, and 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 the X509_REVOKED structure r (i.e. for CRL entry extensions), and are otherwise identical to X509V3_get_d2i() and X509V3_add1_i2d().

X509_get0_extensions(), X509_CRL_get0_extensions(), and X509_REVOKED_get0_extensions() return a stack of all the extensions of a certificate, a CRL, or a CRL entry, respectively.

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

The flags argument consists of two parts OR'ed together: the operation mode and the optional silent flag. The operation mode is the bitwise OR of the flags and the bitmask X509V3_ADD_OP_MASK. The following operation modes are recognized:

  • X509V3_ADD_DEFAULT — appends a new extension only if the extension does not already exist. An error is returned if the extension does already exist.
  • X509V3_ADD_APPEND — appends a new extension, ignoring whether the extension already exists. This is a misfeature and should not be used because certificates must not include the same extension more than once.
  • X509V3_ADD_REPLACE — replaces an extension if it exists otherwise appends a new extension.
  • X509V3_ADD_REPLACE_EXISTING — replaces an existing extension if it exists otherwise returns an error.
  • X509V3_ADD_KEEP_EXISTING — appends a new extension only if the extension does not already exist. An error is not returned if the extension does already exist.
  • X509V3_ADD_DELETE — deletes extension nid if it exists and errors otherwise. No new extension is added.

Any other operation mode results in an error.

If X509V3_ADD_SILENT is OR'd into the flags, any error returned will not be added to the error queue.

The function X509V3_get_d2i() 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 *crit.

X509_get0_uids() returns the issuer and subject unique identifiers of the certificate x in *issuerUID and *subjectUID. If a unique identifier field is not present in x, NULL is returned. Either one of issuerUID and subjectUID can be NULL.

🌸 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 RFC 5280.

  • 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
  • IP Address Delegation — NID_sbgp_ipAddrBlock
  • Autonomous System Identifier Delegation — NID_sbgp_autonomousSysNum

🎀 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

🦋 PKIX CRL Extensions 🦋

The following are CRL extensions from PKIX standards such as RFC 5280.

  • 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 RFC 5280.

  • 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 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

💜 RETURN VALUES 💜

  • X509V3_get_d2i(), X509V3_EXT_d2i(), X509_get_ext_d2i(), X509_CRL_get_ext_d2i(), and X509_REVOKED_get_ext_d2i() return a pointer to an extension specific structure or NULL if an error occurs.
  • X509V3_add1_i2d(), X509_add1_ext_i2d(), X509_CRL_add1_ext_i2d(), and X509_REVOKED_add1_ext_i2d() return 1 if the operation is successful, 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. In some cases of failure, the reason can be determined with ERR_get_error(3).
  • X509V3_EXT_i2d() returns a pointer to an X509_EXTENSION structure if successful; otherwise NULL is returned and an error code can be retrieved with ERR_get_error(3).
  • X509_get0_extensions(), X509_CRL_get0_extensions(), and X509_REVOKED_get0_extensions() return a stack of extensions, or NULL if no extensions are present.

🌈 SEE ALSO 🌈

🕰️ HISTORY 🕰️

  • X509V3_EXT_d2i() first appeared in OpenSSL 0.9.2b. X509V3_EXT_i2d() first appeared in OpenSSL 0.9.3. Both functions have been available since OpenBSD 2.6.
  • X509V3_get_d2i(), X509_get_ext_d2i(), X509_CRL_get_ext_d2i(), and X509_REVOKED_get_ext_d2i() first appeared in OpenSSL 0.9.5 and have been available since OpenBSD 2.7.
  • X509V3_add1_i2d(), X509_add1_ext_i2d(), X509_CRL_add1_ext_i2d(), and X509_REVOKED_add1_ext_i2d() first appeared in OpenSSL 0.9.7 and have been available since OpenBSD 3.2.
  • X509_get0_extensions(), X509_CRL_get0_extensions(), and X509_REVOKED_get0_extensions() first appeared in OpenSSL 1.1.0 and have been available since OpenBSD 6.3.
  • X509_get0_uids() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 7.3.

Okay that’s the whole tea ☕ — cute sign-off vibes: this page is from Debian, dated June 8, 2025, for X509V3_GET_D2I(3). Bye bestie, go decode slay 💅✨

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