- NAME
- SYNOPSIS
- DESCRIPTION
- NOTES
- RETURN VALUES
- SEE ALSO
- HISTORY
- COPYRIGHT

# NAME

X509v3_get_ext_count, X509v3_get_ext, X509v3_get_ext_by_NID, X509v3_get_ext_by_OBJ, X509v3_get_ext_by_critical, X509v3_delete_ext, X509v3_delete_extension, X509v3_add_ext, X509v3_add_extensions, X509_get_ext_count, X509_get_ext, X509_get_ext_by_NID, X509_get_ext_by_OBJ, X509_get_ext_by_critical, X509_delete_ext, X509_add_ext, X509_CRL_get_ext_count, X509_CRL_get_ext, X509_CRL_get_ext_by_NID, X509_CRL_get_ext_by_OBJ, X509_CRL_get_ext_by_critical, X509_CRL_delete_ext, X509_CRL_add_ext, X509_REVOKED_get_ext_count, X509_REVOKED_get_ext, X509_REVOKED_get_ext_by_NID, X509_REVOKED_get_ext_by_OBJ, X509_REVOKED_get_ext_by_critical, X509_REVOKED_delete_ext, X509_REVOKED_add_ext - extension stack utility functions

# SYNOPSIS

    #include <openssl/x509.h>

    int X509v3_get_ext_count(const STACK_OF(X509_EXTENSION) *x);
    const X509_EXTENSION *X509v3_get_ext(const STACK_OF(X509_EXTENSION) *x, int loc);

    int X509v3_get_ext_by_NID(const STACK_OF(X509_EXTENSION) *x,
                              int nid, int lastpos);
    int X509v3_get_ext_by_OBJ(const STACK_OF(X509_EXTENSION) *x,
                              const ASN1_OBJECT *obj, int lastpos);
    int X509v3_get_ext_by_critical(const STACK_OF(X509_EXTENSION) *x,
                                   int crit, int lastpos);
    X509_EXTENSION *X509v3_delete_ext(STACK_OF(X509_EXTENSION) *x, int loc);
    X509_EXTENSION *X509v3_delete_extension(STACK_OF(X509_EXTENSION) **x, int loc);
    STACK_OF(X509_EXTENSION) *X509v3_add_ext(STACK_OF(X509_EXTENSION) **x,
                                             const X509_EXTENSION *ex, int loc);
    STACK_OF(X509_EXTENSION)
         *X509v3_add_extensions(STACK_OF(X509_EXTENSION) **target,
                                const STACK_OF(X509_EXTENSION) *exts);

    int X509_get_ext_count(const X509 *x);
    const X509_EXTENSION *X509_get_ext(const X509 *x, int loc);
    int X509_get_ext_by_NID(const X509 *x, int nid, int lastpos);
    int X509_get_ext_by_OBJ(const X509 *x, const ASN1_OBJECT *obj, int lastpos);
    int X509_get_ext_by_critical(const X509 *x, int crit, int lastpos);
    X509_EXTENSION *X509_delete_ext(X509 *x, int loc);
    int X509_add_ext(X509 *x, const X509_EXTENSION *ex, int loc);

    int X509_CRL_get_ext_count(const X509_CRL *x);
    const X509_EXTENSION *X509_CRL_get_ext(const X509_CRL *x, int loc);
    int X509_CRL_get_ext_by_NID(const X509_CRL *x, int nid, int lastpos);
    int X509_CRL_get_ext_by_OBJ(const X509_CRL *x, const ASN1_OBJECT *obj,
                                int lastpos);
    int X509_CRL_get_ext_by_critical(const X509_CRL *x, int crit, int lastpos);
    X509_EXTENSION *X509_CRL_delete_ext(X509_CRL *x, int loc);
    int X509_CRL_add_ext(X509_CRL *x, const X509_EXTENSION *ex, int loc);

    int X509_REVOKED_get_ext_count(const X509_REVOKED *x);
    const X509_EXTENSION *X509_REVOKED_get_ext(const X509_REVOKED *x, int loc);
    int X509_REVOKED_get_ext_by_NID(const X509_REVOKED *x, int nid, int lastpos);
    int X509_REVOKED_get_ext_by_OBJ(const X509_REVOKED *x, const ASN1_OBJECT *obj,
                                    int lastpos);
    int X509_REVOKED_get_ext_by_critical(const X509_REVOKED *x, int crit, int lastpos);
    X509_EXTENSION *X509_REVOKED_delete_ext(X509_REVOKED *x, int loc);
    int X509_REVOKED_add_ext(X509_REVOKED *x, X509_EXTENSION *ex, int loc);

# DESCRIPTION

X509v3_get_ext_count() retrieves the number of extensions in x.

X509v3_get_ext() retrieves extension loc from x. The index loc can take any value from 0 to X509_get_ext_count(x) - 1. The returned extension is an internal pointer which MUST NOT be freed by the application.

X509v3_get_ext_by_NID() and X509v3_get_ext_by_OBJ() look for an extension with nid or obj from extension STACK x. The search starts from the extension after lastpos or from the beginning if lastpos is -1. If the extension is found, its index is returned, otherwise -1 is returned.

X509v3_get_ext_by_critical() is similar to X509v3_get_ext_by_NID() except it looks for an extension of criticality crit. A zero value for crit looks for a non-critical extension. A nonzero value looks for a critical extension.

X509v3_delete_ext() deletes the extension with index loc from x. The deleted extension is returned and must be freed by the caller. If loc is an invalid index value, NULL is returned.

X509v3_delete_extension() extends X509v3_delete_ext() by deallocating the extension stack *x if it becomes empty, and in that case also setting *x to NULL. This is a convenience wrapper for cases in which a list of extensions is optional and should be omitted if the stack becomes empty.

X509v3_add_ext() inserts extension ex to STACK *x at position loc. If loc is -1, the new extension is added to the end. A new STACK is allocated if *x is NULL. The passed extension ex is duplicated so it must be freed after use.

X509v3_add_extensions() adds the list of extensions exts to STACK *target. The STACK *target is returned unchanged if exts is NULL or an empty list. Otherwise a new stack is allocated if *target is NULL. An extension to be added that has the same OID as a pre-existing one replaces this earlier one.

X509_get_ext_count(), X509_get_ext(), X509_get_ext_by_NID(), X509_get_ext_by_OBJ(), X509_get_ext_by_critical(), X509_delete_ext() and X509_add_ext() operate on the extensions of certificate x. They are otherwise identical to the X509v3 functions.

X509_CRL_get_ext_count(), X509_CRL_get_ext(), X509_CRL_get_ext_by_NID(), X509_CRL_get_ext_by_OBJ(), X509_CRL_get_ext_by_critical(), X509_CRL_delete_ext() and X509_CRL_add_ext() operate on the extensions of CRL x. They are otherwise identical to the X509v3 functions.

X509_REVOKED_get_ext_count(), X509_REVOKED_get_ext(), X509_REVOKED_get_ext_by_NID(), X509_REVOKED_get_ext_by_OBJ(), X509_REVOKED_get_ext_by_critical(), X509_REVOKED_delete_ext() and X509_REVOKED_add_ext() operate on the extensions of CRL entry x. They are otherwise identical to the X509v3 functions.

# NOTES

These functions are used to examine stacks of extensions directly. Applications that want to parse or encode and add an extension should use the extension encode and decode functions instead, such as X509_add1_ext_i2d() and X509_get_ext_d2i().

For X509v3_get_ext_by_NID(), X509v3_get_ext_by_OBJ(), X509v3_get_ext_by_critical() and its variants, a zero index return value is not an error since extension STACK x indices start from zero. These search functions start from the extension after the lastpos parameter so it should initially be set to -1. If it is set to zero, the initial extension will not be checked.

X509v3_delete_ext() and its variants are a bit counter-intuitive because these functions do not free the extension they delete. They return an X509_EXTENSION object which must be explicitly freed using X509_EXTENSION_free().

X509v3_add_ext(), X509v3_add_extensions() and X509_add_ext() ignore any empty values of the `subjectKeyIdentifier` (empty OCTET STRING) or the `authorityKeyIdentifier` (empty SEQUENCE) extensions. These empty values are not added to the extension list. In the case of X509v3_add_extensions() any previous instance of the same extension is deleted, so the call is not necessarily without side-effects in that case.

# RETURN VALUES

X509v3_get_ext_count() returns the extension count or 0 for failure.

X509v3_get_ext(), X509v3_delete_ext(), X509v3_delete_extension() and X509_delete_ext() return an X509_EXTENSION structure or NULL if an error occurs.

X509v3_get_ext_by_OBJ() and X509v3_get_ext_by_critical() return the extension index or -1 if an error occurs.

X509v3_get_ext_by_NID() returns the extension index or negative values if an error occurs.

X509v3_add_ext() returns a STACK of extensions or NULL on error.

X509v3_add_extensions() returns a STACK of extensions or NULL on error or if *target is NULL and exts is NULL or an empty list.

X509_add_ext() returns 1 on success and 0 on error.

# SEE ALSO

X509V3_get_d2i(3)

# HISTORY

X509v3_add_extensions() was added in OpenSSL 3.4.

X509v3_delete_extension() was added in OpenSSL 4.0.

# COPYRIGHT

Copyright 2015-2026 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.