=pod

=head1 NAME

X509_new, X509_new_ex,
X509_free, X509_up_ref,
X509_chain_up_ref,
OSSL_STACK_OF_X509_free
- X509 certificate ASN1 allocation and deallocation functions

=head1 SYNOPSIS

 #include <openssl/x509.h>

 X509 *X509_new(void);
 X509 *X509_new_ex(OSSL_LIB_CTX *libctx, const char *propq);
 void X509_free(X509 *a);
 int X509_up_ref(X509 *a);
 STACK_OF(X509) *X509_chain_up_ref(STACK_OF(X509) *x);
 void OSSL_STACK_OF_X509_free(STACK_OF(X509) *certs);

=head1 DESCRIPTION

The X509 ASN1 allocation routines allocate and free an
X509 structure, which represents an X509 certificate.

X509_new_ex() allocates and initializes a X509 structure with a
library context of I<libctx>, property query of I<propq> and a reference
count of B<1>. Many X509 functions such as X509_check_purpose(), and
X509_verify() use this library context to select which providers supply the
fetched algorithms (SHA1 is used internally). This created X509 object can then
be used when loading binary data using d2i_X509().

X509_new() is similar to X509_new_ex() but sets the library context
and property query to NULL. This results in the default (NULL) library context
being used for any X509 operations requiring algorithm fetches.

X509_free() decrements the reference count of B<X509> structure B<a> and
frees it up if the reference count is zero. If the argument is NULL,
nothing is done.

X509_up_ref() increments the reference count of B<a>.

X509_chain_up_ref() increases the reference count of all certificates in
chain B<x> and returns a copy of the stack, or an empty stack if B<a> is NULL.

OSSL_STACK_OF_X509_free() deallocates the given list of pointers to
certificates after calling X509_free() on all its elements.
If the argument is NULL, nothing is done.

=head1 NOTES

The function X509_up_ref() if useful if a certificate structure is being
used by several different operations each of which will free it up after
use: this avoids the need to duplicate the entire certificate structure.

The function X509_chain_up_ref() doesn't just up the reference count of
each certificate. It also returns a copy of the stack, using sk_X509_dup(),
but it serves a similar purpose: the returned chain persists after the
original has been freed.

=head1 RETURN VALUES

If the allocation fails, X509_new() returns NULL and sets an error
code that can be obtained by L<ERR_get_error(3)>.
Otherwise it returns a pointer to the newly allocated structure.

X509_up_ref() returns 1 for success and 0 for failure.

X509_chain_up_ref() returns a copy of the stack or NULL if an error occurred.

OSSL_STACK_OF_X509_free() has no return value.

=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_sign(3)>,
L<X509V3_get_d2i(3)>,
L<X509_verify_cert(3)>

=head1 HISTORY

X509_new_ex() was added in OpenSSL 3.0.

OSSL_STACK_OF_X509_free() was added in OpenSSL 3.2.

=head1 COPYRIGHT

Copyright 2002-2024 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>.

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