=pod

=head1 NAME

X509_verify, X509_self_signed,
X509_REQ_verify_ex, X509_REQ_verify,
X509_CRL_verify, X509_ACERT_verify -
verify certificate, certificate request, or CRL signature

=head1 SYNOPSIS

 #include <openssl/x509.h>

 int X509_verify(X509 *x, EVP_PKEY *pkey);
 int X509_self_signed(const X509 *cert, int verify_signature);

 int X509_REQ_verify_ex(X509_REQ *a, EVP_PKEY *pkey, OSSL_LIB_CTX *libctx,
                        const char *propq);
 int X509_REQ_verify(X509_REQ *a, EVP_PKEY *r);
 int X509_CRL_verify(X509_CRL *a, EVP_PKEY *r);

 #include <openssl/x509_acert.h>
 int X509_ACERT_verify(X509_CRL *a, EVP_PKEY *r);

=head1 DESCRIPTION

X509_verify() verifies the signature of certificate I<x> using public key
I<pkey>. Only the signature is checked: no other checks (such as certificate
chain validity) are performed.

X509_self_signed() checks whether certificate I<cert> is self-signed.
For success the issuer and subject names must match, the components of the
authority key identifier (if present) must match the subject key identifier etc.
The signature itself is actually verified only if B<verify_signature> is 1, as
for explicitly trusted certificates this verification is not worth the effort.

X509_REQ_verify_ex(), X509_REQ_verify(), X509_CRL_verify() and X509_ACERT_verify()
verify the signatures of certificate requests, CRLs and attribute certificates
respectively.

=head1 RETURN VALUES

X509_verify(),
X509_REQ_verify_ex(), X509_REQ_verify() and X509_CRL_verify()
return 1 if the signature is valid and 0 if the signature check fails.
If the signature could not be checked at all because it was ill-formed,
the certificate or the request was not complete or some other error occurred
then -1 is returned.

X509_self_signed() returns the same values but also returns 1
if all respective fields match and B<verify_signature> is 0.

=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_ENTRY_get_object(3)>,
L<X509_NAME_get_index_by_NID(3)>,
L<X509_NAME_print_ex(3)>,
L<X509V3_get_d2i(3)>,
L<X509_verify_cert(3)>,
L<OSSL_LIB_CTX(3)>

=head1 HISTORY

The X509_verify(), X509_REQ_verify(), and X509_CRL_verify()
functions are available in all versions of OpenSSL.

X509_REQ_verify_ex(), and X509_self_signed() were added in OpenSSL 3.0.

X509_ACERT_verify() was added in OpenSSL 3.4.

X509_self_signed() had its cert parameter modified to be I<const> in OpenSSL 4.0.

=head1 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
L<https://www.openssl.org/source/license.html>.

=cut
