openssl/doc/man3/X509_check_ca.pod

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=head1 NAME

X509_check_ca - check if given certificate is CA certificate

=head1 SYNOPSIS

 #include <openssl/x509v3.h>

 int X509_check_ca(X509 *cert);

=head1 DESCRIPTION

This function checks if given certificate is CA certificate (can be used
to sign other certificates).

=head1 RETURN VALUES

Function return 0, if it is not CA certificate, 1 if it is proper X509v3
CA certificate with B<basicConstraints> extension CA:TRUE,
3, if it is self-signed X509 v1 certificate, 4, if it is certificate with
B<keyUsage> extension with bit B<keyCertSign> set, but without
B<basicConstraints>, and 5 if it has outdated Netscape Certificate Type
extension telling that it is CA certificate.

Actually, any non-zero value means that this certificate could have been
used to sign other certificates.

=head1 SEE ALSO

L<X509_verify_cert(3)>,
L<X509_check_issued(3)>,
L<X509_check_purpose(3)>

=head1 COPYRIGHT

Copyright 2015-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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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