.\"	$OpenBSD: X509_check_ca.3,v 1.7 2022/05/10 19:44:29 tb Exp $
.\"	OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400
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.Dd $Mdocdate: May 10 2022 $
.Dt X509_CHECK_CA 3
.Os
.Sh NAME
.Nm X509_check_ca
.Nd check whether a certificate is a CA certificate
.Sh SYNOPSIS
.In openssl/x509v3.h
.Ft int
.Fo X509_check_ca
.Fa "X509 *cert"
.Fc
.Sh DESCRIPTION
The
.Fn X509_check_ca
function checks whether the given certificate is a CA certificate,
that is, whether it can be used to sign other certificates.
.Sh RETURN VALUES
If
.Fa cert
is a CA certificate, a non-zero value is returned; 0 otherwise.
.Pp
The following return values identify specific kinds of CA certificates:
.Bl -tag -width 2n
.It 1
an X.509 v3 CA certificate with
.Sy basicConstraints
extension CA:TRUE
.It 3
a self-signed X.509 v1 certificate
.It 4
a certificate with
.Sy keyUsage
extension with bit
.Sy keyCertSign
set, but without
.Sy basicConstraints
.It 5
a certificate with an outdated Netscape Certificate Type extension telling
that it is a CA certificate
.El
.Sh SEE ALSO
.Xr BASIC_CONSTRAINTS_new 3 ,
.Xr EXTENDED_KEY_USAGE_new 3 ,
.Xr X509_check_issued 3 ,
.Xr X509_check_purpose 3 ,
.Xr X509_EXTENSION_new 3 ,
.Xr X509_new 3 ,
.Xr X509_verify_cert 3
.Sh HISTORY
.Fn X509_check_ca
first appeared in OpenSSL 0.9.7f and has been available since
.Ox 3.8 .
.Sh BUGS
If
.Fn X509_check_ca
fails to cache X509v3 extension values, the return value may
be incorrect.
An application should
call
.Xr X509_check_purpose 3
with a
.Fa purpose
argument of \-1,
ensuring that the X509v3 extensions are cached,
before calling
.Fn X509_check_ca .