X509_check_ca.3ssl - Man Page

 #include <openssl/x509v3.h>

 int X509_check_ca(X509 *cert);

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

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4, if it is certificate with keyUsage extension with bit keyCertSign set, but without basicConstraints, and 5 if it has outdated Netscape Certificate Type extension telling that it is CA certificate.

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

X509_verify_cert(3), X509_check_issued(3), X509_check_purpose(3)

Copyright 2015-2020 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 <https://www.openssl.org/source/license.html>.

EVP_PKEY_ASN1_METHOD.3ssl(3), X509_check_issued.3ssl(3).