X509_check_ca.3ossl - 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). The certificate must be a complete certificate otherwise an error is returned.

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4, if it is certificate with keyUsage extension with bit keyCertSign set, but without basicConstraints, and 5 if it has outdated Netscape Certificate Type extension telling that it is CA certificate.

This function will also return 0 on error.

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 2015-2021 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 <https://www.openssl.org/source/license.html>.

EVP_PKEY_ASN1_METHOD.3ossl(3), X509_check_issued.3ossl(3).