Mutual authentication using TLS

1: Configuring TLS on the AxoSyslog clients

2: Configuring TLS on the AxoSyslog server

This section describes how to configure mutual authentication between the AxoSyslog server and the client. Configuring mutual authentication is similar to configuring TLS (for details, see Encrypting log messages with TLS), but the server verifies the identity of the client as well. Therefore, each client must have a certificate, and the server must have the certificate of the CA that issued the certificate of the clients. For the concepts of using TLS in syslog-ng, see Secure logging using TLS.

1 - Configuring TLS on the AxoSyslog clients

Purpose:

Complete the following steps on every AxoSyslog client host. Examples are provided using both the legacy BSD-syslog protocol (using the network() driver) and the new IETF-syslog protocol standard (using the syslog() driver):

Steps:

Create an X.509 certificate for the AxoSyslog client.
Copy the certificate (for example, client_cert.pem) and the matching private key (for example, client.key) to the AxoSyslog client host, for example, into the /opt/syslog-ng/etc/syslog-ng/cert.d directory. The certificate must be a valid X.509 certificate in PEM format. If you want to use a password-protected key, see Password-protected keys.
Copy the CA certificate of the Certificate Authority (for example, cacert.pem) that issued the certificate of the AxoSyslog server (or the self-signed certificate of the syslog-ng server) to the AxoSyslog client hosts, for example, into the /opt/syslog-ng/etc/syslog-ng/ca.d directory.
Issue the following command on the certificate: openssl x509 -noout -hash -in cacert.pem The result is a hash (for example, 6d2962a8), a series of alphanumeric characters based on the Distinguished Name of the certificate.
Issue the following command to create a symbolic link to the certificate that uses the hash returned by the previous command and the .0 suffix.
ln -s cacert.pem 6d2962a8.0

Add a destination statement to the syslog-ng.conf configuration file that uses the tls( ca-dir(path_to_ca_directory) ) option and specify the directory using the CA certificate. The destination must use the network() or the syslog() destination driver, and the IP address and port parameters of the driver must point to the AxoSyslog server. Include the client’s certificate and private key in the tls() options.

Example: A destination statement using mutual authentication

The following destination encrypts the log messages using TLS and sends them to the 1999/TCP port of the AxoSyslog server having the 10.1.2.3 IP address. The private key and the certificate file authenticating the client is also specified.

    destination demo_tls_destination {
        network(
            "10.1.2.3" port(1999)
            transport("tls")
            tls(
                ca-dir("/opt/syslog-ng/etc/syslog-ng/ca.d")
                key-file("/opt/syslog-ng/etc/syslog-ng/key.d/client.key")
                cert-file("/opt/syslog-ng/etc/syslog-ng/cert.d/client_cert.pem")
            )
        );
    };

    destination demo_tls_syslog_destination {
        syslog(
            "10.1.2.3" port(1999)
            transport("tls")
            tls(
                ca-dir("/opt/syslog-ng/etc/syslog-ng/ca.d")
                key-file("/opt/syslog-ng/etc/syslog-ng/key.d/client.key")
                cert-file("/opt/syslog-ng/etc/syslog-ng/cert.d/client_cert.pem")
            )
        ); 
    };

Include the destination created in Step 2 in a log statement.

Warning
The encrypted connection between the server and the client fails if the Common Name or the subject_alt_name parameter of the server certificate does not match the hostname or the IP address (as resolved from the AxoSyslog clients and relays) of the server.
Do not forget to update the certificate files when they expire.

2 - Configuring TLS on the AxoSyslog server

Purpose:

Complete the following steps on the AxoSyslog server:

Steps:

Copy the certificate (for example, syslog-ng.cert) of the AxoSyslog server to the AxoSyslog server host, for example, into the /opt/syslog-ng/etc/syslog-ng/cert.d directory. The certificate must be a valid X.509 certificate in PEM format.
Copy the CA certificate (for example, cacert.pem) of the Certificate Authority that issued the certificate of the AxoSyslog clients to the AxoSyslog server, for example, into the /opt/syslog-ng/etc/syslog-ng/ca.d directory.
Issue the following command on the certificate: openssl x509 -noout -hash -in cacert.pem The result is a hash (for example, 6d2962a8), a series of alphanumeric characters based on the Distinguished Name of the certificate.
Issue the following command to create a symbolic link to the certificate that uses the hash returned by the previous command and the .0 suffix.
ln -s cacert.pem 6d2962a8.0
Copy the private key (for example, syslog-ng.key) matching the certificate of the AxoSyslog server to the AxoSyslog server host, for example, into the /opt/syslog-ng/etc/syslog-ng/key.d directory. The key must be in PEM format. If you want to use a password-protected key, see Password-protected keys.

Add a source statement to the syslog-ng.conf configuration file that uses the tls( key-file(key_file_fullpathname) cert-file(cert_file_fullpathname) ) option and specify the key and certificate files. The source must use the source driver (network() or syslog()) matching the destination driver used by the syslog-ng client. Also specify the directory storing the certificate of the CA that issued the client’s certificate.

For the details of the available tls() options, see TLS options.

Example: A source statement using TLS

The following source receives log messages encrypted using TLS, arriving to the 1999/TCP port of any interface of the AxoSyslog server.

    source demo_tls_source {
        network(
            ip(0.0.0.0) port(1999)
            transport("tls")
            tls(
                key-file("/opt/syslog-ng/etc/syslog-ng/key.d/syslog-ng.key")
                cert-file("/opt/syslog-ng/etc/syslog-ng/cert.d/syslog-ng.cert")
                ca-dir("/opt/syslog-ng/etc/syslog-ng/ca.d")
            )
        );
    };

A similar source for receiving messages using the IETF-syslog protocol:

    source demo_tls_syslog_source {
        syslog(
            ip(0.0.0.0) port(1999)
            transport("tls")
            tls(
                key-file("/opt/syslog-ng/etc/syslog-ng/key.d/syslog-ng.key")
                cert-file("/opt/syslog-ng/etc/syslog-ng/cert.d/syslog-ng.cert")
                ca-dir("/opt/syslog-ng/etc/syslog-ng/ca.d")        
            )
        );
    };

Warning

Do not forget to update the certificate and key files when they expire.