syslog-ng Premium Edition 7.0.32 - Administration Guide

The syslog-ng application can send and receive log messages securely over the network using the Transport Layer Security (TLS) protocol using the network() and syslog() drivers.

NOTE: This chapter describes how to use TLS encryption when using the standard syslog protocols, that is, the network() and syslog() drivers, for example, to forward log messages between two syslog-ng nodes, or to send log data to syslog-ng Store Box or another log server. Other destinations that support TLS-encryption are not discussed in this chapter (for example, http()).

TLS uses certificates to authenticate and encrypt the communication, as illustrated on the following figure:

Figure 37: Certificate-based authentication

The client authenticates the server by requesting its certificate and public key. Optionally, the server can also request a certificate from the client, thus mutual authentication is also possible.

In order to use TLS encryption in syslog-ng, the following elements are required:

A certificate on the syslog-ng server that identifies the syslog-ng server.
The certificate of the Certificate Authority that issued the certificate of the syslog-ng server (or the self-signed certificate of the syslog-ng server) must be available on the syslog-ng client.

When using mutual authentication to verify the identity of the clients, the following elements are required:

A certificate must be available on the syslog-ng client. This certificate identifies the syslog-ng client.
The certificate of the Certificate Authority that issued the certificate of the syslog-ng client must be available on the syslog-ng server.

Mutual authentication ensures that the syslog-ng server accepts log messages only from authorized clients.

For more information about configuring TLS communication in syslog-ng, see Encrypting log messages with TLS.

For more information about TLS-related error messages, see Error messages.

Supported OpenSSL versions

The following list contains information about the supported OpenSSL versions in each syslog-ng PE application version.

Linux glibc 2.11

syslog-ng PE version	supported Open SSL version
7.0.1	OpenSSL 1.0.2j
7.0.2	OpenSSL 1.0.2j
7.0.3	OpenSSL 1.0.2j
7.0.4	OpenSSL 1.0.2j
7.0.5	OpenSSL 1.0.2j
7.0.6	OpenSSL 1.0.2m
7.0.7	OpenSSL 1.0.2m
7.0.8	OpenSSL 1.0.2m
7.0.9	OpenSSL 1.0.2o
7.0.10	OpenSSL 1.0.2o
7.0.11	OpenSSL 1.0.2p
7.0.12	OpenSSL 1.0.2q
7.0.13	OpenSSL 1.0.2q
7.0.14	OpenSSL 1.0.2r
7.0.15	OpenSSL 1.0.2s
7.0.16	OpenSSL 1.0.2s
7.0.17	OpenSSL 1.0.2t
7.0.18	OpenSSL 1.0.2t
7.0.19	OpenSSL 1.1.1d
7.0.20	OpenSSL 1.1.1g
7.0.21	OpenSSL 1.1.1g
7.0.22	OpenSSL 1.1.1g
7.0.23	OpenSSL 1.1.1h
7.0.24	OpenSSL 1.1.1j
7.0.25.	OpenSSL 1.1.1k
7.0.26	OpenSSL 1.1.1k
7.0.27	OpenSSL 1.1.1l
7.0.29	OpenSSL 1.1.1m
7.0.30	OpenSSL 1.1.1o
7.0.31	OpenSSL 1.1.1q

Encrypting log messages with TLS

Configuring TLS on the syslog-ng clients

Purpose

Complete the following steps on every syslog-ng 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):

To configure TLS on the syslog-ng clients

Copy the CA certificate to the client host

Copy the CA certificate (for example, cacert.pem) of the Certificate Authority that issued the certificate of the syslog-ng server (or the self-signed certificate of the syslog-ng server) to the syslog-ng client hosts, for example, into the /opt/syslog-ng/etc/syslog-ng/ca.d directory.
Issue commands

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

Add a destination statement to the syslog-ng 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 syslog-ng server.
Example: A destination statement using TLS

The following destination encrypts the log messages using TLS and sends them to the 6514/TCP port of the syslog-ng server having the 10.1.2.3 IP address.
```
destination demo_tls_destination {
    network("10.1.2.3" port(6514)
        transport("tls")
        tls( ca-dir("/opt/syslog-ng/etc/syslog-ng/ca.d"))
    );
};
```
A similar statement using the IETF-syslog protocol and thus the syslog() driver:
```
destination demo_tls_syslog_destination {
    syslog("10.1.2.3" port(6514)
                        transport("tls")
        tls(ca-dir("/opt/syslog-ng/etc/syslog-ng/ca.d"))
    );
};
```

Include the destination in a log statement

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

Caution:

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 contain the hostname or the IP address (as resolved from the syslog-ng clients and relays) of the server.

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

Configuring TLS on the syslog-ng server

Complete the following steps on the syslog-ng server:

To configure TLS on the syslog-ng server

Create an X.509 certificate for the syslog-ng server.

NOTE: The subject_alt_name parameter (or the Common Name parameter if the subject_alt_name parameter is empty) of the server's certificate must contain the hostname or the IP address (as resolved from the syslog-ng clients and relays) of the server (for example, syslog-ng.example.com).

Alternatively, the Common Name or the subject_alt_name parameter can contain a generic hostname, for example, *.example.com.

Note that if the Common Name of the certificate contains a generic hostname, do not specify a specific hostname or an IP address in the subject_alt_name parameter.
Copy the certificate (for example, syslog-ng.cert) of the syslog-ng server to the syslog-ng 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 private key (for example, syslog-ng.key) matching the certificate of the syslog-ng server to the syslog-ng 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 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.
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 syslog-ng 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")
        )
    );
};
```
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")
        )
    );
};
```
Disable mutual authentication for the source by setting the following TLS option in the source statement: tls( peer-verify(optional-untrusted);

If you want to authenticate the clients, you have to configure mutual authentication. For details, see Mutual authentication using TLS.

For the details of the available tls() options, see TLS options.
Example: Disabling mutual authentication

The following source receives log messages encrypted using TLS, arriving to the 1999/TCP port of any interface of the syslog-ng server. The identity of the syslog-ng client is not verified.
```
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")
            peer-verify(optional-untrusted)
        )
    );
};
```
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")
            peer-verify(optional-untrusted)
        )
    );
};
```
Caution:
Do not forget to update the certificate and key files when they expire.

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syslog-ng Premium Edition 7.0.32 - Administration Guide

Secure logging using TLS

Supported OpenSSL versions

Encrypting log messages with TLS

Configuring TLS on the syslog-ng clients

Purpose

Example: A destination statement using TLS

Configuring TLS on the syslog-ng server

Example: A source statement using TLS

Example: Disabling mutual authentication