syslog-ng Open Source Edition 3.22 - Administration Guide

Steps:

1. Create an X.509 certificate for the syslog-ng client.

2. Copy the certificate (for example client_cert.pem) and the matching private key (for example client.key) to the syslog-ng 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.

3. Copy the CA certificate of the Certificate Authority (for example cacert.pem) 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 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

4. 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. 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 syslog-ng 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")
           )
       ); 
   };

5. Include the destination created in Step 2 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 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.

Steps:

1. 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.

2. Copy the CA certificate (for example cacert.pem) of the Certificate Authority that issued the certificate of the syslog-ng clients to the syslog-ng 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

3. 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.

4. 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. 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 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")
               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")        
           )
       );
   };

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

Restrictions and limitations:

• Hazard of data loss! If you use password-protected keys, you must provide the passphrase of the password-protected keys every time syslog-ng OSE is restarted (syslog-ng OSE keeps the passphrases over reloads). The sources and destinations that use these keys will not work until you provide the passwords. Other parts of the syslog-ng OSE configuration will be unaffected.

  This means that if you use a password-protected key in a destination, and you use this destination in a log path that has multiple destinations, neither destinations will receive log messages until you provide the password. In such cases, always use disk-based buffering to avoid data loss.

• The path and the filename of the private key cannot contain whitespaces.

• Depending on your platform, the number of passwords syslog-ng OSE can use at the same time might be limited (for example, on Ubuntu 16.04 you can store 16 passwords if you are running syslog-ng OSE as a non-root user). If you use lots of password-protected private keys in your syslog-ng OSE configuration, increase this limit using the following command: sudo ulimit -l unlimited

Providing the passwords

The syslog-ng-ctl credentials status command allows you to query the status of the private keys that syslog-ng OSE uses in the network() and syslog() drivers. The command returns the list of private keys used, and their status. For example:

syslog-ng-ctl credentials status
Secret store status:
/home/user/ssl_test/client-1/client-encrypted.key SUCCESS

If the status of a key is PENDING, you must provide the passphrase for the key, otherwise syslog-ng OSE cannot use it. The sources and destinations that use these keys will not work until you provide the passwords. Other parts of the syslog-ng OSE configuration will be unaffected. You must provide the passphrase of the password-protected keys every time syslog-ng OSE is restarted.

The following log message also notifies you of PENDING passphrases:

Waiting for password; keyfile='private.key'

You can add the passphrase to a password-protected private key file using the following command. syslog-ng OSE will display a prompt for you to enter the passphrase. We recommend that you use this method.

syslog-ng-ctl credentials add --id=<path-to-the-key>

Alternatively, you can include the passphrase in the --secret parameter:

syslog-ng-ctl credentials add --id=<path-to-the-key> --secret=<passphrase-of-the-key>

Or you can pipe the passphrase to the syslog-ng-ctl command, for example:

echo "<passphrase-of-the-key>" | syslog-ng-ctl credentials add --id=<path-to-the-key>

For details on the syslog-ng-ctl credentials command, see The syslog-ng control tool manual page.

allow-compress()

Description: Enable on-the-wire compression in TLS communication. Note that this option must be enabled both on the server and the client to have any effect. Enabling compression can significantly reduce the bandwidth required to transport the messages, but can slightly decrease the performance of syslog-ng OSE, reducing the number of transferred messages during a given period.

Available in version 3.19 and later.

crl-dir()

Description: Name of a directory that contains the Certificate Revocation Lists for trusted CAs. Similarly to ca-dir() files, use the 32-bit hash of the name of the issuing CAs as filenames. The extension of the files must be .r0.

ecdh-curve-list()

Description: A colon-separated list that specifies the curves that are permitted in the connection when using Elliptic Curve Cryptography (ECC).

This option is only available when syslog-ng is compiled with OpenSSL version 1.0.2 or later. In the case of older versions, prime256v1 (NIST P-256) is used.

The following example curves work for all versions of OpenSSL that are equal to or later than version 1.0.2:

ecdh-curve-list("prime256v1:secp384r1")

peer-verify()

Description: Verification method of the peer, the four possible values is a combination of two properties of validation:

• whether the peer is required to provide a certificate (required or optional prefix), and

• whether the certificate provided needs to be valid or not.

The following table summarizes the possible options and their results depending on the certificate of the peer.

For untrusted certificates only the existence of the certificate is checked, but it does not have to be valid — syslog-ng accepts the certificate even if it is expired, signed by an unknown CA, or its CN and the name of the machine mismatches.

Starting with syslog-ng OSE version 3.10, you can also use a simplified configuration method for the peer-verify option, simply setting it to yes or no. The following table summarizes the possible options and their results depending on the certificate of the peer.

pkcs12-file()

Description: The name of a PKCS #12 file that contains an unencrypted private key, an X.509 certificate, and an optional set of trusted CA certificates.

If this option is used in the configuration, the value of key-file() and cert-file() will be omitted.

You can use the ca-dir() option together with pkcs12-file(). However, this is optional because the PKCS #12 file may contain CA certificates as well.

Passphrase is currently not supported.

$ openssl pkcs12 -export -inkey server.key -in server.crt -certfile ca.crt -out server.p12

source s_tls {
    syslog(
        transport(tls)
        tls(
            pkcs12-file("/path/to/server.p12")
            ca-dir("/path/to/cadir") # optional
            peer-verify(yes)
        )
    );
};

ssl-options()

Description: Sets the specified options of the SSL/TLS protocols. Currently, you can use it to disable specific protocol versions. Note that disabling a newer protocol version (for example, TLSv1.1) does not automatically disable older versions of the same protocol (for example, TLSv1.0). For example, use the following option to permit using only TLSv1.1 or newer:

ssl-options(no-sslv2, no-sslv3, no-tlsv1)

Using ssl-options(none) means that syslog-ng OSE does not specify any restrictions on the protocol used. However, in this case, the underlying OpenSSL library can restrict the available protocols, for example, certain OpenSSL versions automatically disable SSLv2.

This option is available in syslog-ng OSE 3.7 and newer.

destination demo_tls_destination {
    network(
         "172.16.177.147" port(6514)
        transport("tls")
        tls(
            ca-dir("/etc/syslog-ng/ca.d")
            key-file("/etc/syslog-ng/cert.d/clientkey.pem")
            cert-file("/etc/syslog-ng/cert.d/clientcert.pem")
            ssl-options(no-sslv2, no-sslv3, no-tlsv1)
        )
    );
};

trusted-dn()

Description: To accept connections only from hosts using certain certificates signed by the trusted CAs, list the distinguished names of the accepted certificates in this parameter. For example using trusted-dn("*, O=Example Inc, ST=Some-State, C=*") will accept only certificates issued for the Example Inc organization in Some-State state.

trusted-keys()

Description: To accept connections only from hosts using certain certificates having specific SHA-1 fingerprints, list the fingerprints of the accepted certificates in this parameter. For example trusted-keys("SHA1:00:EF:ED:A4:CE:00:D1:14:A4:AB:43:00:EF:00:91:85:FF:89:28:8F", "SHA1:0C:42:00:3E:B2:60:36:64:00:E2:83:F0:80:46:AD:00:A8:9D:00:15").

To find the fingerprint of a certificate, you can use the following command: openssl x509 -in <certificate-filename> -sha1 -noout -fingerprint