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
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Create an X.509 certificate
Create an X.509 certificate for the syslog-ng client.
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Copy the certificate and private key
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.
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Copy the CA certificate to the client host
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.
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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
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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. 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")) ); };
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Include destination in a log statement
Include the destination created in the Step Add a destination statement in a log statement.
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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. |
Complete the following steps on the syslog-ng server:
To configure TLS on the syslog-ng clients
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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.
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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
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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.
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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")) ); };
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Caution:
Do not forget to update the certificate and key files when they expire. |
Starting with syslog-ng PE version 7.0.7, you can use password-protected private keys in the network() and syslog() source and destination drivers.
Restrictions and limitations
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IMPORTANT: Hazard of data loss! If you use password-protected keys, you must provide the passphrase of the password-protected keys every time syslog-ng PE is restarted (syslog-ng PE 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 PE 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 this cases, always use the disk-buffer option to avoid data loss.
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The path and the filename of the private key cannot contain whitespaces.
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Depending on your platform, the number of passwords syslog-ng PE 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 PE as a non-root user). If you use lots of password-protected private keys in your syslog-ng PE 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 PE 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 PE 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 PE configuration will be unaffected. You must provide the passphrase of the password-protected keys every time syslog-ng PE 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 PE 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.
The syslog-ng application can encrypt incoming and outgoing syslog message flows using TLS if you use the network() or syslog() drivers.
NOTE: The format of the TLS connections used by syslog-ng is similar to using syslog-ng and stunnel, but the source IP information is not lost.
To encrypt connections, use the transport("tls") and tls() options in the source and destination statements.
The tls() option can include the following settings:
allow-compress()
| Accepted values: |
yes | no |
| Default: |
no |
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 PE, reducing the number of transferred messages during a given period.
Available in version 7.0.12 and later.
ca-dir()
| Accepted values: |
directory name |
| Default: |
none |
Description: Name of a directory, that contains a set of trusted CA certificates in PEM format. The CA certificate files have to be named after the 32-bit hash of the subject's name. This naming can be created using the c_rehash utility in OpenSSL. For an example, see Configuring TLS on the syslog-ng clients. The syslog-ng PE application uses the CA certificates in this directory to validate the certificate of the peer.
cert-file()
| Accepted values: |
Filename |
| Default: |
none |
Description: Name of a file, that contains an X.509 certificate (or a certificate chain) in PEM format, suitable as a TLS certificate, matching the private key set in the key-file() option. The syslog-ng PE application uses this certificate to authenticate the syslog-ng PE client on the destination server. If the file contains a certificate chain, the file must begin with the certificate of the host, followed by the CA certificate that signed the certificate of the host, and any other signing CAs in order.
cipher-suite()
| Accepted values: |
Name of a cipher, or a colon-separated list |
| Default: |
Depends on the OpenSSL version that syslog-ng PE uses |
Description: Specifies the cipher, hash, and key-exchange algorithms used for the encryption, for example, ECDHE-ECDSA-AES256-SHA384. The list of available algorithms depends on the version of OpenSSL used to compile syslog-ng PE. To specify multiple ciphers, separate the cipher names with a colon, and enclose the list between double-quotes, for example:
cipher-suite("ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384")
crl-dir()
| Accepted values: |
Directory name |
| Default: |
none |
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.
If the crl-dir() is set, and the peer certificate has been revoked, syslog-ng PE rejects the connection. If the peer certificate has not been revoked, or syslog-ng PE cannot access the CRL, syslog-ng PE accepts the connection.
dhparam-file()
| Accepted values: |
string (filename) |
| Default: |
none |
Description: Specifies a file containing Diffie-Hellman parameters, generated using the openssl dhparam utility. Note that syslog-ng PE supports only DH parameter files in the PEM format. If you do not set this parameter, syslog-ng PE uses the 2048-bit MODP Group, as described in RFC 3526.
ecdh-curve-list()
| Accepted values: |
string [colon-separated list] |
| Default: |
none |
Description: A colon-separated list that specifies the curves that are permitted in the connection when using Elliptic Curve Cryptography (ECC).
The syslog-ng PE application automatically uses the highest preference curve that both peers support. If not specified, the list includes every supported curve.
Example:
ecdh-curve-list("prime256v1:secp384r1")
The syslog-ng Premium Edition application currently supports the following curves: sect163k1, sect163r1, sect163r2, sect193r1, sect193r2,, sect233k1, sect233r1, sect239k1, sect283k1, sect283r1,, sect409k1, sect409r1, sect571k1, sect571r1, secp160k1,, secp160r1, secp160r2, secp192k1, prime192v1, secp224k1,, secp224r1, secp256k1, prime256v1, secp384r1, secp521r1,, brainpoolP256r1, brainpoolP384r1, brainpoolP512r1.
key-file()
| Accepted values: |
Filename |
| Default: |
none |
Description: Path and name of a file that contains a private key in PEM format, suitable as a TLS key. If properly configured, the syslog-ng PE application uses this private key and the matching certificate (set in the cert-file() option) to authenticate the syslog-ng PE client on the destination server.
Starting with syslog-ng PE version 7.0.7, you can use password-protected private keys in the network() and syslog() source and destination drivers. The path and the filename cannot contain whitespaces. For details, see Password-protected keys.
peer-verify()
| Accepted values: |
optional-trusted | optional-untrusted | required-trusted | required-untrusted |
| Default: |
required-trusted |
Description: Verification method of the peer, the four possible values is a combination of two properties of validation:
The following table summarizes the possible options and their results depending on the certificate of the peer.
| Local peer-verify() setting |
optional-untrusted |
TLS-encryption |
TLS-encryption |
TLS-encryption |
| optional-trusted |
TLS-encryption |
rejected connection |
TLS-encryption |
| required-untrusted |
rejected connection |
TLS-encryption |
TLS-encryption |
| required-trusted |
rejected connection |
rejected connection |
TLS-encryption |
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.
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Caution:
When validating a certificate, the entire certificate chain must be valid, including the CA certificate. If any certificate of the chain is invalid, syslog-ng PE will reject the connection. |
ssl-options()
| Accepted values: |
comma-separated list of the following options: no-sslv2, no-sslv3, no-tlsv1, no-tlsv11, no-tlsv12, none |
| Default: |
no-sslv2 |
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 PE 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 PE7.0 and newer.
Example: Using ssl-options
The following destination explicitly disables SSL and TLSv1.0
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()
| Accepted values: |
list of accepted distinguished names |
| Default: |
none |
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()
| Accepted values: |
list of accepted SHA-1 fingerprints |
| Default: |
none |
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
NOTE: When using the trusted-keys() and trusted-dn() parameters, note the following:
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First, the trusted-keys() parameter is checked. If the fingerprint of the peer is listed, the certificate validation is performed.
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If the fingerprint of the peer is not listed in the trusted-keys() parameter, the trusted-dn() parameter is checked. If the DN of the peer is not listed in the trusted-dn() parameter, the authentication of the peer fails and the connection is closed.
