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 OSE, reducing the number of transferred messages during a given period.
Available in version
ca-dir()
| Accepted values: | Directory name |
| Default: | none |
Description: The 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 OSE application uses the CA certificates in this directory to validate the certificate of the peer.
This option can be used together with the optional ca-file() option.
ca-file()
| Accepted values: | File name |
| Default: | empty |
Description: Optional. The name of a file that contains a set of trusted CA certificates in PEM format. The syslog-ng OSE application uses the CA certificates in this file to validate the certificate of the peer.
Example format in configuration:
ca-file("/etc/pki/tls/certs/ca-bundle.crt")
NOTE: The ca-file() option can be used together with the ca-dir() option, and it is relevant when peer-verify() is set to other than no or optional-untrusted.
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 OSE application uses this certificate to authenticate the syslog-ng OSE 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 OSE 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 OSE. 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")
For a list of available algorithms, execute the openssl ciphers -v command. The first column of the output contains the name of the algorithms to use in the cipher-suite() option, the second column specifies which encryption protocol uses the algorithm (for example, TLSv1.2). That way, the cipher-suite() also determines the encryption protocol used in the connection: to disable SSLv3, use an algorithm that is available only in TLSv1.2, and that both the client and the server supports. You can also specify the encryption protocols using ssl-options().
You can also use the following command to automatically list only ciphers permitted in a specific encryption protocol, for example, TLSv1.2:
echo "cipher-suite(\"$(openssl ciphers -v | grep TLSv1.2 | awk '{print $1}' | xargs echo -n | sed 's/ /:/g' | sed -e 's/:$//')\")"
Note that starting with version
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.
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 OSE supports only DH parameter files in the PEM format. If you do not set this parameter, syslog-ng OSE 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).
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")key-file()
| Accepted values: | Filename |
| Default: | none |
Description: The name of a file that contains an unencrypted private key in PEM format, suitable as a TLS key. If properly configured, the syslog-ng OSE application uses this private key and the matching certificate (set in the cert-file() option) to authenticate the syslog-ng OSE client on the destination server.
peer-verify()
| Accepted values: | optional-trusted | optional-untrusted | required-trusted | required-untrusted | yes | no |
| Default: | required-trusted |
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).
-
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.
| The remote peer has: | ||||
|---|---|---|---|---|
| no certificate | invalid certificate | valid certificate | ||
| 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.
|
|
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 OSE will reject the connection. |
Starting with syslog-ng OSE version
| The remote peer has: | ||||
|---|---|---|---|---|
| no certificate | invalid certificate | valid certificate | ||
| Local peer-verify() setting | no (optional-untrusted) | TLS-encryption | TLS-encryption | TLS-encryption |
| yes (required-trusted) | rejected connection | rejected connection | TLS-encryption | |
pkcs12-file()
| Accepted values: | Filename |
| Default: | none |
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.
Example: Using pkcs12-file()
In the following example, the first command creates a single PKCS #12 file from the private key, X.509 certificate, and CA certificate files. Then, the second half of the example uses the same PKCS #12 file in the syslog-ng configuration.
Example:
$ openssl pkcs12 -export -inkey server.key -in server.crt -certfile ca.crt -out server.p12
Example configuration:
source s_tls {
syslog(
transport(tls)
tls(
pkcs12-file("/path/to/server.p12")
ca-dir("/path/to/cadir") # optional
peer-verify(yes)
)
);
};sni()
| Accepted values: | yes | no |
| Default: | no |
Description: When set to yes in a destination that uses TLS encryption, this option enables Server Name Indication (also called Server Name Identification, SNI). The syslog-ng OSE sends the hostname or the IP address set in the destination to the server during the TLS handshake.
Available in syslog-ng OSE
Example: Using Server Name Indication
The following destination sends the hostname of its destination during the TLS handshake.
destination demo_tls_destination_with_sni {
network(
"logserver.example.com" 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")
sni(yes)
)
);
};ssl-options()
| Accepted values: | comma-separated list of the following options: no-sslv2, no-sslv3, no-tlsv1, no-tlsv11, no-tlsv12, no-tlsv13, 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 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
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:
-
First, the trusted-keys() parameter is checked. If the fingerprint of the peer is listed, the certificate validation is performed.
-
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.