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
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
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:
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Whether the peer is required to provide a certificate (required or optional prefix).
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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 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 PE
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.
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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.