The file ipsec.secrets holds a table of secrets. These secrets are used by the strongSwan Internet Key Exchange (IKE) daemons pluto (IKEv1) and charon (IKEv2) to authenticate other hosts.
It is vital that these secrets be protected. The file should be owned by the super-user, and its permissions should be set to block all access by others.
The file is a sequence of entries and include directives. Here is an example.
# /etc/ipsec.secrets - strongSwan IPsec secrets file 192.168.0.1 %any : PSK "v+NkxY9LLZvwj4qCC2o/gGrWDF2d21jL" : RSA moonKey.pem email@example.com : EAP "x3.dEhgN" carol : XAUTH "4iChxLT3" dave : XAUTH "ryftzG4A" # get secrets from other files include ipsec.*.secrets
Each entry in the file is a list of optional ID selectors, followed by a secret. The two parts are separated by a colon (:) that is surrounded by whitespace. If no ID selectors are specified the line must start with a colon.
A selector is an IP address, a Fully Qualified Domain Name, user@FQDN, %any or %any6 (other kinds may come).
Matching IDs with selectors is fairly straightforward: they have to be equal. In the case of a “Road Warrior” connection, if an equal match is not found for the Peer's ID, and it is in the form of an IP address, a selector of %any will match the peer's IP address if IPV4 and %any6 will match a the peer's IP address if IPV6. Currently, the obsolete notation 0.0.0.0 may be used in place of %any.
In IKEv1 an additional complexity arises in the case of authentication by preshared secret: the responder will need to look up the secret before the Peer's ID payload has been decoded, so the ID used will be the IP address.
To authenticate a connection between two hosts, the entry that most specifically matches the host and peer IDs is used. An entry with no selectors will match any host and peer. More specifically, an entry with one selector will match a host and peer if the selector matches the host's ID (the peer isn't considered). Still more specifically, an entry with multiple selectors will match a host and peer if the host ID and peer ID each match one of the selectors. If the key is for an asymmetric authentication technique (i.e. a public key system such as RSA), an entry with multiple selectors will match a host and peer even if only the host ID matches a selector (it is presumed that the selectors are all identities of the host). It is acceptable for two entries to be the best match as long as they agree about the secret or private key.
Authentication by preshared secret requires that both systems find the identical secret (the secret is not actually transmitted by the IKE protocol). If both the host and peer appear in the selector list, the same entry will be suitable for both systems so verbatim copying between systems can be used. This naturally extends to larger groups sharing the same secret. Thus multiple-selector entries are best for PSK authentication.
Authentication by public key systems such as RSA requires that each host have its own private key. A host could reasonably use a different private keys for different interfaces and for different peers. But it would not be normal to share entries between systems. Thus thus no-selector and one-selector forms of entry often make sense for public key authentication.
The key part of an entry must start with a token indicating the kind of key. The following types of secrets are currently supported:
defines a pre-shared key
defines an RSA private key
defines an ECDSA private key
defines a PKCS#12 container
defines EAP credentials
defines NTLM credentials
defines XAUTH credentials
defines a smartcard PIN
Details on each type of secret are given below.
Whitespace at the end of a line is ignored. At the start of a line or after whitespace, # and the following text up to the end of the line is treated as a comment.
An include directive causes the contents of the named file to be processed before continuing with the current file. The filename is subject to “globbing” as in sh(1), so every file with a matching name is processed. Includes may be nested to a modest depth (10, currently). If the filename doesn't start with a /, the directory containing the current file is prepended to the name. The include directive is a line that starts with the word include, followed by whitespace, followed by the filename (which must not contain whitespace).
Types of Secrets
- [ <selectors> ] : PSK <secret>
A preshared secret is most conveniently represented as a sequence of characters, which is delimited by double-quote characters ("). The sequence cannot contain newline or double-quote characters.
Alternatively, preshared secrets can be represented as hexadecimal or Base64 encoded binary values. A character sequence beginning with 0x is interpreted as sequence of hexadecimal digits. Similarly, a character sequence beginning with 0s is interpreted as Base64 encoded binary data.
- : RSA <private key file> [ <passphrase> | %prompt ]
- : ECDSA <private key file> [ <passphrase> | %prompt ]
For the private key file both absolute paths or paths relative to /etc/ipsec.d/private are accepted. If the private key file is encrypted, the passphrase must be defined. Instead of a passphrase %prompt can be used which then causes the daemon to ask the user for the password whenever it is required to decrypt the key.
- : P12 <PKCS#12 file> [ <passphrase> | %prompt ]
For the PKCS#12 file both absolute paths or paths relative to /etc/ipsec.d/private are accepted. If the container is encrypted, the passphrase must be defined. Instead of a passphrase %prompt can be used which then causes the daemon to ask the user for the password whenever it is required to decrypt the container. Private keys, client and CA certificates are extracted from the container. To use such a client certificate in a connection set leftid to one of the subjects of the certificate.
- <user id> : EAP <secret>
The format of secret is the same as that of PSK secrets.
EAP secrets are IKEv2 only.
- <user id> : NTLM <secret>
The format of secret is the same as that of PSK secrets, but the secret is stored as NTLM hash, which is MD4(UTF-16LE(secret)), instead of as cleartext.
NTLM secrets can only be used with the eap-mschapv2 plugin.
- [ <servername> ] <username> : XAUTH <password>
The format of password is the same as that of PSK secrets. XAUTH secrets are IKEv1 only.
- : PIN %smartcard[<slot nr>[@<module>]]:<keyid> <pin code> | %prompt
The smartcard selector always requires a keyid to uniquely select the correct key. The slot number defines the slot on the token, the module name refers to the module name defined in strongswan.conf(5). Instead of specifying the pin code statically, %prompt can be specified, which causes the daemon to ask the user for the pin code.
ipsec.conf(5), strongswan.conf(5), ipsec(8)
Originally written for the FreeS/WAN project by D. Hugh Redelmeier. Updated and extended for the strongSwan project <http://www.strongswan.org> by Tobias Brunner and Andreas Steffen.
If an ID is 0.0.0.0, it will match %any; if it is 0::0, it will match %any6.