# strongSwan Configuration # ## Overview ## strongSwan is an OpenSource IPsec-based VPN solution. This document is just a short introduction of the strongSwan **swanctl** command which uses the modern [**vici**](src/libcharon/plugins/vici/README.md) *Versatile IKE Configuration Interface*. The deprecated **ipsec** command using the legacy **stroke** configuration interface is described [**here**](README_LEGACY.md). For more detailed information consult the man pages and [**our wiki**](https://wiki.strongswan.org). ## Quickstart ## Certificates for users, hosts and gateways are issued by a fictitious strongSwan CA. In our example scenarios the CA certificate `strongswanCert.pem` must be present on all VPN endpoints in order to be able to authenticate the peers. For your particular VPN application you can either use certificates from any third-party CA or generate the needed private keys and certificates yourself with the strongSwan **pki** tool, the use of which will be explained in one of the sections following below. ### Site-to-Site Case ### In this scenario two security gateways _moon_ and _sun_ will connect the two subnets _moon-net_ and _sun-net_ with each other through a VPN tunnel set up between the two gateways: 10.1.0.0/16 -- | 192.168.0.1 | === | 192.168.0.2 | -- 10.2.0.0/16 moon-net moon sun sun-net Configuration on gateway _moon_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/moonCert.pem /etc/swanctl/private/moonKey.pem /etc/swanctl/swanctl.conf: connections { net-net { remote_addrs = 192.168.0.2 local { auth = pubkey certs = moonCert.pem } remote { auth = pubkey id = "C=CH, O=strongSwan, CN=sun.strongswan.org" } children { net-net { local_ts = 10.1.0.0/16 remote_ts = 10.2.0.0/16 start_action = trap } } } } Configuration on gateway _sun_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/sunCert.pem /etc/swanctl/private/sunKey.pem /etc/swanctl/swanctl.conf: connections { net-net { remote_addrs = 192.168.0.1 local { auth = pubkey certs = sunCert.pem } remote { auth = pubkey id = "C=CH, O=strongSwan, CN=moon.strongswan.org" } children { net-net { local_ts = 10.2.0.0/16 remote_ts = 10.1.0.0/16 start_action = trap } } } } The local and remote identities used in this scenario are the *subjectDistinguishedNames* contained in the end entity certificates. The certificates and private keys are loaded into the **charon** daemon with the command swanctl --load-creds whereas swanctl --load-conns loads the connections defined in `swanctl.conf`. With `start_action = trap` the IPsec connection is automatically set up with the first plaintext payload IP packet wanting to go through the tunnel. ### Host-to-Host Case ### This is a setup between two single hosts which don't have a subnet behind them. Although IPsec transport mode would be sufficient for host-to-host connections we will use the default IPsec tunnel mode. | 192.168.0.1 | === | 192.168.0.2 | moon sun Configuration on host _moon_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/moonCert.pem /etc/swanctl/private/moonKey.pem /etc/swanctl/swanctl.conf: connections { host-host { remote_addrs = 192.168.0.2 local { auth=pubkey certs = moonCert.pem } remote { auth = pubkey id = "C=CH, O=strongSwan, CN=sun.strongswan.org" } children { net-net { start_action = trap } } } } Configuration on host _sun_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/sunCert.pem /etc/swanctl/private/sunKey.pem /etc/swanctl/swanctl.conf: connections { host-host { remote_addrs = 192.168.0.1 local { auth = pubkey certs = sunCert.pem } remote { auth = pubkey id = "C=CH, O=strongSwan, CN=moon.strongswan.org" } children { host-host { start_action = trap } } } } ### Roadwarrior Case ### This is a very common case where a strongSwan gateway serves an arbitrary number of remote VPN clients usually having dynamic IP addresses. 10.1.0.0/16 -- | 192.168.0.1 | === | x.x.x.x | moon-net moon carol Configuration on gateway _moon_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/moonCert.pem /etc/swanctl/private/moonKey.pem /etc/swanctl/swanctl.conf: connections { rw { local { auth = pubkey certs = moonCert.pem id = moon.strongswan.org } remote { auth = pubkey } children { net-net { local_ts = 10.1.0.0/16 } } } } Configuration on roadwarrior _carol_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/carolCert.pem /etc/swanctl/private/carolKey.pem /etc/swanctl/swanctl.conf: connections { home { remote_addrs = moon.strongswan.org local { auth = pubkey certs = carolCert.pem id = carol@strongswan.org } remote { auth = pubkey id = moon.strongswan.org } children { home { local_ts = 10.1.0.0/16 start_action = start } } } } For `remote_addrs` the hostname `moon.strongswan.org` was chosen which will be resolved by DNS at runtime into the corresponding IP destination address. In this scenario the identity of the roadwarrior `carol` is the email address `carol@strongswan.org` which must be included as a *subjectAlternativeName* in the roadwarrior certificate `carolCert.pem`. ### Roadwarrior Case with Virtual IP ### Roadwarriors usually have dynamic IP addresses assigned by the ISP they are currently attached to. In order to simplify the routing from _moon-net_ back to the remote access client _carol_ it would be desirable if the roadwarrior had an inner IP address chosen from a pre-defined pool. 10.1.0.0/16 -- | 192.168.0.1 | === | x.x.x.x | -- 10.3.0.1 moon-net moon carol virtual IP In our example the virtual IP address is chosen from the address pool `10.3.0.0/16` which can be configured by adding the section pools { rw_pool { addrs = 10.3.0.0/16 } } to the gateway's `swanctl.conf` from where they are loaded into the **charon** daemon using the command swanctl --load-pools To request an IP address from this pool a roadwarrior can use IKEv1 mode config or IKEv2 configuration payloads. The configuration for both is the same vips = 0.0.0.0 Configuration on gateway _moon_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/moonCert.pem /etc/swanctl/private/moonKey.pem /etc/swanctl/swanctl.conf: connections { rw { pools = rw_pool local { auth = pubkey certs = moonCert.pem id = moon.strongswan.org } remote { auth = pubkey } children { net-net { local_ts = 10.1.0.0/16 } } } } pools { rw_pool { addrs = 10.30.0.0/16 } } Configuration on roadwarrior _carol_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/carolCert.pem /etc/swanctl/private/carolKey.pem /etc/swanctl/swanctl.conf: connections { home { remote_addrs = moon.strongswan.org vips = 0.0.0.0 local { auth = pubkey certs = carolCert.pem id = carol@strongswan.org } remote { auth = pubkey id = moon.strongswan.org } children { home { local_ts = 10.1.0.0/16 start_action = start } } } } ### Roadwarrior Case with EAP Authentication ### This is a very common case where a strongSwan gateway serves an arbitrary number of remote VPN clients which authenticate themselves via a password based *Extended Authentication Protocol* as e.g. *EAP-MD5* or *EAP-MSCHAPv2*. 10.1.0.0/16 -- | 192.168.0.1 | === | x.x.x.x | moon-net moon carol Configuration on gateway _moon_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/moonCert.pem /etc/swanctl/private/moonKey.pem /etc/swanctl/swanctl.conf: connections { rw { local { auth = pubkey certs = moonCert.pem id = moon.strongswan.org } remote { auth = eap-md5 } children { net-net { local_ts = 10.1.0.0/16 } } send_certreq = no } } The `swanctl.conf` file additionally contains a `secrets` section defining all client credentials secrets { eap-carol { id = carol@strongswan.org secret = Ar3etTnp } eap-dave { id = dave@strongswan.org secret = W7R0g3do } } Configuration on roadwarrior _carol_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/swanctl.conf: connections { home { remote_addrs = moon.strongswan.org local { auth = eap id = carol@strongswan.org } remote { auth = pubkey id = moon.strongswan.org } children { home { local_ts = 10.1.0.0/16 start_action = start } } } } secrets { eap-carol { id = carol@strongswan.org secret = Ar3etTnp } } ### Roadwarrior Case with EAP Identity ### Often a client EAP identity is exchanged via EAP which differs from the external IKEv2 identity. In this example the IKEv2 identity defaults to the IPv4 address of the client. 10.1.0.0/16 -- | 192.168.0.1 | === | x.x.x.x | moon-net moon carol Configuration on gateway _moon_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/x509/moonCert.pem /etc/swanctl/private/moonKey.pem /etc/swanctl/swanctl.conf: connections { rw { local { auth = pubkey certs = moonCert.pem id = moon.strongswan.org } remote { auth = eap-md5 eap_id = %any } children { net-net { local_ts = 10.1.0.0/16 } } send_certreq = no } } secrets { eap-carol { id = carol secret = Ar3etTnp } eap-dave { id = dave secret = W7R0g3do } } Configuration on roadwarrior _carol_: /etc/swanctl/x509ca/strongswanCert.pem /etc/swanctl/swanctl.conf: connections { home { remote_addrs = moon.strongswan.org local { auth = eap eap_id = carol } remote { auth = pubkey id = moon.strongswan.org } children { home { local_ts = 10.1.0.0/16 start_action = start } } } } secrets { eap-carol { id = carol secret = Ar3etTnp } } ## Generating Certificates and CRLs ## This section is not a full-blown tutorial on how to use the strongSwan **pki** tool. It just lists a few points that are relevant if you want to generate your own certificates and CRLs for use with strongSwan. ### Generating a CA Certificate ### The pki statement pki --gen --type ed25519 --outform pem > strongswanKey.pem generates an elliptic Edwards-Curve key with a cryptographic strength of 128 bits. The corresponding public key is packed into a self-signed CA certificate with a lifetime of 10 years (3652 days) pki --self --ca --lifetime 3652 --in strongswanKey.pem \ --dn "C=CH, O=strongSwan, CN=strongSwan Root CA" \ --outform pem > strongswanCert.pem which can be listed with the command pki --print --in strongswanCert.pem subject: "C=CH, O=strongSwan, CN=strongSwan Root CA" issuer: "C=CH, O=strongSwan, CN=strongSwan Root CA" validity: not before May 18 08:32:06 2017, ok not after May 18 08:32:06 2027, ok (expires in 3651 days) serial: 57:e0:6b:3a:9a:eb:c6:e0 flags: CA CRLSign self-signed subjkeyId: 2b:95:14:5b:c3:22:87:de:d1:42:91:88:63:b3:d5:c1:92:7a:0f:5d pubkey: ED25519 256 bits keyid: a7:e1:6a:3f:e7:6f:08:9d:89:ec:23:92:a9:a1:14:3c:78:a8:7a:f7 subjkey: 2b:95:14:5b:c3:22:87:de:d1:42:91:88:63:b3:d5:c1:92:7a:0f:5d If you prefer the CA private key and X.509 certificate to be in binary DER format then just omit the `--outform pem` option. The directory `/etc/swanctl/x509ca` contains all required CA certificates either in binary DER or in Base64 PEM format. Irrespective of the file suffix the correct format will be determined by strongSwan automagically. ### Generating a Host or User End Entity Certificate ### Again we are using the command pki --gen --type ed25519 --outform pem > moonKey.pem to generate an Ed25519 private key for the host `moon`. Alternatively you could type pki --gen --type rsa --size 3072 > moonKey.der to generate a traditional 3072 bit RSA key and store it in binary DER format. As an alternative a **TPM 2.0** *Trusted Platform Module* available on every recent Intel platform could be used as a virtual smartcard to securely store an RSA or ECDSA private key. For details, refer to the TPM 2.0 [HOWTO](https://wiki.strongswan.org/projects/strongswan/wiki/TpmPlugin). In a next step the command pki --req --type priv --in moonKey.pem \ --dn "C=CH, O=strongswan, CN=moon.strongswan.org" \ --san moon.strongswan.org --outform pem > moonReq.pem creates a PKCS#10 certificate request that has to be signed by the CA. Through the [multiple] use of the `--san` parameter any number of desired *subjectAlternativeNames* can be added to the request. These can be of the form --san sun.strongswan.org # fully qualified host name --san carol@strongswan.org # RFC822 user email address --san 192.168.0.1 # IPv4 address --san fec0::1 # IPv6 address Based on the certificate request the CA issues a signed end entity certificate with the following command pki --issue --cacert strongswanCert.pem --cakey strongswanKey.pem \ --type pkcs10 --in moonReq.pem --serial 01 --lifetime 1826 \ --outform pem > moonCert.pem If the `--serial` parameter with a hexadecimal argument is omitted then a random serial number is generated. Some third party VPN clients require that a VPN gateway certificate contains the *TLS Server Authentication* Extended Key Usage (EKU) flag which can be included with the following option --flag serverAuth If you want to use the dynamic CRL fetching feature described in one of the following sections then you may include one or several *crlDistributionPoints* in your end entity certificates using the `--crl` parameter --crl http://crl.strongswan.org/strongswan.crl --crl "ldap://ldap.strongswan.org/cn=strongSwan Root CA, o=strongSwan,c=CH?certificateRevocationList" The issued host certificate can be listed with pki --print --in moonCert.pem subject: "C=CH, O=strongSwan, CN=moon.strongswan.org" issuer: "C=CH, O=strongSwan, CN=strongSwan Root CA" validity: not before May 19 10:28:19 2017, ok not after May 19 10:28:19 2022, ok (expires in 1825 days) serial: 01 altNames: moon.strongswan.org flags: serverAuth CRL URIs: http://crl.strongswan.org/strongswan.crl authkeyId: 2b:95:14:5b:c3:22:87:de:d1:42:91:88:63:b3:d5:c1:92:7a:0f:5d subjkeyId: 60:9d:de:30:a6:ca:b9:8e:87:bb:33:23:61:19:18:b8:c4:7e:23:8f pubkey: ED25519 256 bits keyid: 39:1b:b3:c2:34:72:1a:01:08:40:ce:97:75:b8:be:ce:24:30:26:29 subjkey: 60:9d:de:30:a6:ca:b9:8e:87:bb:33:23:61:19:18:b8:c4:7e:23:8f Usually, a Windows, OSX, Android or iOS based VPN client needs its private key, its host or user certificate and the CA certificate. The most convenient way to load this information is to put everything into a PKCS#12 container: openssl pkcs12 -export -inkey carolKey.pem \ -in carolCert.pem -name "carol" \ -certfile strongswanCert.pem -caname "strongSwan Root CA" \ -out carolCert.p12 The strongSwan **pki** tool currently is not able to create PKCS#12 containers so that **openssl** must be used. ### Generating a CRL ### An empty CRL that is signed by the CA can be generated with the command pki --signcrl --cacert strongswanCert.pem --cakey strongswanKey.pem \ --lifetime 30 > strongswan.crl If you omit the `--lifetime` option then the default value of 15 days is used. CRLs can either be uploaded to a HTTP or LDAP server or put in binary DER or Base64 PEM format into the `/etc/swanctl/x509crl` directory from where they are loaded into the **charon** daemon with the command swanctl --load-creds ### Revoking a Certificate ### A specific end entity certificate is revoked with the command pki --signcrl --cacert strongswanCert.pem --cakey strongswanKey.pem \ --lifetime 30 --lastcrl strongswan.crl \ --reason key-compromise --cert moonCert.pem > new.crl Instead of the certificate file (in our example moonCert.pem), the serial number of the certificate to be revoked can be indicated using the `--serial` parameter. The `pki --signcrl --help` command documents all possible revocation reasons but the `--reason` parameter can also be omitted. The content of the new CRL file can be listed with the command pki --print --type crl --in new.crl issuer: "C=CH, O=strongSwan, CN=strongSwan Root CA" update: this on May 19 11:13:01 2017, ok next on Jun 18 11:13:01 2017, ok (expires in 29 days) serial: 02 authKeyId: 2b:95:14:5b:c3:22:87:de:d1:42:91:88:63:b3:d5:c1:92:7a:0f:5d 1 revoked certificate: 01: May 19 11:13:01 2017, key compromise ### Local Caching of CRLs ### The `strongswan.conf` option charon { cache_crls = yes } activates the local caching of CRLs that were dynamically fetched from an HTTP or LDAP server. Cached copies are stored in `/etc/swanctl/x509crl` using a unique filename formed from the issuer's *subjectKeyIdentifier* and the suffix `.crl`. With the cached copy the CRL is immediately available after startup. When the local copy has become stale, an updated CRL is automatically fetched from one of the defined CRL distribution points during the next IKEv2 authentication.