# 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, our new
[**documentation site**](https://docs.strongswan.org) and the legacy
[**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://docs.strongswan.org/docs/5.9/tpm/tpm2.html).

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.
