strongSwan

{{title(Setting-up a Simple CA Using the strongSwan PKI Tool)}}

h1. Setting-up a Simple CA Using the strongSwan PKI Tool

{{>toc}}

This how-to sets up a Certificate Authority using strongSwan's [[IpsecPKI|PKI tool]] (available since [[4.3.5]]), keeping it as simple as possible.

h2. CA Certificate

First, [[IpsecPKIGen|generate]] a private key, the default generates a 2048 bit RSA key (if this command blocks, refer to [[IpsecPKIGen#Problems-on-Hosts-with-Low-Entropy|this note about hosts with low entropy]]):

<pre>

ipsec pki --gen > caKey.der

</pre>

For a real-world setup, make sure to keep this key absolutely private.

Now [[IpsecPKISelf|self-sign]] a CA certificate using the generated key:

<pre>

ipsec pki --self --in caKey.der --dn "C=CH, O=strongSwan, CN=strongSwan CA" --ca > caCert.der

</pre>

Adjust the _distinguished name (DN)_ to your needs, it will be included in all issued certificates.

That's it, your CA is ready to issue end-entity certificates.

h2. End Entity Certificates

For *each* peer, i.e. for all VPN clients and VPN gateways in your network, generate an individual private key and [[IpsecPKIIssue|issue]] a matching certificate using your new CA:

<pre>

ipsec pki --gen > peerKey.der

ipsec pki --pub --in peerKey.der | ipsec pki --issue --cacert caCert.der --cakey caKey.der \

                                             --dn "C=CH, O=strongSwan, CN=peer" > peerCert.der

</pre>

The second command [[IpsecPKIPub|extracts the public key]] and [[IpsecPKIIssue|issues a certificate]] using your CA.

If you want to add _subjectAltName_ extensions to your certificates use the _--san_ option (can be provided multiple times), for instance, @--san vpn.strongswan.org@ or @--san peer@strongswan.org@. It is recommended to include the hostname of a gateway as _subjectAltName_ in its certificate.

Depending on your clients there may be additional requirements imposed on gateway certificates, for instance, the [[Win7CertReq|Windows 7 certificate requirements]] or those for [[IOS_(Apple)#Certificate-requirements-for-iOS-interoperability|iOS and Mac OS X clients]].

Distribute each private key and matching certificate to the corresponding peer.

h2. Certificate Revocation Lists (CRL)

In case end entity certificates have to be revoked, Certificate Revocation Lists (CRLs) may be generated with the [[IpsecPkiSigncrl|ipsec pki --signcrl]] command:

<pre>

ipsec pki --signcrl --cacert caCert.der --cakey caKey.der --reason superseded --cert peerCert.der > crl.der

</pre>

The certificate given with @--cacert@ must be either a CA certificate or a certificate with the _crlSign_ extended key usage (@--flag crlSign@).

When [[IpsecPKIIssue|issuing certificates]] an URL to a CRL may be added with the @--crl@ argument.

h2. Install certificates

On *each* peer store the following certificates and keys in the [[IpsecDirectory|/etc/ipsec.d/]] subdirectory tree:

* *[[/IpsecDirectoryPrivate|/etc/ipsec.d/private/]]peerKey.der* holds the private key of the given peer.

* *[[/IpsecDirectoryCerts|/etc/ipsec.d/certs/]]peerCert.der* holds the end entitity certificate of the given peer.

* *[[/IpsecDirectoryCacerts|/etc/ipsec.d/cacerts/]]caCert.der* holds the CA certificate which issued and signed all peer certificates.

Never store the private key *caKey.der* of the Certification Authority (CA) on a host with constant direct access to the Internet (e.g. a VPN gateway), since a theft of this master signing key will completely compromise your PKI.

Optionally, the CRL may be stored in the following directory (if the certificate contains an URL to a CRL, it will be fetched on demand):

* *[[/IpsecDirectoryCrls|/etc/ipsec.d/crls/]]crl.der* holds the CRL signed by the CA (or a certificate containing the _crlSign_ EKU).

h3. Install certificates in Android

Android needs certificates in PKCS#12 format. You can convert the certificates/keys created above to PKCS#12:

<pre>

openssl x509 -inform der -outform pem -in caCert.der -out caCert.pem

openssl x509 -inform der -outform pem -in peerCert.der -out peerCert.pem

openssl rsa -inform der -outform pem -in peerKey.der -out peerKey.pem

openssl pkcs12 -in peerCert.pem -inkey peerKey.pem -certfile caCert.pem -export -out peer.p12

</pre>

peer.p12 can be imported in Android and contains everything needed by the StrongSwan client.