Setting up the public and private keys

Before we can set up a client/server VPN, we need to set up the public key infrastructure (PKI). The PKI comprises the certificate authority, the private keys, and the certificates (public keys) for both the client and server. We also need to generate a Diffie-Hellman parameter file, which is required for perfect forward secrecy.

To set up PKI, we make use of the easy-rsa scripts. These scripts were originally supplied with the OpenVPN distribution itself, but nowadays, they can also be downloaded and installed separately.

Getting ready

The PKI needs to be set up on a trusted computer. This can be the same as the computer on which the OpenVPN server is run, but from a security point of view, it is best if the PKI is kept completely separate from the rest of the OpenVPN services. One option is to keep the PKI certificate authority (CA) key located on a separate external disk, which is attached only when required. Another option would be to keep the CA private...