This document contains some information about the security of the software, more specifically: the configuration choices that were made.

The basic OpenVPN server (and client) crypto configuration:

tls-version-min 1.2
tls-cipher TLS-ECDHE-RSA-WITH-AES-256-GCM-SHA384
dh none
ncp-ciphers AES-256-GCM
cipher AES-256-GCM
tls-crypt /path/to/tls-crypt.key

We chose TLS-ECDHE-RSA-WITH-AES-256-GCM-SHA384 as TLS cipher because it is listed in RFC 7525 (section 4.2). It was the only cipher that could be used with RSA keys and AES-256-GCM. Furthermore, ECDHE is faster than DHE.

For the data channel we chose to use AES-256-GCM.

We do not specify the auth OpenVPN configuration option as it is no longer used when using an AEAD cipher like AES-256-GCM and tls-crypt.

Starting from vpn-server-api 2.1.1 there no longer is a "global" tls-crypt key that is the same for all profiles. From this version on all new installations will use a tls-crypt key per profile.

NOTE: if you already installed your VPN server before the release of vpn-server-api 2.1.1 you will continue to use the same tls-crypt key for all profiles. If you want to switch to using one key per profile you need to delete /var/lib/vpn-server-api/ta.key.

To apply the configuration changes:

$ sudo vpn-maint-apply-changes

If the command is not available, install the vpn-maint-scripts package first.

Please be aware that existing clients will need to fetch a new configuration, unless the eduVPN or Let's Connect! apps are used where that will happen automatically.

CentOS 7 by default provides PHP 5.4. This is not without risks. This version is no longer maintained by the PHP project and depends fully on the Red Hat engineers that update it when (security) issues appear.

See the resources/ directory for PHP setting changes.

We use fkooman/secookie, a library to implement secure PHP sessions (and cookies).

The built-in OAuth server uses public key cryptography signed JWT Bearer tokens of the type EdDSA implemented in php-jwt. The EdDSA JWT token in specified in RFC 8037.

The reason we are using public key cryptography for the Bearer tokens is that no "back channel" is needed between the services verifying the token and issuing the token. This is especially helpful in the case of Guest Usage.

The CA of the VPN service is "online" as it needs to generate valid certificates on the fly. The vpn-ca software is used as CA.

The CA uses keys of length 3072 bits, and signs using RSA-SHA256.