Step 1 : OpenVPN + Easy-RSA & "new-PKI"
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As exposed in the Tools section, we absolutely need 2 pieces of software :
OpenVPN is an "SSL/TLS-based VPN" that is very mature and very widely used all over the multiverse.
Tech Blurb
OpenVPN is NOT one of the old "SSL VPNs" running in a web browser, but uses SSL/TLS cryptography natively. It uses the transport layer on any unused TCP or UDP port, is "NAT-friendly", and uses a single protocol+port (contrarily to protocols like the old PPTP with TCP 1723 + GRE, or IPSEC with ESP + AH + IKE)
For VPNs and network tunnels in general, it is always best to choose the UDP transport layer protocol, rather than TCP. See this excellent, old but still valid, article : Why TCP Over TCP Is A Bad Idea by the creator of CIPE, who moved later on to OpenVPN
But in case you absolutely need it, you can run OpenVPN even on TCP 80 or 443 (web server ports), if unused on your server machine : if you happen to be on a network with very strict Internet access rules, you may have to resort to that.
However in this setup we'll use the "official" OpenVPN UDP port : UDP 1194.
Easy-RSA 2 is a set of command-line utilities to create/manage Public Key Infrastructures (PKIs)
Easy-RSA 2 is developed by the same team as OpenVPN.
Windows installation packages for OpenVPN already include Easy-RSA 2.
So, we download and save the installer from https://openvpn.net/community-downloads/ for our version of Windows (I have built a small temporary Windows 2012R2 to "impersonate" the GM FG machine for this demo) into the folder we previously created at T:\fg-ovpn\source-install :
...and we execute, authorizing it to do its job through the Yes on the "User Access Control" dialog...
...making sure to select "Easy-RSA 2 Certificate Management Scripts" :
...AND allowing the creation of the virtual network card with the "Install" button :
Finally, we'll have our complete installation result looking like this (depends on Windows version AND the version of OpenVPN) :
Tech Blurb :
Note the "TAP-Windows" group above : OpenVPN uses a virtual network card/adapter for each concurrent VPN. So if you need multiple VPNs connected at a time (I often have 2 or 3), you'll need to use the "Add new TAP..." but this is not required for our demo setup.
Let's have a look at the installation folders in Program Files :
We now have the whole required "prime materials" on disk. Let's immediately create a source to initialize "autonomous" blank Public Key Infrastructures in our new-PKI folder :
This folder will be a ready-to-duplicate source folder to create a brand new PKI. We'll keep there both the current version of the Easy-RSA script files and the associated binary programs.
We'll then use it to initialize our own PKI in its own folder . This way, even if we break/uninstall/lose our installation directory for whatever reason, we'll still be able to manage our VPN security (create/revoke certificates), and we'll have the right version of required programs available for that.
Tech Blurb :
Also by creating all PKIs (only 1 is needed for our setup) by duplicating this source folder contents later on, we have the ability to tweak script files or even the openssl configuration file used for that specific PKI if needed, without impacting others.
copy all files from <OpenVPN Installation>\easy-rsa to your new-PKI folder
then copy these (or all, if you want) files from <OpenVPN Installation>\bin to new-PKI as well
Your autonomous "ready-to-duplicate" new-PKI folder is now (nearly) complete :
Since we likely won't be revoking certificates very often, let's just give the CRL a lifetime of 10 years, just like the rest of our PKI.
So we edit openssl-1.0.0.cnf in a text editor (even Right click + Edit with the very limited Windows Notepad is sufficient for this file) as follows : around line 55 you will find :
and replace the 30 with 3650 like this :
Then save and close openssl-1.0.0.cnf and you're done !
There is one issue with this standard configuration : the lifetime of the CRL (Certificate Revocation List) is by default only 30 days, and since our VPN server checks the CRL for evey connection request, it will refuse all connections 30 days after the last CRL update...
