Since we have learned the basics of post-quantum secure VPN tunnels, let’s configure a site-to-site VPN between a Palo Alto Networks firewall and a FortiGate with PQC ciphers to verify vendor interoperability. Spoiler: it works like a charm. ;)

Palo Alto Networks supports PQC ciphers since PAN-OS 11.2, while 12.1 finally brought the ML-KEM algorithm. FortiGates support PQC ciphers since FortiOS 7.6. My lab consists of a PA-440 with PAN-OS 12.1.6 and a FG-70F with FortiOS 7.6.7.

Setup

(Note that I’m not showing a complete site-to-site VPN tutorial, but focusing on the PQC part.)

I’m using the hybrid approach. PQC ciphers are used *additionally* to the classical ECDH key agreement. That is: group21 + mlkem.

Palo Alto Networks NGFW

On the Palo side, you need to configure the IKE/IPsec Crypto, the IKE Gateway and the IPsec tunnel in the following way:

Fortinet FortiGate

On the Forti, it’s these steps that are done completely in the VPN Tunnels pane:

On the CLI, it’s this (excluding the tunnel interface and the static route). Note the set addke1 ml-kem-1024 lines.

Verify

Both firewalls deliver only basic “it’s working” green icons in the GUI:

If you want to verify whether or not post-quantum ciphers are used, the CLI is a must. Note the ML-KEM keywords:

Palo:

show vpn ike-sa detail gateway <name> and

show vpn ipsec-sa tunnel <name>:

Forti:

Please note that neither of the following two commands show the key agreement protocol, hence are not usable here: get vpn ike gateway <name>, get vpn ipsec tunnel name <name>.

–> This is the one: diagnose vpn ike gateway list name <name>:

That’s it. Happy networking. :)

Soli Deo Gloria!

Photo by Hugues de BUYER-MIMEURE on Unsplash.