The Pre-Shared-Key is combined using a PRF with Nonces, and a bunch of other values known to anyone else in the negotiation. The result is a value that can only be mutually attained by two parties if both parties started with the same values -- aka, the same pre-shared-key.
However this pre-shared key is not used to encrypt the data between your device and the VPN servers, only to authenticate the server to the client device. A passive adversary eavesdropping on the connection is unable to decrypt the tunnel data. However there does exist a risk of an active MITM (Man in the middle attack) where the adversary [SOLVED] How to view BOVPN pre-shared key - WatchGuard Apr 13, 2018 Connect VPN using L2TP-IPSec on MAC OS X - Ricmedia PC Help
RandomKeygen is a free mobile-friendly tool that offers randomly generated keys and passwords you can use to secure any application, service or device.
However this pre-shared key is not used to encrypt the data between your device and the VPN servers, only to authenticate the server to the client device. A passive adversary eavesdropping on the connection is unable to decrypt the tunnel data. However there does exist a risk of an active MITM (Man in the middle attack) where the adversary [SOLVED] How to view BOVPN pre-shared key - WatchGuard
Aug 17, 2017
Host to host VPN with PSK - Libreswan Generate a pre shared key (PSK) for use in this VPN. PSK is really not a password, it's a key and you must make absolutely sure it is transferred to remote end in a secure way by using PGP/GPG or ssh. Secure PSK should be at least 32 characters random but 64 chars is better. We can actually cope with even longer PSK sizes but not all