This page is a two-step secret shared key generator using Diffie-Hellman algorithm.
Both peers need to use this page to generate the shared key, so either give a link or send the saved page to your peer.
Enter your own secret. 12 characters at least are recommended, and make it unique. You will need it again in step 2 so write it down.
Click on "Generate phase 1 exchange"
Copy all the digits in the "Phase 1" text area and send it to your peer via whatever unsecured channel you want. Wait for them to send you their own Phase 1 exchange, and agree on key size.
Enter your own secret again and the desired key size.
Paste the Phase 1 exhange received from your peer (not yours) in the appropriate text field.
Click on "Generate PSK"
Copy your secret shared key from the PSK field and voila !
PSK size : characters
PSK alphabet : Full-range
Your own secret : (recommended at least 12 characters)