Another thought:
IF all of the software revisions use the same key, here's a way that's likely to work:
- Use NPSMitsBinaryUpgrade.exe and get to the stage where it's downloading the zip.enc
- Pause the process until it timeouts or kill the net connection
- It'll ask if you want to retry. Meanwhile, set up a quick webserver and either modify the hosts file (if it does another DNS lookup) or set up an iptables rule on your router to forward the resolved IP to your webserver
- It should grab your .zip.enc instead and perform the decryption for you.
If it successfully grabs the file but can't decrypt it, this will tell us that we're going to have to decrypt the exchange between the client and fus to get the key...