Imagine you have a server that is at a location which is not trustworthy. People might have physical access to the machine who are not supposed to look at the data stored on it.
In this scenario I thought about setting up a server with full disk encryption. This means that the key needs to be entered before the system can fully boot. As long as I have physical access entering the key without a third party getting to know it is feasible.
However, when the server needs to be booted remotely I need to enter the key without being present. Linux offers the possibility of running a lightweight SSH server before fully booting the system so that you can enter the key. However, the certificate for this SSH server obviously needs to be stored unencrypted (because it needs to be read before the key is entered) so attackers can access it and fake our server thus gaining knowledge of the key.
Is there any way to make this process secure? In the best case this would even be OS-independent.