This is theoretical question that seems to be interesting (at least for me). What would you do to completely close the whole system from outside world? By close I mean that any human shouldn't be able to login and it should only do some tasks with the simplest interface with outside world that is needed for them. It should be IMPOSSIBLE (ok - to possible extent ;) ) to access internal structure by anyone. However - after cutting power off, and restarting it that way - it should continue its work.
I imagine that HDD should be encrypted, so after cutting power off - it shouldn't be possible to get anything from it.
Is it possible or how close can we get?
PS. I don't even know what tags to use :( .