"since the same, easy-to-discover key is used in every client"<p>OH, COME ON! Seriously? Like even beyond some external attacker, if the key is the same on every client, students could wreck havoc pretty easily if they find it. That's like setting every locker in the school to the same combo and hoping no-one notices.<p>"If the attacker knows the IP address of the server a client is trying to contact, he can just impersonate a freshly-booted client and ask the server to send him the correct SeedValue."<p>OK, no. If you have to have it like this, at least install the SeedValue when you set up the computer.<p>"If the server is unreachable from outside the firewall, clients that are rebooted away from the local network will be unable to obtain a SeedValue. In this situation, the clients insecurely default to accepting arbitrary commands without even the protection of a SeedValue."<p>:HeadDesk: