I don't know about the rest of it, but a former colleague of mine worked on
a secure booting system using a smartcard. I don't see anything on his web
page about it but you could contact him directly.
http://www.citi.umich.edu/u/itoi/
But if you really are concerned about "very skilled hackers" you will need
significant hardware protection, like a processor with integrated boot code
or an epoxy potted processor and boot rom module. Even then you won't be
able to completely protect the system against everyone.
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Linux Smart Card Developers - M.U.S.C.L.E.
(Movement for the Use of Smart Cards in a Linux Environment)
http://www.linuxnet.com/smartcard/index.html
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