It's not clear to me which executables are available for use in the shell script. A shell script will need the interpreter or it's inert. Can the script use standard utilities like chmod or sed? Can it invoke subsidiary languages like awk, or perl? A language can perl can do almost everything that can be done with an executable.

Must the cracker actually damage anything? Lots of crackers simply want a copy of your data and avoid damaging stuff to avoid detection. But in your scenario a cracker like that is tolerable?

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Also what about shared libraries? Are they signed as well?