Even if you could force the external entity to declare the full lineage of the input data (i.e. 100% dependently typed), that would require that the scripting can't be programmable, i.e. the external I/O capability would be eliminated. If you don't understand why, please go learn about the typing systems Coq and Epigram.
I just came again across this initiative
http://www.idni.org/like much of the discussion in this thread,
it occupies the higher stratosphere of crypto-related theory,
but as much as I'm able to make out of it, it endeavors to steer
clear of many pitfalls that have been explored here by employing
purely functional language "that contains a blockchain support built-in"