I may be missing the question, so let me know if I do, but the point here is just that the crypto system is asymmetric. There's three kinds of keys, public, pri

I may be missing the question, so let me know if I do, but the point here is just that the crypto system is asymmetric. There's three kinds of keys, public, private and evaluation (as usual you can derive the others from the private key). Whoever has the public key can encrypt, whoever has the private key can decrypt and evaluation may or may not need the evaluation keys depending on what you're computing. As for which ML models it works for, they theoretical answer is all of them, because you can do arbitrary computation. The practical answer is that currently models of this complexity are probably the best you can do, because everything else would take years to run. It's being worked on though, both in theory land and in the implementation.