My whole point was about using hash to verify the integrity of the data, so no they wouldn't be able to tamper with anything, that's the whole point of it. You

My whole point was about using hash to verify the integrity of the data, so no they wouldn't be able to tamper with anything, that's the whole point of it. You bring a good point about user privacy, and for sure a key can help with that, but at the end of the day, there's not much you can do about this once the physical server is somewhere else, TLS or not, you'll need to trust the one that hold physically that server not to void user privacy. I would still suggest a TLS connection for that server, but it would most probably be self signed with a different root certificate to avoid someone else to be able to make others trust him being Apple over something that wouldn't verify the content with hash coming from platform owned by Apple.