... contract is kinda basic. But we just don't want to send personal data to a 3rd party app: We need to define what data we should mask. Let's say it's this: person: Sergei Zotov address: 9351958120 Maple Avenue, Apt 12B, Chicago, IL 60614, USA company: Apple Inc. We can replace all of this on device with something like this: person: John Doe address: 456 Elm Street, Suite 3, Los Angeles, CA 90001, USA company: Monsters, Inc. Send ... ... conclusions with a grain of salt and remain open to the idea that what we think a model is good at today might not hold tomorrow. Comment from Konrad S.(@konrad_sx): @zot  there may be an alternative