Data is viral.

Anyone who saw your data could keep your data.

That's because data is non-rivalrous; in the limit it's possible to make a perfect copy instantly, without interfering with the original.

Today for a third party to do useful things with your data, they have to see your data.

This requires trusting that third party with that data, since on a technical level they might keep your data.

But what if it was possible to allow third parties to do useful things with your data, without them ever seeing your data?