[unilynx]

For that to work you won't even need a database in the user's browser - you could just store an encryption key as a cookie today which you use to encrypt all your serverside data when the user logs in

The real problem is how you deal with the average user (who doesn't really backup properly) losing or crashing their device and thus their encryption key/data. You quickly end up with serverside storage and an email-based password reset again...

[andersonmvd]

It's complicated indeed. A simple "clear browsing data" would make him lose the data forever hehe. And if you keep the key in the server, it would be "hackable", which is what I was trying to avoid. I haven't looked at it but https://solid.mit.edu/ looked promising.