Blockstack is very easy to get started with and provide user authentication and encrypted data storage out of the box. About offline-mode, I am about to implem

Blockstack is very easy to get started with and provide user authentication and encrypted data storage out of the box. About offline-mode, I am about to implement it by my side as this feature is not part of the Blockstack SDK for now. I am happy that you are taking data privacy very seriously and I guess Blockstack is a good solution to go.