web application – offline sensory data storage

I'm working on an HTML5 web application with a service agent and one of the requirements to complete is to work offline.

In order to realize the offline functionality, we store all the required application data in indexeddb. The problem I think In our opinion, all data in the application is essentially personal information. I've read that sensitive data should not be stored in indexedb.

Regarding offline features if you can not use indexedb, where are you supposed to store this information if you have to store them on the client side? And I suppose client-side encryption would be useless because the client should decrypt it?