Ask HN: Sharing Phonegap localstorage data between devices?

Working on a sensitive data app. The concept is that the content can be share between users or devices.

- Initial Approach: The content can be stored in the "cloud" or on my server similarly to Dropbox; anyone who have permission can access the data - distribute down to multiple users' devices.

- Second Approach: Since the data is considered very sensitive, it is recommended to be stored on the user's mobile.

1) So a copy of the data can be stored in the primary user's device.

2) The Unique Data ID and list of users (no content) can be stored on a database table in my server as reference.

3) Next user registered, calls upon my server; find the Data ID.

4) Extracts the copy from the primary user's mobile. Sends to the next user.

Problems:

- The primary user's device can be offline / out of battery; The next user will not get a copy.

- Any additional security issues in between?

- Missing any nuances that might make this inappropriate?

- Alternative approach?