Ask HN: Secure file sync service with mobile clients?

The recent Dropbox mishaps and intentional violations of users' choices makes the need of a decent secure file syncing service even more pressing.

Secure as in:

- Open source clients

- Data stored encrypted on the servers or usage of P2P syncing without servers

- Encryption keys handled only by the clients

Decent as in:

- Reasonable (or not any) file size limits

- Not too hard to use mobile clients

- Easy to use desktop clients

With these in mind:

- Dropbox is out

- Google drive is out

- Box is out

- Bittorrent sync (now called resilio) was not particularly safe according to one report from 2014 - although things may have now changed?

Is there any option other than setting up your own owncloud server? What are you using?