Deniability and Duress
iPhones require the password(/code) when turned on and (IIRC) under certain other conditions.But I believe  this isn't enough considering recent developments. They write:    It’s important to note that deniability refers to the
    ability to deny some plaintext, not the ability to deny 
    that you’re using a deniable algorithm.

It's now common for border agents in the US to demand login credentials for social media accounts, and search all electronic devises. I can't think of anything more invasive than someone going through my photos and messages. Yet many people are required to visit the US (or countries only reachable via the US). We need methods to separate data into two parts, one being highly private and completely hidden from someone given access to our devises.And while I would welcome a technical solution, it's important not to discount the power of the law. Such invasions of privacy would be illegal in the EU, and contrary to the cynics, laws are generally respected in the developed world. The current news are making me hopeful that (parts of) the US population are also starting to be sympathetic to some rights of foreigners even when they're applying for the privilege of crossing the border.