Imagine you’re at a border crossing, and the guard asks you to hand over all of your electronics for screening. The guard then asks that you unlock your device, provide passwords and decryption keys. Right now, he’s asking nicely, but he happens to be carrying an unpleasant-looking rubber hose, Yes, cryptographers actually do call this “rubber hose cryptanalysis.” and appears to be willing to use it. Now imagine you’re a journalist covering war crimes in the country you’re trying to leave. So, what can you do?
This isn’t a hypothetical situation. The Freedom of the Press Foundation published an open letter to camera manufacturers requesting that they provide “encryption” by default. The thing is, what they want isn’t just encryption, it’s deniability, which is a subtly different thing.
Deniable schemes let you lie about whether you’ve provided full access to some or all of the encrypted text. This is important because, currently, you can’t give the guard in the above example a fake password. He’ll try it, get locked out, and then proceed with the flogging
Michael A. Specter On Deniability and Duress