I'm considering setting up a hidden partition, but I'm becoming increasingly confused the more times I see it claimed that plausible deniability isn't effective. Under not-unusual circumstances, it seems suitable to me.
Perhaps I'm mistaken in my understanding, so here's the impression i have for how it works:
1) You encrypt your entire drive.
2) Within your encrypted drive, you partition off a smaller section as a "hidden" parititon. You put your secrets here. The hidden partition is a subset of random data within a drive full of random data. Even when the drive is decrypted, the hidden section just looks like free space.
Let's say, for the sake of example, that I live in the Notorious UK. The fuzz pull me in, open my laptop, and upon seeing it's encrypted, demand the password. If i deny I go to jail, so of course I give them the password - to the drive, but not the hidden partition.
At this point the claims seem to be that "everyone knows about hidden partitions", and that "if your adversary suspects there's more data, they can just keep rubber hosing you". That might be true in the most severe countries, but in places even a little more civilised I would expect them to need some indication that there's encrypted data present - they might be able to throw you in prison for refusing to give up keys to evidently encrypted data, but I doubt they can lock you up for refusing to give up further keys that may or may not exist, on the grounds that there could be more data, but with no evidence to support the claim that any does.
Does a hidden partition provide plausible deniability in the face of an adversary that requires at least some justification for punishment? I believe it does, but have seen claims that it doesn't.