Failure to provide decryption keys is I think not currently covered by the 5th in USA.
In the UK the punishment for failure to decrypt a device when the police ask is pretty much the punishment for whatever they accuse one of having on the device...
What if you don't have the key? Do they need to prove that you're able and refusing to decrypt the device or are you presumed guilty until you prove you can't?
What about one-time pads where you could make up whatever key you wanted and it would be valid?
I think (and I am not lawyer and not your lawyer) that the onus is on you to prove that you don't have the encryption key (anymore) or have access to it. I don't know what case law exists on this.
To the downvoters. I don't like these things either -- but just downvoting them on HN won't change things.... Vote in your national elections with civil liberties in mind instead.
In the UK the punishment for failure to decrypt a device when the police ask is pretty much the punishment for whatever they accuse one of having on the device...