It depends on what you are charged with.
In a case of say, possession of stolen information, the laws of possession applied to contraband such as drugs would likely apply.
Since the information wouldn't be in your actual possession(literally in your hands or on your person), then they would fall under constructive possession laws.
In most states, constructive possession has 3 parts --
1) You must have knowledge of the presence of the contraband
2) You must know of the contraband's illicit nature
3) You must have the ability to exercise dominion and control over the contraband.
If I slip an encrypted thumb drive full of stolen trade secrets into your suitcase at the airport, you're not automatically in possession of those things because, absent any other information, none of the rules above could be satisfied.
But, if you knew the encryption key to the thumb drive, then that is evidence against you and that knowledge would be protected under the 5th amendment.
If police find a random iPhone in your house that you share with a roommate, they would have to prove constructive possession to tie anything found on that device to you. Knowledge of the password, regardless of what the password is, would be protected under the 5th amendment.
In both cases, the authorities could not compel you to incriminate yourself by forcing you to disclose your knowledge of the password to the device.
IANAL either. If you are ever in such a situation, be prepared to sit in prison for 10 years while you work your way through the appellate courts, because you're in for a long battle.
That sounds like the 'foregone conclusion' doctrine.
When it is a 'foregone conclusion' that the data is present on a device, you can be compelled to produce that data by decryption. However, if you are so compelled, the fact that you were able to decrypt that data can't be used against you. So they will need another way to tie you to the data.
An example is if police saw you had classified documents on your computer (by e.g. a video camera) and later confiscate the computer and find it to be encrypted.
Even if your encrypted laptop contains evidence, you cannot plead the fifth if the prosecutors know it’s there. As long as they can get a warrant and when they get the data say “see your honor? Here is the evidence we knew was there!”, it doesn’t fall under the fifth.
Self incrimination would be if you are charged with tax fraud and proof is on your encrypted drive and the prosecution knows this, but also on that drive is records of money laundering, a separate crime they do not know about. This is when pleading the fifth would apply. By decrypting the laptop, you would incriminate yourself in a second crime, that you were not being charged with. Presumably if you were coerced into decrypting the laptop in this case, you could use the argument that the money laundering evidence can not be admitted into court because it was obtained inappropriately.
IANAL and this ain’t legal advice. Stay in school kids.