The way the law works here in the USA is that anything that requires you to disclose the contents of your mind (a passphrase, an explanation of where you were, your name) cannot be compelled because the fifth amendment precludes the use of that information to convict you.

Things that you ARE (such as fingerprints, DNA, hair color, photo, sample) can be compelled by a court order (e.g. a warrant) because they aren't the contents of your mind but physical aspects of your existence.

That's why the use of a strong passphrase that isn't tied to a biometric is important if you're worried about this sort of thing.

Can't the police/a warrant compel you to open a combination safe? That would be a case of you disclosing a passphrase/something in your mind, but contrary to your assertion.

Nope.

They can certainly open the safe. They just can't compel you to TESTIFY to something.

The contents of your mind are sacrosanct. If they can compel you to divulge a combination, then they can also discern that you had access to that safe by virtue of possession of the combination. Not allowed by our laws.

As I understand it, in the US at least this is indeed the line. Same goes for combination vs keyed locks: you can't be forced to self-incriminate by sharing information, but you can be held in contempt for withholding evidence.

I imagine it gets murky around things like SSH keys, which are technically a kind of password, but too big for a human to remember - and therefore must be "instantiated" in a physical device somewhere.

> I imagine it gets murky around things like SSH keys, which are technically a kind of password, but too big for a human to remember - and therefore must be "instantiated" in a physical device somewhere.

A likely interpretation might be: an SSH key without a keyphrase is like a physical key, and you must hand it over, while a key with a keyphrase is like a combination lock, where you must hand it over but you are not required to state the keyphrase.

Simple password that you can remember encrypting your SSH key, know they can't compel you to give the password unlocking the key.