While there's no legal obligation to know them, there's no legal obligation for you to be let through the border - for non-citizens crossing USA border, the explicit legal presumption(starting from [1]) is that you're not fulfilling the conditions of the visa and you have to convince the immigration officer that you are entitled to entry. If they want to check certain information that is not available for you (no matter if the reason is good or not) and they are not convinced otherwise that you don't have any risks, then there's no "beyond reasonable doubt" like in criminal proceedings - if they are not convinced that you're not going to e.g. work in USA, then they have not only the right, but a duty to deny you entry.

[1] (b) Every alien 10/ (other than a nonimmigrant described in subparagraph (L) or (V) of section 101(a)(15), and other than a nonimmigrant described in any provision of section 101(a)(15)(H)(i) except subclause (b1) of such section) shall be presumed to be an immigrant until he establishes to the satisfaction of the consular officer, at the time of application for a visa, and the immigration officers, at the time of application for admission, that he is entitled to a nonimmigrant status under section 101(a)(15) .

If you say you can't remember your password, they can't force you to remember, but they can tell you to go home.

When you're a foreigner attempting to enter the USA, they can simply deny you entry for failing to do what they want. US CBP has the authority to make arbitrary decisions not to admit foreigners, and CBP faces almost no scrutiny.

Most other countries give their border guards similar authority with respect to foreigners not entitled to enter by some treaty (e.g. EU).

First, IANAL, and I am not an expert for the situation in the US. So you're probably right.

But in the UK, you can go to jail for not disclosing your cryptographic keys. https://en.wikipedia.org/wiki/Key_disclosure_law#United_King...

Here is a story of a person who went to jail for not disclosing his keys: http://www.theregister.co.uk/2009/11/24/ripa_jfl/?page=1 He said he kept silent "because of principle", but I guess he might also have gone to jail if he told them "I don't remember" - Officers would not believe him anyway.

The prosecution has to show that you know the keys to convict you under that law.

Even in the UK the two situations are different. In the cases you cited, not surrendering passwords is considered to be contempt of court. At a border, you might be denied entry, which is bad, but that's it.

The law only exists to the extent that it is enforced. If customs says "give us your passwords or you're not coming through" and you don't have a lawyer handy, then "give us your passwords or you're not coming through" is now the law (until a judge overturns it and possibly charges the officer for breaking another law).

If you can call a lawyer and don't mind waiting several hours, you can challenge it. However most people don't have a lawyer and don't know what to do and are afraid of the officers.

And also, noncitizens do not have a right to contact a lawyer when they are detained at an airport.

If you call a lawyer in such a situation, they'll tell you that Customs has 100% discretion to admit or deny non-citizens and there is no such thing as "challenging" it.