If you hadn't provided a link I would have assumed you were joking. What happens under this law with people who carry USB sticks with truly random noise files on them?
There are serious problems with it. (I speak as someone who's normally okay with 'big government' and legal restrictions.)
In theory you'd have to be doing something to get their attention. The most well known case is of a man who has a psychotic illness and who was also importing "explosives" and behaving in odd ways. But that's what some people with a mental illness do. It's one of the features of illness, that people are not rational and do not do things that are in their best interest.
The "give us your key or go to jail" are not the worst abuses of RIPA though. This would be rare, and people would have legal representation. The local councils mis-using RIPA to see if people are applying to the wrong schools are worse. These are already so common they've had to be cut back, and there's little opportunity for legal representation and the oversight is much less.
They do not have a sense of humor. This would be a cute way of writing a blog post about your day(s) spent in detention before being sent back to your country of origin/citizenship.
The police might think that the white noise file is an encrypted document, demand that you provide the (non-existent) decryption key, and imprison you for "refusing" to provide it.
Then surely they must logically also assume that when the prime minister's FM radio is tuned between channels he is receiving encrypted transmissions from terrorists. Are they going to xkcd-538 him for the key then?
1) These are not the police. Police are trained law enforcement officers. These are customs and immigration employees. They get training, but it's more important that they can get a security clearance.
2) Can you think of a reason for having a file of white noise that you could explain to this person that they would understand and believe?
You really don't have many rights outside immigration/customs. "Probable cause" is "he acted weird." Cars have been destructively disassembled for less.
You may be confounding ICE, CIS, and CBP, which is completely understandable (never mind EOIR, which is over in the DOJ and muddying the waters even more). The majority of CBP are federal "law enforcement" and are required to obtain clearance in addition to the suitability investigation(which is the equivalent of a lifestyle + polygraph background check for s/ts clearance).
If they look at a computer based on information provided by a person entering the country, they have to have clearance. Uncleared or precleared people will often hang out over the shoulder of someone with clearance, so it's not really that "secure", but it ensures that queries are handled by cleared personnel.
