Even after this ruling, at least in the western US stares in the Ninth Circuit, the government can still require a traveller entering the country to produce her portable electronic life for inspection. No justification is required.
Can they take it away and send it off to a lab to be flyspecked? Yes, if they have a reasonable suspicion. The suspicion doesn't have to be right, and it doesn't necessarily have to be based on accurate information. And, even though juries are admonished not to draw conclusions about the guilt of someone claiming Fifth Amendment protections against self-incrimination, the authorities are permitted to assume that someone who won't hand over the encryption keys has something to hide. That itself is not enough, but, when combined with other suspicions about what that something is can form part of the basis for the required reasonable suspicion.
This decision doesn't actually do a whole lot to advance privacy. The government must have at least some reasonable suspicion, but that's all, in the border setting. If they search any way, in any prosecution you can object to the introduction of evidence. Always assuming that circumstances such as being unable to afford a good lawyer don't lead you to plea bargain.
What if you and your stuff are entirely clean of any wrong doing? You may get your stuff back. It might be in working order. You could get an apology/have a nice day form letter. Some of your stuff might go viral. You might have a case against someone for something, but mostly you've been screwed without much hope of redress.
The merits of border searches can be argued while waiting for the cows to come home, but we shouldn't think of this case as a great victory for e-privacy.
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