It brings encryption keys to pretty much the same status as locked safes. The government can't just order you to open it on a whim, but they can if they have reasonable prior evidence that there is illegal material contained within. To illustrate:
Scenario 1: As a citizen, I step off the plane after getting back from a foreign country. Not knowing who I am, ICE goons randomly pull me aside and order me to give up the encryption key to my laptop. They have NO reasonable suspicion that doing so will yield illicit material or evidence of wrongdoing, so the Fifth Amendment applies.
Scenario 2: I'm a corporate officer cooking my books, and I brag to my friend that the feds will never catch me because all the incriminating evidence is encrypted. Unfortunately my friend has agreed to cooperate in a plea deal, and relays the details of this conversation. Now the government has reasonable suspicion (actually, at this point I think it's probable cause) that my encryption key is concealing material evidence, and they can probably force me to reveal it.
/. probably won't be happy with that last sentence, but IMO as long as judges interpret "reasonable suspicion" correctly (which is usually the case), it's probably the right call. The government always has been able to force you to open your safe deposit box if they have a warrant, after all. This is nothing new.