(Although, knowing SCOTUS, I wouldn't expect them to be tech-savvy enough to make a good ruling.)
Honestly the current SCOTUS has largely been finding in line with those things explicitly and literally within the US Constitution. I could see them considering being required to provide a password being required to provide evidence against yourself, which is a Fifth Amendment violation, or compelling speech in violation of the First, like you said. It's not impossible it violates both, and I'd expect to see that argument made in the decision.