When I worked for a fed law enforcement agency, we had a “techies with guns” group. Their job was to serve the warrant, make an arrest, and impound the computer. If the accused pleaded the fifth, the username and password had to be cracked to gain access to the hard drive.
The fifth amendment protects one from incriminating one’s self. However a good prosecutor could argue that by not providing the username and password, the accused is obstructing justice. Sounds like a ruling needs to be made be the Supreme Court.