You might be thinking of the password vs fingerprint phone unlock. Courts decided that while your fingerprint could be compelled, you couldn’t be compelled to reveal your password as that was private knowledge. That isn’t due to copyright though, it’s a 5th Amendment issue here in the US (The Fifth Amendment grants anyone in the U.S. the right to remain silent, which includes the right to not turn over information that could incriminate them in a crime. These days, those protections extend to the passcodes that only a device owner knows).
You might be thinking of the password vs fingerprint phone unlock. Courts decided that while your fingerprint could be compelled, you couldn’t be compelled to reveal your password as that was private knowledge. That isn’t due to copyright though, it’s a 5th Amendment issue here in the US (The Fifth Amendment grants anyone in the U.S. the right to remain silent, which includes the right to not turn over information that could incriminate them in a crime. These days, those protections extend to the passcodes that only a device owner knows).