In the U.S., they can compel someone to provide a password if doing so would not violate the owner's Constitutional rights (such as, for example, if it would be self-incriminatory). Courts in the U.S. have different thresholds at when that line is crossed, but a bright line rule is that providing a password is not self-incriminatory if the criminal case has already been litigated to its conclusion (i.e., the suspect has either been found or plead guilty, or was found not-guilty and double-jeopardy protections apply).