The self-incrimination clause in the U.S. Constitution is rooted more in preventing the government from using coercion than it is in concern over the veracity of any testimony obtained through that coercion (of course torturing people into confessing crimes they did not commit is a major historical motivation for the provision, but mechanistically, it is not concerned with truth).

When it comes to a locked safe, the U.S. Supreme court still muses about whether revealing the combination to a lock is testimonial. For instance:

http://blogs.denverpost.com/crime/2012/01/05/why-criminals-s...

http://illinoisjltp.com/timelytech/is-the-battle-over-for-sm...