I think there might be a circuit split on this issue, but IMO merely divulging a combination or encryption key is not "testimonial" (and therefore not a 5th Ame

I think there might be a circuit split on this issue, but IMO merely divulging a combination or encryption key is not "testimonial" (and therefore not a 5th Amendment violation) except insofar as it admits knowledge of the combination or key itself. But if police can establish separately that you know it, then the "foregone conclusion" exception applies. If you can point to specific precedent that would be helpful.