Originally Posted by SeriouslyLost

The basic rule with CBP is that if they don't have probable cause then you don't have to give them access to anything in particular. You generally do have to answer questions, but only in so far as it helps them determine eligbility to enter the US. Many CPB officers tend to be rather alpha-male about their powers, so they go overboard, but protesting at the time is a choice you make on your own. Security protected devices are not, in and of themselves, probable cause. If they do have probable cause then they can require you to cough it up, but they have various hoops they have to jump through first.

TSA can't ask you to do much of anything outside of their job of screening you for items banned from flying. You can happily tell them to get bent.