In the US, for pretty much all open frequencies that require either no license, a de facto license (owning a device gives you a license, CB), or a certification

In the US, for pretty much all open frequencies that require either no license, a de facto license (owning a device gives you a license, CB), or a certification test based license do not allow any sort of scrambling or encryption unless the gov't is able to decode what you are sending. A third party successfully listening in defeats the entire purpose of obscuring what you are saying. But, if you can afford an expensive license from the FCC for operating on other (commercial) bands, you can secure your communications from prying eyes.