The ONLY thing required for this to happen is secure communications.
That's like saying "the ONLY thing required is world peace".
What admins and engineers have known for a long time, and which people like Snowden provided evidence for is that secure communication is not a given, and highly unlikely to be an option for the masses.
If the government won't let people have a shadow economy they can't monitor or control, expect physical alternatives to take their place. There's plenty of precedence for turning to valuable metals when the currency cannot be trusted. And there are examples of governments banning both gold and silver trade as a kneejerk reaction, but that just moves the market to something else.