Governments should be transparent and the people should be opaque. Any government that attempts to make things otherwise looses legitimacy.
I'm going to add this to my repertoire since it's a lot more concise than most of my rantings on the topic
I feel like we've lost the vocabulary we ought to be using to talk about the legitimacy and role of the state. More people need to read J.S. Mill (and probably Hobbes.) Even today, works by both are surprisingly good reads and embed a lot of thoughtful and timeless wisdom.
I'm not commenting on the government coming in at unveiling encrypted communications, but certainly a better approach than "governments should be transparent and the people should be opaque" would be "governments should be translucent and the people should be translucent too".