But crypto is built from math, which is available to anyone who possesses a brain. Even if you locked down all the academic output related to encryption you can

But crypto is built from math, which is available to anyone who possesses a brain. Even if you locked down all the academic output related to encryption you can't ensure no one will discover another way to hide and transmit secrets either around or through your usually-private-except-for-serious-threats communications network. You'd have better luck trying to lock down harmful bioagents and fissionable materials, but as you alluded, as long as these technologies exist the world faces a security threat. It seems to me the only way to combat these threats is to construct a society where individuals never feel the need to leverage their increasing power, a police state where anyone's communications can be inspected or abused at will by an agent, a heirarchy, or an algorithm seems antithetical to such a society.