[smacktoward]

Governments were plenty able to monopolize math when computing power was scarce and expensive. That monopoly slipped as computer power got cheaper and more widely accessible. Now everybody has a computer in their pocket that's as fast as the world's fastest supercomputers were in 1990, so the monopoly is well and truly dead.

[pdkl95]

They monopolized the people that knew the math, written records that described the math, and the hardware that implemented the math. The actual crypto itself cannot be controlled, and in some cases was found by other through cryptanalysis or independently re-discovered.

That distinction is important - physical things like people or papers or computers can be controlled and hidden. It's much harder to keep knowledge itself bottled up, because there is always a risk that someone clever will discover it on their own.