The knowledge of how to build a crude gun type nuclear bomb was published in open literature decades ago. This is no longer a secret.
There is a lot of highly classified knowledge about nuclear weapons that has been deduced and published in open literature. That information is still treated as secret, restricted and controlled as much as possible by the US government
There is a lot of highly classified knowledge about nuclear weapons that has been deduced and published in open literature. That information is still treated as secret, restricted and controlled as much as possible by the US government