NK bought their nuclear technology from a Pakistani, who is currently living comfortably in a house in Pakistan, protected by the Pakistani state (because he also gave them nuclear capabilities). He stole a lot of the technology from European companies where he worked. This guy (AQ Khan) provided resources to Iran as well (directly and indirectly via NK).
The science isn't actually that hard (I'd feel comfortable I could design/build a gun-type fission weapon myself, given budget and resources, from open sources, with basic engineering education). The hard part is the smuggling, front companies, etc. to get the equipment and materials.
I'm pretty sure by the time NK was looking at going nuclear, the SU wasn't particularly happy with NK. NK was closer to China, and SU didn't really support Chinese proliferation (there were substantial divisions on the SU-China border, after all...)
China didn't really want NK to go nuclear, either.
The science isn't actually that hard (I'd feel comfortable I could design/build a gun-type fission weapon myself, given budget and resources, from open sources, with basic engineering education). The hard part is the smuggling, front companies, etc. to get the equipment and materials.
I'm pretty sure by the time NK was looking at going nuclear, the SU wasn't particularly happy with NK. NK was closer to China, and SU didn't really support Chinese proliferation (there were substantial divisions on the SU-China border, after all...)
China didn't really want NK to go nuclear, either.