Conservative journalist (specializing in the Middle East) Lee Smith last week raised the possibility that Iran and North Korea have a technological partnership or alliance in developing nuclear weapons and missile technology as well. He compared it to the Anglo-American nuclear cooperation agreement that called for American testing of joint designs. Smith thinks that North Korea in its recent nuclear test may have actually been testing an Iranian or joint design. This means that Tehran would never actually have to conduct its own nuclear tests to ensure that it has a reliable design. Mark Fitzpatrick in an article in the UAE's The National seemed to back Smith's basic thesis.
Fitzpatrick claimed that there is already much evidence of joint Iranian-Korean ballistic missile technology cooperation. Here is a link to Yossi Alpher's weekly Q & A for APN that discusses the Arab-North Korea connection. This would mean simply that that already existing cooperation is being extended to the field of uranium enrichment and nuclear weapons design. North Korea's first two tests were of plutonium-derived weapons. American scientists estimate that the recent test explosion was 2.5 times more powerful than the 2009 test, even though a smaller device was involved in 2013. This means that North Korea is making progress in its weaponization efforts. Uranium is converted into plutonium in small amounts during the normal power production of a nuclear reactor. But separation of the plutonium from the uranium is very dangerous because it is highly radioactive and has to be carried out in a special environment. Uranium bombs are not as efficient as plutonium weapons, especially for making hydrogen bombs, but they can do the job and be mass produced if suitable means of developing highly-enriched uranium (HEU) are found such as centrifuge spin separation as used by both Pakistan and Iran using stolen Dutch technology from the 1970s. A. Q. Khan, the metallurgist who stole the blueprints of the Dutch technology while he was working in the Netherlands, then turned around and sold the technology to Iran, Libya, and North Korea after Pakistan developed its own nuclear weapons.
North Korea gave up its plutonium-based technology in return for aid from Japan, South Korea and the United States. It is now forced to rely on HEU as the fuel for its bombs, which are needed to blackmail its neighbors into supplying the regime in the North with food, nuclear reactors, and money. So in order to get Iran to help it develop a centrifuge-based enrichment process, Pyongyang has probably promised to help design and test a nuclear weapon. Ironically, only by actually turning over some technology to other rogue states, can North Korea credibly argue that it is a proliferation threat that needs to be bought off with periodic bribes. This in turn allows Tehran to be able to promise not to test nuclear weapons in any deal that might end Western economic sanctions against Iran. And North Korean test sites are definitely out of range of Israeli aircraft.
Here Jeffrey Lewis, a specialist in nuclear proliferation in East Asia, argues why he believes that Iranian-North Korean cooperation has not extended beyond missile technology.