This is arguably the most authoritative open source analysis of north Korean proliferation activities with Iran. It is extremely well sourced analysis. Unfortunately it is not online so you have to download the PDF from my dropbox at the link below. It is well worth the read for anyone interested in north Korea's proliferation.
Summary: This article looks at North Korea’s military proliferation to Iran – all of it. For those who have questions about North Korea’s long history of proliferation (which is ongoing) to Iran, or perhaps even question that there is a robust proliferation relationship this article will help answer them.
Bruce E. Bechtol Jr. “North Korea and Military Proliferation to Iran: An International
Security Dilemma,” ChiMoKoJa – Histories of China, Mongolia, Korea and Japan, Vol. 2, (2016), 71-95.
Download the 30 page article here: https://www.dropbox.com/s/x5vcorxedlkta5f/North%20Korea%20Iran%20article%20latest%20draft%202016.pdf?dl=0
ChiMoKoJa – Histories of China, Mongolia, Korea and Japan