On September 19, 2016, a configuration error (fixed as of today) on one of the North-Korean servers hosting the .kp zone accidentally allowed TLDR Records Project, featured on the website Github to transfer and publish North Korea’s .kp DNS zone data. In plain English: The complete list of .kp domain names was « leaked » due to a blunder from North Korea’s Register.
The data is available here.
There are about 28 « active » .kp domain names. This number may appear very low for a whole country. However the « North Korean Internet » is not restricted to these 28 domain names. In fact, subject to presumably harsh restrictions, North Korean entities manage to run websites using domain names from other TLDs as seen on the website North Korea Tech. For instance, there is http://www.uriminzokkiri.com/: an information website using a .com TLD and hosted in China.
Moreover, it is important to remember that the North Korean register is not the only register to deny access to its DNS zone. Other registers worldwide, including in the EU, also deny access to this data, due to local rules.