According to the Wilson Center’s North Korea International Documentation Project (NKIDP):
Documents obtained by NKIDP scholar Bernd Schaefer from the archives of East Germany’s state security service, or Stasi, were featured in an article in South Korea’s Dong-a Ilbo. The documents detail procedures for admitting clandestine members of the Korean Workers’ Party from South Korea to East Germany for meetings with North Korean officials. According to the documents, North Korea and East Germany established special procedures for South Korean “comrades” to secretly enter the GDR for meetings with North Korean officials at the DPRK embassy. East Berlin was also used as a stopover for these South Korean “comrades” traveling to Pyongyang for meetings with North Korean officials.
View the article in Korean at the Dong-a Ilbo website. There were additional articles in Korean (here and here) and one in English here.