What is the oldest written source in this country that mentions this right?
North Korea
Article 79 of the Democratic People’s Republic of Korea 1972 constitution grants that citizens and homes are inviolable and that communications are private (Constitute Project, “Korea (Democratic People’s Republic of) 1972 rev. 2016”).
https://constituteproject.org/constitution/Peoples_Republic_of_Korea_2016?lang=en