The secrecy of official documents in ancient China can be traced back to the Xia Dynasty. According to historical records, Tai Shi Ling official collection of graphic method (that is, important national records and archives); during the Shang Dynasty, he set up the official position of keeping the history of the government, which was specially responsible for the custody of government official documents and books; and the Zhou Dynasty inherited the tradition of the Shang Dynasty. the original documents were collected in Tianfu, the earliest central archival institution in the history of our country. In the Qin Dynasty, it was a common practice to seal the documents and use sealing mud in the process of transmission. In the Eastern Han Dynasty, the word sealing mud used to keep office documents secret became a metaphor for guarding the pass. The Book of the later Han Dynasty recorded: (Wang) Yuan please take a pill of mud as the king of Dongfeng Hangu pass for a lifetime. Explain that gatekeeping is like sealing mud, you should be careful not to have the slightest omission.
The main introduction of this passage is the secrecy methods of official documents in past dynasties.