Three hundred years ago, before envelopes, passwords and security codes, writers often struggled to keep thoughts, cares and dreams expressed in their letters private.
원문출처 : https://www.cnn.com/style/article/opening-sealed-letters-study-scn/index.html
원문출처 : https://www.cnn.com/style/article/opening-sealed-letters-study-scn/index.html