Your last word brought to mind the science fiction short, "Come You Nigh: Kay Shuns" by Lawrence A. Perkins, which used exactly this technique as an encryption

Your last word brought to mind the science fiction short, "Come You Nigh: Kay Shuns" by Lawrence A. Perkins, which used exactly this technique as an encryption method! Analog SF, April 1970 - available here: https://www.luminist.org/archives/SF/AN.htm https://www.luminist.org/archives/SF/AN.htm (BTW, that site is one of the hidden treasures of the Internet, on a par with Archive or Wikipedia...)