Among papers of Edward Nicholas, secretary of state to Charles I and Charles II, I found a worksheet of the Vigenere/Beaufort cipher (Egerton MS 2550, f.39). A printed Vegenere table (f.86) seems too neatly printed to belong to the seventeenth century, but I believe the worksheet (at least the main part of it) shows Nicholas experimented with the polyalphabetic scheme.
I uploaded a new article on this: "Polyalphabetic Cipher Exercise by Royalist Minister Edward Nicholas".
It is yet to be found out how and when Nicholas learned of polyalphabetic ciphers.
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