Symbol Ciphers

Baconian: letters as five-letter groups of A and B, in Bacon's 24-letter alphabet (I/J and U/V shared) or a 26-letter one, plain or hidden in a cover text's letter case. Pigpen, the Freemasons' cipher: letters as parts of two grids and two crosses, with a clickable decoding grid. Bacon devised the biliteral cipher as a youth; the 1605 Advancement of Learning mentions it, and De augmentis (1623) sets it out.

• Folger Shakespeare Library, Decoding the Renaissance: 500 Years of Codes and Ciphers (exhibition, 2014–15), “Sir Francis Bacon”
• David Kahn, The Codebreakers: The Story of Secret Writing (New York: Macmillan, 1967)