Tabula recta is a cryptographic term invented by Johannes Trithemius in 1518. The tabula recta was a square table of alphabets, each one made by shifting the previous one to the left, like this:
Trithemius used the tabula recta to define a polyalphabetic cipher which was equivalent to Leon Battista Alberti's cipher disk. The tabula recta is often referred to in discussing pre-computer ciphers, including the Vigenère cipher and Blaise de Vigenère's less well-known (but much stronger) autokey cipher. All polyalphabetic ciphers based on Caesar ciphers can be described in terms of the tabula recta.
