Tabula Recta

The tabula recta is a square table of alphabets, each row of which is made by shifting the previous one to the left. The term was invented by Johannes Trithemius. Trithemius used the tabula recta to define a polyalphabetic cipher which was equivalent to Leon Battista Alberti's cipher disk except that the alphabets are not mixed. The tabula recta is a main reason of how people were able to crack the Vigenère cipher and Blaise de Vigenère's less well-known autokey cipher. All polyalphabetic ciphers based on Caesar ciphers can be explained by the tabula recta in specific terminology.