In cryptography, the tabula recta (from Latin tabula rēcta) 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 in 1508, and used in his cipher.
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 often referred to in discussing precomputer ciphers, including the Vigenère cipher and Blaise de Vigenère's less wellknown autokey cipher. All polyalphabetic ciphers based on Caesar ciphers can be described in terms of the tabula recta.
In order to encrypt a plaintext, one locates the row with the first letter to be encrypted, and the column with the first letter of the key. The letter where the line and column cross is the ciphertext letter.

Other articles related to "tabula recta":
... (Such a simple tableau is called a tabula recta, and mathematically corresponds to adding the plaintext and key letters, modulo 26.) A keyword is then used to choose which ciphertext alphabet to use ... words, but simplified by the fact that usually a tabula recta had been employed ... is practically the same as the Vigenère, except the tabula recta is replaced by a backwards one, mathematically equivalent to ciphertext = key  plaintext ...