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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 the German author and monk Johannes Trithemius〔Salmon, Data privacy, page 63〕 in 1508, and used in his Trithemius cipher. == Trithemius cipher == The Trithemius was published by Johannes Trithemius in his book ''Polygraphia'', which is credited with being the first published work on cryptology. 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 pre-computer ciphers, including the Vigenère cipher and Blaise de Vigenère's less well-known autokey cipher. All polyalphabetic ciphers based on Caesar ciphers can be described in terms of the ''tabula recta''. It uses a letter square with the 26 letters of the alphabet following 26 rows of additional letters, each shifted once to the left. This creates 26 different Caesar ciphers.〔 This method removes the letter frequencies from the ciphertext, making it appear as a random string or block of data. However, if a person is aware that this method is being used, it becomes easy to break. The cipher is vulnerable to attack because it lacks a key, which is said to break Kerckhoffs' principle, a rule of cryptology.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tabula recta」の詳細全文を読む スポンサード リンク
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