CCI ARCHIVES / SCIENCE PHOTO LIBRARY CCI ARCHIVES / SCIENCE PHOTO LIBRARY
Treaty of the figures. Front page from "Le traite des chiffres" (1586) by Blaise de Vigenere. In this book de Vigenere described an autokey cipher that remained unbroken for 200 years. It was based on a grid consisting of 26 rows and columns, with the first row beginning with A, and each subsequent row being made by shifting the previous row to the left. To encrypt a message you locate the row with the first letter of the message and the column with the first letter of the key word. The letter where the line and column cross is used for the coded message. De Vigenere's cipher started the message with the key word, further encrypting it.
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