How did the Polybius checkerboard encode letters into pairs of symbols?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A Vigenere cipher table displays the alphabet in both the top row and left column, with rows shifted to create a grid for encryption and decryption. Highlighted letters illustrate how to use the table. An explanation and example using the words cipher, key, and plaintext appears to the right. — cryptology In encrypting plaintext, the cipher letter is found at the intersection of the column headed by the plaintext letter and the row indexed by the key letter. To decrypt ciphertext, the plaintext letter is found at the head of the column determined by the intersection of the diagonal containing the cipher letter and the row containing the key letter.

The Polybius checkerboard, devised by the Greek historian Polybius, is a system of biliteral substitution that encodes letters into pairs of symbols.

In this method, the alphabet is typically arranged in a square grid (often a 5x5 matrix). Each letter is represented by its corresponding row and column coordinates. For example, if a letter is located in the second row and the fourth column, it would be encoded as the pair "24." This technique is significant in the history of cryptology because it presages many elements of later cryptographic systems by transforming single characters into multiple-symbol equivalents.1