Thus, the plaintext letter X translates to the ciphertext 53.įor the typical Latin alphabet square above we get the following map: A B C D E F G H I J K L M N O P Q R S T U V W X Y Zġ1 12 13 14 15 21 22 23 24 24 25 31 32 33 34 35 41 42 43 44 45 51 52 53 54 55 What makes the Polybius cipher special?īy applying a Polybius cipher encryption you shrink the set of symbols necessary to represent a message from the original alphabet (typically 26 symbols) to the set of symbols you need to denote the coordinates of each letter in the ciphertext (typically 5 symbols). For instance, the letter X is at row 5 and column 3. To encode a message, each letter is translated to its coordinates in the grid – typically first row, then column. └───┴───────────────┘ Typical modern square using the Latin alphabet This is why the letter J is not present in the following square. For this, we first replace one letter by the other before encrypting. Step 2: The numbers are then grouped into blocks of a certain size (this is called the period, and forms part of the. d is in row 3, column 3 of the key square so 3 is written in the top row and 3 is written in the second row. └───┴───────────────┘ Original square using the Greek alphabetįor the Latin alphabet to fit into a 5×5 square, two letters must be combined (usually I and J or C and K). These are then written on top of one another as shown in step 1 (below).
Here’s the original square used by the Greeks who invented the cipher. The Polybius square cipher first distributes the letters of a chosen alphabet into a grid (typically 5×5).
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