Polybius square

The Polybius cipher (also: Polybius cipher ) is a monographic bipartite monoalphabetic substitution ( see also: terminology of cryptography). It transmits characters in character groups. In a narrower sense, the encryption of individual characters ( monograms ) and pairs of characters ( bigrams ) is meant.

To translate into pairs of characters you are looking for the desired individual characters (letters ) out in a Polybius matrix. From the coordinates of the letter one obtains the desired encoding.

The ciphertext from the plaintext HI 23 11 31 31 34

As a method for optical transmission of messages about torches were successively placed in certain pinnacles of two adjacent towers. For example, in the left tower a torch at position 2 and at right a torch tower at position 3 The receiver of the message could watch from afar this torch positions and decrypt using the Polybius square - this as the encoding of the letter H. Already Polybius (ca. 200 BC to 120 BC) describes a similar process in the tenth volume of his history ( chapter 45), and indicates to have improved it by yourself.

The Polybius Square found itself at encryption methods of the 20th century still apply (see ADFGX ).