Polybios cipher
The Polybios cipher (also in Latinized form: Polybius cipher ) is a monographic bipartite monoalphabetic substitution (see also: Terminology of Cryptography ). It transfers characters in character groups. In a narrower sense, this means the encryption of monograms (single characters) as bigrams (pairs of characters). The cipher is named after the ancient Greek historian Polybios (around 200 to 120 BC), who described a similar method of transmitting messages.
In the process, a square matrix , called the Polybios matrix or the Polybios square , is first filled with the letters of the alphabet, in this case the familiar Latin alphabet . In general, a “scrambled” alphabet will be used, ie the letters will be entered in a more or less “random” or at least in an irregular order in order to achieve the highest possible cryptographic security. For the sake of simplicity, the usual alphabetical order of the letters has been chosen here (in the picture).
To encrypt the letters in pairs of characters, the encryptor searches for the respective letter in the matrix and takes the corresponding row and column numbers as a pair of secret characters . For example, you can find the letter H here in the second row and third column and would encode it as 23 .
| 1 | 2 | 3 | 4th | 5 | |
|---|---|---|---|---|---|
| 1 | A. | B. | C. | D. | E. |
| 2 | F. | G | H | I. | K |
| 3 | L. | M. | N | O | P |
| 4th | Q | R. | S. | T | U |
| 5 | V | W. | X | Y | Z |
The plain text HELLO becomes the ciphertext 23 11 31 31 34 .
For the optical transmission of messages, torches were placed one after the other in certain battlements of two neighboring towers. For example, in the left tower a torch at position 2 and at right a torch tower at position 3. The recipient of the message could watch the torch positions and this as encryption of the letter with the help of his own Polybius square of the distance H recognize. So he was able to decrypt the transmitted ciphertext. The ancient Greek historian Polybios (around 200 BC to 120 BC) describes a similar process in the tenth volume of his Histories (Chapter 45) and claims to have improved it himself.
The Polybius cipher found an almost classic application in the knock code of prison communication .
The Polybios cipher was even used in the 20th century as part of more complex encryption methods , such as the ADFGX method used in World War I.
Web links
Individual evidence
- ↑ Polybios cipher: functionality and example. At gcc.Eisbehr.de, accessed on January 4, 2019.
- ^ Polybius: The Histories. Fragments of Book X, Chapter 45.6 f. From Penelope.UChicago.edu, accessed January 4, 2019.
- ^ Theodorus Büttner-Wobst after L. Dindorf: Polybius: Historiae. Chapter 45.6 f. Teubner, Leipzig 1893. On Perseus.Tufts.edu (Greek), accessed on January 4, 2019.