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Polybius Cipher

Tool to decode/encode with the Polybius square cipher automatically (with or without a grid and therefore with or without the keyword).

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Polybius Cipher -

Tag(s) : Substitution Cipher

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Polybius Cipher

Polybius Square Decoder

 

 



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Polybius Square Encoder

 


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Answers to Questions (FAQ)

What is the Polybius cipher? (Définition)

The Polybius cipher, also called Polybius square, is a substitution cipher using a square grid. Each character of the plain message is replaced by a couple of coordinates defining its position in the grid.

How to encrypt using Polybius cipher?

Polybius square uses a 5x5 grid filled with letters for encryption.

Example: To crypt DCODE with the grid

\12345
1ABCDE
2FGHIJ
3KLMNO
4PQRST
5UVWXY

A password can be used to generate a deranged alphabet that fills the grid.

As the latin alphabet has 26 letters and the grid has 25 cells, a letter to remove is chosen, usually it's J, V, W or Z which are deleted. The order of the letters in the grid can be modified using a key to generate a deranged alphabet.

The encryption phase is a substitution of each letter by its coordinates (row, column) in the grid.

Example: D is located row 1, column 4, so coded 14; C is located row 1, column 3, it is coded 13. The ciphered message DCODE is then 14,13,35,14,15

How to decrypt Polybius cipher?

Polybius decryption requires to know the grid and consists in a substitution of couples of coordinates by the corresponding letter in the grid.

Example: The message to decrypt is 351332542114 with the grid (created with DCODE as key and without letter J):

\12345
1DCOEA
2BFGHI
3KLMNP
4QRSTU
5VWXYZ

Split the message in bigrams, couples of numbers that are the coordinates of each plain text letter.

Example: 35,13,32,54,21,14, 35 stands for 3rd row, 5th column, so letter P, and so on. The plain message is POLYBE.

How to recognize Polybius ciphertext?

The ciphered message is constituted of couples of coordinates (generally these are digits from 1 to 5) and so has an even number of characters (the possible pairs are: 11, 12, 13, 14, 15, 21, 22, 23, 24, 25, 31, 32, 33, 34, 35, 41, 42, 43, 44, 45, 51, 52, 53, 54, 55).

Coordinates may have at most 25 distinct values.

References to Greece (Polybius comes from its author Πολύβιος / Polúbios in Greek) are a clue.

How to decipher Polybius without the grid?

Polybius is a substitution by bigrams, replace each couple of coordinates by a random letter (there should be at most 25 distinct ones) and try a monoalphabetical substitution.

What are the variants of the Polybius cipher?

It is possible to use a grid of another size, not necessarily square, maybe rectangular. It is also possible to use other coordinate notation, for example column or row names other than digits from 1 to 5, but also to note them in column-row rather than row-column.

The author (Polybius) had proposed to transmit coded messages remotely, for example, using torches. N in the right hand and M in the left hand for the coordinates N, M for example.

The Nihilists cipher is a variant using an over-encryption of the Polybe code.

When was Polybius Cipher invented?

The greek historian Polybius described this method in 150 before JC.

Source code

dCode retains ownership of the "Polybius Cipher" source code. Except explicit open source licence (indicated Creative Commons / free), the "Polybius Cipher" algorithm, the applet or snippet (converter, solver, encryption / decryption, encoding / decoding, ciphering / deciphering, translator), or the "Polybius Cipher" functions (calculate, convert, solve, decrypt / encrypt, decipher / cipher, decode / encode, translate) written in any informatic language (Python, Java, PHP, C#, Javascript, Matlab, etc.) and all data download, script, or API access for "Polybius Cipher" are not public, same for offline use on PC, mobile, tablet, iPhone or Android app!
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Cite as source (bibliography):
Polybius Cipher on dCode.fr [online website], retrieved on 2022-12-09, https://www.dcode.fr/polybius-cipher

Need Help ?

Please, check our dCode Discord community for help requests!
NB: for encrypted messages, test our automatic cipher identifier!

Questions / Comments

Feedback and suggestions are welcome so that dCode offers the best 'Polybius Cipher' tool for free! Thank you!


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