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

Polybius Cipher - dCode

Tag(s) : Substitution Cipher

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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.

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

__Example:__ To crypt `DCODE` with the grid

\ | 1 | 2 | 3 | 4 | 5 |
---|---|---|---|---|---|

1 | A | B | C | D | E |

2 | F | G | H | I | J |

3 | K | L | M | N | O |

4 | P | Q | R | S | T |

5 | U | V | W | X | Y |

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`

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`):

\ | 1 | 2 | 3 | 4 | 5 |
---|---|---|---|---|---|

1 | D | C | O | E | A |

2 | B | F | G | H | I |

3 | K | L | M | N | P |

4 | Q | R | S | T | U |

5 | V | W | X | Y | Z |

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`.

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.

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.

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.

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

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Cite as source (bibliography):

*Polybius Cipher* on dCode.fr [online website], retrieved on 2023-05-31,

- Polybius Square Decoder
- Polybius Square Encoder
- What is the Polybius cipher? (Définition)
- How to encrypt using Polybius cipher?
- How to decrypt Polybius cipher?
- How to recognize Polybius ciphertext?
- How to decipher Polybius without the grid?
- What are the variants of the Polybius cipher?
- When was Polybius Cipher invented?

polybius,square,greek,greece,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

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