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Grandpré Cipher

Tool to decrypt/encrypt automatically with the Grandpré Cipher, using a large grid and letter coordinates.

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Grandpré Cipher -

Tag(s) : Homophonic Substitution Cipher, GRID_CIPHER

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# Grandpré Cipher

## Grandpré Cipher Decoder

 Coordinate Order Row-Column (by default) Column-Row (rare)

## Grandpré Encoder

 Coordinate Order Row-Column (by default) Column-Row (rare)

### What is the Grandpré cipher? (Definition)

The Grandpré cipher is a homophonic substitution cipher (the same letter can have several encryption) using a 10x10 grid.

The author (Grandpré) calls his process Méthode de Carré 10x10 (10x10 Square Method)

### How to encrypt using Grandpré cipher?

Encryption requires a grid, in the original version described by Grandpré, it is 10x10 in size and consists of 10 words (one per line) and the initials of the first 10 words themselves constitute an 11th word. Row and column coordinates are numbered 1,2,3,4,5,6,7,8,9,0.

Example: Grandpré proposes as a grid (which he calls checkerboard)

1 2 3 4 5 6 7 8 9 0 \ V O L U P T U E U X I N Q U I E T U D E M A J E S T U E U X O B L I G E A N C E U N I F O R M I T E T W I C K E N H A M I N G O L S T A D T E I N S I E D E L N R Y M K I E W I C Z S H R E W S B U R Y

The encrypted message consists of the substitution of the letters of the clear message by their coordinates (line, column) in the grid (if there are several, take one randomly).

Example: GRANDPRE can be coded 73 09 78 22 29 15 03 88

### How to decrypt Grandpré cipher?

Grandpré decryption requires knowledge of the encryption grid (or of the 10 words composing it). The method consists of taking the digits of the code in pairs, the first digit indicating the row and the second the column of the letter in the grid.

Example: 45 56 32 72 29 15 03 66 is decrypted GRANDPRE

### How to recognize a Grandpré ciphertext? (Identification)

A message encrypted by Grandpré consists of digits, arranged in pairs of 2, so has an even length.

The presence of 10 10-letter words can be a clue.

### What are the variants of the Grandpré cipher?

Grandpré's method has evolved and some (including the American Cryptogram Association) recommend 8x8 size squares.

It is also possible to use column numbering starting from 0.

Polybius square is a very similar cipher method, but with a 5x5 square and no repeating letters in the grid.

### What are Grandpré checkerboards?

Grandpré presents 7 grids/checkerboards (called damier) to present its encryption process:

 Damier 1 : `VOLUPTUEUXINQUIETUDEMAJESTUEUXOBLIGEANCEUNIFORMITETWICKENHAMINGOLSTADTEINSIEDELNRYMKIEWICZSHREWSBURY` Damier 2 : `INVENTAIRENIEMCEWICZJACQUEMARTUNIFORMITESCHLESTADTTYPOGRAPHEINTERLAKENCHRYSALIDEEXHALAISONSEBASTOPOL` Damier 3 : `NEVROTOMIEEQUATORIALUNIVERSITEFRAUDULEUXCHAMPIGNONHAWKESBURYAJUSTEMENTTREBIZONDEELLIPSOIDELOGARITHME` Damier 4 : `JUXTAPOSERAUSTERLITZCARTWRIGHTQUILLEBEUFUNIVERSITEELNSIEDELNMADAGASCARAPOCALYPSEROUTSCHOUKDOUARNENEZ` Damier 5 : `HERCULANUMANTIQUAIREWURTZBOURGKLAGENFURTEXHUMATIONSUPERLATIFBIJOUTERIEUNIVERSITEROTHSCHILDYSSINGEAUX` Damier 6 : `BRUXELLOISINDULGENCEVALPARAISOORPHELINATUNIVERSITEABJURATIONQUEENSTOWNUNIFORMITEEINSIEDELNRYMKIEWICZ` Damier 7 : `LOGARITHMEASSUJETTIRBENEFICIERYSSINGEAUXRAPSODISTEINTERLAKENNIEMCEWICZTRAVAILLERHERCULANUMEQUATORIAL`

It also features a long list of 10-letter words (in French).

### When was Grandpré cipher invented?

A. de Grandpré described his process in 1905 in his book, a cryptographic treatise, entitled Cryptographie pratique (Practical Cryptography).

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Grandpré Cipher on dCode.fr [online website], retrieved on 2023-12-05, https://www.dcode.fr/grandpre-cipher

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