Tool to decrypt / encrypt with a columnar transposition, also called column permutations cipher, a cryptographic technique that modifies the order of the letters of a previously written text in a table.

Columnar Transposition Cipher - dCode

Tag(s) : Transposition Cipher

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A columnar transposition cipher is an encryption method that swaps the columns of a table (or a grid) containing the plain message to obtain an encrypted message.

Column transposition encryption writes plaintext in a rectangular array of N columns (inline fill) with N the size of the permutation key.

__Example:__ The text `COLUMNS` is encrypted with the permutation `1,3,2` of the key word `COL`, it is written in the table

Columns | 1,2,3 | Permuted cols | 1,3,2 |

Plaintext | C,O,L | Ciphertext | C,L,O |

U,M,N | U,N,M | ||

S,X,X | S,X,X |

Fill in the empty boxes with a neutral letter (like `X`).

The encrypted message is then read in columns

__Example:__ `CUSLNXOMX`

It is possible to read line by line, in which case the encrypted message would be `CLOUNMSXX`

Decryption by Columnar Transposition is similar to encryption. The difference lies in the writing in the table (in row or in column according to the reading method used during the encryption), as well as in the order of the columns which are permuted before being sorted again in ascending order.

__Example:__ A permutation `1,3,2` was used to obtain the message `CUSLNXOMX` (reading by columns):

Permuted cols | 1,3,2 | Sorted cols | 1,2,3 |

Ciphertext | C,L,O | Plaintext | C,O,L |

U,N,M | U,M,N | ||

S,X,X | S,X,X |

The message consists of the transposed / swapped letters, so it has all the letters of the original message but in a different order.

The coincidence index after transposition of columns is unchanged from that of the plain text language.

For short permutations (up to 5-6 letters), a brute-force algorithm can test all permutations.

Otherwise, by knowing a word of the plain text (if possible with unusual letters), it is possible to find the position of its letters and to deduce the compatible columns permutations.

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Cite as source (bibliography):

*Columnar Transposition Cipher* on dCode.fr [online website], retrieved on 2024-07-18,

- Columnar Transposition Decoder
- Columnar Transposition Encoder
- What is a Columnar Transposition cipher? (Definition)
- How to encrypt using a Columnar Transposition cipher?
- How to decrypt with a Columnar Transposition cipher?
- How to recognize a Columnar Transposition ciphertext?
- How to decipher a Columnar Transposition without the key?

transposition,column,columnar,permutation,disorder,grid,table,rectangle,rectangular

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