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Columnar Transposition Cipher

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

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Columnar Transposition Cipher -

Tag(s) : Transposition Cipher

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Columnar Transposition Cipher

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Columnar Transposition Decoder




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Columnar Transposition Encoder







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

Answers to Questions

How to encrypt using a Columnar Transposition cipher?

Column transposition encryption writes plaintext in an 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

Columns1,2,3Permuted cols1,3,2
PlaintextC,O,LCiphertextC,L,O
U,M,NU,N,M
S,X,XS,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

How to decrypt with a Columnar Transposition cipher?

Decryption by Columnar Transposition is similar to encryption. The difference lies in the writing in the table (in rown 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 cols1,3,2Sorted cols1,2,3
CiphertextC,L,OPlaintextC,O,L
U,N,MU,M,N
S,X,XS,X,X

How to recognize a Columnar Transposition ciphertext?

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.

How to decipher a Columnar Transposition without key?

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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Source code

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