Tool to find a key corresponding to a permutation/transposition during an encryption from transposition numbers.

Transposition Key - dCode

Tag(s) : Transposition Cipher, Word Search

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A transposition key, also called a permutation, is an encryption method that involves rearranging characters in text using a specific key. This key determines how the characters of the original text will be rearranged to produce ciphertext.

To generate a permutation from a word/keyword:

— Choose a word, if possible that does not have a duplicate letter (an isogram/heterogram).

__Example:__ Generate the transposition key for the word `INDEX`

— Associate each letter with its position p.

__Example:__ `I:1,N:2,D:3,E:4,X:5`

— Rearrange the letters in alphabetical order (while keeping the association p created previously).

__Example:__ `D:3,E:4,I:1,N:2,X:5`

— Read the list of positions p, it is the permutation key

__Example:__ The key is `3,4,1,2,5`

There is no fast algorithm to recover the original word from a permutation. Indeed, the same transposition key may have been generated by several different words.

The bruteforce method (attempting all the words in the dictionary) is the only possible attack. dCode has pre-calculated the permutations of the dictionary words and compares these with the requested permutation in order to display which are the possible words.

__Example:__ `1,6,4,2,5,3` is the key generated by the words `CRYPTO`, `CRUISE` or `ALPINE`

A reverse transposition key is a key used to decrypt ciphertext that has been transformed using a transposition key. This inverse key is generated by reversing the order of the positions specified by the original permutation key. By applying this reverse key to the ciphertext, the characters are returned to their original order, revealing the plain text.

To calculate the inverse permutation **from the transposition key**:

— Associate each number with its position p

— Sort the list of numbers in ascending order (keeping the association p)

— Read the list of positions, it is the reverse transposition key

__Example:__ Calculate the inverse transposition to `(1,6,4,2,5,3)` whose positions are '(1:1),(6:2),(4:3),(2:4), (5:5),(3:6)' then sorted by ascending order: '(1:1),(2:4),(3:6),(4:3),(5:5),( 6:2)' or the inverse permutation: `(1,4,6,3,5,2)`

To calculate the inverse permutation **from a word**:

— Calculate the transposition corresponding to the word and apply the steps above.

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Cite as source (bibliography):

*Transposition Key* on dCode.fr [online website], retrieved on 2023-09-27,

transposition,key,permutation,word,keyword

https://www.dcode.fr/transposition-key

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