Tools to decrypt/encrypt with double transposition cipher, as its names indicates, it uses two transposition ciphers, with one or two keys, and applied on lines or columns or both.
Double Transposition Cipher - dCode
Tag(s) : Transposition Cipher
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Example: Encrypt the message DCODE with twice the key KEY. The grid (1) is completed with X and permuted a first time (2)
With the message found after the first permutation, then perform a second transposition, but with the rows. The ciphertext is then obtained by reading the grid in rows from left to right and from top to bottom.
Example: The encrypted intermediate message is CDOEDX (3) and the final encrypted message is OECDDX (4):
The encrypted message must get two reversed transposition, in the opposite order of the original order, to get back the plain text.
Example: The grid (1) becomes after inverse permutation in rows (2)
Example: The intermediate message CDOECX undergoes a second inverse permutation in columns (3) which gives the original starting grid (4) and the plain message DCODEX
It is possible to find the key length by analyzing the prime decomposition of the text length.
By writing the text in the grid/checkerboard, permute the columns in order to find and recreate words on each rows, beginning with common bigrams (such as TH, HE, IN, etc.).
The lines should not follow each other, do not try to read words on several lines.
It is possible to shuffle rows or columns in the desired order.
No date of known author.