Tools to decrypt/encrypt with double transposition cipher, as its name 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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The double transposition applies the simple transposition twice as the name suggests.
Example: Encrypt the message DCODE with the key KEY first, then the key WORD. The grid (1) is permuted a first time (2)
The intermediate message is usually read in columns from bottom to top and then from left to right.
Example: The encrypted intermediate message is CEDDO (3) and the final encrypted message is DEDCO (4):
The encryption will be more robust if the lengths of the keys are coprime.
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.
The UBCHI cipher inserts null letters between the 2 transpositions.
The double transposition cipher has no date nor known author.