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Ubchi Cipher

Tool to encrypt / decrypt with the code UBCHI, a key figure consisting of a double transposition used by the Germans during the First World War.

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Ubchi Cipher -

Tag(s) : Transposition Cipher

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Ubchi Cipher

Ubchi Cipher Decoder




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Ubchi Cipher Encoder




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Tool to encrypt / decrypt with the code UBCHI, a key figure consisting of a double transposition used by the Germans during the First World War.

Answers to Questions

How to encrypt using Ubchi cipher?

The encryption uses two consecutive transposition ciphers with the same permutation key.

Example: Encrypt MESSAGE with the key CODE

Step 1 - Write the message in a grid of width N with N the size of the key.

Example: The key CODE has 4 letters so

CODE
MESS
AGE

In order to simplify the decryption, sometimes the message was supplemented by a null letter like X, so as not to have empty boxes in the grid.

Step 2 - Sort the key alphabetically and swap the columns of the table accordingly

Example:

CDEO
MSSE
AEG

Step 3 - Read the table in columns from top to bottom and from left to right in order to get a new message

Example: Intermediate message: MASESEG

Step 4 - Repeat steps 1 to 3 a second time, the result is the final encrypted message.

Example: 1bis)

CODE
MASE
SEG

2bis)
CDEO
MSEA
SGE

3bis) Final message MSSGEAE

How to decrypt Ubchi cipher?

Decryption begins by determining the form of the grid used during encryption. Count the number of characters in the encrypted message and the permutation key, in order to deduce the number of columns, rows and especially if the last row has empty boxes. This step is not necessary if the message has a length of a multiple of the key (see encryption).

Example: Decipher MSSGEAE (7 letters) with the key CODE (4 letters), the table will have the form

CODE
XXXX
XXX

Step 1 - Sort the key in alphabetical order and fill in the grid in columns with the encrypted message.

Example: The grid fills up

CDEO
MSEA
SGE

Step 2 - Swap the columns of the grid to find the letters of the key in the correct order.

Example: The grid is swapped

CODE
MASE
SEG

Step 3 - Read the grid in lines from left to right then from top to bottom in order to get the message

Example: Intermediate message: MASESEG

Step 4 - Repeat steps 1 to 3 a second time, the result is the original plain message.

Example: 1bis)

CDEO
MSSE
AEG

2bis)
CODE
MESS
AGE

3bis) Original message MESSAGE

How to recognize a Ubchi ciphertext?

Any message encrypted by Ubchi is a transposition of the characters of the original message, so the analysis of the frequency of the letters and the index of coincidence are the same as those of the plain message.

The cipher was abandoned by the Germans following an article in the French newspaper Le Matin in November 1914, which praised the success of the decryption by the French. Any reference to German coded messages or to the newspaper Le Matin is a clue.

How to decipher Ubchi without key?

Attempting permutations by brute force is possible as long as the key is not too large (the number of possible permutations is equal to N! With N the size of the key).

What are the variants of the Ubchi cipher?

The Ubchi figure could be made more complex by repeating the transposition several times or by performing a double transposition by modifying the key the second time.

When Ubchi have been invented ?

The figure was used at the start of the First World War. The principle of encryption by transposition dates from well before.

Source code

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