Columnar Transposition made easy.

Encryption was used through the history of mankind before we invented electrically powered computers. Even though they are not used anymore, they provide an insight into how modern encryption techniques like AES, Asymmetric Encryption originated.

 This article will give you a step-by-step guide to applying the classical encryption method – Columnar Columnar Transposition.

 The ciphertext is obtained by changing the column of the plain-text according to the alphabetic order of the letters of a keyword.

Problem:

Anna wants to send a confidential message to Bob. She is going to use the Columnar Transposition to encrypt the message using a secret word shared with Bob.

Message:

we should go to the movie tonight meet me at the pub

Secret word:

LOVEU

Solution:

Anna will follow the below steps to generate the ciphertext to be sent to Bob.

1. Remove the spaces between each word of the message.

weshouldgototheamovietonightmeetmeatthepub

2. Calculate the number of columns based on the length of the secret word.
  • Secret word: loveu
  • Number of columns: 5

The number of columns is based on the length of the secret word. 

2. Calculate the number of rows to be used during the encryption process.

Remember, we are using the Columnar Transposition so if there are letters more than the length of the keyword you have figure number of rows.

  • Length of the Message after stripping white-spaces: 42
  • Length of the Secret Word: 5
  • Number of rows : 42/5 => 8.4 (9 Rows)
3. Organise the message text into blocks.

To make it clearer, it will be easy to separate the outcome of step 2 (Message after removing spaces) into blocks of 5. How many characters to a single chunk is determined by the length of the keyword.

  • Length of the keyword (AKA: Number of columns): 5
  • Message after removing spaces:  weshouldgototheamovietonightmeetmeatthepub
  • After creating chunks of 5 : 

wesho uldgo tothe amovi etoni ghtme etmea tthep ub

4. Arrange the blocks into a table.
Columnar Transposition using a Table.

Make sure to add special characters (eg. *) as padding’s.

5. Extract the cipher text.

Start re-writing the encrypted message left to right from the first row onward and move till the end of the table.

Extract text from Left to Write the Top to Bottom.

Encrypted Text:

ESOWHLDOUGOTETHMOIAVTOIENHTEGMTMAEETHPTEB*U*

Conclusion:

So what do you guys think? Have a better method to solve this ? Please let us know in the comments section.

This article was a work of a guest author. We value their contribution and respect their wish to remain anonymous. If you want to get in touch with the author please contact us.

Cite this article as: Guest Contributor, "Columnar Transposition made easy.," in Cyber Memos, April 10, 2020, https://cybermemos.com/cyber-security/columnar-transposition-made-easy/.

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