Transposition Cipher

Transposition cipher uses an algorithm to rearrange the letters of a plaintext, forming the ciphertext.

The purpose of the columnar transposition encryption method is to change the positions of the characters without changing their identities. It can be applied by using a password or simply by changing the row column. In the columnar transposition encryption method, while the text to be encrypted with a C value is inserted into the table, the number of columns to be in the table is determined. Let’s try to encrypt ‘AN INFORMATION SECURITY BLOG’ without a key, and assuming C = 5;

ANINF
ORMAT
IONSE
CURIT
YBLOG

Without a Key:

The ciphertext becomes;

AOICYNROUBIMNRLNASIOFTETG

Since we used C = 5, the output of the ciphertext will become as;

AOICY NROUB IMNRL NASIO FTETG

With a Key:

Let’s assume we want to encrypt this sentence with ‘BESEC’ key. We are again creating the same table with the key at the top;

BESEC
ANINF
ORMAT
IONSE
CURIT
YBLOG

Then we number the letters of the key in alphabetical order;

BESEC
13542
ANINF
ORMAT
IONSE
CURIT
YBLOG

Because the letter e occurs twice in the word, we numbered the first one as 3, and the other one as 4. Now, we write the ciphertext according to column number;

AOICYFTETGNROUBNASIOIMNRL

And the output will become;

AOICY FTETG NROUB NASIO IMNRL

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