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;

A | N | I | N | F |

O | R | M | A | T |

I | O | N | S | E |

C | U | R | I | T |

Y | B | L | O | G |

**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;

B | E | S | E | C |

A | N | I | N | F |

O | R | M | A | T |

I | O | N | S | E |

C | U | R | I | T |

Y | B | L | O | G |

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

B | E | S | E | C |

1 | 3 | 5 | 4 | 2 |

A | N | I | N | F |

O | R | M | A | T |

I | O | N | S | E |

C | U | R | I | T |

Y | B | L | O | G |

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