Tuesday, October 5, 2021

Vigenère Cipher | How to create Vigenère table?

     Introduction

There are basically two types of symmetric cipher: Substitution Cipher, Transposition Cipher.

Substitution Cipher: A substitution is a technique in which each letter or bit of the plaintext is substituted or replaced by some other letter, number or symbol to produce cipher text. For Example, ABC  XYZ.

Types of Substitution Cipher: Caesar Cipher, Monoalphabetic Cipher, Vigenère Cipher, Playfair Cipher, One time pad cipher (Vernam cipher), Hill Cipher.

Transposition Cipher: In transposition technique, there is no replacement of alphabets or numbers occurs instead their positions are changed or reordering of position of plain text is done to produce cipher text. For Example, ABCDE    BADEC.

Types of Transposition Cipher: Rail Fence Cipher, Columnar Transposition Cipher.

 

Vigenère Cipher

Vigenère Cipher is a method of encrypting alphabetic text. It uses a simple form of polyalphabetic substitution. A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets. The encryption of the original text is done using the Vigenère square or Vigenère table.

The table consists of the alphabets written out 26 times in different rows, each alphabet shifted cyclically to the left compared to the previous alphabet.

Figure: Vigenere Table

Rules of encryption is as follows:

Step-1: Create Vigenère table as per your given keyword. (If Vigenère table is not given). Given keyword arrange in alphabetical order then create table as per given below.


Step-2: First row represents Plain Text and First column represents Keyword in Vigenère table.


Step-3: In Keyword length is lesser than given plain text then repeat keyword alphabets until it matches the length of plain text.


Step-4: The first letter of the plaintext, “I” is paired with “M”, the first letter of the key. So, use row “M” and column “I” of the Vigenère table, it produces cipher text “U” and so on.

To learn more about Vigenere Cipher, Click here

    
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