Vigenere Cipher - Encryption

Introduction

This tutorial provides a step-by-step guide to understanding and implementing the Vigenere Cipher, a method of encrypting text that uses a keyword to determine the encoding of each letter. The Vigenere Cipher is notable for its historical significance and for being a more secure alternative to simpler ciphers like the Caesar Cipher. By the end of this guide, you will be able to encrypt messages using the Vigenere Cipher.

Step 1: Understanding the Vigenere Cipher Basics

• The Vigenere Cipher uses a keyword to create a series of Caesar Ciphers based on the letters of the keyword.
• Each letter in the plaintext is shifted according to the corresponding letter in the keyword.
• The keyword is repeated if it is shorter than the plaintext.

Step 2: Prepare Your Key

• Choose a keyword that you will use for encryption. For example, let’s use "KEY".
• Ensure the keyword consists only of letters and is not too common to enhance security.

Step 3: Format the Plaintext

• Write down your message that you want to encrypt. For example, "HELLO WORLD".
• Remove any spaces and punctuation for simplicity. The modified plaintext is "HELLOWORLD".

Step 4: Repeat the Keyword

• Repeat the keyword above the plaintext so they align. If the plaintext is longer than the keyword, repeat the keyword as needed.

Plaintext:  H E L L O W O R L D
Keyword:    K E Y K E Y K E Y K

Step 5: Encryption Process

• For each letter in the plaintext, shift it according to the corresponding letter in the keyword:
  • Convert each letter to its numerical equivalent (A=0, B=1, ..., Z=25).
  • Use the formula:

    Encrypted Letter = (Plaintext Letter + Keyword Letter) mod 26
    

• Example calculation:
  • For the first letter: H (7) + K (10) = 17, which corresponds to R.

Continue this process for each letter:

• H + K = R
• E + E = I
• L + Y = J
• L + K = V
• O + E = S
• W + Y = U
• O + K = Y
• R + E = V
• L + Y = J
• D + K = N

Step 6: Complete the Encryption

• Combine the encrypted letters to form the final encrypted message:

Encrypted Message: RIJVSUYVJN

Conclusion

You have successfully encrypted a message using the Vigenere Cipher! Remember to keep your keyword secure, as it is essential for decoding the message. For further exploration, consider trying out decryption methods or experimenting with different keywords to see how they impact the encryption. Happy encrypting!