Cryptography - Implementing Vigenere Cipher

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In the last chapter we saw Vigenere Cipher, its methods, strengths weeknesses. Now we will implement vigenere cipher using different programming langugages like Python, Java, and C++.

Implementation using Python

The Vigenere cipher, a technique for encrypting and decrypting text messages, is implemented in this Python code. The generate_key() function takes a keyword as input, creates a key based on that keyword, then repeats the words as needed to make sure the key fits the text length. The Vigenere cipher algorithm, which shifts each character according to its matching character in the key, is used by the encrypt_text() function to encrypt the text. In the same way, by reversing the encryption process, the decrypt_text() method decrypts the ciphertext and shows the original text.

Example

Following is the implementation of Vigenere Cipher with the help of Python −

def generate_key(text, keyword):
   key = list(keyword)
   if len(text) == len(keyword):
      return key
   else:
      for i in range(len(text) - len(keyword)):
         key.append(key[i % len(keyword)])
   return "".join(key)

def encrypt_text(text, key):
   cipher_text = []
   for i in range(len(text)):
      x = (ord(text[i]) + ord(key[i])) % 26
      x += ord('A')
      cipher_text.append(chr(x))
   return "".join(cipher_text)

def decrypt_text(cipher_text, key):
   original_text = []
   for i in range(len(cipher_text)):
      x = (ord(cipher_text[i]) - ord(key[i]) + 26) % 26
      x += ord('A')
      original_text.append(chr(x))
   return "".join(original_text)

# Driver code
text = "TUTORIALSPOINT"
keyword = "KEY"
key = generate_key(text, keyword)
cipher_text = encrypt_text(text, key)
print("The Encrypted text:", cipher_text)
print("The Original/Decrypted Text:", decrypt_text(cipher_text, key))

Following is the output of the above example −

Input/Output

The Encrypted text: DYRYVGKPQZSGXX
The Original/Decrypted Text: TUTORIALSPOINT

Implementation using Java

A method used for encrypting and decrypting messages is the Vigenere Cipher. The length of the text message and a keyword are used in the code to generate a key. The text message is then encrypted with the help of this key by shifting each character in the alphabet to match its proper location in the key. The same key is used to reverse the encryption process and return each character to its original alphabetic position in order to decrypt the message. With the original message as the result, the parties that have the key can communicate privately with one another.

Example

See the Java implementation below for vigenere cipher −

public class VigenereCipher {
   static String generateKey(String text, String keyword) {
     int textLength = text.length();
     for (int i = 0; ; i++) {
         if (textLength == i)
            i = 0;
         if (keyword.length() == textLength)
            break;
         keyword += (keyword.charAt(i));
      }
      return keyword;
   }

   static String encryptText(String text, String keyword) {
      String ciphertext = "";

      for (int i = 0; i < text.length(); i++) {
         // converting in range 0-25
         int x = (text.charAt(i) + keyword.charAt(i)) % 26;

         // convert into alphabets(ASCII)
         x += 'A';

         ciphertext += (char)(x);
      }
      return ciphertext;
   }

   // Decrypt the encrypted text and return the original text
   static String decryptText(String ciphertext, String keyword) {
     String originalText = "";

      for (int i = 0 ; i < ciphertext.length() && i < keyword.length(); i++) {
         // converting in range 0-25
         int x = (ciphertext.charAt(i) - keyword.charAt(i) + 26) % 26;

         // convert into alphabets(ASCII)
         x += 'A';
         originalText += (char)(x);
      }
      return originalText;
   }

   // Driver code
   public static void main(String[] args) {
      String message = "Hello everyone";
      String keyword = "Best";

      String text = message.toUpperCase();
      String key = keyword.toUpperCase();

      String generatedKey = generateKey(text, key);
      String encryptedText = encryptText(text, generatedKey);

      System.out.println("The Encrypted Text : " + encryptedText);

      System.out.println("The Original/Decrypted Text : " + decryptText(encryptedText, generatedKey));
   }
}

Following is the output of the above example −

Input/Output

The Encrypted Text : IIDEPXWOFVQHOI
The Original/Decrypted Text : HELLOTEVERYONE

Implementation using C++

We will use the C++ programming language to implement the Vigenere Cypher in this code. We will apply a set of Caesar shifts to the plaintext message's characters in this cipher using a key. Each letter in the key relates to a distinct shift value, and the key defines the amount of shift applied to each character. Every character in the plaintext is shifted forward in the alphabet in encryption by the matching number given by the key.

In a similar way, the original plaintext becomes visible in decryption by shifting the ciphertext's characters backward by the same amount shown in the key.

Example

Below is the simple implementation for vigenere cipher using C++ programming language −

#include <iostream>  
#include <string>  
using namespace std;  
 
class VigenereCipher {  
   public:  
      string key;  

   VigenereCipher(string key) {  
      for (int i = 0; i < key.size(); ++i) {  
         if (key[i] >= 'A' && key[i] <= 'Z')  
            this -> key += key[i];  
         else if (key[i] >= 'a' && key[i] <= 'z')  
            this -> key += key[i] + 'A' - 'a';  
      }  
   }  
   
   string encryptFunc(string text) {  
      string out;  
      for (int i = 0, j = 0; i < text.length(); ++i) {  
         char c = text[i];  
         if (c >= 'a' && c <= 'z')  
            c += 'A' - 'a';  
         else if (c < 'A' || c > 'Z')  
            continue;  
         out += (c + key[j] - 2 * 'A') % 26 + 'A';  
         j = (j + 1) % key.length();  
      }  
      return out;  
   }  
   
   string decryptFunc(string text) {  
      string out;  
      for (int i = 0, j = 0; i < text.length(); ++i) {  
         char c = text[i];  
         if (c >= 'a' && c <= 'z')  
            c += 'A' - 'a';  
         else if (c < 'A' || c > 'Z')  
            continue;  
         out += (c - key[j] + 26) % 26 + 'A';  
         j = (j + 1) % key.length();  
      }  
      return out;  
   }  
}; 

int main() {  
   VigenereCipher cipher("VigenereCipher");   
   string plaintext = "Cyber Security";  
   string et = cipher.encryptFunc(plaintext);  
   string dt = cipher.decryptFunc(et);  

   cout << "The Plaintext: " << plaintext << endl;  
   cout << "The Encrypted Text: " << et << endl;  
   cout << "The Decrypted Text: " << dt << endl;  
}  

Following is the output of the above example −

Input/Output

The Plaintext: Cyber Security
The Encrypted Text: XGHIEWVGWZXAC
The Decrypted Text: CYBERSECURITY