Question

Study the VIGENÈRE CIPHER and implemented it with c++

1.In your program, you should have two functions: encryption and decryption.

2. Use any key you like. (Don't use deceptive in the slides)

3. choose a sentence or a paragraph you like as the plaintext.

I have the code I just need the implementation in a different way

// C++ code to implement Vigenere Cipher
#include<bits/stdc++.h>
using namespace std;

// This function generates the key in
// a cyclic manner until it's length isi'nt
// equal to the length of original text
string generateKey(string str, string key)
{
   int x = str.size();

   for (int i = 0; ; i++)
   {
       if (x == i)
           i = 0;
       if (key.size() == str.size())
           break;
       key.push_back(key[i]);
   }
   return key;
}

// This function returns the encrypted text
// generated with the help of the key
string cipherText(string str, string key)
{
   string cipher_text;

   for (int i = 0; i < str.size(); i++)
   {
       // converting in range 0-25
       char x = (str[i] + key[i]) %26;

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

       cipher_text.push_back(x);
   }
   return cipher_text;
}

// This function decrypts the encrypted text
// and returns the original text
string originalText(string cipher_text, string key)
{
   string orig_text;

   for (int i = 0 ; i < cipher_text.size(); i++)
   {
       // converting in range 0-25
       char x = (cipher_text[i] - key[i] + 26) %26;

       // convert into alphabets(ASCII)
       x += 'A';
       orig_text.push_back(x);
   }
   return orig_text;
}

// Driver program to test the above function
int main()
{
   string str = "GEEKSFORGEEKS";
   string keyword = "AYUSH";

   string key = generateKey(str, keyword);
   string cipher_text = cipherText(str, key);

   cout << "Ciphertext : "
       << cipher_text << "\n";

   cout << "Original/Decrypted Text : "
       << originalText(cipher_text, key);
   return 0;
}

Answer 1

I've taken your code and edited it in a manner that suits the question. Hope this helps :)

 // C++ code to implement Vigenere Cipher #include<bits/stdc++.h> using namespace std; //Converts a string to uppercase string upper_string(string str) {     for(int i=0;str[i]!='\0';i++)   {               if (str[i] >= 'a' && str[i] <= 'z') //checking for lowercase characters                   str[i] = str[i] - 32; //converting lowercase to uppercase       }       return str; } // This function generates the key in // a cyclic manner until it's length isi'nt // equal to the length of original text string generateKey(string str, string key) { int x = str.size(); for (int i = 0; ; i++) { if (x == i) i = 0; if (key.size() == str.size()) break; key.push_back(key[i]); } return key; } // This function returns the encrypted text // generated with the help of the key string encryption(string str, string key) { string cipher_text; for (int i = 0; i < str.size(); i++) { // converting in range 0-25 char x = (str[i] + key[i]) %26; // convert into alphabets(ASCII) x += 'A'; cipher_text.push_back(x); } return cipher_text; } // This function decrypts the encrypted text // and returns the original text string decryption(string cipher_text, string key) { string orig_text; for (int i = 0 ; i < cipher_text.size(); i++) { // converting in range 0-25 char x = (cipher_text[i] - key[i] + 26) %26; // convert into alphabets(ASCII) x += 'A'; orig_text.push_back(x); } return orig_text; } // Driver program to test the above function int main() { //string str = "ATTACKATDAWN"; //string keyword = "LEMON"; string str,keyword,cipher_text; int ch; cout<<"\nEnter the keyword:"; cin>>keyword; keyword=upper_string(keyword); cout<<"\nEnter 1 to Encrypt plain text.\nEnter 2 to decrypt encrypted text.\n"; cin>>ch; cout<<"\nEnter the string:"; cin>>str; str=upper_string(str); string key = generateKey(str, keyword); if(ch==1) { cipher_text = encryption(str, key); cout << "Ciphertext : "<< cipher_text << "\n"; } else if(ch==2) { cout << "Original/Decrypted Text : "<< decryption(str, key); } else { cout<<"\nInvalid Option!!!"; } return 0; }

Outputs:

Enter the keyword: lemon Enter 1 to Encrypt plain text. Enter 2 to decrypt encrypted text. 1 Enter the string:attackatdawn Ciphertext : LXFOPVEFRNHR

Enter the keyword: lemon Enter 1 to Encrypt plain text. Enter 2 to decrypt encrypted text. 2 Enter the string:lxfopvefrnhr Original/Decrypted Text : ATTACKATDAWN