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Articles Home » C++ » C++ Program to Implement the Vigenere Cipher

C++ Program to Implement the Vigenere Cipher

This is a C++ Program to implement Vigenere cipher. The Vigenère cipher is a method of encrypting alphabetic text by using a series of different Caesar ciphers based on the letters of a keyword. It is a simple form of polyalphabetic substitution.

Here is source code of the C++ Program to Implement the Vigenere Cypher. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

```
#include <iostream>
```
```
#include <string>
```
```
using namespace std;
```
```
 
```
```
class Vigenere
```
```
{
```
```
    public:
```
```
        string key;
```
```
 
```
```
        Vigenere(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 encrypt(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 decrypt(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()
```
```
{
```
```
    Vigenere cipher("VIGENERECIPHER");
```
```
 
```
```
    string original =
```

            "Beware the Jabberwock, my son! The jaws that bite, the claws that catch!";

    string encrypted = cipher.encrypt(original);

    string decrypted = cipher.decrypt(encrypted);

```
 
```
```
    cout << original << endl;
```

    cout << "Encrypted: " << encrypted << endl;

    cout << "Decrypted: " << decrypted << endl;

```
}
```

Output:

$ g++ VigenereCipher.cpp
$ a.out
 
Beware the Jabberwock, my son! The jaws that bite, the claws that catch!
Encrypted: WMCEEIKLGRPIFVMEUGXQPWQVIOIAVEYXUEKFKBTALVXTGAFXYEVKPAGY
Decrypted: BEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCH
 
------------------
(program exited with code: 0)
Press return to continue

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