VernamCipher.cpp

#include <iostream>
#include <string>
#include <algorithm>
#include <stdexcept>
using namespace std;

void unexp_handler()
{
	cout<<"\n-----Key length should not be greater than the Plain tect----\n";
	abort();
}

int main(int argc, char const *argv[])
{
	set_unexpected(unexp_handler);
	string plaintext, key, ciphertext, alphabet;

    if (argc==2) {
    	plaintext = argv[1];
    	cout<<"Key:\t";
    	cin>>key;

    } else if (argc == 3) {
    	plaintext = argv[1];
    	key = argv[2];
    } else {
    	cout<<"Plain Text:\t";
    	cin>>plaintext;
    	cout<<"Key:\t";
    	cin>>key;
    }

    transform(plaintext.begin(), plaintext.end(), plaintext.begin(), ::tolower);
    transform(key.begin(), key.end(), key.begin(), ::tolower);
    int ptlen = plaintext.length();
    int klen  = key.length();
    if (klen > ptlen)
    {
    	unexpected();
    }
    
    for(int i = 97; i < 123; i++)
    {
        alphabet.insert(alphabet.end(), (char)i);
    }
    for(int i = 0; i < klen; i++)
    {
    	ciphertext.insert(ciphertext.end(), alphabet[(alphabet.find(plaintext[i]) ^ alphabet.find(key[i]))%26]);
    }
    for (int i = klen; i < ptlen; i++)
    {
    	ciphertext.insert(ciphertext.end(), alphabet[(alphabet.find(plaintext[i]) ^ alphabet.find(plaintext[i-klen]))%26]);
    }
    cout<<"Cipher Text:\t"<<ciphertext<<endl;

	return 0;
}