S-DES Encryption

#include <iostream>
#include <string>

using namespace std;

//Prototype functions
string SDESEncrypt(string plainText, string key, int currentRound);
string SDESDecrypt(string cipherText, string key, int currentRound);
string XOR(string inputOne, string inputTwo);
string expansion(string input);


//Defines the S-boxes needed for S-DES
string s1box[2][8] = { "101", "010", "001", "110", "011", "100", "111", "000",
"001", "100", "110", "010", "000", "111", "101", "011" };

string s2box[2][8] = { "100", "000", "110", "101", "111", "001", "011", "010",
"101", "011", "000", "111", "110", "010", "001", "100" };


int main()
{
    string plaintext = "100010110101";
    string key = "111000111";
    string encrypted;

    encrypted = SDESEncrypt(plaintext, key, 1);
    cout << "The encrypted text for round 1 is: " << encrypted << endl;

    encrypted = SDESEncrypt(encrypted, key, 2);
    cout << "The encrypted text for round 2 is: " << encrypted << endl;

    encrypted = SDESEncrypt(encrypted, key, 3);
    cout << "The encrypted text for round 3 is: " << encrypted << endl;

    encrypted = SDESEncrypt(encrypted, key, 4);
    cout << "The encrypted text for round 4 is: " << encrypted << endl;

    system("PAUSE");
    return 0;
}

string SDESEncrypt(string plainText, string key, int currentRound)
{
    string leftZero, rightZero, leftOne, rightOne, encrypted, roundKey, sBoxResult;
    int row = 0, column = 0;
    //Calculates the value of the current rounds key
    for (int i = 0; i < 8; i++)
        roundKey += key[(currentRound + i - 1) % 8];

    //Splits the input into a left and right string
    for (int i = 0; i < 6; i++)
        leftZero += plainText[i];

    for (int i = 6; i < 12; i++)
        rightZero += plainText[i];

    //The left output is equal to the right half input
    leftOne = rightZero;

    //Expands the right half of the input
    rightOne = expansion(rightZero);

    //Xors the right half with the key
    rightOne = XOR(rightOne, roundKey);


    //S-Box Function for S-Box 1
    if (rightOne[0] == '1')
        row = 1;

    if (rightOne[1] == '1')
        column += 4;
    if (rightOne[2] == '1')
        column += 2;
    if (rightOne[3] == '1')
        column += 1;

    //S-box function for S-Box 2
    sBoxResult += s1box[row][column];

    row = 0, column = 0;

    if (rightOne[4] == '1')
        row = 1;

    if (rightOne[5] == '1')
        column += 4;
    if (rightOne[6] == '1')
        column += 2;
    if (rightOne[7] == '1')
        column += 1;

    sBoxResult += s2box[row][column];

    //XORs leftzero with the result of the S-Box function
    rightOne = XOR(sBoxResult, leftZero);

    //Puts left half and right half together
    encrypted = leftOne + rightOne;

    return(encrypted);
}

string SDESDecrypt(string cipherText, string key, int currentRound)
{
    return("TEST");
}

//This function can XOR to binary numbers
string XOR(string inputOne, string inputTwo)
{
    for (int i = 0; i < inputOne.length(); i++)
    {
        if ((inputOne[i] == '1' && inputTwo[i] == '0') || (inputOne[i] == '0' && inputTwo[i] == '1'))
            inputOne[i] = '1';

        else
            inputOne[i] = '0';
    }

    return(inputOne);
}

//This is the expansion function from S-DES
string expansion(string input)
{
    string expanded;
    expanded += input[0];
    expanded += input[1];
    expanded += input[3];
    expanded += input[2];
    expanded += input[3];
    expanded += input[2];
    expanded += input[4];
    expanded += input[5];

    return(expanded);
}