VigenereCipher.cpp

#include <iostream>

using namespace std;

string message;
string mappedKey;

void messageAndKey(){
    string msg;
    cout << "Enter message: ";
    getline(cin, msg);
    cin.ignore();

    //message to uppercase
    for(int i = 0; i < msg.length(); i++){
        msg[i] = toupper(msg[i]);
    }

    string key;
    cout << "Enter key: ";
    getline(cin, key);
    cin.ignore();

    //key to uppercase
    for(int i = 0; i < key.length(); i++){
        key[i] = toupper(key[i]);
    }

    //mapping key to message
    string keyMap = "";
    for (int i = 0,j = 0; i <msg.length();i++){
        if(msg[i] ==32){
            keyMap += 32;
        } else {
            if(j<key.length()){
                keyMap += key[j];
                j++;
            } else {
                j = 0;
                keyMap += key[j];
                j++;
            }
        } //if-else
    } //for

//    cout << msg << "\n" << keyMap;
    message = msg;
    mappedKey = keyMap;
}

int tableArr[26][26];
void createVigenereTable(){
    for (int i = 0; i < 26; i++){
        for (int j = 0; j < 26; j++){
            int temp;
            if((i+65)+j > 90){
                temp = ((i+65)+j) - 26;

                //adding ASCII of alphabet letter in table index position
                tableArr[i][j] = temp;
            } else {
                temp = (i+65)+j;

                //adding ASCII of alphabet letter in table index position
                tableArr[i][j] = temp;
            }
        } // for j loop
    } // for i loop

    //testing the table
//    for(int i = 0; i <26; i++){
//        for(int j = 0; j < 26; j++){
//            cout << (char)tableArr[i][j] << " ";
//        }
//        cout << endl;
//    }
}

void cipherEncryption(string message, string mappedKey){
    createVigenereTable();
    string encryptedText = "";
    for(int i = 0; i < message.length(); i++){
        if(message[i] == 32 && mappedKey[i] == 32){
            encryptedText += " ";
        } else {
            int x = (int)message[i]-65;
            int y = (int)mappedKey[i]-65;
            encryptedText += (char)tableArr[x][y];
        }
    }

    cout << "Encrypted Text: " << encryptedText;
}

int itrCount(int key, int msg){
    int counter = 0;
    string result = "";

    //starting from ASCII of letter of Key and ending at letter of message
    // to get full 26 letters of alphabet
    for(int i = 0; i < 26; i++){
        if(key+i > 90){
            result += (char)(key+(i-26));
        } else {
            result += (char)(key+i);
        }
    } //for

    for(int i = 0; i < result.length(); i++){
        if(result[i] == msg){
            break;
        } else {
            counter++;
        }
    }
    return counter;
}


void cipherDecryption(string message, string mappedKey){
    string decryptedText = "";
    for(int i = 0; i < message.length(); i++){
        if(message[i] == 32 && mappedKey[i] == 32){
            decryptedText += " ";
        } else {
            int temp = itrCount((int)mappedKey[i], (int)message[i]);
            decryptedText += (char)(65+temp);
        }
    }

    cout << "Decrypted Text: " << decryptedText;
}


int main()
{
    cout << "Message and key can only be alphabetic" << endl;
    int choice;
    cout << "1. Encryption\n2. Decryption\nChoose(1,2): ";
    cin >> choice;
    cin.ignore();

    if (choice == 1){
        cout << "Encryption" << endl;
        messageAndKey();
        cipherEncryption(message, mappedKey);

    } else if (choice == 2){
        cout << "Decryption" << endl;
        messageAndKey();
        cipherDecryption(message, mappedKey);

    } else {
        cout << "Wrong Choice" << endl;
    }

    return 0;
}