Is there a way I can decrypt and encrypt by verifying that the values ​entered are equal to the variable "E" and "d" of my Function VoidAlgorithmRSA?

Question

I just started 2 months ago

And this program will be part of my grades from one of my courses in college. My end goal is trying to apply the public key to encrypt a message and apply the private key to decrypt the same message. I've been thinking how to solve it but im just overthinking to much.

#include <iostream>
#include <vector>
#include <string>
#include <cctype>
#include <cstdlib>
#include <algorithm>
#include <iterator>
#include <sstream>

using namespace std;

//Declaracion de funciones
void encrypt(int);
void decrypt(int);
void welcome();
string choose();
int numberKey();
void toLower(string & makeLower);
void goAgain();
void algoritmoRSA();

//Variables no globales

int main()
{
    welcome();
    string choiceNum = choose();

    if (choiceNum == "claves") {
        algoritmoRSA();
    }

    else if (choiceNum == "encriptar")
    {

        int keyNum = numberKey(); //Integra el valor para pasar a la siguiente funcion 
        // 1-36
        encrypt(keyNum);
        choiceNum.clear();
        goAgain();
    }
  


    else if (choiceNum == "desencriptar") {

        int keyNum = numberKey(); //Integra el valor para pasar a la siguiente funcion 
        // 1-36
        decrypt(keyNum);
        choiceNum.clear();;
        goAgain();
    }
    else if (choiceNum == "exit") {
        exit(0);
    }

    else {
        choiceNum.clear();
        cout << "\nError\n";
    }

    goAgain();
    return 0;
}

void algoritmoRSA()
{
    int p, q;
    cout << endl;
    cout << " ingresa p,q (p, q son numeros primos) " << endl;
    cin >> p >> q;

    int m = p * q;
    int n = (p - 1) * (q - 1);
    int E;
    cout << endl;
    cout << endl;
    cout << " ingresa e (e y " << n << " son primos) y 1 < e < " << n << endl;
    cin >> E;

    int d;
    for (d = 1;; d++)
    {
        if (d * E % n == 1)
            break;
    }


    cout << endl << endl;


    cout << "{ " << m << "," << E << " }" << " es la clave privada " << endl;
    cout << "{ " << m << "," << d << " }" << " es la clave publica " << endl;



}


/* Function que muestra el mensaje de bienvenida al usuario
 *
 */
void welcome() {
   cout << "\n ******************************************* ";
    cout << "\n * * ";
    cout << "\n * ~~~~ Criptografia - Grupo 07 ~~~~ * ";
    cout << "\n * * ";
    cout << "\n * Autores:  ";
    cout << "\n * Jhames Patrick Fher Leon Chavez - u202118734 * ";
    cout << "\n * Leandro Nahuel Perez Arteaga - u201911037 * ";
    cout << "\n * Frank Edward Vegas García - u202118069 * ";
    cout << "\n * Carlos Alberto Cardoza Najarro - u201819510 * ";
    cout << "\n * Gustavo Alexander Cervantes Cahua - u20191a267* ";
    cout << "\n * * ";
    cout << "\n ******************************************* ";
    cout << endl;
}



// Funcion que le permite al usuario la funcion que desea hacer // *returna userInput


string choose() {
    try {
        string userInput;
        cout << endl;
        cout << "Hola, por favor escoja la accion que desea realizar! (encriptar, desencriptar, claves, exit)" << endl;
        cout << endl;
        cin >> userInput;

        while (userInput != "encriptar" && userInput != "desencriptar" && userInput != "claves" && userInput != "exit")
        {
            cout << "Usted ingreso una opcion incorrecta. \n";
            cout << "Por favor intente de nuevo. \n";
            cout << "Ingrese la opcion correcta: ";
            cin.clear();
            cin >> userInput;
        }
        return userInput; // encriptar, desencriptar, conocer las posibles claves o exit.

    }
    catch (exception e) {
        cout << "La funcion escogida no podra ser ejecutada";
        return NULL;
    }
}




//Funcion que acepta una llave para el programa despues * retorna keyNum

int numberKey() {
    try {
        int keyNum;     // Integra el valor para el input de la llave
                        // 1-36

        cout << "Por favor ingrese un numero con el que desea encriptar o desencriptar el mensaje: ";
        cin >> keyNum;

        while (keyNum > 36 || keyNum < 0 || (!cin << keyNum))
        {
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(), '\n');
            cout << "Usted ingreso un numero invalido. \n";
            cout << "Ingrese un numero apropiado para la llave que este entre el siguiente intervalo: (1-36)" << endl;
            cin >> keyNum;
        }
        return keyNum;

    }
    catch (exception e) {
        cout << "La funcion numero de llave no podra ser ejecutada";
        return NULL;
    }

}




// Function que encripta el mensaje basado en el mensaje del usuario

void encrypt(int keyNum)
{
    try {

        vector<string> library = { "a","b", "c", "d", "e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z", "0","1","2","3","4","5","6","7","8","9" };
        string wordStorage; // String para guardar las letras minusculas
                            // Cualquier mensaje puede ser escrito

        cout << "Por favor ingrese el mensaje que desea encriptar: ";
        string getMessage;  // Cualquier mensaje


        cin.get();
        getline(cin, getMessage);
        cout << endl << "Su texto traducido es: ";

        for (int i = 0; i < getMessage.size(); i++)
        {
            wordStorage = getMessage[i];
            toLower(wordStorage);
            
            for (int h = 0; h < library.size(); h++) {
                if (library[h] == wordStorage && ((h + keyNum) < 36)) {
                    int y = h + keyNum;
                    cout << library[y];
                }
                else if (library[h] == wordStorage && ((h + keyNum) > 36)) {
                    int o = h + keyNum - 36;
                    cout << library[o];
                }

                else if (library[h] != wordStorage && h < 1) {
                    if (find(library.begin(), library.end(), wordStorage) != library.end())
                        cout << "";
                    else
                        cout << wordStorage;
                }
            }
        }
        cout << endl << endl;
    }
    catch (exception e) {
        cout << " La funcion de encriptado no pudo ser ejecutada";
    }
}



//Funcion que desencripta el mensaje que se evaluara con la llave

void decrypt(int keyNum)
{
    try {
        vector<string> library = { "a","b", "c", "d", "e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z", "0","1","2","3","4","5","6","7","8","9" };

        string getMessage, wordStorage;
        cout << "Por favor ingrese el mensaje a desecriptar: ";
        string inputMessage;
        cin.get();
        getline(cin, getMessage);
        cout << endl << "Su texto traducido es: ";

        for (int i = 0; i < getMessage.size(); i++)
        {
            wordStorage = getMessage[i];
            toLower(wordStorage);

            for (int h = 0; h < library.size(); h++) {
                if (library[h] == wordStorage && ((h - keyNum) < 36)) {
                    int y = h - keyNum; //int value muestra el valor si aparece en el vector
                    cout << library[y];
                }

                else if (library[h] == wordStorage && ((h - keyNum) > 36)) {
                    int o = h - keyNum + 36; // int muestra el valor si se enumera más allá de los limites de la matriz
                    cout << library[o];
                }

                else if (library[h] != wordStorage && h < 1) {
                    if (find(library.begin(), library.end(), wordStorage) != library.end())
                        cout << "";
                    else
                        cout << wordStorage; //Muestra char si no esta en la matriz
                }
            }
        }
        cout << endl;

    }
    catch (exception e) {
        cout << "La funcion de desencriptar no podra ser ejecutada";
    }
}


//Funcion que convierte strings a letras minusculas

void toLower(string & makeLower)
{
    try {
        for (int i = 0; i < makeLower.length(); i++) //Empieza desde 0 y sigue subiendo hasta que el largo del string (Incrementa por 1 loop)
        {
            makeLower[i] = tolower(makeLower[i]);//Obtiene el caracter de la cadena y usar la funcion prefabricada tolower de la biblioteca cctype
        }
    }
    catch (exception e) {
        cout << "Para bajar la funcion no se pudo implementar";
    }
}


//Funcion que le pregunta al usuario si quiere hacer algo mas y corre el programa nuevamente de ser asi


void goAgain() {

    try {

        string choiceNumb = choose();
        if (choiceNumb == "encriptar")
        {
            int keyNum = numberKey();
            encrypt(keyNum);
            goAgain();
        }

        else if (choiceNumb == "desencriptar") {

            int keyNum = numberKey();
            decrypt(keyNum);
            goAgain();
        }
        else if (choiceNumb == "exit") {
            exit(0);
        }
        else {

            cout << "\nError\n";
        }
        goAgain();

    }
    catch (exception e) {
        cout << " La funcion para volver a hacerlo no podra ser ejecutada";
    }
}

Thanks for trying to help!