Question

I have a linux machine and a Windows machine I have a C++ program witch acts as a server on the linux machine and a Qt application witch acts as a client on windows machine. I use the socket as a encryption key (basic xor encryption)

The problem is when I hit multiple times connect I get bogus strings. I think the problem is in qt application here is my code. I have tried to put a global flag busy to prevent the user from hitting the connect button manny times but this flag never gets triggered.

Why? Should I use a mutex? If yes how?

void MainWindow::performRead()
{
    QTcpSocket * sock = static_cast<QTcpSocket*>(this->sender());
    if (key == 0)
    {
    busy = true;
    QString recv(sock->readLine());
    key = recv.toInt();
    qDebug() << "Cheia este " << key;

    char * response = enc_dec("#AUTH|admin|admin",strlen("#AUTH|admin|admin"),key);
    sock->write(response);
    }
    else
    {
        busy = true;
        while (sock->bytesAvailable() > 0)
        {  
        unsigned short word;
        sock->read((char*)(&word),2);
        qDebug()<<word;
        QByteArray bts = sock->read(word);
        char * decodat = enc_dec((char*)bts.data(),bts.length() - 2,key);
        char testx[2];
        sock->peek(&testx[0],2);
        qDebug() << decodat;
        }
    }

    busy = false;
}

void MainWindow::on_pushButton_clicked()
{
    if (!busy)
    {
    key = 0;
    QTcpSocket * sock = new QTcpSocket();
    connect(sock,SIGNAL(readyRead()),this,SLOT(performRead()));
    sock->connectToHost("194.110.212.46",6550);
    }
    else qDebug()<<"Can't you see I am busy??" << endl;
}

char * enc_dec(char * str,int len, int key)
{
    unsigned char keys[2];
    keys[0] = (unsigned char)key;
    keys[1] = keys[0] ^ 255;
    char * nou = new char[len + 1];
    nou[len] = '\0';
    for (int i = 0; i < len; i++)
    {
        char tmpy = str[i] ^ keys[i % 2];
        nou[i] = tmpy;
    }
    return nou;
}

Answer 1

Your code is pretty messed up, here are my suggestions:

• Do not connect the socket on every button hit – you are overwriting what you had before, and do unnecessary work – TCP connection establishment is expensive,
• Maybe have a “Connect” and “Disconnect” buttons, and only allow reading from socket when connection is established,
• Try making sure everything works without your “encryption” first,
• Use real encryption after that.