function ChangePass($username, $password, $newpassword) {
    $bdd = connect_DB();
    try {
        $req = $bdd->prepare("UPDATE user SET password = :newpass WHERE username = :username AND password = :password");
        $req->execute(array(
            'newpass' => md5($newpassword),
            'username' => $username,
            'password' => md5($password)
        ));
    }

    catch (Exception $e) {
        die('Erreur: '.$e->getMessage());
    }

    $bdd = NULL;
}