php session_start if isset _SESSION login isset _SESSION passwd Header

<?php 
session_start();
if (!isset($_SESSION['login'])  ||
!isset($_SESSION['passwd']))
    Header("Location: 3.php");  
 

    if($_SESSION['passwd']==$_SESSION['checkPass'])
    {
        echo "Вы успешно вошли!<br>";
        echo "Ваш ник:".$_SESSION['checkName']."<br>";
        echo "Ваш пароль:".$_SESSION['checkPass']."<br>";
        echo "Ваше слово:".$_SESSION['checkWord']."<br>";
        if (!isset($_GET['Ок'])){
            echo "<form>
              Новый пароль: <input type=password name=passwd>
              <input type=submit name=ОК value=Ок>
            </form>";
          }
          else
          {
            $_SESSION['passwd']=$_GET['passwd'];
            $oldUser = $_SESSION['checkName'].":".$_SESSION['checkPass'].":".$_SESSION['checkWord'];
            $newUser =  $_SESSION['checkName'].":".$_SESSION['passwd'].":".$_SESSION['checkWord'];
            $fileText=file_get_contents($_SESSION['checkFile']);
            $fileText=str_replace($oldUser, $newUser,$fileText);
            file_put_contents($_SESSION['checkFile'], $fileText);
            $_SESSION['checkPass'] = $_SESSION['passwd'];
            Header("Location: 3.2.php");  
          }
          
    }
    else
    {
       

       if (!isset($_GET['Ок'])){
        echo "<form>
          Секретное слово ?: <input type=text name=secretWord>
          <input type=submit name=Ок value=Ок>
        </form>";
      }
      else
      {
        $word=$_GET['secretWord'];
          if($word==$_SESSION['checkWord'])
          {
              echo "Ваш пароль:".$_SESSION['checkPass'];
              echo "<a href=\"3.php\">Попробовать снова</a>";
          }
          else 
          {
            echo "Секретное слово введено не верно";
            echo "<a href=\"3.php\">Попробовать снова</a>";
          }
      }
    }

?>