PHP Problem

 <?php
    header('Access-Control-Allow-Origin: *');

    $db = new PDO('mysql:host=localhost;dbname=my_db', 'my_name');

    $secret_key = "EF";

    $enc_str = "dmFyMT0wJnZhcjI9MC4wMDEmdmFyMz1FRg==";

    $dec_str = base64_decode($enc_str);
    $split = explode("&", $dec_str);

    $decoded = json_encode($split);
    echo ($decoded);

    if($secret_key == $decoded['var3'])
    {

        $sql = "REPLACE INTO Cache VALUES (:var1, :var2, :var3)"; // Create a statement
        $stmt = $db->prepare($sql);
        $stmt->bindParam(':var1', $var1, PDO::PARAM_STR);
        $stmt->bindParam(':var2', $var2, PDO::PARAM_STR);
        $stmt->bindParam(':var3', $var3, PDO::PARAM_STR);

        $var1 = $decoded['var1'];
        $var2 = $decoded['var2'];
        $var3 = $decoded['var3'];

        $stmt->execute();

        echo ' SUCCESS';
    }
    else
    {
        echo ' FAILED: Illegal use detected';
    }
$db = NULL;
?>