SESSION HANDLING PDO

<?php
/*
 * Secure Session Mgmt
 */
    class _session {
        private $_connection; //Connection settings (Must be a PDO object)

        private $r_stmt;// Variable to store the read statement
        private $w_stmt;// Variable to store the write statement
        private $delete_stmt;// Variable to store the delete statement
        private $gc_stmt; //Variable to store the Garbage collection statement s
        private $key_stmt; //Variable to store the get key stmt

        function __construct(&$connection) {
            //Set connection
            $this->_connection = $connection;
            // set our custom session functions.
            session_set_save_handler(
                    array($this, 'open'),
                    array($this, 'close'),
                    array($this, 'read'),
                    array($this, 'write'),
                    array($this, 'destroy'),
                    array($this, 'gc'));

            // This line prevents unexpected effects when using objects as save handlers.
            register_shutdown_function('session_write_close');
         }
         public function start_session($session_name, $secure) {
            // Make sure the session cookie is not accessable via javascript.
            $httponly = true;

            // Hash algorithm to use for the sessionid. (use hash_algos() to get a list of available hashes.)
            $session_hash = 'sha512';

            // Check if hash is available
            if (in_array($session_hash, hash_algos())) {
               // Set the has function.
               ini_set('session.hash_function', $session_hash);
            }
            // How many bits per character of the hash.
            // The possible values are '4' (0-9, a-f), '5' (0-9, a-v), and '6' (0-9, a-z, A-Z, "-", ",").
            ini_set('session.hash_bits_per_character', 5);

            // Force the session to only use cookies, not URL variables.
            ini_set('session.use_only_cookies', 1);

            // Get session cookie parameters
            $cookieParams = session_get_cookie_params();
            // Set the parameters
            session_set_cookie_params($cookieParams["lifetime"], $cookieParams["path"], $cookieParams["domain"], $secure, $httponly);
            // Change the session name
            session_name($session_name);
            // Now we cat start the session
            session_start();
            // This line regenerates the session and delete the old one.
            // It also generates a new encryption key in the database.
            session_regenerate_id(true);
         }
         public function open (){
             //Connection have already being set
            return true;
         }
         public function close(){
             //Connection can be unset by declaring the connection object to null
             //Or simply unset($connection)
             return true;
         }
         public function read($id){
             $qry = "SELECT data
                     FROM sessions
                     WHERE id = :id";
             //Prepare the qry only one time
             if (!isset($this->r_stmt)){
                 $this->r_stmt = $this->_connection->prepare($qry);
             }
             $this->r_stmt->bindParam(':id', $id, PDO::PARAM_INT);
             if($this->r_stmt->execute()){
                 //Fetch only one row from DB as $row ['data']
                $row = $this->r_stmt->fetch(PDO::FETCH_ASSOC);
                $key = $this->getkey($id);
                $data = $this->decrypt($row['data'], $key);
                return $data;
             }
             else{
                 echo "Something went wrong! read();";
                 return false;
             }
         }
         public function write($id, $data) {
            // Get unique key
            $key = $this->getkey($id);
            // Encrypt the data
            $data = $this->encrypt($data, $key);
            $time = time();
            $qry  = "REPLACE
                    INTO sessions (id,data,session_key,set_time)
                    VALUES (:id,:data,:session,:time)";
            if(!isset($this->w_stmt)) {
               $this->w_stmt = $this->_connection->prepare($qry);
            }

            $this->w_stmt->bindParam(':id', $id, PDO::PARAM_INT);
            $this->w_stmt->bindParam(':time', $time, PDO::PARAM_STR);
            $this->w_stmt->bindParam(':data', $data, PDO::PARAM_STR);
            $this->w_stmt->bindParam(':session', $key, PDO::PARAM_STR);

            if($this->w_stmt->execute()){
                return true;
            }
            else{
                echo "Something went wrong! write();";
                return false;
            }

         }
         public function destroy($id) {
             $qry ="DELETE
                 FROM sessions
                 WHERE id = :id";
            if(!isset($this->delete_stmt)) {
               $this->delete_stmt = $this->_connection->prepare($qry);
            }
            $this->delete_stmt->bindParam(':id', $id, PDO::PARAM_INT);

            if($this->delete_stmt->execute()){
                return true;
            }
            else{
                echo "Something went wrong! delete();";
                return false;
            }
         }
         public function gc($max) {
             $qry  = "DELETE
                      FROM sessions
                      WHERE set_time < :max";
            if(!isset($this->gc_stmt)) {
               $this->gc_stmt = $this->_connection->prepare($qry);
            }
            $old = time() - $max;
            $this->delete_stmt->bindParam(':old', $old, PDO::PARAM_INT);
            if($this->gc_stmt->execute()){
                return true;
            }
            else{
                echo "Something went wrong! gbc();";
                return false;
            }
         }
         private function getkey($id) {
            $qry = "SELECT session_key
                FROM sessions
                WHERE id = :id LIMIT 1";
            if(!isset($this->key_stmt)) {
               $this->key_stmt = $this->_connection->prepare($qry);
            }
            $this->key_stmt->bindParam(':id', $id, PDO::PARAM_INT);
            if($this->key_stmt->execute()){
               $row = $this->r_stmt->fetch(PDO::FETCH_ASSOC);
               if(count($row) != 1){
                    return $row['session_key'];
               }
               else {
                   $random_key = hash('sha512', uniqid(mt_rand(1, mt_getrandmax()), true));
                   return $random_key;
               }
            }
            else {
               echo "Something went wrong! getkey();";
               return false;
            }
         }
         private function encrypt($data, $key) {
            $salt = 'cH!swe!retReGu7W6bEDRup7usuDUh9THeD2CHeGE*ewr4n39=E@rAsp7c-Ph@pH';
            $key = substr(hash('sha256', $salt.$key.$salt), 0, 32);
            $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);
            $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
            $encrypted = base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $data, MCRYPT_MODE_ECB, $iv));
            return $encrypted;
         }
        private function decrypt($data, $key) {
           $salt = 'cH!swe!retReGu7W6bEDRup7usuDUh9THeD2CHeGE*ewr4n39=E@rAsp7c-Ph@pH';
           $key = substr(hash('sha256', $salt.$key.$salt), 0, 32);
           $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);
           $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
           $decrypted = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, base64_decode($data), MCRYPT_MODE_ECB, $iv);
           return $decrypted;
        }

    }

    //Connection Details
$db_host = "localhost";
$db_user = "root";
$db_password = "";
$db_database = "";
$pdo = new PDO("mysql:host=$db_host;dbname=$db_database;charset=utf8", $db_user, $db_password);
 $session = new _session($pdo);
// Set to true if using https
$session->start_session('_s', false);

$_SESSION['something'] = 'password';
echo $_SESSION['something'];
?>