as we know, in php, we can use session_encode() and session_decode() to encode/decode the session data, but, if you have tried these two 
functionality, you will see the they are not going as you think. so here, i find these two functionality which will help you to do that.
/* *
     * serialize session
     * 
     * @param array $data
     * @param boolean $safe
     * @return string 
      */
     function serialize_session( $array,  $safe =  true)
    {
         //  the session is passed as refernece, even if you dont want it to
         if ( $safe)
        {
             $array =  unserialize( serialize( $array));
        }
$raw = '';
         $line = 0;
         $keys =  array_keys( $array);
         foreach ( $keys  as  $key)
        {
             $value =  $array[ $key];
             $line++;
             $raw .=  $key . '|';
             if ( is_array( $value) &&  isset( $value['huge_recursion_blocker_we_hope']))
            {
                 $raw .= 'r:' .  $value['huge_recursion_blocker_we_hope'] . ';';
            }
             else
            {
                 $raw .=  serialize( $value);
            }
             $array[ $key] =  array('huge_recursion_blocker_we_hope' =>  $line);
        }
return  $raw;
    }
/* *
     * unserialize session
     * 
     * @param string $data
     * @return array 
      */
     function unserialize_session( $data)
    {
         $vars =  preg_split('/([a-za-z_\x7f-\xff][a-za-z0-9_\x7f-\xff^|]*)\|/',  $data, -1, preg_split_no_empty | preg_split_delim_capture);
         for ( $i = 0;  $vars[ $i];  $i++)
        {
             $result[ $vars[ $i++]] =  unserialize( $vars[ $i]);
        }
         return  $result;
    }