Codeigniter Rename file on upload

I’m trying to add time as the prefix of the image name along with the original name when uploading, But I couldn’t figure it out. Please help me with the following code to add a prefix to my original file name when uploading.

<?php

class Upload extends CI_Controller {

    function __construct()
    {
        parent::__construct();
        $this->load->helper(array('form', 'url'));
    }

    function index()
    {
        $this->load->view('upload_form', array('error' => ' ' ));
    }

    function do_upload()
    {


        $config['upload_path'] = 'Public/uploads/';
        $config['allowed_types'] = 'gif|jpg|png';
        $config['max_size'] = '1024';
        $config['max_width']  = '1024';
        $config['max_height']  = '768';



        $this->load->library('upload', $config);


        if ( ! $this->upload->do_upload())
        {
            $error = array('error' => $this->upload->display_errors());

            $this->load->view('upload_form', $error);
        }
        else
        {
            $data = array('upload_data' => $this->upload->data());

            $this->load->view('upload_success', $data);
        }
    }
}
?>

Answer

You can encrypt file name with use of CI native option:

$config['encrypt_name'] = TRUE;

OR

You can do it with your own code:

$new_name = time().$_FILES["userfiles"]['name'];
$config['file_name'] = $new_name;