删除Codeigniter中文件上传中的扩展名

I want to upload my files with an encrypted name with CodeIgniter. But, I try the 2 possibilities :

$config['file_name'] = md5($id);

Or :

$config['encrypt_name'] = TRUE;

Both works, but I have the file extension in my encripted name. Is it possible to remove it when uploading my file ? When I see the Upload system library, the $file->ext is used everywhere.. Why put the file extension in an encrypted name ? Thanks.

There really is a much easier way of doing this:

if ($this->upload->do_upload())  // If file was uploaded
{           
    $data = $this->upload->data(); // Returns information about your uploaded file.
    $new_name=md5($id);
    $thumbnail = $new_name.$data['file_ext']; // Here it is
}

Open system/libraries/Upload.php

Remove or Comment out this code from do_upload function

// If no extension was provided in the file_name config item, use the uploaded one
if (strpos($this->_file_name_override, '.') === FALSE)
{
  $this->file_name .= $this->file_ext;
}
else
{
  // An extension was provided, let's have it!
  $this->file_ext = $this->get_extension($this->_file_name_override);
}