Pues aqui esta:
Código PHP:
$enc = new EncryptDecrypt();
$user = $enc->encriptar($_POST['username'], $this->config->item('encryption_key'));
$pass = $enc->encriptar($_POST['password'], $this->config->item('encryption_key'));
$cond = array(
'usuario' => utf8_encode($user),
'pass' => utf8_encode($pass)
);
$query = $this->db->get_where('usuarios', $cond);
if ($query->num_rows() != 0) {
$row = $query->row();
$session_data = array(
"id" => $row->id,
"usuario" => $row->usuario,
"logged_in" => TRUE
);
$this->session->set_userdata($session_data);
Recuerda que uso CodeIgniter