my auth is secure?

Try to prefer, $this->session->userdata(..) instead of  $ci->session->userdata(..). That avoid you to create again an instance of $CI.

thanks casa fo your reply, about this or CI, i put login and logout methods in user_helper so cant use $this,

Code:

Don't use MD5, use bcrypt via http://php.net/password

how i can use encrypt ket (in config file) as salt for this function?

ressan.ir
CI is nice