i never know that mobile authenticator need mobile numbers eh

from what other forumers said, you need to put phone numbers according to address in battle.net account.
so if you put US address in your account, you cannot use Malaysian phone number.

wish I have a smartphone now, I need the autheticator.

copy paste doesnt work.

Keyloggers tap into your system key typing function. Copy pasting doesn't work.
The best practise is to use authenticator to add 2 factor security.

If you feel like challenging yourself, install diablo on ubuntu, block all outgoing ports except 80 and 443, encrypt your pc and dns traffic, and play diablo

Diablo III uses the following ports:

80: HTTP
1119: Game client; Patch version queries by the Launcher
6881-6999: Launcher; Downloading
If you need assistance with port forwarding on your router, you may wish to visit PortForward.com, a third-party site that contains port forwarding walkthroughs for most router models. If this doesn't resolve your issue, contact your router's manufacturer for assistance.