How to restrict this poll for authenticaticated users only

I like your plugin and its great, I made some changes to it by getting a stacked process bar and horizontal buttons.
But soon I realised that anyone can come and vote, I would atleast want it to be registered by MD5 of Ip.
It would be a great plugin if I can somehow enable authentication for it, and record that the person has voted.

Can you guide me in the right direction.

https://www.ads-software.com/extend/plugins/plumba/