Unique IPs in a voting system

Question

I\'m creating a voting system for my PHP/MySQL website and I would like to make sure one user can only vote once. What would be a good way of doing this? So far I have thoug

Answer 1

The Unobtainably-Perfect: (Unique Govt Number)

• User votes using a verifiable unique identifier like a social-security or passport number

The Close-Enough-For-Reality: (Email/3rd Party Auth)

• user registers an account with an email address and password (or google/facebook)
• 1 email address = 1 vote
• Users can't clear cookies and get extra votes, App doesn't shut 1000's out with shared IPs

The Good-Thought-But-False-Pretense (IP addresses)

• Office buildings: 1000's of users on the same external IP get shut-out
• Universites: Connect to wireless in classroom. Vote. Move to next classroom. Reconnect and vote again

The Crash-And-Burn (Cookies)

1. Vote
2. ctrl shft del enter
3. vote
4. repeat