Best way to Identify a user uniquely

Question

I am building a Like/Dislike feature. For this purpose I need to identify the particular user liking or disliking the post. I have an idea that without user logins this cannot be done perfectly, but whats the closest to perfect technique, Issues I have are stated below:

• Cookies can be cleared, and vary form browser to browser
• Most of the users dont have a dedicated public IP, and their IP keeps on changing for every session
• a combo of cookies and IP might also not serve the purpose

So which technique shall I use to implement it ?

The language I am using for this is PHP

Answer 1

I think the best still be a cookie, not perfect , but if you do not want to use login mechanism , cookie is the best.

Answer 2

You cannot get a perfect unique identity of a user really. Simply imagine a user that has two separate computers with separate browsers and separate internet connections. You will not be able to identify his two connections as being from the same user.

Once you accept this you can go as fancy as you want to. Cookies are generally nice, as although they can be cleared many users don't clear them really. If you are worried about abusive users though, IPs serve you better.

Additionally, you could include browsers' user-agent etc. The more different identification clues you include, the harder it gets to spoof the system. However, you should keep in mind, that you can spend a significant amount of effort for that, yet will never get a perfect solution anyways.

Answer 3

A login would be the best, but if you cannot follow that route you could use a combination of cookie, IP and other elements. With a large enough combination of parameters you could identify users with pretty good accuracy (even if not 100%).

This is very interesting and could point you in the right direction.

Answer 4

Let's consider all the options for identification:

Can't use IP: You have no control over all the NATs and dynamic IPs in between the server and the browser.
Can use cookies: You have almost full control over them. (Best option here)
Can use some sort of 'user' identification: But you don't want to use them here. Instead you can use some variant of it. Make the use enter it's email id. I can't think of any other user identification without user input.

Answer 5

Recently I read an article about this question and was surprised of how many methods exist for such task. IP and cookies are just "the tip of the iceberg". Look at evercookie, js library that produces "extremely persistent cookies".

Answer 6

Given enough information you should be able to uniquely identify most browsers. This doesn't stop people from changing browsers. The link below explains more.

https://panopticlick.eff.org/

The best thing to do is to integrate facebook like.

Answer 7

Hi,

If you didn't already you should see what flash cookies have to offer - http://en.wikipedia.org/wiki/Local_Shared_Object

In my opinion these are closest to what you need.