I have a system that will be paying users per unique view on a page. I need to prevent 80% of fraudulent automated traffic from being counted. I need to avoid captcha.I would like to implement a client side proof of work system wherein I would send the page a small hash, the page would decrypt it, send it back with AJAX after a second or two, and then I count the view.
If I had a proof of work system, possible combined with IP monitoring and blacklisting, would this be suitable for preventing most of the fraudulent traffic?
My question is: would this work, cryptographically? What cryptographic work would be just as fast in the browser as it would be implemented in assembly or C/C++? (so that spammers would not just write a faster software to do that work in a fraction of the time) What cryptographic work would take only a second or two in the browser of a mobile phone?