WebSOS: an overlay-based system for protecting web servers from denial of service attacks

Our prototype requires no modifications to either servers or browsers, and makes use of Graphical Turing Tests, web proxies, and client authentication using the SSL/TLS protocol, all readily supported by modern browsers. We then extend this system with a credential-based micropayment scheme that combines access control and payment authorization in one operation. Turing tests ensure that malicious code, such as a worm, cannot abuse a user's micropayment wallet. We use the WebSOS prototype to conduct a performance evaluation over the Internet using PlanetLab, a testbed for experimentation with network overlays. We determine the end-to-end latency using both a chord-based approach and our shortcut extension. Our evaluation shows the latency increase by a factor of 7 and 2 respectively, confirming our simulation results.