Jonatan Svensson jonats@kth.se, Johan Zeeck jzeeck@kth.se
Denial of Service attacks are a serious threat to server robustness and stability. This thesis seeks to examine the possibility of implementing a proof-of-work protocol which effectively prevents this type of attacks. Its main focus is to investigate a general concept that includes sending puzzles over the Internet layer, creating a cost as a puzzle per request which is easily adjusted depending on current server load. The cost validates that the request is in fact legitimate by forcing the client to process a solution to the given puzzle before granting resources on the server. An implementation of the protocol is explained and the results of the testing confirm that proof-of-work could be an effective method to counter standard DoS attacks.