mod_kaPoW
Ed Kaiser, Wu-chang Feng · 2007
Unwanted traffic remains a fundamental problem for networked systems. Proof-of-work (PoW) is a defense mechanism that adds a client-specific challenge at the start of a networked protocol. The challenge acts as a filter for clients based on their willingness to solve a computational task of varying difficulty. The difficulty is tailored to the individual client and is set proportional to its relative load on the server.