Proof-of-work (POW)

A proof-of-work is a technique that requires a client to give “evidence” that it spent some time doing a time consuming work, building its reputation as a valid client. It is originally used as a security measure to prevent denial of attacks and spam. The client is usually challenged by solving a feasible but computationally difficult problem. This requires a certain amount of time to have a solution depending on the client's CPU power. The solution to the problem serves as the proof-of-work. Bitcoin uses a proof-of-work technique to address fundamental problems of a fully decentralized peer-to-peer digital currency.