🔗 Proof-of-work system

🔗 Numismatics 🔗 Numismatics/Cryptocurrency 🔗 Cryptocurrency

A proof-of-work (PoW) system (or protocol, or function) is a consensus mechanism. It deters denial-of-service attacks and other service abuses such as spam on a network by requiring some work from the service requester, usually meaning processing time by a computer. The concept was invented by Cynthia Dwork and Moni Naor as presented in a 1993 journal article. The term "proof of work" was first coined and formalized in a 1999 paper by Markus Jakobsson and Ari Juels.

A key feature of these schemes is their asymmetry: the work must be moderately hard (yet feasible) on the requester side but easy to check for the service provider. This idea is also known as a CPU cost function, client puzzle, computational puzzle, or CPU pricing function. It is distinct from a CAPTCHA, which is intended for a human to solve quickly, while being difficult to solve for a computer.