Proof of work
lastmod 2026-04-17created 2022-08-114 edits
A proof-of-work (PoW) system (or protocol, or function) is an economic measure to deter denial-of-service (DoS) attacks and other service abuses (e.g. 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" (POW) was first coined and formalized by Markus Jakobsson and Ari Juels in a 1999 paper. An early example of a proof-of-work system used to give value to a currency is the shell money of the Solomon Islands.
List of proof-of-work functions
Below is a list of currently known proof-of-work functions:
- Integer square root modulo a large prime
- Weakened Fiat–Shamir signatures
- Ong–Schnorr–Shamir signature (broken by Pollard)
- Partial hash inversion This paper formalizes the idea of a proof of work (POW) and introduces the independent idea of a bread pudding protocol, a reusable proof-of-work (RPOW) system. (as Hashcash)
- Hash sequences
- Puzzles
- Diffie-Hellman–based puzzle
- Moderate
- Mbound
- Hokkaido
- Cuckoo Cycle
- Merkle tree–based
- Guided tour puzzle protocol
See also
- Secure Coding
- Authentication
- CAPTCHA
- Cap (CAPTCHA) - Lightweight, PoW-based open-source CAPTCHA alternative.
- Security