Crypto glossary
Proof of personhood
Proof of personhood covers methods to show that a unique human is behind an account, without necessarily revealing who, to defend against Sybil attacks.
Crypto networks let anyone create unlimited addresses, which breaks systems built on one person, one vote or one share: airdrops get farmed by bots, quadratic funding gets gamed and governance can be captured by fake accounts. Proof of personhood aims to verify uniqueness, that each participant is a distinct human, while revealing as little personal data as possible.
Approaches vary. Biometric systems scan a physical trait, most prominently the iris-scanning devices of the World project, formerly Worldcoin, and issue a credential backed by zero-knowledge proofs. Social approaches rely on existing members vouching for newcomers or on analysis of social graphs. Scoring systems aggregate many signals, such as verified accounts, on-chain history and attendance at events, into a score that apps can check.
Every method trades off privacy, accessibility and resistance to fraud. Biometric schemes have faced regulatory action in several countries, including temporary suspensions in Spain and Kenya, over data protection concerns. Social and scoring systems can be gamed by organised farms and may exclude people without online footprints. No approach is yet widely accepted as both robust and fair.
Example
A grants programme allows each verified human to vote once, so a farmer who created 500 wallets still gets a single vote because only one of them passes the personhood check.