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Concept
Proof of personhood
Summary
Proof of personhood (PoP) is a means of resisting malicious attacks on peer to peer networks, particularly, attacks that utilize multiple fake identities, otherwise known as a Sybil attack. Decentralized online platforms are particularly vulnerable to such attacks by their very nature, as notionally democratic and responsive to large voting blocks. PoP is a resistance method for permissionless consensus, in which each unique human participant obtains one equal unit of voting power and associated rewards. In contrast with proof of work, proof of stake, and other approaches that confer voting power and rewards in a blockchain or cryptocurrency proportionately to a participant's investment in some activity or resource, proof of personhood aims to guarantee each unique human participant an equal amount of voting power and rewards, independent of economic investment.
The problem of Sybil attacks using many virtual identities has been recognized for decades as a fundamental challenge for distributed systems that expect each human user to have only one account or identity. CAPTCHAs attempt to rate-limit automated Sybil attacks by using automated Turing tests to distinguish humans from machines creating accounts or requesting services. Even when successful in this goal, however, CAPTCHAs allow one human to obtain multiple accounts or shares of a resource simply by solving multiple CAPTCHAs in succession, and thus do not satisfy the one-per-person goal in proof of personhood. Aside from CAPTCHAs allowing people to obtain multiple users, there are additional complications. Many users who are visually impaired or have learning disabilities may struggle to complete the puzzles. Additionally, some recently developed AI has succeeded in solving the CAPTCHA issue.
Distributed systems could require users to authenticate using strong identities verified by a government or trusted third party, using an identity verification service or self-sovereign identity system for example, but strong identification requirements conflict with the privacy, anonymity, and low barrier to entry goals widely valued in permissionless blockchains and cryptocurrencies.
Official source
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