Proof-of-Personhood (PoP)
Proof-of-personhood (PoP), also known as the "unique-human problem," is a mechanism designed to verify that an individual is both a real human and a unique entity, without necessarily revealing their actual identity
1. In digital systems, PoP creates a registry of public keys where each key is guaranteed to be controlled by a distinct human being
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Importance and Use Cases
The rise of artificial intelligence has increased the need for dependable human verification, as AI can now mimic human behavior through generative text and deepfakes
3. PoP serves several critical functions:
- Sybil Resistance: It prevents a single actor from creating multiple accounts to subvert decentralized governance or "capture" voting systems 1.
- Anti-Spam: It helps services prevent denial-of-service attacks without requiring high access fees that might exclude lower-income users 1.
- Resource Distribution: It enables the fair distribution of resources, such as Universal Basic Income (UBI) tokens or quadratic funding through platforms like Gitcoin Passport 31.
- Privacy-Preserving Identity: It offers an alternative to government-backed systems (like passports or credit cards) that often sacrifice privacy or are subject to centralized control 1.
Verification Methods
Different projects employ various strategies to establish proof-of-personhood:
Biometric Verification
This method uses physical data to confirm humanness.
Worldcoin is a prominent example, using a hardware device called an "Orb" to scan a person's iris
34. The iris is used because it is a permanent biometric data point that is difficult to brute-force
3. While highly effective against AI, this method raises privacy concerns regarding the handling of sensitive biometric data
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Social and Graph-Based Attestations
Some protocols rely on social relationships or human interaction:
- BrightID: Defines humanness based on social attestations and connections 31.
- Proof of Humanity: Uses a combination of video uploads and social vouching, though it may be more vulnerable to advanced AI mimicry than biometric solutions 3.
- Idena: Uses "synchronous flips" (simple CAPTCHA-like tests) to prove humanness at a specific point in time 15.
Other Methods
- Physical Verification: Attending real-world events where attendees are issued a token or NFT to represent their verified status 46.
- Time-locked Wallets: Requiring users to lock funds for a period to monitor activity, providing evidence of unique human behavior 4.
- Zero-Knowledge Proofs (ZK-Proofs): Allowing users to prove attributes (like age or uniqueness) without revealing the underlying personal data 4.
Risks and Challenges
PoP systems face several inherent risks, including privacy concerns, potential hacking vulnerabilities, and the risk of centralization
5. There is also the challenge of "ID selling," where individuals might be coerced or incentivized to scan their biometrics for someone else
1. Some protocols mitigate this by allowing users to re-register and cancel previous IDs, making sold IDs less credible
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