Who Watches the Watchmen? A Review of Subjective Approaches for Sybil-resistance in Proof of Personhood Protocols (2008.05300v5)

Abstract: Most current self-sovereign identity systems may be categorized as strictly objective, consisting of cryptographically signed statements issued by trusted third party attestors. This failure to provide an input for subjectivity accounts for a central challenge: the inability to address the question of "Who verifies the verifier?". Instead, these protocols outsource their legitimacy to mechanisms beyond their internal structure, relying on traditional centralized institutions such as national ID issuers and KYC providers to verify the claims they hold. This reliance has been employed to safeguard applications from a vulnerability previously thought to be impossible to address in distributed systems: the Sybil attack problem, which describes the abuse of an online system by creating many illegitimate virtual personas. Inspired by the progress in cryptocurrencies and blockchain technology, there has recently been a surge in networked protocols that make use of subjective inputs such as voting, vouching, and interpreting, to arrive at a decentralized and sybil-resistant consensus for identity. In this article, we will outline the approaches of these new and natively digital sources of authentication -- their attributes, methodologies strengths, and weaknesses -- and sketch out possible directions for future developments.

Proof of Personhood Protocols: A Scholarly Examination

The paper "Proof of Personhood: A Review" offers an in-depth exploration of the landscape surrounding the emergent Proof of Personhood (PoP) protocols intended to address the enduring challenge of Sybil attacks. Traditionally, such attacks have plagued distributed identity systems by allowing malicious entities to create multiple pseudonymous identities, thus disrupting democratic processes by manipulating consensus mechanisms. This paper meticulously reviews various subjective approaches that aim to ensure Sybil-resistance while fostering decentralized identity systems that hold the promise of authenticating unique human identities without relying on centralized institutions.

Conceptual Framework and Research Background

The foundational motivation for PoP systems is to enable democratic governance within blockchain networks by ensuring that voting power derives from singular human entities rather than traditional resource-based mechanisms such as Proof of Work or Proof of Stake. These traditional methods have often contributed to plutocratic governance structures, driven by wealth or computational power. PoP systems, conversely, seek to restructure these networks towards democratic signaling through one-person-one-vote systems. The theoretical and practical challenges of such a shift are significant, particularly in the face of Sybil attacks designed to subvert digital networks.

The paper explores previous efforts for identity verification, outlining both decentralized approaches—emphasized in blockchain systems—and centralized methods—exemplified by major internet service providers who act as credential authorities. The central critique revealed here is the dependency on centralized attestations, which compromises the desired decentralized nature and privacy-preserving aspects of these identity systems.

Key Attributes and Evaluation of PoP Protocols

The authors present a broad taxonomy of approaches, dividing them into several categories: Reverse Turing Tests, Pseudonym Parties, Web of Trust, Intersectional Identity frameworks, Token Curated Registries, and Decentralized Autonomous Organizations. Each offers a distinct method for distinguishing humans from artificial identities, aiming to create a robust but accessible protocol for verifying personhood.

The paper provides an evaluative perspective on several existing implementations:

• Idena Network employs synchronous human-generated reverse Turing tests known as FLIP tests combined with virtual pseudonym parties, highlighting its decentralized nature but also noting challenges in scalability and reliance on synchronous validation ceremonies for continued network participation.
• Humanity DAO leverages Token Curated Registries, demonstrating the potential for decentralized consensus but illustrating vulnerabilities to fixed-protocol attacks and centralization.
• Kleros and Upala embrace amalgamated approaches involving web-of-trust and economic incentive models, addressing identity singularity through innovative verification group scores and legal adjudication mechanisms.
• BrightID utilizes intersectional web-of-trust models, emphasizing connections through social graphs and being interoperable with social media platforms; however, scalability remains a significant challenge.
• Duniter presents a relative monetary theory implemented through unique user dividends, creating a grassroots network with slower growth limited by regional constraints.
• Equality Protocol serves as a meta-protocol, evaluating identity protocols but potentially favoring capital-rich users and currently restricted in scope to DAO memberships.

Implications and Future Directions

The paper posits significant practical and theoretical implications. Practically, PoP protocols offer a path towards egalitarian governance structures necessary for advancing civic engagement in blockchain platforms. They have potential applications in areas like Universal Basic Income, Peer-to-Peer Governance, Public Goods Funding, and Quadratic Voting systems. Theoretically, these systems are showcasing the increasing importance of subjective inputs as a reliable substitute for traditional computational or financial proof mechanisms.

The future of PoP protocols will likely involve hybrid models that integrate the strengths of various approaches while mitigating their weaknesses. The continuous evolution of machine learning presents a formidable challenge, necessitating ongoing innovation in AI-resistant mechanisms. Moreover, as privacy remains a cornerstone, any advancements must carefully balance transparency versus anonymity in identity verification processes.

Ultimately, while PoP systems are nascent and undergoing iterative refinement, they hold the promise of redefining identity governance frameworks, enabling decentralized networks to honor democratic principles with enhanced security and inclusivity. They align with broader social movements advocating for self-sovereign identity solutions capacitated with privacy preservation and human dignity at their core.