Sustained Participation as a Security Resource: The Bounded Participation Channel

2026-09-28

AI Summary

This study addresses the vulnerability of zero-cost identity maintenance in anti-Sybil defenses by proposing Bounded Participation Channels (BPC), which transform persistent identity survival into a quantifiable security resource through periodic verification. Theoretically, we establish a linear structure cost theorem that achieves solver-independent security guarantees while decoupling task solvability from throughput constraints. Technically, BPC integrates hash constructions, publicly verifiable proofs, real-time challenge mechanisms, and large language model benchmarking. Experimental results demonstrate that even when AI systems achieve exceptionally high accuracy, they remain fundamentally constrained by throughput limitations. These findings confirm that the proposed mechanism effectively mitigates automated identity maintenance attacks, thereby bridging a critical gap in sustained Sybil defense.

Abstract

Can sustained, per-identity participation be engineered into a security resource? Most anti-Sybil defenses price identity creation rather than identity survival. Once admitted, an adversary may sustain many identities without paying a recurring cost. We introduce the Bounded Participation Channel (BPC), a formal primitive for repeatedly verifying participation window by window. BPC issues fresh, identity-bound challenges under a strict deadline and enforces four structural properties: identity binding, freshness, real-time response, and bounded per-channel throughput. Together, these yield a provable cost theorem: sustaining $s$ identities over $T$ windows requires $C(s,T) \geq sT/\tau_h$ participation channel-windows. The guarantee is solver-agnostic: a channel may be operated by a human, an AI system, or a hybrid. We give a hash-based construction with publicly verifiable participation proofs, characterize four admissible challenge families, and evaluate two against GPT-4o, Gemini 2.5 Flash, and Claude Sonnet 4.5 across 600 trials. Despite near-perfect accuracy (97--100%) on the perceptual tasks, the evaluated automated channels remain throughput-bounded under the tested deployment conditions. The results illustrate a key distinction: solvability does not imply unlimited throughput. By requiring participation to be re-earned by every identity in every time window, BPC turns sustained participation into a measurable security resource with a linear structural cost floor, independent of whether the participation is supplied by humans, AI systems, or hybrids.

Problem

• Sybil defense
• sustained participation
• identity survival cost
• anti-Sybil mechanism

Innovation

• Bounded Participation Channel
• Anti-Sybil defense
• Throughput-bounded challenges
• Solver-agnostic security
• Recurring identity cost