Permissionless consensus protocols require a scarce resource to regulate leader election and provide Sybil resistance. Existing paradigms such as Proof of Work and Proof of Stake instantiate this scarcity through parallelizable resources like computation or capital. Once acquired, these resources can be subdivided across many identities at negligible marginal cost, making linear Sybil cost fundamentally unattainable. We introduce Proof of Commitment (PoCmt), a consensus primitive grounded in a non-parallelizable resource: real-time human engagement. Validators maintain a commitment state capturing cumulative human effort, protocol participation, and online availability. Engagement is enforced through a Human Challenge Oracle that issues identity-bound, time-sensitive challenges, limiting the number of challenges solvable within each human window. Under this model, sustaining multiple active identities requires proportional human-time effort. We establish a cost-theoretic separation showing that protocols based on parallelizable resources admit zero marginal Sybil cost, whereas PoCmt enforces a strictly linear cost profile. Using a weighted-backbone analysis, we show that PoCmt achieves safety, liveness, and commitment-proportional fairness under partial synchrony. Simulations complement the analysis by isolating human-time capacity as the sole adversarial bottleneck and validating the predicted commitment drift and fairness properties. These results position PoCmt as a new point in the consensus design space, grounding permissionless security in sustained human effort rather than computation or capital.

翻译：无许可共识协议需要一种稀缺资源来调节领导者选举并提供女巫攻击抵抗。现有范式如工作量证明和权益证明通过可并行化的资源（如计算或资本）来实例化这种稀缺性。一旦获得，这些资源可以以可忽略的边际成本细分为多个身份，使得线性女巫成本从根本上无法实现。我们提出承诺证明（PoCmt），一种基于非并行化资源——实时人类参与——的共识原语。验证者维护一个捕获累积人类努力、协议参与和在线可用性的承诺状态。参与通过人类挑战预言机强制执行，该预言机发布身份绑定、时间敏感的挑战，限制每个人类时间窗口内可解决的挑战数量。在此模型下，维持多个活跃身份需要成比例的人类时间投入。我们建立了一个成本理论分离，表明基于可并行化资源的协议允许零边际女巫成本，而PoCmt强制执行严格线性的成本曲线。通过加权骨干分析，我们证明PoCmt在部分同步条件下实现了安全性、活性和承诺比例公平性。模拟通过将人类时间能力分离为唯一的对抗性瓶颈，并验证预测的承诺漂移和公平性特性，对分析进行了补充。这些结果将PoCmt定位为共识设计空间中的一个新点，将无许可安全性建立在持续的人类努力而非计算或资本之上。