Closing the Proof-of-Stake Security Gap: A Signature-Based Defense Against Malicious Validators in Long-Range Attacks

Abstract

Long-range attacks pose a significant threat to the integrity of Proof-of-Stake (PoS) blockchains by enabling adversaries to reconstruct an alternative chain history embedded with fraudulent transactions. These attacks can deceive honest participants into accepting a maliciously crafted branch as the canonical chain. While Key Evolving Signature (KES) schemes are widely adopted to mitigate such threats, they typically rely on the assumption that validators behave honestly. In this work, we challenge this assumption by demonstrating how a malicious validator can exploit inherent limitations in existing KES-based mechanisms to mount a successful long-range attack. To address this critical vulnerability, we introduce a novel cryptographic construction that combines one-time signatures with commitment schemes. Our approach imposes constraints on the signing capabilities of validators, thereby significantly reducing the feasibility of long-range attacks. We provide rigorous formal security proofs to substantiate the robustness of our scheme and conduct a comprehensive performance evaluation. The results show that our solution is both computationally and storage efficient, making it a practical and scalable defense mechanism for real-world PoS blockchain deployments.