Timestamp Manipulation: Incentive Attacks on Timestamp-Based Proof-of-Work Blockchains with Minimal Additional Risk

Nakamoto consensus is the most widely adopted decentralized consensus mechanism in cryptocurrency systems. Since its proposal in 2008, many studies have investigated incentive attacks, where the adversary aims to earn more rewards than its fair share but the security properties are not violated. One notable example is the recent Riskless Uncle Maker (RUM) attack on timestamp-based Nakamoto blockchains (CCS'23) such as Ethereum 1.x (deprecated in Sep 2022) and Ethereum Classic (still active) and EthereumPoW (still active). Specifically, the RUM attack shows that an adversary with 25% relative hash power can achieve a normalized profit share of 26.12%. In this work, we propose two new incentive attacks on timestamp-based Nakamoto consensus: Unrestricted Uncle Maker (UUM) and Staircase-Unrestricted Uncle Maker (SUUM). Compared with RUM, both attacks achieve higher profit without risking reward loss. We demonstrate through theoretical analysis and experimental validation that if an adversary controls 25% relative hash power, it can achieve a normalized profit share of 28.41% and 33.30% in UUM and SUUM, respectively. We further conduct an empirical analysis on three major ETH 1.x-based blockchains, namely Ethereum 1.x, Ethereum Classic, and EthereumPoW. Our on-chain observations reveal persistent SUUM-style behavior in four large mining pools. Compared to honest mining, the estimated additional revenues gained by these mining pools are nearly three million USD (2,961,078 to be specific).