Full Selfish Mining: Exploiting Fork-State Awareness and Intermittent Rational Mining

Selfish mining (SM) has been extensively studied as a fundamental security threat to Proof-of-Work (PoW) blockchains. However, existing analyses implicitly assume that honest miners mine continuously, regardless of short-term profitability. In practice, miners may suspend mining when expected profit is negative. This economically rational behavior introduces a previously overlooked attack opportunity. In this paper, we show that under SM attacks, honest miners\u2019 profitability varies across observable blockchain states. We analytically prove that rational miners can improve their revenue by adopting an intermittent mining strategy\u2014mining only in non-fork states and temporarily stop mining during equal-length forks\u2014even when their baseline expected profit is negative. Building on these findings, we further expand the classical selfish-mining strategy space and propose Full Selfish Mining (FSM), a new mining attack strategy that deliberately maximizes the duration and frequency of equal-length fork states to exploit rational miners\u2019 intermittent participation. Experimental results demonstrate that FSM significantly amplifies adversarial power: an adversary can increase his revenue with just over 22% of total mining power, and can even launch a 51% attack with as little as 28% of total mining power. These results reveal a more threatening landscape and reshape PoW security thresholds.