Paper 2026/2275

Defeating Time-Average Selfish Mining Across Epoch Boundaries in Nakamoto Consensus

Abstract

Selfish mining profits in Nakamoto consensus because difficulty adjustment mechanisms (DAMs) misinterpret uncounted orphans as hash-rate contraction. Although orphan-aware DAMs record orphaned proof-of-work, strict same-epoch inclusion rules enable an orphan exclusion attack (OEA): an adversary can race private forks near epoch boundaries to permanently exclude honest tail orphans from retargeting, restoring substantial profits in short-epoch protocols. We propose the pipelined buffer difficulty adjustment mechanism (PB-DAM), which partitions each epoch into an accountable prefix and a settlement buffer of depth $d$. Pipelining estimation windows across epochs grants honest miners a grace period to report prefix uncles while advancing buffer work to subsequent retargets, closing the boundary gap without heuristic damping. Random-walk excursion bounds demonstrate that OEA success decays exponentially with $d$ for all $\alpha \le \alpha^\star < 1/2$, reducing the time-averaged profit advantage to $O(\varepsilon)$. Under stylized dynamic scheduling models, intermittent idling is analytically shown to be unable to raise the gross reward rate above $\alpha$. Simulations confirm that buffer depths $d = 16$ neutralize selfish mining even at $L = 64$ when $\alpha = 0.40$, and systems recover from a $50\%$ hash-rate crash within $2.2 \pm 0.8$ epochs, incurring under $1\%$ block capacity overhead.