Paper 2019/752

Sucker punch makes you richer: Rethinking incentives in Proof-of-Work-based Blockchains

Runchao Han and Zhimei Sui and Jiangshan Yu and Joseph Liu and Shiping Chen

Abstract

Honest majority is the key security assumption of Proof-of-Work (PoW) based blockchains like Bitcoin. However, recent 51% attacks render this assumption unrealistic in practice. In this paper, we propose the “sucker punch attack”, where an attacker temporarily utilises external mining power to launch 51% attacks on a blockchain, and gains a better revenue than performing honest mining. The sucker punch attack indicates that the currently employed incentive mechanisms may incentivise profit-driven miners to turn into evil and break the “honest majority” assumption, rather than incentivising miners to stay honest and keep the system safe. We develop a Markov Decision Process based model to evaluate the attack, and provide an anslysis on the feasibility and profitability of launching sucker punch attacks on mainstream PoW-based blockchains. Our results show that the attacks are feasible and profitable on most of them. In addition, we also leverage our model to investigate the recent 51% attack on Ethereum Classic (Jan. 2019), which is suspected to be an incident of our sucker punch attacks. We provide insights on the attacker strategy and expected revenue, and show that the attacker’s strategy is near optimal.

Note: All types of feedback are welcome.