BDoS: Blockchain Denial of Service

TL;DR

This paper introduces BDoS, a novel incentive-based DoS attack on PoW cryptocurrencies that can halt blockchain operations with less than half the total mining power, exploiting reward mechanisms to discourage miner participation.

Contribution

It presents the first incentive-based DoS attack on PoW blockchains, demonstrating how reward mechanism exploitation can cause system disruption with significantly less resources than previous attacks.

Findings

BDoS can halt Bitcoin with 21% of mining power as of March 2020.

Bitcoin's vulnerability to BDoS increases as mining profitability drops.

BDoS differs from selfish mining by aiming to disrupt rather than increase revenue.

Abstract

Proof-of-work (PoW) cryptocurrency blockchains like Bitcoin secure vast amounts of money. Their operators, called miners, expend resources to generate blocks and receive monetary rewards for their effort. Blockchains are, in principle, attractive targets for Denial-of-Service (DoS) attacks: There is fierce competition among coins, as well as potential gains from short selling. Classical DoS attacks, however, typically target a few servers and cannot scale to systems with many nodes. There have been no successful DoS attacks to date against prominent cryptocurrencies. We present Blockchain DoS (BDoS), the first incentive-based DoS attack that targets PoW cryptocurrencies. Unlike classical DoS, BDoS targets the system's mechanism design: It exploits the reward mechanism to discourage miner participation. Previous DoS attacks against PoW blockchains require an adversary's mining power to match that of all other miners. In contrast, BDoS can cause a blockchain to grind to a halt with significantly fewer resources, e.g., 21% as of March 2020 in Bitcoin, according to our empirical study. We find that Bitcoin's vulnerability to BDoS increases rapidly as the mining industry matures and profitability drops. BDoS differs from known attacks like Selfish Mining in its aim not to increase an adversary's revenue, but to disrupt the system. Although it bears some algorithmic similarity to those attacks, it introduces a new adversarial model, goals, algorithm, and game-theoretic analysis. Beyond its direct implications for operational blockchains, BDoS introduces the novel idea that an adversary can manipulate miners' incentives by proving the existence of blocks without actually publishing them.