BDoS: Blockchain Denial of Service
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Proof-of-work (PoW) cryptocurrency blockchains like Bitcoin secure vast amounts of money. Participants expend resources to participate and receive monetary rewards for their efforts. Despite rivalry among cryptocurrencies and financial incentive to disrupt blockchain availability, Denial of Service (DoS) attacks against blockchains are rare. Arguably, this is due to their cost: Known attacks either target individual participants or require the control of the majority of the system resources. In this work, we present an incentive-based attack on blockchain availability, Blockchain-DoS (BDoS), with a significantly lower cost. Despite a plethora of work on revenue-driven attacks, to the best of our knowledge, this is the first incentive-based sabotage DoS attack. We consider an attacker with an exogenous motivation, who is willing to spend resources in order to stop blockchain progress. The attacker commits to a behavior that incentivizes the other participants to stop mining, bringing the blockchain to a halt. We analyze the miner behavior as a game with iterated elimination of strictly dominated strategies (IESDS). We observe that the success of the attack depends on a variety of factors: the mining power of the attacker, the mining power of the largest non-attacking miner, and the profitability of the mining process. We find that under realistic conditions, based on a new analysis of public data, an attack on Bitcoin-like cryptocurrencies requires as little as 20 the mining power. The situation is even worse if miners can use their equipment in another blockchain rather than turn it off. We propose countermeasures to deter BDoS.
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