Sluggish Mining: Profiting from the Verifier’s Dilemma

Abstract

Miners in Ethereum need to make a choice when they receive a block: they can fully validate the block by executing every transaction in order to validate the new state, but this consumes precious time that could be used on mining the next block. Alternatively, miners could skip some of the verification stages and proceed with the mining, taking the risk of building on top of a potentially invalid block. This is referred to as the verifier’s dilemma. Although the gas limit imposed on Ethereum blocks mitigates this attack by forcing an upper bound on the time spent during verification, the slowdown that can be achieved within a block can still be enough to have an impact on profitability. In this paper we present a mining strategy based around sluggish contracts; these computationally intensive contracts are purposely designed to have a slow execution time in the Ethereum Virtual Machine to provide an advantage over other miners by slowing their contract verification time. We validate our proposed mining strategy by designing and evaluating a set of candidate sluggish smart contracts. Furthermore, we provide a detailed analysis that shows under which conditions our strategy becomes profitable alongside a series of suggestions to detect this type of strategy in the future.