Revisiting Transaction Ledger Robustness in the Miner Extractable Value Era

In public transaction ledgers such as Bitcoin and Ethereum, it is generally assumed that miners do not have any preference on the contents of the transactions they include, such that miners eventually include all transactions they receive. However, Daian et al. S &P’20 showed that in practice this is not the case, and the so called miner extractable value can dramatically increase miners’ profit by re-ordering, delaying or even suppressing transactions. Consequently an “unpopular” transaction might never be included in the ledger if miners decide to suppress it, making, e.g., the standard liveness property of transaction ledgers (Garay et al. Eurocrypt’15) impossible to be guaranteed in this setting. In this work, we formally define the setting where miners of a transaction ledger are dictatorial, i.e., their transaction selection and ordering process is driven by their individual preferences on the transaction’s contents. To this end, we integrate dictatorial miners into the transaction ledger model of Garay et al. by replacing honest miners with dictatorial ones. Next, we introduce a new property for a transaction ledger protocol that we call content preference robustness (CPR). This property ensures rational liveness, which guarantees inclusion of transactions even when miners are dictatorial, and it provides rational transaction order preservation which ensures that no dictatorial miner can improve its utility by altering the order of received candidate transactions. We show that a transaction ledger protocol can achieve CPR if miners cannot obtain a-priori knowledge of the content of the transactions. Finally, we provide a generic compiler based on time-lock puzzles that transforms any robust transaction ledger protocol into a CPR ledger.