In the Ethereum system, the exclusion of specific transactions is currently feasible with minimal effort due to a power imbalance among entities. This censorship opportunity threatens the dependability of time-sensitive services deployable on Ethereum. In this paper, we look at this threat from an access control perspective and attribute it to a lack of accountability for censorship, a lack of policy definition and enforcement, as well as to the lack of disincentivization of policy violation. We propose an approach to enforceable policies in Ethereum. Furthermore, we demonstrate how a specific policy can address the shortcomings of existing censorship mitigation techniques, particularly Inclusion Lists. Under the assumption that block assemblers are unwilling to incur significant financial penalties as well as that the local view on the network messages is sufficiently consistent, the proposed approach guarantees the inclusion of a transaction in a block within 27 seconds in a non-saturated network. The empirical validation of sufficiently consistent views on outstanding transactions is currently in progress.

We present a simple approach to mitigate transaction-ordering dependent Maximum-Extractable-Value (MEV) opportunities in Ethereum. The approach is built on top of Proposer-Builder-Separation, restricts the freedom to order transactions within a block arbitrarily, and relies primarily on a non-malleable signature scheme and separation of responsibilities. In addition, we generalize the proposed approach to show that the property of unpredictable transaction arrangement can be transferred also to other blockchain systems. We discuss the gain in MEV mitigation, important limitations, and open issues.