Temporary Block Withholding Attacks on Filecoin’s Expected Consensus

Filecoin is the most impactful storage-oriented cryptocurrency. In this system, miners dedicate their storage space to the network and verify transactions to earn rewards. Nowadays, Filecoin’s network capacity has surpassed 15 exbibytes.

In this paper, we propose three temporary block withholding attacks to challenge Filecoin’s expected consensus (EC). Specifically, we first deconstruct EC following old-fashioned methods (which have been widely developed since 2009) to analyze the advantages and disadvantages of EC’s design. We then present three temporary block withholding schemes by leveraging the shortcomings of EC. We build Markov Decision Process (MDP) models for the three attacks to calculate the adversary’s gains. We develop Monte Carlo simulators to mimic the mining strategies of the adversary and other miners and indicate the impacts of the three attacks on expectation. As a result, we show that our three attacks have significant impacts on Filecoin’s mining fairness and transaction throughput. For instance, when honest miners who control more than half the global storage power update their tipsets (i.e., the collection of blocks in the same epoch that have the same parents) after the default transmission cutoff time, an adversary with 1% of the global storage power is able to launch temporary block withholding attacks without a loss in revenue, which could affect Filecoin’s security and performance. Finally, we discuss the implications of our attacks and propose several countermeasures to mitigate them.