Temporary Censorship Attacks in the Presence of Rational Miners

Smart contracts allow for exchange of coins according to program rules. While it is well known that so called bribery contracts can influence the incentive mechanism of a Nakamoto-style consensus, we present a more fine-grained bribery attack incentivizing a temporary censorship against a specific account. To this end, we introduce three different bribery contracts on the blockchain where each uniquely manipulates the rewards that a rational miner would receive. Additionally, we formalize the established bribery mechanisms as a Markov game and show for each game the existence of equilibria leading to successful censorships. Finally, we compare the bribery mechanisms with respect to the scalability of the attack costs and the strategic dominance. Our work is motivated by off-chain protocols including payment and state channels which require to publish transactions within a certain amount of time. In such off-chain protocols a temporary censorship attack can result into significant financial damage.