Rational Censorship Attack: Breaking Blockchain with a Blackboard

TL;DR

This paper reveals a game-theoretic rational censorship attack on blockchain systems where colluding nodes can control rewards by censoring others, highlighting vulnerabilities and potential countermeasures.

Contribution

It introduces a formal game-theoretic model of a rational censorship attack that exploits voting power and coordination via a public blackboard in blockchain networks.

Findings

Colluding nodes can censor others to monopolize rewards.

The attack strategy is a subgame perfect equilibrium.

Knowledge of total voting power is crucial for attack success.

Abstract

Censorship resilience is a fundamental assumption underlying the security of blockchain protocols. Additionally, the analysis of blockchain security from an economic and game theoretic perspective has been growing in popularity in recent years. In this work, we present a surprising rational censorship attack on blockchain censorship resilience when we adopt the analysis of blockchain security from a game theoretic lens and assume all users are rational. In our attack, a colluding group with sufficient voting power censors the remainder nodes such that the group alone can gain all the rewards from maintaining the blockchain. We show that if nodes are rational, coordinating this attack just requires a public read and write blackboard and we formally model the attack using a game theoretic framework. Furthermore, we note that to ensure the success of the attack, nodes need to know the total true voting power held by the colluding group. We prove that the strategy to join the rational censorship attack and also for nodes to honestly declare their power is a subgame perfect equilibrium in the corresponding extensive form game induced by our attack. Finally, we discuss the implications of the attack on blockchain users and protocol designers as well as some potential countermeasures.