Correctness and fairness of committee-based blockchains: A case study of Tendermint’s repeated consensus

In this paper, we propose a methodology to design and analyze the correctness and fairness of committee-based blockchains. We specify the problem that these blockchains implement, specifically, the Byzantine repeated consensus problem. Moreover, we define the problem of fair reward distribution among committee members and study the impact of synchronous assumptions on fairness . It is common knowledge that in permisionless blockchain systems, the main threat is the tragedy of commons that may yield the system to collapse if the rewarding mechanism is not adequate. At minimum, the reward mechanism must be fair , i.e., distribute the rewards in proportion to the merit of the participants. We prove, for the first time in blockchain systems, that in repeated-consensus based blockchains there exists an (eventual) fair rewarding mechanism if and only if the system is (eventual) synchronous. As a case study, we study Tendermint both from Byzantine Repeated Consensus perspective and its fairness with respect to the rewarding of committee members. We prove that in eventual synchronous systems, a modified version of Tendermint solves: (i) one-shot consensus for the validation of one single block with message complexity O ( n 3 ) where is the size of the validators set and (ii) a variant of the repeated consensus problem for multiple blocks. Our second contribution is related to the fairness of the Tendermint rewarding mechanism. We show that the rewarding in Tendermint is not fair, but a small modification of Tendermint is eventually fair.