A Review of Consensus Protocols in Permissioned Blockchains
Nenad Tomić
Abstract
Consensus protocols are used for the distributed management of large databases in an environment without trust among participants. The choice of a specific protocol depends on the purpose and characteristics of the system itself. The subjects of the paper are consensus protocols in permissioned blockchains. The objective of this paper is to identify functional advantages and disadvantages of observed protocol. The analysis covers a total of six consensus protocols for permissioned blockchains. The following characteristics were compared: security, trust among participants, throughput and scalability. The results show that no protocol shows absolute dominance in all aspects of the comparison. Paxos and Raft are intended for systems in which there is no suspicion of unreliable users, but only the problem of a temporary shutdown. Practical Byzantine Fault Tolerance is intended for systems with a small number of nodes. Federated Byzantine Fault Tolerance shows better scalability and is more suitable for large systems, but can withstand a smaller number of malicious nodes. Proof-of-authority can withstand the largest number of malicious nodes without interfering with the functioning of the system. When choosing a consensus protocol for a blockchain application, one should take into account priority characteristics.