What happens when consensus protocols don’t follow routine? This work discusses the process of assessing and gaining confidence in the resilience of a consensus protocols exposed to faults and adversarial nodes. The authors advocate to follow the established practice in cryptography and computer security, relying on public reviews, detailed models, and formal proofs; the designers of several practical systems appear to be unaware of this.

Moreover, the authors review the consensus protocols in some prominent permissioned blockchain platforms with respect to their fault models and resilience against attacks. The protocol comparison covers Hyperledger Fabric, Tendermint, Symbiont, R3 Corda, Iroha, Kadena, Chain, Quorum, MultiChain, Sawtooth Lake, Ripple, Stellar, and IOTA.

Developing consensus protocols is similar to engineering cryptographic systems and blockchain developers should look towards the established experience in cryptography, security, and the theory of distributed systems for building trustworthy systems. Otherwise, it might be dangerous to entrust financial value to new protocols. Open discussion, expert reviews, broad validation, and standards recommendations should be employed. The overview of consensus protocols and their properties contributes to this effort, by establishing a common ground for formal protocol reviews and more technical comparisons. Once enough systems become available publicly and are widely used, it will be interesting to compare their performance through benchmarks and to observe their resilience to actual attacks or network incidents.