Blockchain Consensus Protocols in the Wild (1707.01873v2)

Abstract: A blockchain is a distributed ledger for recording transactions, maintained by many nodes without central authority through a distributed cryptographic protocol. All nodes validate the information to be appended to the blockchain, and a consensus protocol ensures that the nodes agree on a unique order in which entries are appended. Consensus protocols for tolerating Byzantine faults have received renewed attention because they also address blockchain systems. This work discusses the process of assessing and gaining confidence in the resilience of a consensus protocols exposed to faults and adversarial nodes. We 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, we 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.

• The paper provides an in-depth analysis of permissioned blockchain consensus protocols, emphasizing resilience and rigorous security validation.
• It applies established cryptographic methods, including formal proofs and empirical testing, to assess mechanisms in systems like Hyperledger Fabric, Tendermint, and Corda.
• The study advocates for standardizing blockchain security practices and dismissing unverified protocol superiority to improve overall robustness.

Blockchain Consensus Protocols in the Wild

The paper "Blockchain Consensus Protocols in the Wild" provides a comprehensive examination of consensus protocols used within permissioned blockchain systems. The research seeks to demystify the resilience and trustworthiness of these protocols by drawing parallels with established cryptographic security methodologies.

Overview of Blockchain Consensus

The absence of a central authority in blockchains necessitates a robust consensus protocol to ensure all participating nodes agree on the transaction order appended to the ledger. Particularly, Byzantine fault-tolerant (BFT) consensus protocols have been central to accommodating adversarial settings. This paper emphasizes the significance of rigorous public review, detailed modeling, and formal proofs for blockchain systems, a practice well-established in cryptography and security.

Protocol Analysis

The paper explores numerous permissioned blockchain platforms, analyzing their consensus mechanisms concerning fault tolerance and attack resilience. Here's a summary of key protocol insights:

1. Hyperledger Fabric: Initially implemented PBFT and transitioned to an architecture allowing modular consensus implementations such as Apache Kafka and BFT-SMaRt. Kafka provides crash resilience while PBFT offers Byzantine fault tolerance against malicious nodes.
2. Tendermint: Described as an extension of PBFT, Tendermint integrates a leader rotation mechanism after every block to enhance fault resilience, albeit initial challenges related to liveness were noted.
3. Symbiont: Implements a BFT consensus using a customized BFT-SMaRt protocol, achieving high throughput similar to test metrics observed in academic settings.
4. R3 Corda: Unlike blockchains that order all transactions in a single execution, Corda organizes transactions into states pointing to a notary system. It supports Raft for crash tolerance and BFT-SMaRt for Byzantine fault tolerance.
5. Other Platforms: Systems like Iroha, Kadena, Chain, and Quorum employ a variety of approaches ranging from adaptations of existing consensus protocols to proprietary solutions that were either inadequately scrutinized or remained ambiguous in design.

Security Implications

The paper stresses the critical need for blockchain designers to adopt security practices analogous to those in cryptographic systems. The call to dismiss claims of unverified protocol superiority aligns with the rejection of "security by obscurity" in the cryptographic field. The paper promotes a framework for evaluating blockchain protocols, encouraging empirical testing and theoretical validation to ensure resilience and security in adversarial environments.

Future Directions

The research implicitly encourages the blockchain community to further investigate and standardize consensus protocols, drawing from cryptographic practices and leveraging peer-reviewed correctness proofs. This could eventually lead to the establishment of industry standards and increased protocol robustness, aligning financial trust with technical assurance.

In the evolving landscape of distributed ledger technologies, the insights from this paper provide a foundational understanding of current consensus mechanisms, informing future enhancements in permissioned blockchain security and performance.