FairLedger: A Fair Blockchain Protocol for Financial Institutions

Financial institutions are currently looking into technologies for permissioned blockchains. A major effort in this direction is Hyperledger, an open source project hosted by the Linux Foundation and backed by a consortium of over a hundred companies. A key component in permissioned blockchain protocols is a byzantine fault tolerant (BFT) consensus engine that orders transactions. However, currently available BFT solutions in Hyperledger (as well as in the literature at large) are inadequate for financial settings; they are not designed to ensure fairness or to tolerate selfish behavior that arises when financial institutions strive to maximize their own profit. We present FairLedger, a permissioned blockchain BFT protocol, which is fair, designed to deal with rational behavior, and, no less important, easy to understand and implement. The secret sauce of our protocol is a new communication abstraction, called detectable all-to-all (DA2A), which allows us to detect participants (byzantine or rational) that deviate from the protocol, and punish them. We implement FairLedger in the Hyperledger open source project, using Iroha framework, one of the biggest projects therein. To evaluate FairLegder's performance, we also implement it in the PBFT framework and compare the two protocols. Our results show that in failure-free scenarios FairLedger achieves better throughput than both Iroha's implementation and PBFT in wide-area settings

Factors that Impact Blockchain Scalability

Blockchain systems (more precisely Distributed Ledger Technologies(DLTs)) represent a different digital ecosystem compared with traditional computer systems. One major difference are the performance and scalability factors which will be discussed and analytically investigated in this paper. Indoing so, we provide guidance for defining a research agenda focusing on the investigation of the crucial role of scalability for DLT systems. System performance - measured in terms of (1) consensus response time (blockchain network latency or time to convergence/agreement); (2) number of transactionsper second or throughput, and (3) computing (and power) resources consumed - can be understood by considering the design dimensions of a DLT system, namely: (i) the type of DLT system needed from a requirements perspectivewhich in turn determines; (ii) the complexity of the consensus protocol used; (iii) the topography of the anticipated traffic flow on the network; (iv) the performance and complexity of the domain-specific language that implementssmart contracts; and (v) by the anticipated growth in size and complexity of the distributed ledger itself.Blockchain systems (more precisely Distributed Ledger Technologies(DLTs)) represent a different digital ecosystem compared with traditional computer systems. One major difference are the performance and scalability factors which will be discussed and analytically investigated in this paper. Indoing so, we provide guidance for defining a research agenda focusing on the investigation of the crucial role of scalability for DLT systems. System performance - measured in terms of (1) consensus response time (blockchain network latency or time to convergence/agreement); (2) number of transactionsper second or throughput, and (3) computing (and power) resources consumed - can be understood by considering the design dimensions of a DLT system, namely: (i) the type of DLT system needed from a requirements perspectivewhich in turn determines; (ii) the complexity of the consensus protocol used; (iii) the topography of the anticipated traffic flow on the network; (iv) the performance and complexity of the domain-specific language that implementssmart contracts; and (v) by the anticipated growth in size and complexity of the distributed ledger itself

Efficient Synchronous Byzantine Consensus

We present new protocols for Byzantine state machine replication and Byzantine agreement in the synchronous and authenticated setting. The celebrated PBFT state machine replication protocol tolerates $f$ Byzantine faults in an asynchronous setting using $3f+1$ replicas, and has since been studied or deployed by numerous works. In this work, we improve the Byzantine fault tolerance threshold to $n=2f+1$ by utilizing a relaxed synchrony assumption. We present a synchronous state machine replication protocol that commits a decision every 3 rounds in the common case. The key challenge is to ensure quorum intersection at one honest replica. Our solution is to rely on the synchrony assumption to form a post-commit quorum of size $2f+1$, which intersects at $f+1$ replicas with any pre-commit quorums of size $f+1$. Our protocol also solves synchronous authenticated Byzantine agreement in expected 8 rounds. The best previous solution (Katz and Koo, 2006) requires expected 24 rounds. Our protocols may be applied to build Byzantine fault tolerant systems or improve cryptographic protocols such as cryptocurrencies when synchrony can be assumed