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

Every Bit Counts in Consensus

Consensus enables n processes to agree on a common valid L-bit value, despite t < n/3 processes being faulty and acting arbitrarily. A long line of work has been dedicated to improving the worst-case communication complexity of consensus in partial synchrony. This has recently culminated in the worst-case word complexity of O(n^2). However, the worst-case bit complexity of the best solution is still O(n^2 L + n^2 kappa) (where kappa is the security parameter), far from the \Omega(n L + n^2) lower bound. The gap is significant given the practical use of consensus primitives, where values typically consist of batches of large size (L > n). This paper shows how to narrow the aforementioned gap while achieving optimal linear latency. Namely, we present a new algorithm, DARE (Disperse, Agree, REtrieve), that improves upon the O(n^2 L) term via a novel dispersal primitive. DARE achieves O(n^{1.5} L + n^{2.5} kappa) bit complexity, an effective sqrt{n}-factor improvement over the state-of-the-art (when L > n kappa). Moreover, we show that employing heavier cryptographic primitives, namely STARK proofs, allows us to devise DARE-Stark, a version of DARE which achieves the near-optimal bit complexity of O(n L + n^2 poly(kappa)). Both DARE and DARE-Stark achieve optimal O(n) latency

Enhancing Blockchain Performance and Security: Pushing the Limits of Decentralized Applications

Decentralized Applications (DApps) have seen exponential growth in the past decade leading to a new paradigm known as Web3. Web3 is the ecosystem formed by the execution of multiple DApps. Blockchains offer a platform for DApp executions. However, the performance and security of current blockchains is limited and impair the adoption of Web3. More specifically, for demanding DApp workloads, modern blockchains perform poorly or lose transactions. This thesis presents various contributions to enhance blockchain performance and security to widen the adoption of Web3. To enhance blockchain performance for DApp executions, we first present the Smart Redbelly Blockchain (SRBB). SRBB enhances DApp performance by reducing blockchain congestion. SRBB alone is not sufficient to service multiple demanding DApp workloads. Therefore, we introduce a DApp-oriented dynamic transparent sharding mechanism that concurrently execute DApps in separate shards. To boost the DApp performance of SRBB, we present a decoupled variant of SRBB known as Collachain. While blockchain performance is critical, existing blockchain designs are vulnerable to the formation of an oligarchy in the governance that can dictate the outcome of the protocol. Such an oligarchy can lead to the insecure execution of DApps, impairing the adoption of Web3. To mitigate the formation of an oligarchy in blockchain governance, we finally present a proportional governance protocol that proportionally elects a diverse set of governors to mitigate an oligarchy in the governance process