Mysticeti: Low-Latency DAG Consensus with Fast Commit Path

We introduce Mysticeti-C a byzantine consensus protocol with low-latency and high resource efficiency. It leverages a DAG based on Threshold Clocks and incorporates innovations in pipelining and multiple leaders to reduce latency in the steady state and under crash failures. Mysticeti-FPC incorporates a fast commit path that has even lower latency. We prove the safety and liveness of the protocols in a byzantine context. We evaluate Mysticeti and compare it with state-of-the-art consensus and fast path protocols to demonstrate its low latency and resource efficiency, as well as more graceful degradation under crash failures. Mysticeti is the first byzantine protocol to achieve WAN latency of 0.5s for consensus commit, at a throughput of over 50k TPS that matches the state-of-the-art

The Impact of RDMA on Agreement

Remote Direct Memory Access (RDMA) is becoming widely available in data centers. This technology allows a process to directly read and write the memory of a remote host, with a mechanism to control access permissions. In this paper, we study the fundamental power of these capabilities. We consider the well-known problem of achieving consensus despite failures, and find that RDMA can improve the inherent trade-off in distributed computing between failure resilience and performance. Specifically, we show that RDMA allows algorithms that simultaneously achieve high resilience and high performance, while traditional algorithms had to choose one or another. With Byzantine failures, we give an algorithm that only requires $n \geq 2f_P + 1$ processes (where $f_P$ is the maximum number of faulty processes) and decides in two (network) delays in common executions. With crash failures, we give an algorithm that only requires $n \geq f_P + 1$ processes and also decides in two delays. Both algorithms tolerate a minority of memory failures inherent to RDMA, and they provide safety in asynchronous systems and liveness with standard additional assumptions.Comment: Full version of PODC'19 paper, strengthened broadcast algorith

Generalized Paxos Made Byzantine (and Less Complex)

One of the most recent members of the Paxos family of protocols is Generalized Paxos. This variant of Paxos has the characteristic that it departs from the original specification of consensus, allowing for a weaker safety condition where different processes can have a different views on a sequence being agreed upon. However, much like the original Paxos counterpart, Generalized Paxos does not have a simple implementation. Furthermore, with the recent practical adoption of Byzantine fault tolerant protocols, it is timely and important to understand how Generalized Paxos can be implemented in the Byzantine model. In this paper, we make two main contributions. First, we provide a description of Generalized Paxos that is easier to understand, based on a simpler specification and the pseudocode for a solution that can be readily implemented. Second, we extend the protocol to the Byzantine fault model

Scalable low latency consensus for blockchains

Tese de mestrado, Segurança Informática, Universidade de Lisboa; Faculdade de Ciências, 2021State machine replication (SMR) is a classical technique to implement consistent and fault­tolerant replicated services. This type of system is usually built on top of consensus protocols that have high throughput but have problems scaling to settings with a large number of participants or wide­area sce narios due to the required number of messages exchanged to reach a consensus. We propose ProBFT (Probabilistic Byzantine Fault Tolerance), a consensus protocol specifically de signed to tackle the scalability problem of BFT protocols. ProBFT is a consensus protocol with optimal latency (three communication steps, as in PBFT) but with a reduced number of messages exchanged in each phase (O(n √ n) instead of PBFT’s O(n 2 )). ProBFT is a probabilistic protocol built on top of well­known primitives, such as probabilistic Byzantine quorums and verifiable random functions, which provides high probabilities of safety and liveness when the overwhelming majority of replicas is correct. We also propose a state machine replication protocol called PROBER (PRObabilistic ByzantinE Replication) that builds on top of two consensus protocols, ProBFT and PBFT. PROBER makes use of ProBFT to provide fast and probabilistic replies to the clients and uses PBFT to eventually determinis tically commit the history of operations guaranteeing that the system will not roll back the requests after such commit. This periodic deterministic commit allows the clients to enjoy the low latency provided by ProBFT while still having the guarantees provided by a deterministic protocol. We provide a detailed description of both protocols and analyse the probabilities for safety and live ness depending on the current number of Byzantine replicas

SklCoin: Toward a Scalable Proof-of-Stake and Collective Signature Based Consensus Protocol for Strong Consistency in Blockchain

The proof-of-work consensus protocol suffers from two main limitations: waste of energy and offering only probabilistic guarantees about the status of the blockchain. This paper introduces SklCoin, a new Byzantine consensus protocol and its corresponding software architecture. This protocol leverages two ideas: 1) the proof-of-stake concept to dynamically form stake proportionate consensus groups that represent block miners (stakeholders), and 2) scalable collective signing to efficiently commit transactions irreversibly. SklCoin has immediate finality characteristic where all miners instantly agree on the validity of blocks. In addition, SklCoin supports high transaction rate because of its fast miner election mechanis