910 research outputs found
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 Byzantine
faults in an asynchronous setting using replicas, and has since been
studied or deployed by numerous works. In this work, we improve the Byzantine
fault tolerance threshold to 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 , which
intersects at replicas with any pre-commit quorums of size . 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
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 processes (where
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 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
Tight Bounds for Connectivity and Set Agreement in Byzantine Synchronous Systems
In this paper, we show that the protocol complex of a Byzantine synchronous
system can remain -connected for up to rounds,
where is the maximum number of Byzantine processes, and .
This topological property implies that rounds are
necessary to solve -set agreement in Byzantine synchronous systems, compared
to rounds in synchronous crash-failure systems. We
also show that our connectivity bound is tight as we indicate solutions to
Byzantine -set agreement in exactly synchronous
rounds, at least when is suitably large compared to . In conclusion, we
see how Byzantine failures can potentially require one extra round to solve
-set agreement, and, for suitably large compared to , at most that
Building Regular Registers with Rational Malicious Servers and Anonymous Clients
The paper addresses the problem of emulating a regular register in a synchronous distributed system where clients invoking and operations are anonymous while server processes maintaining the state of the register may be compromised by rational adversaries (i.e., a server might behave as rational malicious Byzantine process). We first model our problem as a Bayesian game between a client and a rational malicious server where the equilibrium depends on the decisions of the malicious server (behave correctly and not be detected by clients vs returning a wrong register value to clients with the risk of being detected and then excluded by the computation). We prove such equilibrium exists and finally we design a protocol implementing the regular register that forces the rational malicious server to behave correctly
Stellar Consensus by Instantiation
Stellar introduced a new type of quorum system called a Federated Byzantine Agreement System. A major difference between this novel type of quorum system and a threshold quorum system is that each participant has its own, personal notion of a quorum. Thus, unlike in a traditional BFT system, designed for a uniform notion of quorum, even in a time of synchrony one well-behaved participant may observe a quorum of well-behaved participants, while others may not.
To tackle this new problem in a more general setting, we abstract the Stellar Network as an instance of what we call Personal Byzantine Quorum Systems. Using this notion, we streamline the theory behind the Stellar Network, removing the clutter of unnecessary details, and refute the conjecture that Stellar\u27s notion of intact set is optimally fault-tolerant. Most importantly, we develop a new consensus algorithm for the new setting
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