1,266 research outputs found
Parameterizable Byzantine Broadcast in Loosely Connected Networks
We consider the problem of reliably broadcasting information in a multihop
asynchronous network, despite the presence of Byzantine failures: some nodes
are malicious and behave arbitrarly. We focus on non-cryptographic solutions.
Most existing approaches give conditions for perfect reliable broadcast (all
correct nodes deliver the good information), but require a highly connected
network. A probabilistic approach was recently proposed for loosely connected
networks: the Byzantine failures are randomly distributed, and the correct
nodes deliver the good information with high probability. A first solution
require the nodes to initially know their position on the network, which may be
difficult or impossible in self-organizing or dynamic networks. A second
solution relaxed this hypothesis but has much weaker Byzantine tolerance
guarantees. In this paper, we propose a parameterizable broadcast protocol that
does not require nodes to have any knowledge about the network. We give a
deterministic technique to compute a set of nodes that always deliver authentic
information, for a given set of Byzantine failures. Then, we use this technique
to experimentally evaluate our protocol, and show that it significantely
outperforms previous solutions with the same hypotheses. Important disclaimer:
these results have NOT yet been published in an international conference or
journal. This is just a technical report presenting intermediary and incomplete
results. A generalized version of these results may be under submission
Multi-hop Byzantine reliable broadcast with honest dealer made practical
We revisit Byzantine tolerant reliable broadcast with honest dealer algorithms in multi-hop networks. To tolerate Byzantine faulty nodes arbitrarily spread over the network, previous solutions require a factorial number of messages to be sent over the network if the messages are not authenticated (e.g., digital signatures are not available). We propose modifications that preserve the safety and liveness properties of the original unauthenticated protocols, while highly decreasing their observed message complexity when simulated on several classes of graph topologies, potentially opening to their employment
Fault Tolerance in Networks of Bounded Degree
Achieving processor cooperation in the presence of faults is a major problem in distributed systems. Popular paradigms such as Byzantine agreement have been studied principally in the context of a complete network. Indeed, Dolev [J. Algorithms, 3 (1982), pp. 14–30] and Hadzilacos [Issues of Fault Tolerance in Concurrent Computations, Ph.D. thesis, Harvard University, Cambridge, MA, 1984] have shown that Ω(t) connectivity is necessary if the requirement is that all nonfaulty processors decide unanimously, where t is the number of faults to be tolerated. We believe that in forseeable technologies the number of faults will grow with the size of the network while the degree will remain practically fixed. We therefore raise the question whether it is possible to avoid the connectivity requirements by slightly lowering our expectations.
In many practical situations we may be willing to “lose” some correct processors and settle for cooperation between the vast majority of the processors. Thus motivated, we present a general simulation technique by which vertices (processors) in almost any network of bounded degree can simulate an algorithm designed for the complete network. The simulation has the property that although some correct processors may be cut off from the majority of the network by faulty processors, the vast majority of the correct processors will be able to communicate among themselves undisturbed by the (arbitrary) behavior of the faulty nodes.
We define a new paradigm for distributed computing, almost-everywhere agreement, in which we require only that almost all correct processors reach consensus. Unlike the traditional Byzantine agreement problem, almost-everywhere agreement can be solved on networks of bounded degree. Specifically, we can simulate any sufficiently resilient Byzantine agreement algorithm on a network of bounded degree using our communication scheme described above. Although we “lose” some correct processors, effectively treating them as faulty, the vast majority of correct processors decide on a common value
EESMR: Energy Efficient BFT-SMR for the masses
Modern Byzantine Fault-Tolerant State Machine Replication (BFT-SMR) solutions
focus on reducing communication complexity, improving throughput, or lowering
latency. This work explores the energy efficiency of BFT-SMR protocols. First,
we propose a novel SMR protocol that optimizes for the steady state, i.e., when
the leader is correct. This is done by reducing the number of required
signatures per consensus unit and the communication complexity by order of the
number of nodes n compared to the state-of-the-art BFT-SMR solutions.
Concretely, we employ the idea that a quorum (collection) of signatures on a
proposed value is avoidable during the failure-free runs. Second, we model and
analyze the energy efficiency of protocols and argue why the steady-state needs
to be optimized. Third, we present an application in the cyber-physical system
(CPS) setting, where we consider a partially connected system by optionally
leveraging wireless multicasts among neighbors. We analytically determine the
parameter ranges for when our proposed protocol offers better energy efficiency
than communicating with a baseline protocol utilizing an external trusted node.
We present a hypergraph-based network model and generalize previous fault
tolerance results to the model. Finally, we demonstrate our approach's
practicality by analyzing our protocol's energy efficiency through experiments
on a CPS test bed. In particular, we observe as high as 64% energy savings when
compared to the state-of-the-art SMR solution for n=10 settings using BLE.Comment: Appearing in Middleware 202
When the Hammer Meets the Nail: Multi-Server PIR for Database-Driven CRN with Location Privacy Assurance
We show that it is possible to achieve information theoretic location privacy
for secondary users (SUs) in database-driven cognitive radio networks (CRNs)
with an end-to-end delay less than a second, which is significantly better than
that of the existing alternatives offering only a computational privacy. This
is achieved based on a keen observation that, by the requirement of Federal
Communications Commission (FCC), all certified spectrum databases synchronize
their records. Hence, the same copy of spectrum database is available through
multiple (distinct) providers. We harness the synergy between multi-server
private information retrieval (PIR) and database- driven CRN architecture to
offer an optimal level of privacy with high efficiency by exploiting this
observation. We demonstrated, analytically and experimentally with deployments
on actual cloud systems that, our adaptations of multi-server PIR outperform
that of the (currently) fastest single-server PIR by a magnitude of times with
information theoretic security, collusion resiliency, and fault-tolerance
features. Our analysis indicates that multi-server PIR is an ideal
cryptographic tool to provide location privacy in database-driven CRNs, in
which the requirement of replicated databases is a natural part of the system
architecture, and therefore SUs can enjoy all advantages of multi-server PIR
without any additional architectural and deployment costs.Comment: 10 pages, double colum
When Distributed Consensus Meets Wireless Connected Autonomous Systems: A Review and A DAG-based Approach
The connected and autonomous systems (CAS) and auto-driving era is coming
into our life. To support CAS applications such as AI-driven decision-making
and blockchain-based smart data management platform, data and message
exchange/dissemination is a fundamental element. The distributed message
broadcast and forward protocols in CAS, such as vehicular ad hoc networks
(VANET), can suffer from significant message loss and uncertain transmission
delay, and faulty nodes might disseminate fake messages to confuse the network.
Therefore, the consensus mechanism is essential in CAS with distributed
structure to guaranteed correct nodes agree on the same parameter and reach
consistency. However, due to the wireless nature of CAS, traditional consensus
cannot be directly deployed. This article reviews several existing consensus
mechanisms, including average/maximum/minimum estimation consensus mechanisms
that apply on quantity, Byzantine fault tolerance consensus for request, state
machine replication (SMR) and blockchain, as well as their implementations in
CAS. To deploy wireless-adapted consensus, we propose a Directed Acyclic Graph
(DAG)-based message structure to build a non-equivocation data dissemination
protocol for CAS, which has resilience against message loss and unpredictable
forwarding latency. Finally, we enhance this protocol by developing a
two-dimension DAG-based strategy to achieve partial order for blockchain and
total order for the distributed service model SMR
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