26 research outputs found
Quantum Clock Synchronization with a Single Qudit
Clock synchronization for nonfaulty processes in multiprocess networks is
indispensable for a variety of technologies. A reliable system must be able to
resynchronize the nonfaulty processes upon some components failing causing the
distribution of incorrect or conflicting information in the network. The task
of synchronizing such networks is related to detectable Byzantine agreement
(DBA), which can classically be solved using recursive algorithms if and only
if less than one-third of the processes are faulty. Here we introduce a
nonrecursive quantum algorithm that solves the DBA and achieves clock
synchronization in the presence of arbitrary many faulty processes by using
only a single quantum system
A Software-based Low-Jitter Servo Clock for Inexpensive Phasor Measurement Units
This paper presents the design and the implementation of a servo-clock (SC)
for low-cost Phasor Measurement Units (PMUs). The SC relies on a classic
Proportional Integral (PI) controller, which has been properly tuned to
minimize the synchronization error due to the local oscillator triggering the
on-board timer. The SC has been implemented into a PMU prototype developed
within the OpenPMU project using a BeagleBone Black (BBB) board. The
distinctive feature of the proposed solution is its ability to track an input
Pulse-Per-Second (PPS) reference with good long-term stability and with no need
for specific on-board synchronization circuitry. Indeed, the SC implementation
relies only on one co-processor for real-time application and requires just an
input PPS signal that could be distributed from a single substation clock
Post-Quantum Key Exchange Protocols
If an eavesdropper Eve is equipped with quantum computers, she can easily
break the public key exchange protocols used today. In this paper we will
discuss the post-quantum Diffie-Hellman key exchange and private key exchange
protocols.Comment: 11 pages, 2 figures. Submitted to SPIE DSS 2006; v2 citation typos
fixed; v3 appendix typos correcte
Making Byzantine Consensus Live
Partially synchronous Byzantine consensus protocols typically structure their execution into a sequence of views, each with a designated leader process. The key to guaranteeing liveness in these protocols is to ensure that all correct processes eventually overlap in a view with a correct leader for long enough to reach a decision. We propose a simple view synchronizer abstraction that encapsulates the corresponding functionality for Byzantine consensus protocols, thus simplifying their design. We present a formal specification of a view synchronizer and its implementation under partial synchrony, which runs in bounded space despite tolerating message loss during asynchronous periods. We show that our synchronizer specification is strong enough to guarantee liveness for single-shot versions of several well-known Byzantine consensus protocols, including HotStuff, Tendermint, PBFT and SBFT. We furthermore give precise latency bounds for these protocols when using our synchronizer. By factoring out the functionality of view synchronization we are able to specify and analyze the protocols in a uniform framework, which allows comparing them and highlights trade-offs
Liveness and Latency of Byzantine State-Machine Replication
Byzantine state-machine replication (SMR) ensures the consistency of replicated state in the presence of malicious replicas and lies at the heart of the modern blockchain technology. Byzantine SMR protocols often guarantee safety under all circumstances and liveness only under synchrony. However, guaranteeing liveness even under this assumption is nontrivial. So far we have lacked systematic ways of incorporating liveness mechanisms into Byzantine SMR protocols, which often led to subtle bugs. To close this gap, we introduce a modular framework to facilitate the design of provably live and efficient Byzantine SMR protocols. Our framework relies on a view abstraction generated by a special SMR synchronizer primitive to drive the agreement on command ordering. We present a simple formal specification of an SMR synchronizer and its bounded-space implementation under partial synchrony. We also apply our specification to prove liveness and analyze the latency of three Byzantine SMR protocols via a uniform methodology. In particular, one of these results yields what we believe is the first rigorous liveness proof for the algorithmic core of the seminal PBFT protocol
Quantum Permutation Synchronization
We present QuantumSync, the first quantum algorithm for solving a synchronization problem in the context of computer vision. In particular, we focus on permutation synchronization which involves solving a non-convex optimization problem in discrete variables. We start by formulating synchronization into a quadratic unconstrained binary optimization problem (QUBO). While such formulation respects the binary nature of the problem, ensuring that the result is a set of permutations requires extra care. Hence, we: (i) show how to insert permutation constraints into a QUBO problem and (ii) solve the constrained QUBO problem on the current generation of the adiabatic quantum computers D-Wave. Thanks to the quantum annealing, we guarantee global optimality with high probability while sampling the energy landscape to yield confidence estimates. Our proof-of-concepts realization on the adiabatic D-Wave computer demonstrates that quantum machines offer a promising way to solve the prevalent yet difficult synchronization problems
MuON: Epidemic based mutual anonymity in unstructured P2P networks
A mutual anonymity system enables communication between a client and a service provider without revealing their identities. In general, the anonymity guarantees made by the protocol are enhanced when a large number of participants are recruited into the anonymity system. Peer-to-peer (P2P) systems are able to attract a large number of nodes and hence are highly suitable for anonymity systems. However, the churn (changes in system membership) within P2P networks, poses a significant challenge for low-bandwidth reliable anonymous communication in these networks.
This paper presents MuON, a protocol to achieve mutual anonymity in unstructured P2P networks. MuON leverages epidemic-style data dissemination to deal with churn. Simulation results and security analysis indicate that MuON provides mutual anonymity in networks with high churn, while maintaining predictable latencies, high reliability, and low communication overhead