Optimistic fair exchange (OFE) is a protocol for solving the problem of exchanging items or services in a fair manner between two parties, a signer and a verifier, with the help of an arbitrator which is called in only when a dispute happens between the two parties. In almost all the previous work on OFE, after obtaining a partial signature from the signer, the verifier can present it to others...

In this paper we make an analogy between the time that storage must be maintained in a optimistic simulation and the blocking time in a conservative simulation. By exploring this analogy, we design two new Global Virtual Time (GVT) protocols for Time Warp systems. The rst protocol is based on null message clock advancement in conservative approaches. Our main contribution is a new protocol insp...

The growing imbalance between network latency and throughput is causing nodes in distributed systems to appear to be moving farther apart. Many distributed systems are turning to replication as a mechanism to make resources appear closer. However, maintaining one-copy consistency in a system containing replicated elements has proven diicult. In particular, the checks required to make consistent...

We study the problem of global maximization of a function f given a finite number of evaluations perturbed by noise. We consider a very weak assumption on the function, namely that it is locally smooth (in some precise sense) with respect to some semi-metric, around one of its global maxima. Compared to previous works on bandits in general spaces (Kleinberg et al., 2008; Bubeck et al., 2011a) o...

We present an efficient and fair protocol for secure two-party computation in the optimistic model, where a partially trusted third party T is available, but not involved in normal protocol executions. T is needed only if communication is disrupted or if one of the two parties misbehaves. The protocol guarantees that although one party may terminate the protocol at any time, the computation rem...

Traditionally, fault tolerance has been considered a pivotal component of system design. However, as modern commodity hardware becomes increasingly reliable, building dedicated fault tolerance systems becomes unnecessary. Therefore, while in this paper we propose nothing novel and make no technical contributions, we nevertheless identify a unique approach to fault tolerance, which we dub optimi...

We consider the problem of planning in a stochastic and discounted environment with a limited numerical budget. More precisely, we investigate strategies exploring the set of possible sequences of actions, so that, once all available numerical resources (e.g. CPU time, number of calls to a generative model) have been used, one returns a recommendation on the best possible immediate action to fo...

We consider an asynchronous system with the Ω failure detector, and investigate the number of communication steps required by various broadcast protocols in runs in which the leader does not change. Atomic Broadcast, used for example in state machine replication, requires three communication steps. Optimistic Atomic Broadcast requires only two steps if all correct processes receive messages in ...

Starting with the Thomspon sampling algorithm, recent years have seen a resurgence of interest in Bayesian algorithms for the Multi-armed Bandit (MAB) problem. These algorithms seek to exploit prior information on arm biases and while several have been shown to be regret optimal, their design has not emerged from a principled approach. In contrast, if one cared about Bayesian regret discounted ...

Computer simulation of large and complex systems in various elds of science and engineering requires tremendous computational resources, and is limited by sequential simulation algorithms in most practical cases. Parallel simulation ooers the potential to accelerate simulations so as to facilitate the study of complex dynamic systems with large problem sizes, to explore large parameter spaces, ...