Publications de Rachid Guerraoui

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A three-tier application is organized as three layers: human users interact with front-end clients (e.g browsers); middle-tier application servers (e.g. Web servers) contain the application's business logic, and perform transactions against back-end databases. Although three-tier applications are becoming mainstream, they usually fail to provide sufficient reliability guaranteesto the users. Usually, replication and transaction-processing techniques are applied to specific parts of the application, but thei

How efficiently can a malicious device disrupt a single-hop wireless network? Imagine two honest players attempting to exchange information in the presence of a malicious adversary that can disrupt communication by jamming or overwriting messages. Assume t ...

Cross-validation is commonly used to select the recommendation algorithms that will generalize best on yet unknown data. Yet, in many situations the available dataset used for cross-validation is scarce and the selected algorithm might not be the best suit ...

This paper studies the time complexity of reading unauthenticated data from a distributed storage made of a set of failure-prone base objects. More specifically, we consider the abstraction of a robust read/write storage that provides wait-free access to u ...

With the recent advent of blockchains, we have witnessed a plethora of blockchain proposals. These proposals range from using work to using time, storage or stake in order to select blocks to be appended to the chain. As a drawback it makes it difficult for the application developer to choose the right blockchain to support their applications. In particular, the scalability and performance one can obtain from a specific blockchain is typically unknown. The claimed results are often obtained in isolation by

Gossip protocols are considered very effective to disseminate information in a large scale dynamic distributed system. Their inherent simplicity makes them easy to implement and deploy. However, whereas their probabilistic guarantees are often enough to di ...

This paper shows for the first time that distributed computing can be both reliable and efficient in an environment that is both highly dynamic and hostile. More specifically, we show how to maintain clusters of size O(log N), each containing more than two thirds of honest nodes with high probability, within a system whose size can vary polyno-mially with respect to its initial size. Furthermore, the communication cost induced by each node arrival or departure is polylogarithmic with respect to N, the maxim

Many applications, such as content moderation and recommendation, require reviewing and scoring a large number of alternatives. Doing so robustly is however very challenging. Indeed, voters' inputs are inevitably sparse: most alternatives are only scored b ...

Exploiting Atomic Broadcast in Replicated Databases F.Pedone, R.Guerraoui and A.Schiper Database replication protocols have historically been built on top of distributed database systems, and have consequently been designed and implemented using distributed transactional mechanisms, such as atomic commitment. We argue in this paper that this approach is not always adequate to efficiently support database replication and that more suitable alternatives, such as atomic broadcast primitives, should be employed

The demand for real-time data storage in distributed control systems (DCSs) is growing. Yet, providing real- time DCS guarantees is challenging, especially when more and more sensor and actuator devices are connected to industrial plants and message loss n ...

The fair exchange problem is key to trading electronic items in systems of mutually untrusted parties.We consider modern variants of such systems where each party is equipped with a tamper proof security module. The security modules trust each other but can only communicate by exchanging messages through their host parties. These are untrusted and could intercept and drop those messages. We show that the fair exchange problem at the level of untrusted parties can be reduced to an atomic commit problem at th

Although useful in the development of distributed systems, current reliable distributed environments, such as group communication toolkits (e.g., ISIS, TOTEM, PHOENIX) or transactional monitors (e.g., ENCINA, TUXEDO), are hardly extensible or customisable for specific application needs. The limitations of those systems are mainly due to their underlying distributed protocols, which are usually designed and implemented in an ad hoc manner. This paper presents BAST, an object-oriented framework for building f

The fair exchange problem is key to trading electronic items in systems of mutually untrusted parties. We consider modern variants of such systems where each party is equipped with a tamper proof security module. The security modules trust each other but can only communicate by exchanging messages through their host parties. These are untrusted and could intercept and drop those messages. We show that the fair exchange problem at the level of untrusted parties can be reduced to an atomic commit problem at t

The growing interest in peer-to-peer applications has underlined the importance of scalability in modern distributed systems. Not surprisingly, much research effort has been invested in gossip-based broadcast protocols. These trade the traditional strong reliability guarantees against very good ``scalability'' properties. Scalability is in that context usually expressed in terms of throughput, but there is only little work on how to reduce the overhead of membership management at large scale. This paper pre

We consider the problem of computing an aggregation function in a \emph{secure} and \emph{scalable} way. Whereas previous distributed solutions with similar security guarantees have a communication cost of

O(n^3)

, we present a distributed protocol that requires only a communication complexity of

O(n\log^3 n)

, which we prove is near-optimal. Our protocol ensures perfect security against a computationally-bounded adversary, tolerates

(1/2-\epsilon)n

malicious nodes for any constant

1/2 > \epsilon > 0

his paper determines the computational strenght of the shared memory abstraction (a register) emulated over a message passing system, and compares it with fundamental message passing abstractions like consensus and various forms of reliable broadcast. We introduce the notion of Quorum failure detectors and show that this notion captures the exact amount of information about failures needed to emulate a shared memory in a distributed message passing system where processes can fail by crashing. As a corollary

This paper presents a pragmatic way to build a Reliable CORBA Event Service. Our approach is pragmatic in the sense that, rather than building the service from scratch, we show how to obtain it, through a simple transformation, from any standard (unreliable) CORBA 2.0 Event Service. Our extension does not introduce any modification to the CORBA specification, nor any communication overhead. The Reliable CORBA Event Service provides the adequate semantics for building reliable notification-based applications

Scaling to a large number of cores with non-uniform communication latency and unpredictable response time may call for viewing a modern many-core architecture as a distributed system. In this view, the cores replicate shared data and ensure consistency among replicas through a message-passing based agreement protocol. In this paper, we present the first in-depth study of messagepassing agreement on many-cores. In particular, we focus on the possibility of such a protocol being non-blocking. We highlight a n

We propose a new mechanism to preserve privacy while leveraging user profiles in distributed recommender systems. Our mechanism relies on two contributions: (i) an original obfuscation scheme, and (ii) a randomized dissemination protocol. We show that our ...

Rachid Guerraoui

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Exactly-Once Transactions

Of Malicious Motes and Suspicious Sensors: On the Efficiency of Malicious Interference in Wireless Networks

The Imitation Game: Algorithm Selection by Exploiting Black-Box Recommenders

How Fast Can a Very Robust Read Be?

Diablo-v2: A Benchmark for Blockchain Systems

Boosting Gossip for Live Streaming

Highly Dynamic Distributed Computing with Byzantine Failures

Robust Sparse Voting

Exploiting Atomic Broadcast in Replicated Databases

Right On Time Distributed Shared Memory

Reducing Fair Exchange to Atomic Commit

Bast, A Framework for Reliable Distributed Computing

Reducing Fair Exchange to Atomic Commit

Exploiting Atomic Broadcast in Replicated Databases

Lightweight Probabilistic Broadcast

Scalable and Secure Aggregation in Distributed Networks

Shared Memory vs Message Passing

Reliability with CORBA Event Channels

Consensus inside

Privacy-preserving distributed collaborative filtering