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See detailPISTIS: From a Word-of-Mouth to a Gentleman’s Agreement
Kozhaya, David; Decouchant, Jérémie UL; Rahli, Vincent et al

E-print/Working paper (2020)

The accelerated digitalisation of society along with technological evolution have extended the geographical span of cyber-physical systems. Two main threats have made the reliable and real-time control of ... [more ▼]

The accelerated digitalisation of society along with technological evolution have extended the geographical span of cyber-physical systems. Two main threats have made the reliable and real-time control of these systems challenging: (i) uncertainty in the communication infrastructure induced by scale, openness and heterogeneity of the environment and devices; and (ii) targeted attacks maliciously worsening the impact of the above-mentioned communication uncertainties, disrupting the correctness of real-time applications. This paper addresses those challenges by showing how to build distributed protocols that provide both real-time with practical performance, and scalability in the presence of network faults and attacks. We provide a suite of real-time Byzantine protocols, which we prove correct, starting from a reliable broadcast protocol, called PISTIS, up to atomic broadcast and consensus. This suite simplifies the construction of powerful distributed and decentralized monitoring and control applications, including state-machine replication. Extensive empirical evaluations show- case PISTIS’s robustness, latency, and scalability. For example, PISTIS can withstand message loss (and delay) rates up to 40% in systems with 49 nodes and provides bounded delivery latencies in the order of a few milliseconds. [less ▲]

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See detailRT-ByzCast: Byzantine-Resilient Real-Time Reliable Broadcast
Kozhaya, David; Decouchant, Jérémie UL; Verissimo, Paulo UL

in IEEE Transactions on Computers (2019), 68(3),

Today’s cyber-physical systems face various impediments to achieving their intended goals, namely, communication uncertainties and faults, relative to the increased integration of networked and wireless ... [more ▼]

Today’s cyber-physical systems face various impediments to achieving their intended goals, namely, communication uncertainties and faults, relative to the increased integration of networked and wireless devices, hinder the synchronism needed to meet real-time deadlines. Moreover, being critical, these systems are also exposed to significant security threats. This threat combination increases the risk of physical damage. This paper addresses these problems by studying how to build the first real-time Byzantine reliable broadcast protocol (RTBRB) tolerating network uncertainties, faults, and attacks. Previous literature describes either real-time reliable broadcast protocols, or asynchronous (non real-time) Byzantine ones. We first prove that it is impossible to implement RTBRB using traditional distributed computing paradigms, e.g., where the error/failure detection mechanisms of processes are decoupled from the broadcast algorithm itself, even with the help of the most powerful failure detectors. We circumvent this impossibility by proposing RT-ByzCast, an algorithm based on aggregating digital signatures in a sliding time-window and on empowering processes with self-crashing capabilities to mask and bound losses. We show that RT-ByzCast (i) operates in real-time by proving that messages broadcast by correct processes are delivered within a known bounded delay, and (ii) is reliable by demonstrating that correct processes using our algorithm crash themselves with a negligible probability, even with message loss rates as high as 60%. [less ▲]

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See detailRepuCoin: Your Reputation is Your Power
Yu, Jiangshan; Kozhaya, David; Decouchant, Jérémie UL et al

in IEEE Transactions on Computers (2019)

Existing proof-of-work cryptocurrencies cannot tolerate attackers controlling more than 50% of the network’s computing power at any time, but assume that such a condition happening is “unlikely”. However ... [more ▼]

Existing proof-of-work cryptocurrencies cannot tolerate attackers controlling more than 50% of the network’s computing power at any time, but assume that such a condition happening is “unlikely”. However, recent attack sophistication, e.g., where attackers can rent mining capacity to obtain a majority of computing power temporarily, render this assumption unrealistic. This paper proposes RepuCoin, the first system to provide guarantees even when more than 50% of the system’s computing power is temporarily dominated by an attacker. RepuCoin physically limits the rate of voting power growth of the entire system. In particular, RepuCoin defines a miner’s power by its ‘reputation’, as a function of its work integrated over the time of the entire blockchain, rather than through instantaneous computing power, which can be obtained relatively quickly and/or temporarily. As an example, after a single year of operation, RepuCoin can tolerate attacks compromising 51% of the network’s computing resources, even if such power stays maliciously seized for almost a whole year. Moreover, RepuCoin provides better resilience to known attacks, compared to existing proof-of-work systems, while achieving a high throughput of 10000 transactions per second (TPS). [less ▲]

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See detailByzantine Resilient Protocol for the IoT
Fröhlich, Antônio Augusto; Scheffel, M.Roberto; Kozhaya, David et al

in IEEE Internet of Things Journal (2018)

Wireless sensor networks, often adhering to a single gateway architecture, constitute the communication backbone for many modern cyber-physical systems. Consequently, faulttolerance in CPS becomes a ... [more ▼]

Wireless sensor networks, often adhering to a single gateway architecture, constitute the communication backbone for many modern cyber-physical systems. Consequently, faulttolerance in CPS becomes a challenging task, especially when accounting for failures (potentially malicious) that incapacitate the gateway or disrupt the nodes-gateway communication, not to mention the energy, timeliness, and security constraints demanded by CPS domains. This paper aims at ameliorating the fault-tolerance of WSN based CPS to increase system and data availability. To this end, we propose a replicated gateway architecture augmented with energy-efficient real-time Byzantineresilient data communication protocols. At the sensors level, we introduce FT-TSTP, a geographic routing protocol capable of delivering messages in an energy-efficient and timely manner to multiple gateways, even in the presence of voids caused by faulty and malicious sensor nodes. At the gateway level, we propose a multi-gateway synchronization protocol, which we call ByzCast, that delivers timely correct data to CPS applications, despite the failure or maliciousness of a number of gateways. We show, through extensive simulations, that our protocols provide better system robustness yielding an increased system and data availability while meeting CPS energy, timeliness, and security demands. [less ▲]

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