A Byzantine Fault-Tolerant Ordering Service for the Hyperledger Fabric Blockchain Platform

Hyperledger Fabric (HLF) is a flexible permissioned blockchain platform designed for business applications beyond the basic digital coin addressed by Bitcoin and other existing networks. A key property of HLF is its extensibility, and in particular the support for multiple ordering services for building the blockchain. Nonetheless, the version 1.0 was launched in early 2017 without an implementation of a Byzantine fault-tolerant (BFT) ordering service. To overcome this limitation, we designed, implemented, and evaluated a BFT ordering service for HLF on top of the BFT-SMaRt state machine replication/consensus library, implementing also optimizations for wide-area deployment. Our results show that HLF with our ordering service can achieve up to ten thousand transactions per second and write a transaction irrevocably in the blockchain in half a second, even with peers spread in different continents

Improving the Scalability of DPWS-Based Networked Infrastructures

The Devices Profile for Web Services (DPWS) specification enables seamless discovery, configuration, and interoperability of networked devices in various settings, ranging from home automation and multimedia to manufacturing equipment and data centers. Unfortunately, the sheer simplicity of event notification mechanisms that makes it fit for resource-constrained devices, makes it hard to scale to large infrastructures with more stringent dependability requirements, ironically, where self-configuration would be most useful. In this report, we address this challenge with a proposal to integrate gossip-based dissemination in DPWS, thus maintaining compatibility with original assumptions of the specification, and avoiding a centralized configuration server or custom black-box middleware components. In detail, we show how our approach provides an evolutionary and non-intrusive solution to the scalability limitations of DPWS and experimentally evaluate it with an implementation based on the the Web Services for Devices (WS4D) Java Multi Edition DPWS Stack (JMEDS).Comment: 28 pages, Technical Repor

Byzantine state machine replication for the masses

Tese de doutoramento, Informática (Ciência da Computação), Universidade de Lisboa, Faculdade de Ciências, 2018The state machine replication technique is a popular approach for building Byzantine fault-tolerant services. However, despite the widespread adoption of this paradigm for crash fault-tolerant systems, there are still few examples of this paradigm for real Byzantine fault-tolerant systems. Our view of this situation is that there is a lack of robust implementations of Byzantine fault-tolerant state machine replication middleware, and that the performance penalty is too high, specially for geo-replication. These hindrances are tightly coupled to the distributed protocols used for enforcing such resilience. This thesis has the objective of finding methodologies for enhancing robustness and performance of state machine replication systems. The first contribution is Mod-SMaRt, a modular protocol that preserves optimal latency in terms of the communications steps exchanged among processes. By being a modular protocol, it becomes simpler to validate and implement, thus resulting in greater robustness; by also preserving optimal message-exchanges among processes, the protocol is capable of delivering desirable performance. The second contribution is concerned with implementing Mod-SMaRt into BFTSMART, a reliable and high-performance codebase that was maintained and improved over the entire course of the PhD that offers multicore-awareness, reconfiguration support, and a flexible API. The third contribution presents WHEAT, a protocol derived from Mod-SMaRt that uses optimizations shown to be effective in reducing latency via a practical evaluation conducted in a geo distributed environment. We additionally conducted an evaluation of both BFT-SMART and WHEAT applied to a relational database middleware and an ordering service for a permissioned blockchain platform. These evaluations revealed encouraging results for both systems and validated our work conducted in the geo-distributed context.A técnica de replicação máquina de estados é um paradigma popular usado em vários sistemas distribuídos modernos. No entanto, apesar da adoção deste paradigma em sistemas reais tolerantes a faltas por paragem, ainda existem poucos exemplos de sistemas reais tolerantes a faltas bizantinas. Segundo a nossa experiência nesta área de investigação, isto deve-se ao fato de existirem poucas concretizações robustas para replicação máquina de estados tolerante a faltas bizantinas, assim como uma perda de desempenho demasiado elevada, especialmente em ambientes geo-replicados. A razão fundamental para a existência destes obstáculos vem dos protocolos distribuídos necessários para assegurar este tipo de resiliência. Esta tese tem como objetivo explorar metodologias para a robustez e eficiência da replicação máquina de estados. A primeira contribuição da tese é o algoritmo Mod-SMaRt, um protocolo modular que preserva latência ótima em termos de passos de comunicação executados pelos processos. Sendo um protocolo modular, torna-se mais simples de validar e concretizar, o que resulta em maior robustez; ao preservar troca de mensagens ótima entre processos, também é capaz de entregar um desempenho desejável. A segunda contribuição consiste em concretizar o protocolo Mod SMaRt na ferramenta BFT-SMART, uma biblioteca fiável de alto desempenho, mantida e melhorada ao longo de todo o período correspondente ao doutoramento, capaz de suportar arquiteturas multi-núcleo, reconfiguração do grupo de réplicas, e uma API de programação flexível. A terceira contribuição consiste em um protocolo derivado do Mod-SMaRt designado WHEAT, que usa otimizações que demostraram serem eficientes na redução da latência segundo uma avaliação prática em ambiente geo-replicado. Adicionalmente, foram também realizadas avaliações de ambos os protocolos quando aplicados num middleware para base de dados relacionais, e num serviço de ordenação para uma plataforma blockchain. Ambas as avaliações revelam resultados encorajadores para ambos os sistemas e validam o trabalho realizado em contexto geo-distribuído.Projeto IRCoC (PTDC/EEI-SCR/6970/2014); Comissão Europeia, FP7 (Seventh Framework Programme for Research and Technological Development), projetos FP7/2007-2013, ICT-25724

Blockchain Enabled Platforms for the Internet of Things

The Blockchain and the Internet of Things (IoT) have gained a lot of attention in the last few years, since both technologies enable the possibility of creating a more connected and independent world. This combination enables the design of computing systems and cyber-physical environments without the need of centralized trusted entities, giving users the freedom and control of their operations, in a decentralized ledger model. By using storing and logging mechanisms supported by the Blockchain, data is immutable and independently audited, guaranteeing that it is neither modified nor deleted. At the same time, applications can benefit from the reliability and fault-tolerance assumptions provided by the Blockchain in supporting transactions between users and involved devices. In this thesis, it was studied and proposed a generic solution for a Blockchain-enabled IoT software architecture. The proposed solution enables the advantages of using decentralized logging and ledgering, without the interference of central authorities, inherently supported by the base Blockchain reliability, availability and security foundations. These capabilities are envisaged as key-benefits for a new generation of clean-slate approaches for IoT applications with the required scalability criteria. The research conducted in the dissertation work, studied the base software foundations, relevant components and implementation options that enable the identified advantages of using Blockchain components and services, to leverage more scalable and trustable IoT platforms. Our proposed solution aims to provide an architecture that contributes to a more appropriate design for secure and reliable IoT systems. In this trend we propose a better use of edge-based support for local-enabled processing environments supporting IoT devices and users’ interactions, with operations intermediated by proximity hubs acting as gateways to the Blockchain, where the operations are regulated and controlled by verifiable smart-contracts involving data and transactions

A study of e-mail patterns

Although electronic mail is an increasingly important service, there are few empirical studies of e-mail traffic. We have observed over 2.85 million messages passing through our departmental servers over the course of seven months, and derived distributions that approximate several important e-mail parameters including message sizes, message senders and receivers and the burstiness of message deliveries. Our work is unique in that we also analyse message payloads: attachment content types, e-mail redundancy, and the use of e-mail as a sharing mechanism. These data can be used in developing e-mail workloads for mail system engineering or benchmarking. To this end, we provide an improved version of Postmark, a small-file Internet benchmark, that better approximates mail server characteristics. Copyright © 2007 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57338/1/816_ftp.pd

A theoretical and computational basis for CATNETS

The main content of this report is the identification and definition of market mechanisms for Application Layer Networks (ALNs). On basis of the structured Market Engineering process, the work comprises the identification of requirements which adequate market mechanisms for ALNs have to fulfill. Subsequently, two mechanisms for each, the centralized and the decentralized case are described in this document. These build the theoretical foundation for the work within the following two years of the CATNETS project. --Grid Computing

Proof-of-Concept Application - Annual Report Year 2

This document first gives an introduction to Application Layer Networks and subsequently presents the catallactic resource allocation model and its integration into the middleware architecture of the developed prototype. Furthermore use cases for employed service models in such scenarios are presented as general application scenarios as well as two very detailed cases: Query services and Data Mining services. This work concludes by describing the middleware implementation and evaluation as well as future work in this area. --Grid Computing

Theoretical and Computational Basis for Economical Ressource Allocation in Application Layer Networks - Annual Report Year 1

This paper identifies and defines suitable market mechanisms for Application Layer Networks (ALNs). On basis of the structured Market Engineering process, the work comprises the identification of requirements which adequate market mechanisms for ALNs have to fulfill. Subsequently, two mechanisms for each, the centralized and the decentralized case are described in this document. --Grid Computing