Efficient and Modular Consensus-Free Reconfiguration for Fault-Tolerant Storage

Quorum systems are useful tools for implementing consistent and available storage in the presence of failures. These systems usually comprise of a static set of servers that provide a fault-tolerant read/write register accessed by a set of clients. We consider a dynamic variant of these systems and propose FreeStore, a set of fault-tolerant protocols that emulates a register in dynamic asynchronous systems in which processes are able to join/leave the set of servers during the execution. These protocols use a new abstraction called view generators, that captures the agreement requirements of reconfiguration and can be implemented in different system models with different properties. Particularly interesting, we present a reconfiguration protocol that is modular, efficient, consensus-free and loosely coupled with read/write protocols. An analysis and an experimental evaluation show that the proposed protocols improve the overall system performance when compared with previous solutions

Sharing Memory between Byzantine Processes using Policy-enforced Tuple Spaces

Abstract—Despite the large amount of Byzantine fault-tolerant algorithms for message-passing systems designed through the years, only recent algorithms for the coordination of processes subject to Byzantine failures using shared memory have appeared. This paper presents a new computing model in which shared memory objects are protected by fine-grained access policies, and a new shared memory object, the Policy-Enforced Augmented Tuple Space (PEATS). We show the benefits of this model by providing simple and efficient consensus algorithms. These algorithms are much simpler and require less shared memory operations, using also less memory bits than previous algorithms based on access control lists (ACLs) and sticky bits. We also prove that PEATS objects are universal, i.e., that they can be used to implement any other shared memory object, and present lock-free and wait-free universal constructions. Index Terms—Byzantine fault-tolerance, shared memory algorithms, tuple spaces, consensus, universal constructions. Ç

Controle de velocidade de motor C.C. usando microcomputador

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica

Extending the SDSI / SPKI model through federation webs

Classic security systems use a trust model centered in the authentication procedure, which depends on a naming service. Even when using a Public Key Infrastructure as X.509, such systems are not easily scalable and can become single failure points or performance bottlenecks