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Publicações

Publicações por HASLab

2006

2006 Eurographics Symposium on Parallel Graphics and Visualization

Autores
Santos, LP;

Publicação
Computer Graphics Forum

Abstract
The 2006 Eurographics Symposium on Parallel Graphics and Visualization took place at Universidade do Minho, Barga, Portugal. There were a total of 47 registered participants which represents a significant increase in the number of attendees compared to previous editions of the event. The goal was to enable people to attend all events in an attempt to answer a reciprocal interest on research works. It was believed that by organizing related events in the same geographical area it is able to attract more participants for each events. The first keynote was on Rendering on Demand by Alan Chalmers from the University of Bristol. The second keynote was devoted entirely to commodity visualization clusters and many other papers generated results using clusters.

2006

Secure Cryptographic Workflow in the Standard Model

Autores
Barbosa, M; Farshim, P;

Publicação
IACR Cryptology ePrint Archive

Abstract

2006

Secure cryptographic workflow in the standard model

Autores
Barbosa, M; Farshim, P;

Publicação
Progress in Cryptology - INDOCRYPT 2006, Proceedings

Abstract
Following the work of Al-Riyami et al. we define the notion of key encapsulation mechanism supporting cryptographic workflow (WF-KEM) and prove a KEM-DEM composition theorem which extends the notion of hybrid encryption to cryptographic workflow. We then generically construct a WF-KEM from an identity-based encryption (IBE) scheme and a secret sharing scheme. Chosen ciphertext security is achieved using one-time signatures. Adding a public-key encryption scheme we are able to modify the construction to obtain escrow-freeness. We prove all our constructions secure in the standard model.

2005

Testing the dependability and performance of group communication based database replication protocols

Autores
Sousa, A; Pereira, J; Soares, L; Correia, A; Rocha, L; Oliveira, R; Moura, F;

Publicação
2005 INTERNATIONAL CONFERENCE ON DEPENDABLE SYSTEMS AND NETWORKS, PROCEEDINGS

Abstract
Database replication based on group communication systems has recently been proposed as an efficient and resilient solution for large-scale data management. However, its evaluation has been conducted either on simplistic simulation models, which fail to assess concrete implementations, or on complete system implementations which are costly to test with realistic large-scale scenarios. This paper presents a tool that combines implementations of replication and communication protocols under study with simulated network, database engine, and traffic generator models. Replication components can therefore be subjected to realistic large scale loads in a variety of scenarios, including fault-injection, while at the same time providing global observation and control. The paper shows first how the model is configured and validated to closely reproduce the behavior of a real system, and then how it is applied, allowing us to derive interesting conclusions both on replication and communication protocols and on their implementations.

2005

Group-based replication of on-line transaction processing servers

Autores
Correia, A; Sousa, A; Soares, L; Pereira, J; Moura, F; Oliveira, R;

Publicação
DEPENDABLE COMPUTING, PROCEEDINGS

Abstract
Several techniques for database replication using group communication have recently been proposed, namely, the Database State Machine, PostgresR, and the NODO protocol. Although all rely on a totally ordered multicast for consistency, they differ substantially on how multicast is used. This results in different performance trade-offs which are hard to compare as each protocol is presented using a different load scenario and evaluation method. In this paper we evaluate the suitability of such protocols for replication of On-Line Transaction Processing (OLTP) applications in clusters of servers and over wide area networks. This is achieved by implementing them using a common infra-structure and by using a standard workload. The results allows us to select the best protocol regarding performance and scalability in a demanding but realistic usage scenario.

2005

Recursion patterns and time-analysis

Autores
Barbosa, A; Cunha, A; Pinto, JS;

Publicação
ACM SIGPLAN NOTICES

Abstract
This paper explores sonic ideas concerning the time-analysis of functional programs defined by instantiating typical recursion patterns such as folds, unfolds. and hylomorphisms. The concepts in this paper are illustrated through a rich set of examples in the Haskell programming language. We concentrate on unfolds and folds (also known as anamorphisms and catamorphisms respectively) of recursively defined types, as well as the more general hylomorphism pattern. For the latter, we use as case-studies two famous sorting algorithms, mergesort and quicksort. Even though time analysis is not compositional, we argue that splitting functions to expose the explicit construction of the recursion tree and its later consumption helps with this analysis.

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