Publications

Using randomization to identify social influence in mobile networks

Belo R., Ferreira P.

Proceedings - 2012 ASE/IEEE International Conference on Privacy, Security, Risk and Trust and 2012 ASE/IEEE International Conference on Social Computing, SocialCom/PASSAT 2012

2012

Conference Paper

Abstract:

Identification of social influence in observational data is a difficult task. Endogeneity issues such as homophily, correlated unobservables and simultaneity raise challenges to the researchers interested in establishing causality and in consistently measuring its magnitude. In this paper we apply randomization techniques to identify social influence in a mobile network setting. Randomization methods consist in generating pseudo-samples of the original data by selectively permuting the values of some variables among observations, and estimating empirical distributions of a parameter of interest under the null hypothesis that such permutations are random. We show that randomization methods are a viable strategy to identify social influence in contexts where all adoption is observed and the date of adoption is available. Furthermore, we show that these methods provide a lower bound for the magnitude of the effect of peer influence. We use a comprehensive panel of data from a large European mobile carrier in one country. The data comprise Call Detailed Records for all the subscribers in this carrier for a period of 11 months. We also have information on pricing plans, adoption of products, promotions and handsets. We estimate the effect of peer influence in six of these promotions. We provide evidence for negative peer influence in their adoption. Peer influence reduces adoption for these promotions between 3% and 9%. Peer influence helps to share information about new promotions but also signals who has already adopted them and, in many cases, such as free calls, having neighbors who adopted the promotion is enough to benefit from it.

Vehicular connectivity models: From single-hop links to large-scale behavior

Meireles R., Ferreira M., Barros J.

IEEE Vehicular Technology Conference

2009

Conference Paper

Abstract:

Focusing on large-scale vehicular ad-hoc networks (VANETs), we consider the interplay between single-hop channel models and large-scale network connectivity. Building on a realistic urban traffic simulator, we progressively increase the sophistication of the wireless link while evaluating the resulting connectivity profiles. Our results show that large-scale VANET connectivity, whose understanding is paramount towards the development of protocols and applications for this class of networks, is equally influenced by the choice of model and by the fine-tuning of its key parameters. Analyzing the distributions of both node degree and the duration of connection, we conclude that (a) as far as large-scale node degree behavior is concerned, a complex shadow fading environment is well approximated by a simpler and more tractable unit-disk model and, (b) unit-disk models allow longer connections than other models.

Vehicular sensing: Emergence of a massive urban scanner

Ferreira M., Fernandes R., Conceicao H., Gomes P., D'Orey P.M., Moreira-Matias L., Gama J., Lima F., Damas L.

Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering

2012

Conference Paper

Abstract:

Vehicular sensing is emerging as a powerful mean to collect information using the variety of sensors that equip modern vehicles. These sensors range from simple speedometers to complex video capturing systems capable of performing image recognition. The advent of connected vehicles makes such information accessible nearly in real-time and creates a sensing network with a massive reach, amplified by the inherent mobility of vehicles. In this paper we discuss several applications that rely on vehicular sensing, using sensors such as the GPS receiver, windshield cameras, or specific sensors in special vehicles, such as a taximeter in taxi cabs. We further discuss connectivity issues related to the mobility and limited wireless range of an infrastructure-less network based only on vehicular nodes.

Vehicular testbed management

Afonso J., Cardote A., Sargento S.

Proceedings - International Symposium on Computers and Communications

2014

Conference Paper

Abstract:

The deployment of vehicular network testbeds encompasses a myriad of new challenges regarding resource management, execution of experiments on the nodes, and the collection of the resulting data, when compared to traditional testbeds. Vehicular nodes have very unpredictable mobility patterns, especially in cities, and use a specific communication protocol; therefore, the commonly used solutions for large scale testbeds are not directly applicable. This is the case of our vehicular network testbed developed in the framework of the DRIVE-IN and Future Cities! (DRIVE-IN and Future Cities!) 1 projects. This paper tackles the aforementioned issues by proposing the design and implementation of a testbed management system based on the cOntrol and Management Framework (OMF). The base functionalities of OMF were extended to integrate node control over cellular networks, as well as to guarantee that experiments are always safely deployed, minimizing the risk of node corruption and malfunctioning. The management platform is capable of uploading new software to the vehicular nodes, conduct experiments using the specific vehicular wireless (IEEE 802.11p) interface, collect the resulting data, as well as storing and managing information about all the nodes. The results obtained from real-world experiments show that the the proposed platform is able to manage a Vehicular Ad-hoc NETwork (VANET) testbed.

Very-efficient simulatable flipping of many coins into a well (and a new universally-composable commitment scheme)

Brandao L.T.A.N.

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

2016

Conference Paper

Abstract:

This paper presents new cryptographic protocols for a stand-alone simulatable two-party parallel coin-flipping (into a well) and a universally composable commitment scheme, with near optimal asymptotic communication rate, in the static and computational malicious model. The approach, denoted expand-mask-hash, uses in both protocols a pseudo-random generator (PRG) and a collision-resistant hash function (CR-Hash) to combine separate extractable commitments and equivocable commitments (associated with short bit-strings) into a unified extractable-and-equivocable property amplified to a larger target length, amortizing the cost of base commitments. The new stand-alone coin-flipping protocol is based on a simple augmentation of the traditional coin-flipping template. To the knowledge of the author, it is the first proposal shown to simultaneously be two-side-simulatable and have an asymptotic (as the target length increases) communication rate converging to two bits per flipped coin and computation rate per party converging to that of PRG-generating and CR-hashing a bit-string with the target length. The new universally composable commitment scheme has efficiency comparable to very recent state-of-the-art constructions – namely asymptotic communication rate as close to 1 as desired, for each phase (commit and open) – while following a distinct design approach. Notably it does not require explicit use of oblivious transfer and it uses an erasure encoding instead of stronger error correction codes.

Virtual network mapping into heterogeneous substrate networks

Nogueira J., Melo M., Carapinha J., Sargento S.

Proceedings - IEEE Symposium on Computers and Communications

2011

Conference Paper

Abstract:

As the interest on Network Virtualization continues to grow, so does the awareness of the many technical obstacles to transpose before the envisioned virtualized network environment may become a reality. A significant obstacle lies on the efficient assignment of virtual resources into physical ones. Performing the so-called mapping of a virtual network into a substrate network is a computationally intensive task, due to the dual optimization required for nodes and links placement. The purpose of this paper is to tackle this problem taking into consideration real-life scenarios of network operators, where the limitations imposed by the heterogeneity of the virtual and substrate networks must be accounted for. To that end, this paper proposes a heuristic algorithm for virtual resources mapping in the physical infrastructure that supports the heterogeneity of networks, in both links and nodes. The mapping heuristic was evaluated both through simulation and in a real experimental virtualization platform. Through the simulation results, it is shown that the mapping approach is able to embed a high percentage of the Virtual Network (VNet) requests respecting all links and node constraints. With respect to the experimental results, the proposed algorithm was shown to be fast, requiring a mapping time in the order of low tens of milliseconds, and linearly scalable with the increase in the number of existing VNets

Virtual traffic lights in partial deployment scenarios

Conceicao H., Ferreira M., Steenkiste P.

IEEE Intelligent Vehicles Symposium, Proceedings

2013

Conference Paper

Abstract:

Vehicular ad hoc networks (VANETs) are seen as an important enabling technology for improving both traffic safety and efficiency. Virtual Traffic Lights (VTLs) are a promising proposal for reducing travel time by efficiently controlling road intersections. VTLs use vehicle-to-vehicle communication to dynamically optimize traffic flow and they display traffic light information on the windshield. However, research so far has assumed that all vehicles are equipped with VTL support and it has ignored the incremental deployment phase, which could last decades. In this paper we present a solution for a VTL partial deployment scenario that is based on the idea of having VTL equipped cars display traffic light information on the outside of the vehicle. This allows drivers in non-equipped vehicles, or even pedestrians, to see the light color and respond accordingly. We show that the benefits of VTLs in terms of intersection throughput and average delay reduction grow as a function of the penetration rate of equipped vehicles.

Vision Augmented Robot Feeding

Candeias A., Rhodes T., Marques M., Costeira J.P.; Veloso M.

Computer Vision – ECCV 2018 Workshops: Munich, Germany, September 8-14 Proceedings

2018

Conference Paper

Vulnerability Analysis as Trustworthiness Evidence in Security Benchmarking: A Case Study on Xen.

Gonçalves C., Antunes N.

5th IEEE International Workshop on Reliability and Security Data Analysis (RSDA 2020) (co-located ISSRE 2020)

2020

Conference Paper

Abstract:

Hypervisors govern the resources of virtualized systems and are a crucial component of many cloud solutions. As a critical component, cloud providers should assess the hypervisor’s security to mitigate risk before adoption. Ideally, a benchmark should be applied to compare the security of different systems objectively, but security benchmarking is still an open problem. Notwithstanding, the evaluation of the system’s trustworthiness has been adopted as a promising approach as part of this complex evaluation process. In this work, we present a vulnerability data analysis of the Xen hypervisor. Additionally, we address the problem of how to apply this analysis results as trustworthiness evidence that can be applied in security benchmarks. Our results present an insightful characterization of Xen’s vulnerabilities evaluating their lifespan, distribution, and modeling. We also show that vulnerability data analysis can qualitatively characterize the Xen hypervisor’s trustworthiness and possibly reflect the security development efforts into its codebase.