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Comunicació presentada al SACMAT'17. 22nd ACM Symposium on Access Control Models and Technologies, celebrat els dies 21 a 23 de juny de 2017 a Indianapolis, EUA. ; Relationships like friendship to limit access to resources have been part of social network applications since their beginnings. Describing access control policies in terms of relationships is not particular to social networks and it arises naturally in many situations. Hence, we have recently seen several proposals formalizing different Relationship-based Access Control (ReBAC) models. In this paper, we introduce a class of Datalog programs suitable for modeling ReBAC and argue that this class of programs, that we called ReBAC Datalog policies, provides a very general framework to specify and implement ReBAC policies. To support our claim, we first formalize the merging of two recent proposals for modeling ReBAC, one based on hybrid logic and the other one based on path regular expressions. We present extensions to handle negative authorizations and temporal policies. We describe mechanism for policy analysis, and then discuss the feasibility of using Datalog-based systems as implementations. ; Edelmira Pasarella was partially supported by the Spanish Ministry for Economy and Competitiveness (MINECO) and the European Union (FEDER funds) under Grant Ref.: TIN2013-46181-C2-1-R COMMAS. Jorge Lobo was partially supported by the Secretaria d'Universitats i Recerca de la Generalitat de Catalunya, the Maria de Maeztu Units of Excellence Programme and the Spanish Ministry for Economy and Competitiveness (MINECO) under Grant Ref.: TIN2016-81032-P.

Comunicació presentada a: IEEE 28th Computer Security Foundations Symposium celebrat del 13 al 17 de juliol de 2015 a Verona, Itàlia. ; In this paper we show that the logical framework proposed by Becker et al. [1] to reason about security policy behavior in a trust management context can be captured by an operational framework that is based on the language proposed by Miller in 1989 to deal with scoping and/or modules in logic programming. The framework of Becker et al. uses propositional Horn clauses to represent both policies and credentials, implications in clauses are interpreted in counterfactual logic, a Hilbert-style proof system is defined and a system based on SAT is used to prove whether properties about credentials, permissions and policies are valid, i.e. true under all possible policies. Our contributions in this paper are three. First, we show that this kind of validation can rely on an operational semantics (derivability relation) of a language very similar to Miller's language, which is very close to derivability in logic programs. Second, we are able to establish that, as in propositional logic, validity of formulas is a co-NP-complete problem. And third, we present a provably correct implementation of a goal-oriented algorithm for validity. ; Edelmira Pasarella is partially supported by funds from the Spanish Ministry for Economy and Competitiveness (MINECO) and the European Union (FEDER funds) under grant COMMAS (ref. TIN2013-46181-C2-1-R). Jorge Lobo is partially supported by the US Army Research Lab and the UK Ministry of Defence under agreement number W911NF-06-3-0001 and by the Secretaria d'Universitats i Recerca de la Generalitat de Catalunya.

Comunicació presentada al SACMAT '20: The 25th ACM Symposium on Access Control Models and Technologies, celebrat del 10 al 12 de juny de 2020 a Barcelona, Espanya. ; There has been over the past decade a rapid change towards computational environments that are comprised of large and diverse sets of devices, many of them mobile, which can connect in flexible and context-dependent ways. Examples range from networks where we can have communications between powerful cloud centers, to the myriad of simple sensor devices on the IoT. As the management of these dynamic environments becomes ever more complex, we want to propose policy migrations as a methodology to simplify the management of security policies by re-utilizing and re-deploying existing policies as the systems change. We are interested in understanding the challenges raised answering the following question: given a security policy that is being enforced in a particular source computational device, what does it entail to migrate this policy to be enforced in a different target device? Because of the differences between devices and because these devices cannot be seen in isolation but in the context where they are deployed, the meaning of the policy enforced in the source device needs to be re-interpreted and implemented in the context of the target device. The aim of the paper is to present a formal framework to evaluate the appropriateness of the migration. ; This research was sponsored by the U.S. Army Research Laboratory and the U.K. Ministry of Defence under Agreement Number W911NF-16-3-0001. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the U.S. Army Research Laboratory, the U.S. Government, the U.K. Ministry of Defence or the U.K. Government. The U.S. and U.K. Governments are authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation hereon. Jorge Lobo was also supported by the Spanish Ministry of Economy and Competitiveness under Grant Numbers TIN201681032P, MDM20150502, and the U.S. Army Research Office under agreement number W911NF1910432.

Network Function Virtualization (NFV) is bringing closer the possibility to truly migrate enterprise data centers into the cloud. However, for a Cloud Service Provider to offer such services, important questions include how and when to scale out/in resources to satisfy dynamic traffic/application demands. In previous work [1], we have proposed a platform called Network Function Center (NFC) to study research issues related to NFV and Network Functions (NFs). In a NFC, we assume NFs to be implemented on virtual machines that can be deployed in any server in the network. In this paper we present further experiments on the use of Genetic Algorithms (GAs) for scaling out/in NFs when the traffic changes dynamically. We combined data from previous empirical analyses [2], [3] to generate NF chains and for getting traffic patterns of a day and run simulations of resource allocation decision making. We have implemented different fitness functions with GA and compared their performance when scaling out/in over time. ; This research was sponsored by the U.S. Army Research Laboratory and the U.K. Ministry of Defence and was accomplished under Agreement Number W911NF-06-3-0001. The views and conclusions contained in this document are those of the author(s) and should not be interpreted as representing the official policies, either expressed or implied, of the U.S. Army Research Laboratory, the U.S. Government, the U.K. Ministry of Defence or the U.K. Government. The U.S. and U.K. Governments are authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation here on. Jorge Lobo was also partially supported by the Secretaria dUniversitats i Recerca de la Generalitat de Catalunya.

By allowing network functions to be virtualized and run on commodity hardware, NFV enables new properties (e.g., elastic scaling), and new service models for Service Providers, Enterprises, and Telecommunication Service Providers. However, for NFV to be offered as a service, several research problems still need to be addressed. In this paper, we focus and propose a new service chaining algorithm. Existing solutions suffer two main limitations: First, existing proposals often rely on mixed Integer Linear Programming to optimize VM allocation and network management, but our experiments show that such approach is too slow taking hours to find a solution. Second, although existing proposals have considered the VM placement and network configuration jointly, they frequently assume the network configuration cannot be changed. Instead, we believe that both computing and network resources should be able to be updated concurrently for increased flexibility and to satisfy SLA and Qos requirements. As such, we formulate and propose a Genetic Algorithm based approach to solve the VM allocation and network management problem. We built an experimental NFV platform, and run a set of experiments. The results show that our proposed GA approach can compute configurations to to three orders of magnitude faster than traditional solutions. ; This research was sponsored by the U.S. Army Research Laboratory and the U.K. Ministry of Defence and was accomplished under Agreement Number W911NF-06-3-0001. The views and conclusions contained in this document are those of the author(s) and should not be interpreted as representing the official policies, either expressed or implied, of the U.S. Army Research Laboratory, the U.S. Government, the U.K. Ministry of Defence or the U.K. Government. The U.S. and U.K. Governments are authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation here on.

Comunicació presentada a: AAAI Conference on Artificial Intelligence celebrat del 27 de gener a l'1 de febrer de 2019 a Hawaii, Estats Units d'Amèrica. ; In this paper we introduce an extension of context-free grammars called answer set grammars (ASGs). These grammars allow annotations on production rules, written in the language of Answer Set Programming (ASP), which can express context-sensitive constraints. We investigate the complexity of various classes of ASG with respect to two decision problems: deciding whether a given string belongs to the language of an ASG and deciding whether the language of an ASG is non-empty. Specifically, we show that the complexity of these decision problems can be lowered by restricting the subset of the ASP language used in the annotations. To aid the applicability of these grammars to computational problems that require context-sensitive parsers for partially known languages, we propose a learning task for inducing the annotations of an ASG. We characterise the complexity of this task and present an algorithm for solving it. An evaluation of a (prototype) implementation is also discussed. ; This research was sponsored by the U.S. Army Research Laboratory and the U.K. Ministry of Defence under Agreement Number W911NF-16-3-0001. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the U.S. Army Research Laboratory, the U.S. Government, the U.K. Ministry of Defence or the U.K. Government. The U.S. and U.K. Governments are authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation hereon. It was also partially supported by the Spanish Ministry of Economy and Competitiveness under Grant Numbers TIN-2016-81032-P & MDM-2015-0502.

Climate change can induce shifts in species ranges. Of special interest are range shifts in regions with a conflict of interest between land use and the conservation of threatened species. Here we focus on the 94 threatened terrestrial vertebrates occurring in the Madrid region (Central Spain) and model their distributions using data for the whole peninsular Spain to evaluate which vertebrate groups are likely to be more sensitive to climatic change. First, we generated predictive models to quantify the extent to which species distributions are explained by current climate. We then extrapolated the models temporally to predict the effects of two climate-change scenarios on species distributions. We also examined the impact on a recently proposed reserve relative to other interconnected zones with lower protection status but categorized as Areas of Community Importance by the European Union. The variation explained by climatic predictors was greater in ectotherms. The change in species composition differed between the proposed reserve and the other protected areas. Endothermic and ectothermic vertebrates had different patterns of changes in species composition but those of ectotherms matched with temperature departures predicted by climate change. Our results, together with the limited dispersal capacity of herptiles, suggest that trade-offs between different design criteria accounting for animal group differences are necessary for reserve selection. ; Financial support was provided to P.A. by the Comunidad de Madrid (GR/AMB/0920/2004) and by an I3P-PC2005L postdoctoral contract, by the Spanish Ministry of Science and Innovation (CGL2006-03000/BOS to M.Á.R., CGL2006-10196 to J.M.L and AP2005-0636 to M.Á.O.-T.), and by an FP7 Marie Curie Intra-European Fellowship (PHYLONICHE) from the European Commission to M.Á.O.-T. ; Peer reviewed

Here we present the code to generate MoBIs (Maps of Biogeographical Ignorance) for single species. The method is based on the calculation of different dimensions of biodiversity data (spatial, temporal and taxonomic). Specifically, in this method, we calculated completeness of each cell by generating accumulation curves with records of all individuals of a group. We also set taxonomy quality values for each identifier considering their experience with the group. For the temporal dimension, we adjust a decay curve to quantify temporal decay of information with time so that older records of the species are least informative and recent ones are the most informative. These components are summarized to generate an index varying from 0 to 1 (lower and higher ignorance, respectively) for each cell for a species. Finally, for cells without data we performed an interpolation, based on the BI calculated for neighbor cells. ; Funding – This work has been funded by the Brazilian CNPq PVE grant 314523/2014-6. GT was supported by CAPES REUNI doctorate fellowship and PDSE grant no. 11842121. RJL is supported by the European Union's Horizon 2020 research and innovation programme under grant agreement no. 854248.

Species distribution models (SDMs) are subject to many sources of uncertainty, lim-iting their application in research and practice. One of their main limitations is the quality of the distributional data used to calibrate them, which directly influences the accuracy of model predictions. We propose a standardized methodology to cre-ate maps, describing the limitations of occurrence data for covering the distribution of a species. We develop a set of tools based on the general framework of Maps of Biogeographical Ignorance to describe the main sources of data-driven uncertainty: taxonomic stability, environmental similarity, geographical proximity and temporal decay of the underlying biodiversity data. The so-derived indicators of data-driven uncertainty account for inventory completeness, taxonomic quality, time since the surveys and geographical (and environmental) distance to localities with information. These indicators form the basis of ignorance maps, which can be used to visualize the reliability of SDM projections in geographical space, to estimate the uncertainty of these predictions and to identify target survey areas. To demonstrate the application of our approach, we use data on fourteen Iberian species of Scarabaeidae dung beetles. Data-driven uncertainty is widespread even for this well-surveyed group; more than 60% of the region has distributional uncertainty values higher than 0.6, and 30% higher than 0.7. Ignorance maps can be jointly evaluated with SDM predictions to generate spatially explicit maps of uncertainty, identifying where predictions are reli-able/unreliable. Neglecting such uncertainty can severely affect SDM effectiveness, as it can introduce biases and inaccuracies into the measured species–environment rela-tionships. These errors could result in incorrect theoretical or practical applications, including ill-advised conservation actions. We therefore advocate for the routine use of ignorance maps or similar techniques as supporting information in SDM applications. ; This work has been funded by the Brazilian CNPq PVE grant 314523/2014-6 and the Brazilian National Inst. for Science and Technology in Ecology, Evolution and Biodiversity Conservation (INCT-EECBio), supported by MCTIC/CNPq (465610/2014-5) and the Fundação de Amparo à Pesquisa do Estado de Goiás (201810267000023). GT was supported by CAPES REUNI doctorate fellowship and PDSE grant no. 11842121. RJL is supported by the European Union's Horizon 2020 research and innovation programme under grant agreement no. 854248. ; Peer reviewed

Comunicació presentada a: The Second International Conference on Autonomous Infrastructure, Management and Security, celebrada a Bremen, Alemanya, de l'1 al 3 de juliol de 2008 ; This paper addresses the problem of specifying and establishing secure collaborations between autonomous entities that need to interact and depend on each other in order to accomplish their goals. We call such collaborations missionoriented dynamic communities. We propose an abstract model for policy-based collaboration that relies on a set of task-oriented roles. Nodes are discovered dynamically and assigned to one or more roles, and then start enforcing the policies associated with these roles according to the description of the community. In this paper we describe a basic set of management roles that are needed to provide management and security functions for dynamic communities. Policies are used to specify management protocols as these can be easily modified to reflect different adaptive strategies. We focus on collaboration between nodes in the context of mobile ad-hoc networks. Our implementation is based on a surveillance scenario using unmanned autonomous vehicles (UAVs). However our approach to dynamic communities could be applied to emergency services at a disaster site, search and rescue applications or many military scenarios. ; Research was sponsored by the U.S. Army Research Laboratory and the U.K. Ministry of Defence and was accomplished under Agreement Number W911NF-06-3-0001.