211 research outputs found
T-generable indistinguishability operators and their use for feature selection and classification.
Peer ReviewedPostprint (author's final draft
Reduction of attributes in averaged similarities
Similarity Relations may be constructed from a set of fuzzy attributes. Each fuzzy attribute generates a simple similarity, and these simple similarities are combined into a complex similarity afterwards. The Representation Theorem establishes one such way of combining similarities, while averaging them is a different and more realistic approach in applied domains. In this paper, given an averaged similarity by a family of attributes, we propose a method to find families of new attributes having fewer elements that generate the same similarity. More generally, the paper studies the structure of this important class of fuzzy relations.Peer ReviewedPostprint (author's final draft
Uncertainty and indistinguishability. Application to modelling with words.
El concepte d'igualtat és fonamental en qualsevol teoria donat que és una noció essencial a l'hora de discernir entre els elements objecte del seu estudi i possibilitar la definició de mecanismes de classificació.Quan totes les propietats són perfectament precises (absència d'incertesa), hom obtè la igualtat clà ssica a on dos objectes són considerats iguals si i només si comparteixen el mateix conjunt de propietats. Però, què passa quan considerem l'aparició d'incertesa, com en el cas a on els objectes compleixen una determinada propietat només fins a un cert grau?. Llavors, donat que alguns objectes seran més similars entre si que d'altres, sorgeix la necessitat de una noció gradual del concepte d'igualtat.Aquestes consideracions refermen la idea de que certs contextos requereixen una definició més flexible, que superi la rigidesa de la noció clà ssica d'igualtat. Els operadors de T-indistingibilitat semblen bons candidats per aquest nou tipus d'igualtat que cerquem.D'altra banda, La Teoria de l'Evidència de Dempster-Shafer, com a marc pel tractament d'evidències, defineix implÃcitament una noció d'indistingibilitat entre els elements del domini de discurs basada en la seva compatibilitat relativa amb l'evidència considerada. El capÃtol segon analitza diferents mètodes per definir l'operador de T-indistingibilitat associat a una evidència donada.En el capÃtol tercer, després de presentar un exhaustiu estat de l'art en mesures d'incertesa, ens centrem en la qüestió del còmput de l'entropia quan sobre els elements del domini s'ha definit una relació d'indistingibilitat. Llavors, l'entropia hauria de ser mesurada no en funció de l'ocurrència d'events diferents, sinó d'acord amb la variabilitat percebuda per un observador equipat amb la relació d'indistingibilitat considerada. Aquesta interpretació suggereix el "paradigma de l'observador" que ens porta a la introducció del concepte d'entropia observacional.La incertesa és un fenomen present al món real. El desenvolupament de tècniques que en permetin el tractament és doncs, una necessitat. La 'computació amb paraules' ('computing with words') pretén assolir aquest objectiu mitjançant un formalisme basat en etiquetes lingüÃstiques, en contrast amb els mètodes numèrics tradicionals. L'ús d'aquestes etiquetes millora la comprensibilitat del llenguatge de representació delconeixement, a l'hora que requereix una adaptació de les tècniques inductives tradicionals.En el quart capÃtol s'introdueix un nou tipus d'arbre de decisió que incorpora les indistingibilitats entre elements del domini a l'hora de calcular la impuresa dels nodes. Hem anomenat arbres de decisió observacionals a aquests nou tipus, donat que es basen en la incorporació de l'entropia observacional en la funció heurÃstica de selecció d'atributs. A més, presentem un algorisme capaç d'induir regles lingüÃstiques mitjançant un tractament adient de la incertesa present a les etiquetes lingüÃstiques o a les dades mateixes. La definició de l'algorisme s'acompanya d'una comparació formal amb altres algorismes està ndards.The concept of equality is a fundamental notion in any theory since it is essential to the ability of discerning the objects to whom it concerns, ability which in turn is a requirement for any classification mechanism that might be defined. When all the properties involved are entirely precise, what we obtain is the classical equality, where two individuals are considered equal if and only if they share the same set of properties. What happens, however, when imprecision arises as in the case of properties which are fulfilled only up to a degree? Then, because certain individuals will be more similar than others, the need for a gradual notion of equality arises.These considerations show that certain contexts that are pervaded with uncertainty require a more flexible concept of equality that goes beyond the rigidity of the classic concept of equality. T-indistinguishability operators seem to be good candidates for this more flexible and general version of the concept of equality that we are searching for.On the other hand, Dempster-Shafer Theory of Evidence, as a framework for representing and managing general evidences, implicitly conveys the notion of indistinguishability between the elements of the domain of discourse based on their relative compatibility with the evidence at hand. In chapter two we are concerned with providing definitions for the T-indistinguishability operator associated to a given body of evidence.In chapter three, after providing a comprehensive summary of the state of the art on measures of uncertainty, we tackle the problem of computing entropy when an indistinguishability relation has been defined over the elements of the domain. Entropy should then be measured not according to the occurrence of different events, but according to the variability perceived by an observer equipped with indistinguishability abilities as defined by the indistinguishability relation considered. This idea naturally leads to the introduction of the concept of observational entropy.Real data is often pervaded with uncertainty so that devising techniques intended to induce knowledge in the presence of uncertainty seems entirely advisable.The paradigm of computing with words follows this line in order to provide a computation formalism based on linguistic labels in contrast to traditional numerical-based methods.The use of linguistic labels enriches the understandability of the representation language, although it also requires adapting the classical inductive learning procedures to cope with such labels.In chapter four, a novel approach to building decision trees is introduced, addressing the case when uncertainty arises as a consequence of considering a more realistic setting in which decision maker's discernment abilities are taken into account when computing node's impurity measures. This novel paradigm results in what have been called --observational decision trees' since the main idea stems from the notion of observational entropy in order to incorporate indistinguishability concerns. In addition, we present an algorithm intended to induce linguistic rules from data by properly managing the uncertainty present either in the set of describing labels or in the data itself. A formal comparison with standard algorithms is also provided
Fifty years of similarity relations: a survey of foundations and applications
On the occasion of the 50th anniversary of the publication of Zadeh's significant paper Similarity Relations and Fuzzy Orderings, an account of the development of similarity relations during this time will be given. Moreover, the main topics related to these fuzzy relations will be reviewed.Peer ReviewedPostprint (author's final draft
Generation and Characterization of Fuzzy T-preorders
This article studies T-preorders that can be generated in a natural way by a single fuzzy subset. These T-preorders are called one-dimensional and are of great importance, because every T-preorder can be generated by combining one-dimensional T-preorders.; In this article, the relation between fuzzy subsets generating the same T-preorder is given, and one-dimensional T-preorders are characterized in two different ways: They generate linear crisp orderings on X and they satisfy a Sincov-like functional equation. This last characterization is used to approximate a given T-preorder by a one-dimensional one by relating the issue to Saaty matrices used in the Analytical Hierarchical Process. Finally, strong complete T-preorders, important in decision-making problems, are also characterized.Peer ReviewedPostprint (author’s final draft
Practical Isolated Searchable Encryption in a Trusted Computing Environment
Cloud computing has become a standard computational paradigm due its numerous
advantages, including high availability, elasticity, and ubiquity. Both individual users and
companies are adopting more of its services, but not without loss of privacy and control.
Outsourcing data and computations to a remote server implies trusting its owners, a
problem many end-users are aware. Recent news have proven data stored on Cloud
servers is susceptible to leaks from the provider, third-party attackers, or even from
government surveillance programs, exposing users’ private data.
Different approaches to tackle these problems have surfaced throughout the years.
Naïve solutions involve storing data encrypted on the server, decrypting it only on the
client-side. Yet, this imposes a high overhead on the client, rendering such schemes
impractical. Searchable Symmetric Encryption (SSE) has emerged as a novel research
topic in recent years, allowing efficient querying and updating over encrypted datastores
in Cloud servers, while retaining privacy guarantees. Still, despite relevant recent advances,
existing SSE schemes still make a critical trade-off between efficiency, security,
and query expressiveness, thus limiting their adoption as a viable technology, particularly
in large-scale scenarios.
New technologies providing Isolated Execution Environments (IEEs) may help improve
SSE literature. These technologies allow applications to be run remotely with
privacy guarantees, in isolation from other, possibly privileged, processes inside the CPU,
such as the operating system kernel. Prominent example technologies are Intel SGX and
ARM TrustZone, which are being made available in today’s commodity CPUs.
In this thesis we study these new trusted hardware technologies in depth, while exploring
their application to the problem of searching over encrypted data, primarily focusing
in SGX. In more detail, we study the application of IEEs in SSE schemes, improving their
efficiency, security, and query expressiveness.
We design, implement, and evaluate three new SSE schemes for different query types,
namely Boolean queries over text, similarity queries over image datastores, and multimodal
queries over text and images. These schemes can support queries combining different
media formats simultaneously, envisaging applications such as privacy-enhanced medical diagnosis and management of electronic-healthcare records, or confidential photograph
catalogues, running without the danger of privacy breaks in Cloud-based provisioned
services
Articles indexats publicats per autors de l'ETSAB
Aquest document recull els articles publicats per investigadors de l'ETSAB en
revistes del Web of Science i de Scopus des de l'any 2000 fins el 2011.Preprin
Advanced Features in Protocol Verification: Theory, Properties, and Efficiency in Maude-NPA
The area of formal analysis of cryptographic protocols has been an active
one since the mid 80’s. The idea is to verify communication protocols
that use encryption to guarantee secrecy and that use authentication of
data to ensure security. Formal methods are used in protocol analysis to
provide formal proofs of security, and to uncover bugs and security flaws
that in some cases had remained unknown long after the original protocol
publication, such as the case of the well known Needham-Schroeder
Public Key (NSPK) protocol. In this thesis we tackle problems regarding
the three main pillars of protocol verification: modelling capabilities,
verifiable properties, and efficiency.
This thesis is devoted to investigate advanced features in the analysis
of cryptographic protocols tailored to the Maude-NPA tool. This tool
is a model-checker for cryptographic protocol analysis that allows for
the incorporation of different equational theories and operates in the
unbounded session model without the use of data or control abstraction.
An important contribution of this thesis is relative to theoretical aspects
of protocol verification in Maude-NPA. First, we define a forwards
operational semantics, using rewriting logic as the theoretical framework
and the Maude programming language as tool support. This is the first
time that a forwards rewriting-based semantics is given for Maude-NPA.
Second, we also study the problem that arises in cryptographic protocol
analysis when it is necessary to guarantee that certain terms generated
during a state exploration are in normal form with respect to the protocol
equational theory.
We also study techniques to extend Maude-NPA capabilities to support
the verification of a wider class of protocols and security properties.
First, we present a framework to specify and verify sequential protocol
compositions in which one or more child protocols make use of information obtained from running a parent protocol. Second, we present a
theoretical framework to specify and verify protocol indistinguishability
in Maude-NPA. This kind of properties aim to verify that an attacker
cannot distinguish between two versions of a protocol: for example, one
using one secret and one using another, as it happens in electronic voting
protocols.
Finally, this thesis contributes to improve the efficiency of protocol
verification in Maude-NPA. We define several techniques which drastically
reduce the state space, and can often yield a finite state space,
so that whether the desired security property holds or not can in fact
be decided automatically, in spite of the general undecidability of such
problems.Santiago Pinazo, S. (2015). Advanced Features in Protocol Verification: Theory, Properties, and Efficiency in Maude-NPA [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/4852
Geometry and symmetries of multi-particle systems
The quantum dynamical evolution of atomic and molecular aggregates, from
their compact to their fragmented states, is parametrized by a single
collective radial parameter. Treating all the remaining particle coordinates in
d dimensions democratically, as a set of angles orthogonal to this collective
radius or by equivalent variables, bypasses all independent-particle
approximations. The invariance of the total kinetic energy under arbitrary
d-dimensional transformations which preserve the radial parameter gives rise to
novel quantum numbers and ladder operators interconnecting its eigenstates at
each value of the radial parameter.
We develop the systematics and technology of this approach, introducing the
relevant mathematics tutorially, by analogy to the familiar theory of angular
momentum in three dimensions. The angular basis functions so obtained are
treated in a manifestly coordinate-free manner, thus serving as a flexible
generalized basis for carrying out detailed studies of wavefunction evolution
in multi-particle systems.Comment: 37 pages, 2 eps figure
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