Sergio Sánchez García

Quality-Control Algorithm for Adaptive Streaming Services Over Wireless Channels

Dynamic Adaptive Streaming over HTTP (DASH) is a recent MPEG standard for IP video delivery whose aim is the convergence of existing adaptive-streaming proprietary solutions. However, it does not impose any adaptation logic for selecting the quality of the media segments requested by the client, which is crucial to cope effectively with bandwidth fluctuations, notably in wireless channels. We therefore propose a solution to this control problem through Stochastic Dynamic Programming (SDP). This approach requires a probabilistic characterization of the system, as well as the definition of a cost function that the control strategy aims to minimize. This cost function is designed taking into account factors that may influence the quality perceived by the users. Unlike previous works, which compute control policies online by learning from experience, our algorithm solves the control problem offline, leading promptly to better results. In addition, we compared our algorithm to others during a streaming simulation and we analyzed the objective results by means of a Quality of Experience (QoE) oriented metric. Moreover, we conducted subjective tests to complete the evaluation of the performance of our algorithm. The results show that our proposal outperforms the other approaches in terms of both the QoE-oriented metric and the subjective evaluation.

Solving identity delegation problem in the e-government environment

At present, many countries allow citizens or entities to interact with the government outside the telematic environment through a legal representative who is granted powers of representation. However, if the interaction takes place through the Internet, only primitive mechanisms of representation are available, and these are mainly based on non-dynamic offline processes that do not enable quick and easy identity delegation. This paper proposes a system of dynamic delegation of identity between two generic entities that can solve the problem of delegated access to the telematic services provided by public authorities. The solution herein is based on the generation of a delegation token created from a proxy certificate that allows the delegating entity to delegate identity to another on the basis of a subset of its attributes as delegator, while also establishing in the delegation token itself restrictions on the services accessible to the delegated entity and the validity period of delegation. Further, the paper presents the mechanisms needed to either revoke a delegation token or to check whether a delegation token has been revoked. Implications for theory and practice and suggestions for future research are discussed.At present, many countries allow citizens or entities to interact with the government outside the telematic environment through a legal representative who is granted powers of representation. However, if the interaction takes place through the Internet, only primitive mechanisms of representation are available, and these are mainly based on non-dynamic offline processes that do not enable quick and easy identity delegation. This paper proposes a system of dynamic delegation of identity between two generic entities that can solve the problem of delegated access to the telematic services provided by public authorities. The solution herein is based on the generation of a delegation token created from a proxy certificate that allows the delegating entity to delegate identity to another on the basis of a subset of its attributes as delegator, while also establishing in the delegation token itself restrictions on the services accessible to the delegated entity and the validity period of delegation. Further, the paper presents the mechanisms needed to either revoke a delegation token or to check whether a delegation token has been revoked. Implications for theory and practice and suggestions for future research are discussed.

A careful design for a tool to detect child pornography in P2P networks

This paper addresses the social problem of child pornography on peer-to-peer (P2P) networks on the Internet and presents an automated system with effective computer and telematic tools for seeking out and identifying data exchanges with pedophilic content on the Internet. The paper analyzes the social and legal context in which the system must operate and describes the processes by which the system respects the rights of the persons investigated and prevents these tools from being used to establish processes of surveillance and attacks on the privacy of Internet users.

Detection of distributed steganographic information in social networks

The peak of the new communications and social interactions through the Web makes less effective the use of classic automated tools of data acquisition. The massive appearance of authentication mechanisms, closed groups of users and, especially, mechanisms like captchas, makes really complex that automated tools can, in a simple manner, compile information and analyze it later. This paper reasons out how the characteristics of the present social networks can facilitate the presence of steganographic information. SDA steganalysis architecture is shown. SDA is composed of different tools to solve, as far as possible, the commented analysis problems. The paper emphasizes one tool, DCST, adapted to the steganalysis of Web content, mainly dynamic, typically present in the new social networks.

Solving Identity Management and Interoperability Problems at Pan-European Level

In a globalized digital world, it is essential for persons and entities to have a recognized and unambiguous electronic identity that allows them to communicate with one another. The management of this identity by public administrations is an important challenge that becomes even more crucial when interoperability among public administrations of different countries becomes necessary, as persons and entities have different credentials depending on their own national legal frameworks. More specifically, different credentials and legal frameworks cause interoperability problems that prevent reliable access to public services in a cross-border scenarios like todays European Union. Work in this doctoral thesis try to analyze the problem in a carefully detailed manner by studying existing proposals (basically in Europe), proposing improvements in defined architectures and performing practical work to test the viability of solutions. Moreover, this thesis will also address the long-standing security problem of identity delegation, which is especially important in complex and heterogeneous service delivery environments like those mentioned above. This is a position paper.

SPLASH: a hybrid 3D modeling/rendering approach mixing splats and meshes

We propose a hybrid 3D modeling and rendering approach called SPLASH to combine the modeling flexibility and robustness of SPLAts together with the rendering simplicity and maturity of meSHes. Together with this novel SPLASH concept, we also propose a system turning a 3D point cloud, obtained for example through an SfM (Structure from Motion) approach, into a multi-textured hybrid 3D model whose shape is described by a triangle mesh plus a collection of elliptical splats.

Improvements of pan-european IDM architecture to enable identity delegation based on x.509 proxy certificates and SAML

To foster the secure use of telematic services provided by public institutions, most European countries – and others in the rest of the world – are promoting electronic identification systems among their citizens to enable fully reliable identification. However, in todays globalized environment, it is becoming more common for citizens and entities of a given country, with their own electronic credentials under the legal framework of their country, to seek access to the public services provided by other countries with different legal frameworks and credentials. At present, a number of projects in the European Union are attempting to solve the problem through the use of pan-European identity management systems that ensure interoperability between the public institutions of different Member States. However, the solutions adopted to date are inadequate, for they do not envision all possible cases of user interaction with institutions. Specifically, they fail to address a very important aspect provided in different national legal systems, namely delegation of identity, by which a citizen can authorize another to act on his or her behalf in accessing certain services provided by public institutions. This paper provides a thorough analysis of problems of delegation and proposes an architecture based on X.509 Proxy Certificates and SAML assertions to enable delegation in provision of services in the complex and heterogeneous environment presented by the public institutions of the European Union as a whole.

Textured splat-based point clouds for rendering in handheld devices

We propose a novel technique for modeling and rendering a 3D point cloud obtained from a set of photographs of a real 3D scene as a set of textured elliptical splats. We first obtain the base splat model by calculating, for each point of the cloud, an ellipse approximating locally the underlying surface. We then refine the base model by removing redundant splats to minimize overlaps, and merging splats covering flat regions of the point cloud into larger ellipses. We later apply a multi-texturing process to generate a single texture atlas from the set of photographs, by blending information from multiple cameras for every splat. Finally, we render this multi-textured, splat-based 3D model with an efficient implementation of OpenGL ES 2.0 vertex and fragment shaders which guarantees its fluid display on handheld devices.

Analysis of electronic and telematic voting systems in binding experiences

This paper is about analysis and assess of three experiences on telematic and electronic voting dealing with such aspects as security and achievement of the social requirements. These experiences have been chosen taking into account the deepness of the public documentation and the technological challenge they faces.

Digital identity applied to telematic voting involving European citizens. Social and legal implications

This paper describes the characteristics of systems of electronic voting in which both the vote itself and the authorization to vote circulate through computer networks (telematic voting), with a focus on the problems arising from the need to ensure correct identification of citizens seeking to access the voting system in a Europe-wide environment. The advantages offered by such a system are discussed, as are the major social and legal implications these solutions may entail.