On the efficiency of revocation in RSA-based anonymous systems

© 2016 IEEEThe problem of revocation in anonymous authentication systems is subtle and has motivated a lot of work. One of the preferable solutions consists in maintaining either a whitelist L-W of non-revoked users or a blacklist L-B of revoked users, and then requiring users to additionally prove, when authenticating themselves, that they are in L-W (membership proof) or that they are not in L-B (non-membership proof). Of course, these additional proofs must not break the anonymity properties of the system, so they must be zero-knowledge proofs, revealing nothing about the identity of the users. In this paper, we focus on the RSA-based setting, and we consider the case of non-membership proofs to blacklists L = L-B. The existing solutions for this setting rely on the use of universal dynamic accumulators; the underlying zero-knowledge proofs are bit complicated, and thus their efficiency; although being independent from the size of the blacklist L, seems to be improvable. Peng and Bao already tried to propose simpler and more efficient zero-knowledge proofs for this setting, but we prove in this paper that their protocol is not secure. We fix the problem by designing a new protocol, and formally proving its security properties. We then compare the efficiency of the new zero-knowledge non-membership protocol with that of the protocol, when they are integrated with anonymous authentication systems based on RSA (notably, the IBM product Idemix for anonymous credentials). We discuss for which values of the size k of the blacklist L, one protocol is preferable to the other one, and we propose different ways to combine and implement the two protocols.Postprint (author's final draft

Contribución al conocimiento de los kinorrincos ciclorrágidos (Kinorhyncha Cyclorhagida) : biogrografía, taxonomía, morfología

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Biológicas, Departamento de Zoología y Antropología Física, leída el 18-06-2014Depto. de Biodiversidad, Ecología y EvoluciónFac. de Ciencias BiológicasTRUEunpu

Development of an Analytic Nodal Diffusion Solver in Multigroups for 3D Reactor Cores with Rectangular or Hexagonal Assemblies.

More accurate modelling of physical phenomena involved in present and future nuclear reactors requires a multi-scale and multi-physics approach. This challenge can be accomplished by the coupling of best-estimate core-physics, thermal-hydraulics and multi-physics solvers. In order to make viable that coupling, the current trends in reactor simulations are along the development of a new generation of tools based on user-friendly, modular, easily linkable, faster and more accurate codes to be integrated in common platforms. These premises are in the origin of the NURESIM Integrated Project within the 6th European Framework Program, which is envisaged to provide the initial step towards a Common European Standard Software Platform for nuclear reactors simulations. In the frame of this project and to reach the above-mentioned goals, a 3-D multigroup nodal solver for neutron diffusion calculations called ANDES (Analytic Nodal Diffusion Equation Solver) has been developed and tested in-depth in this Thesis. ANDES solves the steady-state and time-dependent neutron diffusion equation in threedimensions and any number of energy groups, utilizing the Analytic Coarse-Mesh Finite-Difference (ACMFD) scheme to yield the nodal coupling equations. It can be applied to both Cartesian and triangular-Z geometries, so that simulations of LWR as well as VVER, HTR and fast reactors can be performed. The solver has been implemented in a fully encapsulated way, enabling it as a module to be readily integrated in other codes and platforms. In fact, it can be used either as a stand-alone nodal code or as a solver to accelerate the convergence of whole core pin-by-pin code systems. Verification of performance has shown that ANDES is a code with high order definition for whole core realistic nodal simulations. In this paper, the methodology developed and involved in ANDES is presented

Imágenes de una revolución: la caída del muro de Berlín en los medios de comunicación

El presente trabajo de fin de grado trata del tratamiento que los medios de comunicación dieron a la caída del muro de Berlín en 1989, a través de una exposición de imágenes, publicadas por los periódicos más influyentes de España en la época: El País, La Vanguardia y el ABC.Grado en Relaciones Laborales y Recursos Humano

Las matrices de Toeplitz en la construcción de códigos convolucionales perforados

En este trabajo presentamos la modelización de la técnica de perforación de códigos convolucionales introducida por McEliece desde el punto de vista de sistemas. Aplicando esta técnica a un (2, 1, 1)-código convolucional óptimo y teniendo en cuenta las propiedades de las matrices de Toeplitz, construimos un nuevo (3, 2, 1)-código óptimo

Introduction of LGBT diversity through storytelling in the English Primary Classroom

The main objective of this end-of-degree project is to demonstrate that LGBT diversitycan be included at Primary Schools, more specifically in EFL as a way of fostering aninclusive education. For achieving this objective, the paper starts by addressing the legalsituation of the inclusion of LGBT diversity in Spanish Primary classrooms andbibliography on its implementation in the Primary education.With this in mind, this dissertation designs a Unit Plan on LGBT diversity, gender rolesand stereotypes and prejudices. This Unit Plan is designed for the EFL classroom, sostudents will learn English while they are taught about the diversity in our world. TheUnit Plan finds in traditional and modern fairy tales a contrast between stereotypes andprejudices and inclusiveness. These tales are introduced through storytelling, which is atool often used in the Communicative Language Teaching (CLT). CLT allows thecreation of a communicative environment in class, where the LGBT diversity isintroduced. The main of this process of revision of traditional fairy tales and encounteringnew fairy tales is that students are able to produce an alternative and inclusive ending fora fairy tale of their choice.<br /