Efficiency in the cake-eating problem with quasi-geometric discounting

This paper shows that any equilibrium allocation in the cake-eating problem with quasi-geometric discounting is not Pareto efficient. However, efficiency can be established by introducing a planner who controls the initial endowment and makes transfers over time. It is shown than any Pareto efficient allocation can be supported by a perfect equilibrium with transfers.Pareto efficiency

Formally verified countermeasures against cache based attacks in virtualization platforms

Cache based attacks are a class of side-channel attacks that are particularly effective in virtualized or cloud-based environments, where they have been used to recover secret keys from cryptographic implementations. One common approach to thwart cache-based attacks is to use constant-time implementations, which do not branch on secrets and do not perform memory accesses that depend on secrets. However, there is no rigorous proof that constant-time implementations are protected against concurrent cache attacks in virtualization platforms; moreover, many prominent implementations are not constant-time. An alternative approach is to rely on system-level mechanisms. One recent such mechanism is stealth memory, which provisions a small amount of private cache for programs to carry potentially leaking computations securely. We weaken the definition of constant-time, introducing a new program classification called S-constant-time, that captures the behavior of programs that correctly use stealth memory. This new definition encompasses some widely used cryptographic implementations. However, there was no rigorous analysis of stealth memory and S-constant-time, and no tool support for checking if applications are S-constant-time. In this thesis, we propose a new information-flow analysis that checks if an x86 application executes in constant-time or S-constant-time. Moreover, we prove that (S-)constant-time programs do not leak confidential information through the cache to other operating systems executing concurrently on virtualization platforms. The soundness proofs are based on new theorems of independent interest, including isolation theorems for virtualization platforms, and proofs that (S-)constant-time implementations are non-interfering with respect to a strict information flow policy which disallows that control flow and memory accesses depend on secrets. We formalize our results using the Coq proof assistant and we demonstrate the effectiveness of our analyses on cryptographic implementations, including PolarSSL AES, DES and RC4, SHA256 and Salsa20.Los ataques basados en el cache son una clase de ataques de canal lateral (side-channel) particularmente efectivos en entornos virtualizados o basados en la nube, donde han sido usados para recuperar claves secretas de implementaciones criptográficas. Un enfoque común para frustrar los ataques basados en cache es usar implementaciones de tiempo constante (constant-time), las cuales no tienen bifurcaciones basadas en secretos, y no realizan accesos a memoria que dependan de secretos. Sin embargo, no existe una prueba rigurosa de que las implementaciones de tiempo constante están protegidas de ataques concurrentes de cache en plataformas de virtualización. Además, muchas implementaciones populares no son de tiempo constante. Un enfoque alternativo es utilizar mecanismos a nivel del sistema. Uno de los más recientes de estos es stealth memory, que provee una pequeña cantidad de cache privado a los programas para que puedan llevar a cabo de manera segura computaciones que potencialmente filtran información. En este trabajo se debilita la definición de tiempo constante, introduciendo una nueva clasificación de programas llamada S-constant-time, que captura el comportamiento de programas que hacen un uso correcto de stealth memory. Esta nueva definición abarca implementaciones criptográficas ampliamente utilizadas. Sin embargo, hasta el momento no había un análisis riguroso de stealth memory y S-constant-time, y ningún soporte de herramientas que permitan verificar si una aplicación es S-constant-time. En esta tesis, proponemos un nuevo análisis de flujo de información que verifica si una aplicación x86 ejecuta en constant-time o S-constant-time. Además, probamos que los programas (S-)constant-time no filtran información confidencial a través del cache a otros sistemas operativos ejecutando concurrentemente en plataformas de virtualización. La pruebas de corrección están basadas en propiedades que incluyen teoremas, de interés en sí mismos, de aislamiento para plataformas de virtualización y pruebas de que las implementaciones (S-)constant-time son no interferentes con respecto a una política estricta de flujo de información que no permite que el control de flujo y los accesos a memoria dependan de secretos. Formalizamos nuestros resultados utilizando el asistente de pruebas Coq, y mostramos la efectividad de nuestros análisis en implementaciones criptográficas que incluyen PolarSSL AES, DES y RC4, SHA256 y Salsa20

Timing of Wage Setting when Firms Invest in R&D

Also published as Working Paper Ikerlanak 2003-08unions, R&D, productivity of labor, wage setting

Partial cross-ownership and strategic environmental policy

This paper analyzes the effect that passive investment in rival firms has on the setting of cooperative and non-cooperative environmental taxes. We consider two firms located in different countries, one of which owns a stake in its rival. We show that partial cross-ownership affects the taxes set by the countries in the cooperative and non-cooperative cases. Depending on the stake that one firm has in its rival we show that cooperative taxes may he higher or lower than non-cooperative taxes. Moreover, for intermediate values of the stake, the non-cooperative tax is higher in one country and lower in the other than the cooperative tax.environmental taxes, international trade, local pollution, partial ownership

Halving poverty in Mexico

We estimate the required time and the minimum necessary growth rate to halve poverty incidence and poverty intensity in Mexico’s rural and urban areas for a series of counterfactual distribution and growth scenarios. Results show that, given the current income distribution, per capita incomes in the rural area would have to grow faster –in some cases eight times faster– than they have done historically to shrink poverty by half by 2015. In contrast, income in the urban sector would have to grow around 1 per cent per year to reach the same goal, which seems a more reasonable outcome given its behavior in past years.economic growth, millennium development goals, poverty goals, poverty measurement, Mexico.

Contributions to security and privacy protection in recommendation systems

A recommender system is an automatic system that, given a customer model and a set of available documents, is able to select and offer those documents that are more interesting to the customer. From the point of view of security, there are two main issues that recommender systems must face: protection of the users' privacy and protection of other participants of the recommendation process. Recommenders issue personalized recommendations taking into account not only the profile of the documents, but also the private information that customers send to the recommender. Hence, the users' profiles include personal and highly sensitive information, such as their likes and dislikes. In order to have a really useful recommender system and improve its efficiency, we believe that users shouldn't be afraid of stating their preferences. The second challenge from the point of view of security involves the protection against a new kind of attack. Copyright holders have shifted their targets to attack the document providers and any other participant that aids in the process of distributing documents, even unknowingly. In addition, new legislation trends such as ACTA or the ¿Sinde-Wert law¿ in Spain show the interest of states all over the world to control and prosecute these intermediate nodes. we proposed the next contributions: 1.A social model that captures user's interests into the users' profiles, and a metric function that calculates the similarity between users, queries and documents. This model represents profiles as vectors of a social space. Document profiles are created by means of the inspection of the contents of the document. Then, user profiles are calculated as an aggregation of the profiles of the documents that the user owns. Finally, queries are a constrained view of a user profile. This way, all profiles are contained in the same social space, and the similarity metric can be used on any pair of them. 2.Two mechanisms to protect the personal information that the user profiles contain. The first mechanism takes advantage of the Johnson-Lindestrauss and Undecomposability of random matrices theorems to project profiles into social spaces of less dimensions. Even if the information about the user is reduced in the projected social space, under certain circumstances the distances between the original profiles are maintained. The second approach uses a zero-knowledge protocol to answer the question of whether or not two profiles are affine without leaking any information in case of that they are not. 3.A distributed system on a cloud that protects merchants, customers and indexers against legal attacks, by means of providing plausible deniability and oblivious routing to all the participants of the system. We use the term DocCloud to refer to this system. DocCloud organizes databases in a tree-shape structure over a cloud system and provide a Private Information Retrieval protocol to avoid that any participant or observer of the process can identify the recommender. This way, customers, intermediate nodes and even databases are not aware of the specific database that answered the query. 4.A social, P2P network where users link together according to their similarity, and provide recommendations to other users in their neighborhood. We defined an epidemic protocol were links are established based on the neighbors similarity, clustering and randomness. Additionally, we proposed some mechanisms such as the use SoftDHT to aid in the identification of affine users, and speed up the process of creation of clusters of similar users. 5.A document distribution system that provides the recommended documents at the end of the process. In our view of a recommender system, the recommendation is a complete process that ends when the customer receives the recommended document. We proposed SCFS, a distributed and secure filesystem where merchants, documents and users are protectedEste documento explora c omo localizar documentos interesantes para el usuario en grandes redes distribuidas mediante el uso de sistemas de recomendaci on. Se de fine un sistema de recomendaci on como un sistema autom atico que, dado un modelo de cliente y un conjunto de documentos disponibles, es capaz de seleccionar y ofrecer los documentos que son m as interesantes para el cliente. Las caracter sticas deseables de un sistema de recomendaci on son: (i) ser r apido, (ii) distribuido y (iii) seguro. Un sistema de recomendaci on r apido mejora la experiencia de compra del cliente, ya que una recomendaci on no es util si es que llega demasiado tarde. Un sistema de recomendaci on distribuido evita la creaci on de bases de datos centralizadas con informaci on sensible y mejora la disponibilidad de los documentos. Por ultimo, un sistema de recomendaci on seguro protege a todos los participantes del sistema: usuarios, proveedores de contenido, recomendadores y nodos intermedios. Desde el punto de vista de la seguridad, existen dos problemas principales a los que se deben enfrentar los sistemas de recomendaci on: (i) la protecci on de la intimidad de los usuarios y (ii) la protecci on de los dem as participantes del proceso de recomendaci on. Los recomendadores son capaces de emitir recomendaciones personalizadas teniendo en cuenta no s olo el per l de los documentos, sino tambi en a la informaci on privada que los clientes env an al recomendador. Por tanto, los per les de usuario incluyen informaci on personal y altamente sensible, como sus gustos y fobias. Con el n de desarrollar un sistema de recomendaci on util y mejorar su e cacia, creemos que los usuarios no deben tener miedo a la hora de expresar sus preferencias. Para ello, la informaci on personal que est a incluida en los per les de usuario debe ser protegida y la privacidad del usuario garantizada. El segundo desafi o desde el punto de vista de la seguridad implica un nuevo tipo de ataque. Dado que la prevenci on de la distribuci on ilegal de documentos con derechos de autor por medio de soluciones t ecnicas no ha sido efi caz, los titulares de derechos de autor cambiaron sus objetivos para atacar a los proveedores de documentos y cualquier otro participante que ayude en el proceso de distribuci on de documentos. Adem as, tratados y leyes como ACTA, la ley SOPA de EEUU o la ley "Sinde-Wert" en España ponen de manfi esto el inter es de los estados de todo el mundo para controlar y procesar a estos nodos intermedios. Los juicios recientes como MegaUpload, PirateBay o el caso contra el Sr. Pablo Soto en España muestran que estas amenazas son una realidad

Gabriela Mistral, recadera de Chile y de América

Indexación: Revista UNABLa poderosa vigencia de Gabriela Mistral es mensaje de vasta humanidad y sentido trascendental de lo existente, A la vez chilena y americana, hispana y amerindia, su impetuosa riqueza virtióse en "Recado", meditación animada de oralidad y acento femenino, Reserva estética y ética, la prosa mistraliana recopilada durante las últimas décadas, confirma la orientación de un espíritu adelantado que supo legar un mensaje perdurable y urgente de considerar. Abstract: Gabriela Mistral's powerful validity is a message of vast humanity and momentous sense ofthat which exists. At the same time Chilean, American, Spanish and Amerindian, her impulsive richness is seen in "Recado" an animated meditation of spoken and feminine discourse. Ethical and aesthetical reserve, the mistralian prose compiled in the last decades confums the orientation of an advanced spirit which knew how to bequeath a lasting and urgent message to be considered