Um algoritmo de criptografia de chave pública semanticamente seguro baseado em curvas elípticas

Esta dissertação apresenta o desenvolvimento de um novo algoritmo de criptografia de chave pública. Este algoritmo apresenta duas características que o tornam único, e que foram tomadas como guia para a sua concepção. A primeira característica é que ele é semanticamente seguro. Isto significa que nenhum adversário limitado polinomialmente consegue obter qualquer informação parcial sobre o conteúdo que foi cifrado, nem mesmo decidir se duas cifrações distintas correspondem ou não a um mesmo conteúdo. A segunda característica é que ele depende, para qualquer tamanho de texto claro, de uma única premissa de segurança: que o logaritmo no grupo formado pelos pontos de uma curva elíptica de ordem prima seja computacionalmente intratável. Isto é obtido garantindo-se que todas as diferentes partes do algoritmo sejam redutíveis a este problema. É apresentada também uma forma simples de estendê-lo a fim de que ele apresente segurança contra atacantes ativos, em especial, contra ataques de texto cifrado adaptativos. Para tanto, e a fim de manter a premissa de que a segurança do algoritmo seja unicamente dependente do logaritmo elíptico, é apresentada uma nova função de resumo criptográfico (hash) cuja segurança é baseada no mesmo problema.

Infrastructure privatization in a neoclassical economy : macroeconomic impact and welfare computation

In this paper a competitive general equilibrium model is used to investigate the welfare and long run allocation impacts of privatization. There are two types of capital in this model economy, one private and the other initially public ("infrastructure"), and a positive externality due to the latter is assumed. A benevolent government can improve upon decentralized allocation internalizing the externality, but it introduces distortions in the economy through the finance of its investments. It is shown that even making the best case for public action - maximization of individuals' welfare, no• operation inefficiency and free supply to society of infrastructure services - privatization is welfare improving for a large set of economies. Hence, arguments against privatization based solely on under-investment are incorrect, as this maybe the optimal action when the financing of public investment are considered. When operation inefficiency is introduced in the public sector, gains from privatization are much higher and positive for most reasonable combinations of parameters .

The executive toolbox: building legislative support in a multiparty presidential regime

How do presidents win legislative support under conditions of extreme multipartism? Comparative presidential research has offered two parallel answers, one relying on distributive politics and the other claiming that legislative success is a function of coalition formation. We merge these insights in an integrated approach to executive-legislative relations, also adding contextual factors related to dynamism and bargaining conditions. We find that the two presidential “tools” – pork and coalition goods – are substitutable resources, with pork functioning as a fine-tuning instrument that interacts reciprocally with legislative support. Pork expenditures also depend upon a president’s bargaining leverage and the distribution of legislative seats.

Infrastructure privatization in a neoclassical economy: macroeconomic impact and welfare computation

In this paper a competi tive general equilibrium model is used to investigate the welfare and long run allocation impacts of privatization. There are two types of capital in this model economy, one private and the other initially public ("infrastructure"), and a positive extemality due to the latter is assumed. A benevolent governrnent can improve upon decentralized allocation intemalizing the extemality, but it introduces distortions in the economy through the finance of its investments. It is shown that even making the best case for public action - maximization of individuais' welfare, no operation inefficiency and free supply to society of infrastructure services - privatization is welfare improving for a large set of economies. Hence, arguments against privatization based solely on under-investment are incorrect, as this maybe the optimal action when the financing of public investment are considered. When operation inefficiency is introduced in the public sector, gains from privatization are much higher and positive for most reasonable combinations of parameters.

Who is the cowboy in Washington?: beating google at their own game with neuroscience and cryptography

Who was the cowboy in Washington? What is the land of sushi? Most people would have answers to these questions readily available,yet, modern search engines, arguably the epitome of technology in finding answers to most questions, are completely unable to do so. It seems that people capture few information items to rapidly converge to a seemingly 'obvious' solution. We will study approaches for this problem, with two additional hard demands that constrain the space of possible theories: the sought model must be both psychologically and neuroscienti cally plausible. Building on top of the mathematical model of memory called Sparse Distributed Memory, we will see how some well-known methods in cryptography can point toward a promising, comprehensive, solution that preserves four crucial properties of human psychology.

Too difficult to manage, too big to ignore: party choice in multiparty presidential systems

In consensual (proportional) highly fragmented multiparty settings, political parties have two historical choices to make or pathways to follow: i) playing a majoritarian role by offering credible candidates to the head of the executive; or ii) playing the median legislator game. Each of those choices will have important consequences not only for the party system but also for the government. The purpose of this paper is to investigate the role played by median legislator parties on coalition management strategies of presidents in a comparative perspective. We analyze in depth the Brazilian case where the Partido do Movimento Democrático Brasileiro (PMDB) has basically functioned as the median legislator party in Congress by avoiding the approval of extreme policies, both on the left and on the right. Based on an expert survey in Latin America, we built an index of Pmdbismo and identified that there is a positive correlation between partisan fragmentation and median legislator parties. In addition, we investigate the effect of having a median legislator party in the governing coalition. We found that it is cheaper and less difficult for the government to manage the coalition having the median legislative party on board.

Cabinet composition and assessment of a multiparty presidential system

This doctoral dissertation provides a detailed analysis of the Brazilian cabinet according to the concepts of a multiparty presidential system. Appointing politicians as ministers is one of the most important coalition-building tools and has been widely used by minority presidents. This dissertation will therefore analyze the high-level Brazilian national bureaucracy between 1995 and 2014. It argues that the ministries – or departments – are not equal, and that allied parties therefore take into account the different characteristics of a ministry when demanding positions as a patronage strategy or for use as other kinds of political assets. After reviewing the literature on the theme, followed by a comparative analysis of the Brazilian, Chilean, Mexican, and Guatemalan cabinets, all the Brazilian ministries will be weighed and ranked on a scale that is able to measure their political importance and attractiveness. This rank takes into account variables such as the budgetary power, the ability to spend money according the ministers’ will, the ability to hire new employees, the ministries’ influence over other governmental agents such as companies, agencies, and so on, the ministers’ tenure in office. Finally, a proxy is provided that seeks to identify the normative power a department may hold. All of these characteristics will then be taken into account in considering the representatives’ opinion, thus helping to ascertain whether the cabinet appointment has been coalescent among the several parties that belong to the president’s coalition.

A new method for real time computation of power quality indices based on instantaneous space phasors

One of the important issues about using renewable energy is the integration of dispersed generation in the distribution networks. Previous experience has shown that the integration of dispersed generation can improve voltage profile in the network, decrease loss, etc. but can create safety and technical problems as well. This work report the application of the instantaneous space phasors and the instantaneous complex power in observing performances of the distribution networks with dispersed generators in steady state. New IEEE apparent power definition, the so-called Buchholz-Goodhue effective apparent power, as well as new proposed power quality (oscillation) index in the three-phase distribution systems with unbalanced loads and dispersed generators, are applied. Results obtained from several case studies using IEEE 34 nodes test network are presented and discussed. (C) 2006 Elsevier B.V. All rights reserved.

Sliding mode for detection and accommodation of computation time delay fault

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effectiveness-ntu computation with a mathematical model for cross-flow heat exchangers

Due to the wide range of design possibilities, simple manufactured, low maintenance and low cost, cross-flow heat exchangers are extensively used in the petroleum, petrochemical, air conditioning, food storage, and others industries. In this paper a mathematical model for cross-flow heat exchangers with complex flow arrangements for determining epsilon -NTU relations is presented. The model is based on the tube element approach, according to which the heat exchanger outlet temperatures are obtained by discretizing the coil along the tube fluid path. In each cross section of the element, tube-side fluid temperature is assumed to be constant because the heat capacity rate ratio C*=Cmin/Cmax tends toward zero in the element. Thus temperature is controlled by effectiveness of a local element corresponding to an evaporator or a condenser-type element. The model is validated through comparison with theoretical algebraic relations for single-pass cross-flow arrangements with one or more rows. Very small relative errors are obtained showing the accuracy of the present model. epsilon -NTU curves for several complex circuit arrangements are presented. The model developed represents a useful research tool for theoretical and experimental studies on heat exchangers performance.

A controller design used in Lorenz synchronization chaotic system for secure communication based on LMI fuzzy control system

This paper describes a mathematical study about chaotic system and about the unified approach of chaos control via fuzzy control system based in Linear Matrix Inequality to design a controller which synchronizes the transmission/reception system. This system, that was based in Lorenz chaotic circuit, can be used for transmit signals in secure way.