PKI Scalability Issues

This report surveys different PKI technologies such as PKIX and SPKI and the issues of PKI that affect scalability. Much focus is spent on certificate revocation methodologies and status verification systems such as CRLs, Delta-CRLs, CRS, Certificate Revocation Trees, Windowed Certificate Revocation, OCSP, SCVP and DVCS.Comment: 23 pages, 2 figure

Unified architecture of mobile ad hoc network security (MANS) system

In this dissertation, a unified architecture of Mobile Ad-hoc Network Security (MANS) system is proposed, under which IDS agent, authentication, recovery policy and other policies can be defined formally and explicitly, and are enforced by a uniform architecture. A new authentication model for high-value transactions in cluster-based MANET is also designed in MANS system. This model is motivated by previous works but try to use their beauties and avoid their shortcomings, by using threshold sharing of the certificate signing key within each cluster to distribute the certificate services, and using certificate chain and certificate repository to achieve better scalability, less overhead and better security performance. An Intrusion Detection System is installed in every node, which is responsible for colleting local data from its host node and neighbor nodes within its communication range, pro-processing raw data and periodically broadcasting to its neighborhood, classifying normal or abnormal based on pro-processed data from its host node and neighbor nodes. Security recovery policy in ad hoc networks is the procedure of making a global decision according to messages received from distributed IDS and restore to operational health the whole system if any user or host that conducts the inappropriate, incorrect, or anomalous activities that threaten the connectivity or reliability of the networks and the authenticity of the data traffic in the networks. Finally, quantitative risk assessment model is proposed to numerically evaluate MANS security

Grid Infrastructure for Domain Decomposition Methods in Computational ElectroMagnetics

The accurate and efficient solution of Maxwell's equation is the problem addressed by the scientific discipline called Computational ElectroMagnetics (CEM). Many macroscopic phenomena in a great number of fields are governed by this set of differential equations: electronic, geophysics, medical and biomedical technologies, virtual EM prototyping, besides the traditional antenna and propagation applications. Therefore, many efforts are focussed on the development of new and more efficient approach to solve Maxwell's equation. The interest in CEM applications is growing on. Several problems, hard to figure out few years ago, can now be easily addressed thanks to the reliability and flexibility of new technologies, together with the increased computational power. This technology evolution opens the possibility to address large and complex tasks. Many of these applications aim to simulate the electromagnetic behavior, for example in terms of input impedance and radiation pattern in antenna problems, or Radar Cross Section for scattering applications. Instead, problems, which solution requires high accuracy, need to implement full wave analysis techniques, e.g., virtual prototyping context, where the objective is to obtain reliable simulations in order to minimize measurement number, and as consequence their cost. Besides, other tasks require the analysis of complete structures (that include an high number of details) by directly simulating a CAD Model. This approach allows to relieve researcher of the burden of removing useless details, while maintaining the original complexity and taking into account all details. Unfortunately, this reduction implies: (a) high computational effort, due to the increased number of degrees of freedom, and (b) worsening of spectral properties of the linear system during complex analysis. The above considerations underline the needs to identify appropriate information technologies that ease solution achievement and fasten required elaborations. The authors analysis and expertise infer that Grid Computing techniques can be very useful to these purposes. Grids appear mainly in high performance computing environments. In this context, hundreds of off-the-shelf nodes are linked together and work in parallel to solve problems, that, previously, could be addressed sequentially or by using supercomputers. Grid Computing is a technique developed to elaborate enormous amounts of data and enables large-scale resource sharing to solve problem by exploiting distributed scenarios. The main advantage of Grid is due to parallel computing, indeed if a problem can be split in smaller tasks, that can be executed independently, its solution calculation fasten up considerably. To exploit this advantage, it is necessary to identify a technique able to split original electromagnetic task into a set of smaller subproblems. The Domain Decomposition (DD) technique, based on the block generation algorithm introduced in Matekovits et al. (2007) and Francavilla et al. (2011), perfectly addresses our requirements (see Section 3.4 for details). In this chapter, a Grid Computing infrastructure is presented. This architecture allows parallel block execution by distributing tasks to nodes that belong to the Grid. The set of nodes is composed by physical machines and virtualized ones. This feature enables great flexibility and increase available computational power. Furthermore, the presence of virtual nodes allows a full and efficient Grid usage, indeed the presented architecture can be used by different users that run different applications

An Optimal and Distributed Method for Voltage Regulation in Power Distribution Systems

This paper addresses the problem of voltage regulation in power distribution networks with deep-penetration of distributed energy resources, e.g., renewable-based generation, and storage-capable loads such as plug-in hybrid electric vehicles. We cast the problem as an optimization program, where the objective is to minimize the losses in the network subject to constraints on bus voltage magnitudes, limits on active and reactive power injections, transmission line thermal limits and losses. We provide sufficient conditions under which the optimization problem can be solved via its convex relaxation. Using data from existing networks, we show that these sufficient conditions are expected to be satisfied by most networks. We also provide an efficient distributed algorithm to solve the problem. The algorithm adheres to a communication topology described by a graph that is the same as the graph that describes the electrical network topology. We illustrate the operation of the algorithm, including its robustness against communication link failures, through several case studies involving 5-, 34-, and 123-bus power distribution systems.Comment: To Appear in IEEE Transaction on Power System

Collaborative Caching for efficient and Robust Certificate Authority Services in Mobile Ad-Hoc Networks

Security in Mobile Ad-Hoc Network (MANET) is getting a lot of attention due to its inherent vulnerability to a wide spectrum of attacks. Threats exist in every layer of MANET stack, and different solutions have been adapted for each security problem. Additionally, availability is an important criterion in most MANET solutions, but many security frameworks did not consider it. Public-Key Infrastructure (PKI) is no exception, and its deployment in MANET needs major design and implementation modifications that can fit constraints unique to this environment. Our focus in this dissertation is to adapt and increase the availability of Certificate Authority (CA) services, as a major PKI entity, in MANET. Several attempts have been proposed to deal with the problem of deploying CA in MANET to provide a generic public-key framework, but each either ends up sacrificing system security or availability. Here, the main goal of our work is to provide a solution that addresses performance and security issues of providing MANET-based PKI. Particularly, we would like to maintain the availability of the services provided by CA while keeping the network\u27s packet overhead as low as possible. In this dissertation, we present a MANET-based framework suitable for exchanging public-key certificates by collaborative caching between MANET clients. We show that our system can meet the challenges of providing robust and secure CA services in MANET. Augmented by simulation results, we demonstrate quantitatively the feasibility of our work as we were able to reduce network overhead associated with threshold based CA queries up to 92% as compared to related work in addition to having a very short response time. The dependency on CA servers has been reduced, and the system was able to tolerate as much as two-third inoperative CA servers without noticeable decrease in the service performance

Elasticity optimism

Estimates of the elasticity of substitution between domestic and foreign varieties are small in macroeconomic data, and substantially larger in disaggregated studies. This may be an artifact of heterogeneity. We use disaggregated multilateral trade data to structurally identify elasticities of substitution in US goods. We spell out a partial equilibrium model to aggregate them adequately at the country level. We compare aggregate elasticities that impose equality across sectors, to estimates allowing for heterogeneity. The former are similar in value to conventional macroeconomic estimates; but they are more than twice larger -up to 7- with heterogeneity. The parameter is central to calibrated models in most of international economics. We discuss the difference our corrected estimate makes in various areas of international economics, including the dynamics of external balances, the international transmission of shocks, international portfolio choice and optimal monetary policy.Trade Elasticities, Aggregation, Calibration, Global Imbalances, International Transmission, International Portfolio, Monetary Policy.