Security Analysis of the Unrestricted Identity-Based Aggregate Signature Scheme

Aggregate signatures allow anyone to combine different signatures signed by different signers on different messages into a single short signature. An ideal aggregate signature scheme is an identity-based aggregate signature (IBAS) scheme that supports full aggregation since it can reduce the total transmitted data by using an identity string as a public key and anyone can freely aggregate different signatures. Constructing a secure IBAS scheme that supports full aggregation in bilinear maps is an important open problem. Recently, Yuan {\it et al.} proposed an IBAS scheme with full aggregation in bilinear maps and claimed its security in the random oracle model under the computational Diffie-Hellman assumption. In this paper, we show that there exists an efficient forgery attacker on their IBAS scheme and their security proof has a serious flaw.Comment: 9 page

Against Hirose's Argument for Saving the Greater Number

Faced with the choice between saving one person and saving two others, what should we do? It seems intuitively plausible that we ought to save the two, and many forms of consequentialists offer a straightforward rationale for the intuition by appealing to interpersonal aggregation. But still many other philosophers attempt to provide a justification for the duty to save the greater number without combining utilities or claims of separate individuals. I argue against one such attempt proposed by Iwao Hirose. Despite being consequentialist, his argument is aggregation-free since it relies on a non-aggregative value judgement method, instead of interpersonal aggregation, to establish that (other things being equal) a state of affairs is better when more people survive therein. I do not take issue with its consequentialist element; rather, I claim that there is no good reason to adopt the method in question, and thus no good reason to be moved by his argument overall. What we are in search of is not merely a logically possible method that can produce the conclusion that we already want, but one that we have good reason to adopt. Hirose's argument elegantly demonstrates how it could possibly be true that it is right to save the greater number; but it fails to show that we have reason to believe so - even when we do not combine the interests of different individuals

Central Management of Local Performance: A Comparison of England and Korea

The author analyses performance measurement in the public sector and empirically tests the validity, legitimacy and functionality of Comprehensive Performance Assessment in England and Joint Performance Assessment in Korea on the basis of comparative methodology.Since the 1980s, New Public Management (NPM) has deeply influenced the public sector across the world, and thus measuring or managing performance has become a principal element of government reform. In terms of borrowing models and techniques from the private sector, performance measurement has been significantly extended into government, but differences between the two sectors have led to difficulties and criticism of this practice with a wide inconsistent variety of different theoretical explanations about it. In this context, this thesis investigates the effectiveness of performance measurement and theoretical explanations of conditions for its success in the public sector. It focuses through a comparative methodology on Comprehensive Performance Assessment and Joint Performance Assessment that have recently been introduced between the levels of government in England and Korea for the improvement of local government performance and accountability. Extensive analysis of literature and case studies have allowed the thesis to find firstly, that the introduction of such unique assessment systems, by which the centre assesses localities, was deeply affected by the environmental commonalities of both countries such as centralisation in inter-governmental relations and enthusiasm for NPM. Second, the empirical evaluation of both tools shows that they have in practice been valid for accurate assessment, and directly functional for improvement and indirectly for accountability to the public. Their high validity and functionality proved to be mainly attributable to two characteristics. One was institutionally that both frameworks were based on a balanced approach to performance and the disclosure of assessment results to the public for facilitating competition between localities. The other was that both had impacted on internal management of local government which led to change in organisational culture with more focus on performance. However, it identified a necessity for local authorities to participate in the development process of those tools to ensure legitimacy of central management of local performance since they enjoy their own electorally based political support. The research has also found the importance of assessors’ expertise for accurate assessment and a possibility that performance measurement can contribute to the resolution of political tension and cooperation between central and local government when it focuses more on outcomes than input and process. A deeper theoretical and practical understanding of these successful experiences and important policy elements in contemporary public management contributes significantly to knowledge in the three settings of evaluation of policy instruments, comparison between countries and central-local relations. Finally, the study assists each country and others to draw lessons from each other

Gravitational waves from cosmic bubble collisions

Cosmic bubbles are nucleated through the quantum tunneling process. After nucleation they would expand and undergo collisions with each other. In this paper, we focus in particular on collisions of two equal-sized bubbles and compute gravitational waves emitted from the collisions. First, we study the mechanism of the collisions by means of a real scalar field and its quartic potential. Then, using this model, we compute gravitational waves from the collisions in a straightforward manner. In the quadrupole approximation, time-domain gravitational waveforms are directly obtained by integrating the energy-momentum tensors over the volume of the wave sources, where the energy-momentum tensors are expressed in terms of the scalar field, the local geometry and the potential. We present gravitational waveforms emitted during (i) the initial-to-intermediate stage of strong collisions and (ii) the final stage of weak collisions: the former is obtained numerically, in \textit{full General Relativity} and the latter analytically, in the flat spacetime approximation. We gain qualitative insights into the time-domain gravitational waveforms from bubble collisions: during (i), the waveforms show the non-linearity of the collisions, characterized by a modulating frequency and cusp-like bumps, whereas during (ii), the waveforms exhibit the linearity of the collisions, featured by smooth monochromatic oscillations.Comment: 17 pages, 5 figure

Equilibrium Environmental Taxes on Intermediate-Good Production When Markets are Vertically Related in Open Economies

vertically related market, pollution tax on the intermediate-good, trans-boundary pollution, rent capture