Galindo–Garcia identity-based signature (GG IBS) is an efficient identity-based signature (IBS) whose security is proven under the discrete logarithm (DL) assumption. Since the original security reduction of GG IBS is loose, there are some works to improve the reduction factor. However, such improvements do not achieve the tight security reduction sufficiently, or the efficiency of the resulting scheme is much worse than the original scheme. In this paper, we propose a new improvement of GG IBS. The proposed scheme has a tight security reduction from the decisional Diffie–Hellman (DDH) assumption with respect to a security model which is weaker than that of GG IBS. Our IBS has a better efficiency than the previous improvement of GG IBS whose security is also proven under the DDH assumption.

Refugee issues are among the most imminent and important problems facing modern societies. This review essay systematically reviews recent social scientific literature that quantitatively measures national refugee policies. In so doing, we compare several recent and prominent cross-national data sets on this topic, namely those constructed by de Haas, Natter, and Vezzoli (2015), Hatton (2016), Helbling et al. (2017), Blair, Grossman, and Weinstein (2022), and Savun (2022). We point to both the advantages and disadvantages of the respective data sets while providing suggestions on how to practically apply them and how to merge their scopes and perspectives in a more comprehensive manner in order to better fit researchers' and practitioners' scopes of interest. We conclude this article by suggesting future research agendas by highlighting the significance and feasibility of a compilation of a more extensive data set based on the existing ones.

Since the 1930s, mathematicians and computer scientists have been interested in computation. While mathematicians investigate recursion theory, computer scientists investigate computational complexity based on Turing machine model to understand what a computation is. Beside them, there is another approach of research on computation, which is the investigation of puzzles and games. Once we regard the rules used in puzzles and games as the set of basic operations of computation, we can perform some computation by solving puzzles and playing games. In fact, research on puzzles and games from the viewpoint of theoretical computer science has continued without any break in the history of theoretical computer science. Sometimes the research on computational complexity classes has proceeded by understanding the tons of puzzles. The wide collection of complete problems for a specific computational complexity class shares a common property, which gives us a deep understanding of the class. In this survey paper, we give a brief history of research on computational complexities of puzzles and games with related results and trends in theoretical computer science.

A connected graph is called of non-QE class if it does not admit a quadratic embedding in a Euclidean space. A non-QE graph is called primary if it does not contain a non-QE graph as an isometrically embedded proper subgraph. The graphs on six vertices are completely classified into the classes of QE graphs, of non-QE graphs, and of primary non-QE graphs.

We construct and analyze a mathematical model to consider the relation of the social structure to the infection risk for a spreading transmissible disease in a community. We take into account different phases of human activity, whether it takes place solely in the private situation or both private and social spheres, followed by the division of the community members into two classes: active and less active. The analysis on our mathematical model implies that there are critical conditions for the class size and human activity with respect to the infection risk for a community. Further, we try to discuss how the social structure and situation could be related to the infection risk for a community.