DoubleEcho: Mitigating Context-Manipulation Attacks in Copresence Verification

Copresence verification based on context can improve usability and strengthen security of many authentication and access control systems. By sensing and comparing their surroundings, two or more devices can tell whether they are copresent and use this information to make access control decisions. To the best of our knowledge, all context-based copresence verification mechanisms to date are susceptible to context-manipulation attacks. In such attacks, a distributed adversary replicates the same context at the (different) locations of the victim devices, and induces them to believe that they are copresent. In this paper we propose DoubleEcho, a context-based copresence verification technique that leverages acoustic Room Impulse Response (RIR) to mitigate context-manipulation attacks. In DoubleEcho, one device emits a wide-band audible chirp and all participating devices record reflections of the chirp from the surrounding environment. Since RIR is, by its very nature, dependent on the physical surroundings, it constitutes a unique location signature that is hard for an adversary to replicate. We evaluate DoubleEcho by collecting RIR data with various mobile devices and in a range of different locations. We show that DoubleEcho mitigates context-manipulation attacks whereas all other approaches to date are entirely vulnerable to such attacks. DoubleEcho detects copresence (or lack thereof) in roughly 2 seconds and works on commodity devices

TYPES OF POLITENESS STRATEGIES AND DEGREES OF POLITENESS PERFORMED BY ENGLISH MAJOR STUDENTS IN REQUESTING FOR HELP

In social interaction, people need to pay attention to the face of others to maintain relationships and avoid losing their faces. To do this, people should use politeness strategies in communication. This study aims to investigate which type of politeness strategies are mostly used and the level of politeness shown by English major students in the High Quality Program in requesting help. This study is based on the theory of Brown and Levinson (1987). Based on the analysis of the data obtained from the questionnaire, negative politeness strategies were applied the most. This also performs a high degree of politeness. It shows that students majoring in English studies (High Quality Program) had an awareness of using politeness strategies in requesting help.<p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/edu_01/0704/a.php" alt="Hit counter" /></p&gt

An Overview of Sustainable Ocean Resources for Socio-economic Development in Vietnam

Vietnam is one of the nation with long coastal with many valuable resources, which is the basis for the economy development from the ocean-based activities. This paper outlined the main maritime resources and their contribution to the socio-economic development in Vietnam. The raw data was collected from the readable sources such as General Statistics Office of Vietnam, Vietnam meteorological and meteorological data center…. as well as from the practical investigation. This raw data was processed and analyzed in order to have a general view on the majority marine resources in Vietnam. The results showed that there were 5 main resources (oil, fisheries, natural hydrate, green energy, and tourism) from the ocean, which significantly contribute to the economy development of Vietnam. The highest contribution of the oil value to the GDP was witnessed in 2011 with 26.6% of the GDP. While the value of the fisheries and tourism increased every year, the natural hydrate and energy from the ocean are still young areas, however, they come one step closer to the exploitation, which can greatly contribute to the Vietnam economy growth. With these valuable resources from the sea, Vietnam need to have reasonable policies and strategies for the management, exploitation, and export in order to able to effectively use of these resources for the sustainable economy development. Keywords: Ocean resources, sustainable development, fisheries, crude oil exploitation DOI: 10.7176/JRDM/69-05 Publication date:September 30th 202

Estimating Water Content and Grain Size of Intertidal Flat Sediments Using Visible to Shortwave-Infrared Reflectance and Sentinel 2A Data: A Case Study of the Red River Delta, Vietnam

Sediment properties such as water content (WC) and grain size (GS) are essential to characterize the environmental conditions of tidal flats. This article aimed to develop appropriate models to estimate the WC and GS of surface sediments for an intertidal flat on the Red river delta (Vietnam) using Sentinel 2A (S2A) images. The spectral reflectance, WC, and GS of 96 sub-samples from 12 sediment samples collected on December 17, 2017 were measured to clarify their relationships. The WC was highly correlated with the reflectance ratio of two shortwave-infrared bands, R(2190)/R(1610) (R² = 0.93). The median GS (D₅₀) at 0%, 15%, and 20% of WC was significantly correlated with the reflectance ratio of the near-infrared band (842 nm) versus the visible-green band (560 nm) (R² > 0.78). Next, D₅₀ was estimated from a multivariate regression model using this band ratio, the visible-red band (665 nm), and WC. The accuracy of the models was verified by comparisons with WC and D₅₀ from 20 samples collected on March 12th 2019 (RMSE of both WC and D₅₀ 30%) in very fine sediments (silts), which is consistent with other intertidal flats with similar sediment types. This article was limited to fine sediment samples. Therefore, our next step is to incorporate coarse sediments into the models to provide more universal mapping of WC and sediment types