• KIPS Transactions on Computer and Communication Systems
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• v.4 no.4
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• pp.135-140
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• 2015

The WDSS improves defensive capacity against web application layer DDoS attack by using web cache server and L7 switch which are added on the DDoS shelter system. When web DDoS attack occurs, security agents divert traffic from backbone network to sub-network of the WDSS and then DDoS protection device and L7 switch block abnormal packets. In the meantime, web cache server responds only to requests of normal clients and maintains stable web service. In this way, the WDSS can counteract the web DDoS attack which generates small traffic and depletes server-client session resource. Furthermore, the WDSS does not require IP tunneling because it is not necessary to retransfer the normal requests to original web server. In this paper, we validate operation of the WDSS and verify defensive capability against web application layer DDoS attacks. In order to do this, we built the WDSS on backbone network of an ISP. And we performed web DDoS tests by using a testing system that consists of zombie PCs. The tests were performed by three types and various amounts of web DDoS attacks. Test results suggest that the WDSS can detect small traffic of the web DDoS attacks which do not have repeat flow whereas the formal DDoS shelter system cannot.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1588-1596
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• 2015

In the Internet of Things (IoT), resource-constrained devices such as sensors are capable of communicating and exchanging data over the Internet. The IETF standard group has specified an application protocol CoAP, which uses UDP as a transport protocol, allows such a lightweight device to transmit data. Also, the IETF recommended the DTLS binding for securing CoAP. However, additional features should be added to the DTLS protocol to resolve several problems such as packet loss, reordering, fragmentation and replay attack. Consequently, performance of DTLS is worse than TLS. It is highly required for lightweight devices powered by small battery to design and implement a security protocol in an energy efficient manner. This paper thus discusses about DTLS performance in the perspective of energy consumption. To analyze the performance, we implemented IEEE 802.15.4 based test network consisting of constrained sensor devices in the Cooja simulator. We measured energy consumptions required for each of DTLS client and server in the test network. This paper compares the energy consumption and amount of transmitted data of each flight of DTLS handshake, and the processing and receiving time. We present the analyzed results with regard to code size, cipher primitive and fragmentation as well.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1551-1559
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• 2015

Recently, the performance of smart devices is almost similar to that of the existing PCs, thus the users of smart devices can perform similar works such as messengers, SNSs(Social Network Services), smart banking, etc. originally performed in PC environment using smart devices. Although the development of smart devices has led to positive impacts, it has caused negative changes such as an increase in security threat aimed at mobile environment. Specifically, the threats of mobile devices, such as leaking private information, generating unfair billing and performing DDoS(Distributed Denial of Service) attacks has continuously increased. Over 80% of the mobile devices use android platform, thus, the number of damage caused by mobile malware in android platform is also increasing. In this paper, we propose android based malware detection mechanism using time-series analysis, which is one of statistical-based detection methods.We use auto-regressive moving-average model which is extracting accurate predictive values based on existing data among time-series model. We also use fast and exact malware detection method by extracting possible malware data through Z-Score. We validate the proposed methods through the experiment results.

• The Korean Journal of Financial Management
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• v.24 no.3
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• pp.29-62
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• 2007

We examine the methods to increase MBS values given parameters of default risks of individual mortgages and their correlation, and analyze the effects of these parameters on the efficiency of the methods. First, the values of MBS can be improved when they are comprised of low-correlation mortgages regardless of specific forms of investors' utility functions. Second, the values of MBS can also be raised even after their components mortgages are determined. More specifically, when investors' utilities are heterogeneous, CMO's of a less risky tranche and a riskier tranche are highly valued compared with pass-through securities of two identical tranches. When investors' utilities are homogeneous(risk averse), however, the latter meets the needs of investors better than the former does. Third, it can be shown that the efficiency of the methods in this paper is an increasing function of default risks of mortgage loans or of the correlation between them, and a decreasing function of the amount of the price fall of MBS when in default.

• Journal of the Korean Association of Geographic Information Studies
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• v.13 no.3
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• pp.14-28
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• 2010

The aim of this study is to investigate crime hotspot areas using the spatio-temporal cluster analysis which is possible to search simultaneously time range as well as space range as an alternative method of existing hotspot analysis only identifying crime occurrence distribution patterns in urban area. As for research method, first, crime data were collected from criminal registers provided by official police authority in M city, Gyeongnam and crime occurrence patterns were drafted on a map by using Geographic Information Systems(GIS). Second, by utilizing Ripley K-function and Space-Time Scan Statistics analysis, the spatio-temporal distribution of crime was examined. The results showed that the risk of crime was significantly clustered at relatively few places and the spatio-temporal clustered areas of crime were different from those predicted by existing spatial hotspot analysis such as kernel density analysis and k-means clustering analysis. Finally, it is expected that the results of this study can be not only utilized as a valuable reference data for establishing urban planning and crime prevention through environmental design(CPTED), but also made available for the allocation of police resources and the improvement of public security services.

• Journal of Korean society of Dental Hygiene
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• v.11 no.5
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• pp.671-683
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• 2011

Objectives : The purpose of this study was to examine the oral health knowledge and actual oral health care of the selected subjects, their decision making about prosthetic treatment, the state and characteristics of their prosthetic treatment and their satisfaction with prosthetic treatment in an attempt to provide some information on the improvement of the quality of life related to oral health and the promotion of oral health. Methods : The subjects in this study were 250 people who received education in two different lifelong education institutions in the city of Busan. After a survey was conducted from May 23 to June 15, 2011, the answer sheets from 217 respondents were analyzed. Results : 1. As for the general characteristics of the respondents, the men(52.1%) outnumbered the women. Those who were in their 60 and up(47.5%) made up the largest age group, and the married people(65.4%) outnumbered the unmarried ones. By occupation, the company employees(20.3%) made up the biggest group. By education, the greatest group was high-school graduates(36.1%). By monthly mean income, the biggest group gained an income of 2.01 million won or more(36.9%). As to medical security, community-based insurance was most prevailing (36.9%). In terms of health promotion, the largest group worked out to stay fit(52.4%). 2. Regarding oral health knowledge, they had a good knowledge about the cause of dental caries(56.7%), but they weren't well aware of the right time for regular dental checkup(47.9%). In relation to oral health care, regular scaling wasn't prevailing(16.9%). 3. Regarding connections between the general characteristics and satisfaction with prosthesis, the less-educated respondents expressed significantly more dissatisfaction(p=0.015). By monthly mean income, those who had a smaller income were dissatisfied in general(p=0.028). Conclusions : The findings of the study illustrated that it's required to spread awareness of the importance of oral health among people in general, and that differentiated incremental oral health care should be provided for different age groups. In order to raise the satisfaction of patients with prosthesis, how to relieve their pain and anxiety and how to adjust prosthetic treatment cost properly should carefully be considered. In addition, the government should take measures to offer assistance for the low-income classes in preparation for an increase in the elderly population.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4A
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• pp.291-300
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• 2002

In this paper, a way of constituting optimized S box and G function was suggested in the block cipher whose structure is similar to SEED, which is KOREA standard of 128-bit block cipher. S box can be formed with nonlinear function and an affine transform. Nonlinear function must be strong with differential attack and linear attack, and it consists of an inverse number over GF(2$\^$8/) which has neither a fixed point, whose input and output are the same except 0 and 1, nor an opposite flexed number, whose output is one's complement of the input. Affine transform can be constituted so that the input/output correlation can be the lowest and there can be no fixed point or opposite fixed point. G function undergoes diffusive linear transform with 4 S-box outputs using the matrix of 4$\times$4 over GF(2$\^$8/). G function can be constituted so that MDS(Maximum Distance Separable) code can be formed, SAC(Strict Avalanche Criterion) can be met, there can be no weak input, where a fried point, an opposite fried point, and output can be two's complement of input, and the construction of hardware can be made easy. The S box and G function suggested in this paper can be used as a constituent of the block cipher with high security, in that they are strong with differential attack and linear attack with no weak input and they are excellent at diffusion.

• Journal of Internet Computing and Services
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• v.18 no.2
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• pp.21-30
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• 2017

IoT(Internet of Things) can enable networking and computing using any devices is rapidly proliferated. In the existing IoT environment, bottlenecks and service delays can occur because it processes data and provides services to users using central processing based on Cloud. For this reason, Edge Computing processes data directly in IoT nodes and networks to provide the services to the users has attracted attention. Also, numerous researchers have been attracted to intelligent service efficiently based on Edge Computing. In this paper, expert system-based context awareness scheme for Edge Computing in IoT environment is proposed. The proposed scheme can provide customized services to the users using context awareness and process data in real-time using the expert system based on efficient cooperations of resource limited IoT nodes. The context awareness services can be modified by the users according to the usage purpose. The three service modes in the security system based on smart home are used to test the proposed scheme and the stability of the proposed scheme is proven by a comparison of the resource consumptions of the servers between the proposed scheme and the PC-based expert system.

• Korean Journal of Agricultural and Forest Meteorology
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• v.20 no.2
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• pp.166-174
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• 2018

Potato(Solanum tuberosum L.) is one of the major food crop in the world following rice, wheat, and maize. It is thus important to project yield predict of potato under climate change conditions for assessment of food security. A crop growth modelling is widely used to simulate crop growth condition and total yield of various crops under a given climate condition. The decision support system for agrotechnology transfer (DSSAT) cropping system model, which was developed by U.S. which package integrating several models of 27 different crops, have been used to project crop yield for the impact assessment of climate change on crop production. In this study, we simulated potato yield using RCP 8.5 climate change scenario data, as inputs to the DSSAT model in five regions of Korea. The genetic coefficients of potato cultivar for 'superior', which is one of the most widely cultivated potato variety in Korea were determined. The GenCalc program, which is a submodule of the DSSAT package, was used to determine the genetic coefficients for the superior cultivar. The values of genetic coefficients were validated using results of 39 experiments performed over seven years in five regions. As a case study, the potato yield was projected that total yields of potato across five regions would increase by 26% in 2050s but decrease by 17% in 2090s, compared with 2010s. These results suggested that the needs for cultivation and irrigation technologies would be considerably large for planning and implementation of climate change adaptation for potato production in Korea.

• Journal of Korea Water Resources Association
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• v.49 no.3
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• pp.187-196
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• 2016

Standardized Precipitation Evapotranspiration Index (SPEI) considering evapotranspiration and precipitation is generally used to quantify the drought severity. Also, Reconnaissance Drought Index (RDI) has been frequently used in the arid regions which is suffering severe droughts, but drought analysis in association with RDI has been the focus of few studies in South Korea. Therefore, this study compared two meterological drought indices based on precipitation and evapotranspiration using Thornthwaite, Hargreaves, and Blaney-Criddle evaportranspiration calculation methods. Meteorological data of sixteen weather stations which are operated by Korea Meteorological Administration (KMA) were used to quantify drought and to compare characteristics of drought for the Han River Basin from 1992 to 2015. As a result, in case of Han River Basin, severe drought sharply increased in recent years. While the correlation coefficients are relatively high between the SPEIs and RDIs, the drought severity and year of severe drought are partially different. Therefore, it is necessary that RDI will be also measured to quantify severity and occurrence year of drought.