• Journal of Information Processing Systems
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• v.6 no.3
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• pp.335-346
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• 2010

The present study investigates the difficulty of solving the mathematical problem, namely the DLP (Discrete Logarithm Problem) for ephemeral keys. The DLP is the basis for many public key cryptosystems. The ephemeral keys are used in such systems to ensure security. The DLP defined on a prime field $Z^*_p of random prime is considered in the present study. The most effective method to solve the DLP is the ICM (Index Calculus Method). In the present study, an efficient way of computing the DLP for ephemeral keys by using a new variant of the ICM when the factors of p-1 are known and small is proposed. The ICM has two steps, a pre-computation and an individual logarithm computation. The pre-computation step is to compute the logarithms of a subset of a group and the individual logarithm step is to find the DLP using the precomputed logarithms. Since the ephemeral keys are dynamic and change for every session, once the logarithms of a subset of a group are known, the DLP for the ephemeral key can be obtained using the individual logarithm step. Therefore, an efficient way of solving the individual logarithm step based on the newly proposed precomputation method is presented and the performance is analyzed using a comprehensive set of experiments. The ephemeral keys are also solved by using other methods, which are efficient on random primes, such as the Pohlig-Hellman method, the Van Oorschot method and the traditional individual logarithm step. The results are compared with the newly proposed individual logarithm step of the ICM. Also, the DLP of ephemeral keys used in a popular password key exchange protocol known as Chang and Chang are computed and reported to launch key recovery attack.

• Journal of the Korean earth science society
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• v.35 no.7
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• pp.537-542
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• 2014

The Gravity Recovery and Climate Experiment (GRACE) has observed the Earth's mass redistribution mainly caused by the variations of groundwater, ice sheet, and sea level since its launch in April 2002. The global gravity model estimated by the GRACE observation is corrected by barometric pressure, and thus represents the change of Earth mass on the Earth's surface and below Earth's surface excluding air mass. However, the total air mass varies due to the water exchange between the Earth's surface and the atmosphere. As a result, the nominal GRACE gravity model should include the Earth's gravity spectrum associated with the total air mass variations, degree 0 and order 0 coefficients of spherical harmonics ($C_{00}$). Because the water vapor content varies mainly on a seasonal time scale, a change of $C_{00}$ (${\delta}C_{00}$) is particularly important to seasonal variations of sea level, and mass balance between northern and southern hemisphere. This result implies that ${\delta}C_{00}$ coefficients should be accounted for the examination of continental scale mass change possibly associated with the climate variations.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.20.2-20.2
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• 2011

The NASA Antarctica balloon experiment CREAM has successfully collected the data of energetic cosmic rays during flights in past years. We will present the recent analysis results of the CREAM experiment. We will also report on the launch and recovery process of the latest flight. The silicon charge detector of the CREAM has played the key role in the precision measurement of the charge constitution of energetic cosmic rays. We proposed the upgrade of the CREAM experiment with the installment of a new large silicon charge detector on top of the CREAM instrument. The charge measurement of the large silicon detector with no material in front is expected to improve the accuracy of the CREAM charge measurement drastically when combined with the measurement of the existing double layer silicon detector. We will present the fabrication of the large silicon detector and its performance in the radiation source test as well as in the beam test.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.597-606
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• 2020

Because the USV(Unmanned Surface Vehicle) is capable of remote control or autonomous navigation at sea, it can secure the superiority of combat power while minimizing human losses in a future combat environment. To plan the technology for the development of USV, the trend analysis of related technology and the selection of promising technology should be preceded, but there has been little research in this area. The purpose of this paper was to measure and evaluate the technology trends quantitatively. For this purpose, this study analyzed the technology trends and selected promising/declining technologies using topic modeling of papers and patent data. As a result of topic modeling, promising technologies include control and navigation, verification/validation, autonomous level, mission module, and application technology, and declining technologies include underwater communication and image processing technology. This study also identified new technology areas that were not included in the existing technology classification, e.g., technology related to research and development of USV, artificial intelligence, launch/recovery, and operation, such as cooperation with manned and unmanned systems. The technology trends and new technology areas identified through this study may be used to derive key technologies related to the development of the USV and establish appropriate R&D policies.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.8
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• pp.737-742
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• 2015

Course correction munition are a weapson system for precision attacks and are assembled by applying a ballistic control system to existing projectiles. The roll control system is a subsystem of the ballistic control system and is placed between the guidance and control units inside of the projectile, which undergoes a 5000g lateral acceleration. Thus, it is very important to design the system to endure this load. Many developed countries evaluate the performance and safety of course correction munitions' parts using live-fire gun launch tests or a soft recovery system. However, these methods are expensive and slow. Thus, in this study, we develop impact analysis model of the roll control system using CAE. We apply the code to simulate impact phenomenon and use Johnson-Cook material model for modeling the high strain rate effect on the materials. We also design bearings in detail to analyze their behavior and verify the reliability of CAE model through gas-gun impact tests of the roll control system.

• The Southeast Asian review
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• v.27 no.1
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• pp.95-129
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• 2017

This study surveys and reviews political change, economic performance, and regional cooperation that were carried out in 2016 by Southeast Asian countries and ASEAN. This paper reports that what has followed the inauguration of new governments in Myanmar, the Philippines, Vietnam, and Laos fails to live up to the expectation and optimism that arose in the aftermath of elections and party congresses that took place in the first half of the year. In other countries such as Malaysia, Thailand, and Cambodia, where authoritarian regimes are faced with strong oppositions, the prospects for democratic change worsened to a substantial degree, as schisms and internal strives complicated the opposition camp as a result of instigation and intervention by the authoritarian leaders and their followers. In stable political systems, both democratic and authoritarian, no significant changes that may entail serious political implications were noticed. In 2016, the national economy of almost each and every country continued its slow but steady recovery that had started in 2014 and grew by 5% on the average. For 2017 onward, however, the earlier optimism that it would grow at least as fast dimmed down as uncertainty about the world economy looms larger due to the unexpected win by Donald Trump as U.S. president and the expected 'hard landing' of the Chinese economy around 2018. ASEAN declared the launch of the ASEAN Economic Community (AEC) only one day before the New Year, but its track record looked already bad and unpromising by the end of 2016. ASEAN leaders were tied up by their domestic politics and affairs too tightly to take time off to work seriously to observe the schedule as laid out in the AEC Blueprint 2025. Korea's relationship with Southeast Asian countries and ASEAN was "as good as it gets" in 2016 as ever but could become subject to tough review in the near future, if the Ministry of Foreign Affairs is found out to have been implicated in the ongoing Choi Sun Sil scandal and if the opposition wins the next presidential election to be held by this year.