• Journal of KIISE:Databases
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• v.28 no.4
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• pp.732-741
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• 2001

In the relational database systems the join operation is one of the most time-consuming query operations. Many parallel join algorithms have been developed 개 reduce the execution time Multiple hash join algorithm using allocation tree is one of the most efficient ones. However, it may have some delay on the processing each node of allocation tree, which is occurred in tuple-probing phase by the difference between one page reading time of outer relation and the processing time of already read one. This delay problem was solved by using the concept of synchronization of page execution time with we had proposed In this paper the effects of the performance improvements in each node of the allocation tree are extended to the whole allocation tree and the performance evaluation about that is processed. In addition we propose an efficient algorithm for multiple hash joins in limited number of processor environments according to the relationship between the number of input relations in the allocation tree and the number of processors allocated to the tree. Finally. we analyze the performance by building the analytical cost model and verify the validity of it by various performance comparison with previous method.

• Journal of KIISE:Databases
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• v.33 no.5
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• pp.463-475
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• 2006

In applications such as a traffic management system, analysis using a spatial hierarchy of a spatial data warehouse and a simple aggregation is required. Over the past few years, several studies have been made on solution using a spatial index. Many studies have focused on using extended R-tree. But, because it just provides either the current aggregation or the total aggregation, decision support of traffic policy required historical analysis can not be provided. This paper proposes hybrid index based on extended aR-tree for the spatio-temporal aggregation. The proposed method supports a spatial hierarchy and the current aggregation by the R-tree. The sorted hash table using the time structure of the extended aR-tree provides a temporal hierarchy and a historical aggregation. Therefore, the proposed method supports an efficient decision support with spatio-temporal analysis and is Possible currently traffic analysis and determination of a traffic policy with historical analysis.

• Journal of Korea Spatial Information System Society
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• v.6 no.1 s.11
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• pp.73-85
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• 2004

Recently, as the growth of the wireless Internet, PDA and HPC, the focus of research and development related with GIS(Geographic Information System) has been changed to the Real-Time Mobile GIS to service LBS. To offer LBS efficiently, there must be the Real-Time GIS platform that can deal with dynamic status of moving objects and a location index which can deal with the characteristics of location data. Location data can use the same data type(e.g., point) of GIS, but the management of location data is very different. Therefore, in this paper, we studied the Real-Time Mobile GIS using the HBR-tree to manage mass of location data efficiently. The Real-Time Mobile GIS which is developed in this paper consists of the HBR-tree and the Real-Time GIS Platform HBR-tree. we proposed in this paper, is a combined index type of the R-tree and the spatial hash Although location data are updated frequently, update operations are done within the same hash table in the HBR-tree, so it costs less than other tree-based indexes Since the HBR-tree uses the same search mechanism of the R-tree, it is possible to search location data quickly. The Real-Time GIS platform consists of a Real-Time GIS engine that is extended from a main memory database system. a middleware which can transfer spatial, aspatial data to clients and receive location data from clients, and a mobile client which operates on the mobile devices. Especially, this paper described the performance evaluation conducted with practical tests if the HBR-tree and the Real-Time GIS engine respectively.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.11a
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• pp.861-864
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• 2012

타임스탬프 서비스 형태에서 서비스제공자, 이용자에 따라 현재의 타임스탬프 모델보다 보안의 강도를 높이면서 최적의 성능을 보장할 수 있도록 모델을 설계하고 비교 분석한다. 문서를 그룹하여 타임스탬프를 발급 받으려는 이용자는 Multi Linear Hash Tree 구조를 제안하고 타임스탬프 서비스 제공업체는 Multi Prefix 이진 트리 구조를 제안한다.

• Journal of the Korea Society of Computer and Information
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• v.12 no.2 s.46
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• pp.231-242
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• 2007

The existing pattern mining methods[1,2,3,4,5,6,11,12,13] do not use location generalization method on the set of location history data of moving object, but even so they simply do extract only frequent patterns which have no spatio-temporal constraint in moving patterns on specific space. Therefore, it is difficult for those methods to apply to frequent pattern mining which has spatio-temporal constraint such as optimal moving or scheduling paths among the specific points. And also, those methods are required more large memory space due to using pattern tree on memory for reducing repeated scan database. Therefore, more effective pattern mining technique is required for solving these problems. In this paper, in order to develop more effective pattern mining technique, we propose new location generalization method that converts data of detailed level into meaningful spatial information for reducing the processing time for pattern mining of a massive history data set of moving object and space saving. The proposed method can lead the efficient spatial moving pattern mining of moving object using by creating moving sequences through generalizing the location attributes of moving object into 2D spatial area based on $R^*$-Tree and Area Grid Hash Table(AGHT) in preprocessing stage of pattern mining.

• Journal of the Korea Society of Computer and Information
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• v.23 no.2
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• pp.53-61
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• 2018

In this paper, the author proposes an efficient group key agreement scheme in a mobile environment where group members frequently join and leave. This protocol consists of basic protocols and general ones and is expected to be suitable for communications between a mobile device with limited computing capability and a key distributing center (or base station) with sufficient computing capability. Compared with other schemes, the performance of the proposed protocol is a bit more efficient in the aspects of the overall cost for both communication and computation where the computational efficiency of the scheme is achieved by using exclusive or operations and a one-way hash function. Also, in the aspect of security, it guarantees both forward and backward secrecy based on the computational Diffie-Hellman (CDH) assumption so that secure group communication can be made possible. Furthermore, the author proves its security against a passive adversary in the random oracle model.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.11a
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• pp.599-602
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• 2010

인터넷 검색 사이트는 사용자들이 검색한 단어들의 순위를 매기는 실시간 검색 순위 서비스를 제공하는데 검색되는 단어들의 순위를 매기기 위해서는 각 단어들의 분포도를 알 수 있는 어절 빈도 계산을 수행해야 한다. 어절 빈도는 BST(Binary Search Tree)를 수행하여 계산할 수 있는데, 사용자에 의하여 검색되는 단어들은 길이와 그 형태가 다양하여 빈도 계산시에 BST 의 깊이가 깊어져서 계산 시간이 오래 걸리게 된다. 본 논문에서는 문자 해시를 이용하여 깊이가 깊은 BST 의 탐색 속도를 개선하는 알고리즘을 제안하였다. 이 방법으로 빈도 계산 속도를 비교하였을 때 문자 해시의 범위에 의해 1KB 의 추가적인 기억공간의 사용하여 9.3%의 성능 개선 효과가 있었고, 해시 공간을 10KB 추가로 사용할 때는 24.3%, 236KB 일 때는 40.6%로의 효율로 BST 의 빈도 계산 속도를 향상 시킬 수 있었다.

• International Journal of Advanced Culture Technology
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• v.11 no.1
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• pp.343-348
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• 2023

As the IoT market continues to grow, security threats to IoT devices with limited resources are also increasing. However, the application of security technology to the existing system to IoT devices with limited resources is impossible due to the inherent characteristics of IoT devices. Various methods for solving related problems have been studied in existing studies to solve this problem. Therefore, this study analyzes the characteristics of domestic IoT authentication standards and existing research to propose an algorithm that applies blockchain-based authentication and lightweight encryption algorithms to IoT equipment with limited resources. In this study, a key generation method was applied using a Lamport hash-chain and data integrity between IoT devices were provided using a Merkle Tree, and an LEA encryption algorithm was applied using confidentiality in data communication. In the experiment, it was verified that the efficiency is high when the LEA encryption algorithm, which is a lightweight encryption algorithm, is applied to IoT devices with limited resources.

• The KIPS Transactions:PartC
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• v.16C no.1
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• pp.21-26
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• 2009

Presently, the demand for IPTV, to satisfy a variety of goals, is exploding. IPTV is coming into the spotlight as a killer application in upcoming IP convergence networks such as triple play which is the delivery of voice, internet, and video service to a subscriber. IPTV utilizes CAS, which controls the subscriber access to content for a profit. Although the current CAS scheme provides access control via subscriber authentication, there is no authentication scheme for the content transmitted from service providers. Thus, there is a vulnerability of security, through which an adversary can forge content between the service provider and subscribers and distribute malicious content to subscribers. In this paper, based on a hash tree scheme, we proposed efficient and strong source authentication protocols which remove the vulnerability of the current IPTV system. We also evaluate our protocol from a view of IPTV requirements.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.05a
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• pp.467-470
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• 2012

This paper proposes a technique of sybil attack detection using an ID-based certificate on sensor network. First, it can solve the broadcast storm problem happening when keys are distributed to sensor nodes. Second, it prevents the replay attack by periodically generating and changing the keys of sensor nodes with Key-chain technique. Third, it authenticates sensor node's ID using hash function. So, it maximizes sensor node's memory usage, reduces communication overhead. Finally it detects Sybil attack through ID-based certificate. Therefore, the proposed technique of Sybil attack detection using ID-based certificate consider simultaneously energy efficiency and stability on sensor network environment, and can trust the provided information through sensor network.