• Journal of KIISE:Software and Applications
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• v.27 no.1
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• pp.41-49
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• 2000

This paper describes a method of generating MPHFs(Minimal Perfect Hash Functions) for large static search key sets. The MOS(Mapping-Ordering-Searching) approach is widely used presently in MPHF generation. In this research, the MOS approach is improved and a SOMS(Selecting-Ordering-Mapping-Searching) approach is proposed, where the Selecting step is newly introduced and the Orderng step is performed before the Mapping step to generate MPHFs more effectively. The MPHF generation algorithm proposed in this research is probabilistic and the expected processing time is linear to the number of keys. Experimental results show that MPHFs are generated fast and the space needed to represent the hash functions is small.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.11C
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• pp.1040-1045
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• 2002

This paper focuses on a hash-based, distributed Wet caching network that eliminates inter-cache communication. An agent program on cache servers, a mapping program on the DNS server, and other components comprised in a distributed Web caching network were modified and developed to implement a so-called "consistent" hashing. Also, a dynamic load balancing algorithm is proposed to address the load-balancing problem that is a key performance issue on distributed architectures. This algorithm effectively balances the load among cache servers by distributing the calculated amount of mapping items that have higher popularity than others. Therefore, this developed network can resolve the imbalanced load that is caused by a variable page popularity, a non-uniform distribution of a hash-based mapping, and a variation of cache servers.

• ETRI Journal
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• v.30 no.6
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• pp.790-798
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• 2008

Recently, NAND flash memory has emerged as a next generation storage device because it has several advantages, such as low power consumption, shock resistance, and so on. However, it is necessary to use a flash translation layer (FTL) to intermediate between NAND flash memory and conventional file systems because of the unique hardware characteristics of flash memory. This paper proposes a new clustered FTL (CFTL) that uses clustered hash tables and a two-level software cache technique. The CFTL can anticipate consecutive addresses from the host because the clustered hash table uses the locality of reference in a large address space. It also adaptively switches logical addresses to physical addresses in the flash memory by using block mapping, page mapping, and a two-level software cache technique. Furthermore, anticipatory I/O management using continuity counters and a prefetch scheme enables fast address translation. Experimental results show that the proposed address translation mechanism for CFTL provides better performance in address translation and memory space usage than the well-known NAND FTL (NFTL) and adaptive FTL (AFTL).

• Journal of the Korea Institute of Information Security & Cryptology
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• v.23 no.4
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• pp.695-707
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• 2013

DHT(Distributed Hash Table) networks such as Kademlia are vulnerable to the ID mapping attack caused by the voluntary DHT mapping structure where the location of a node is solely determined by itself on the network topology. This causes security problems such as eclipse, DRDoS and botnet C&C on DHT networks. To prevent ID mapping attacks, we propose a non-voluntary DHT mapping scheme and perform analysis on NAT compatibility, attack resistance, and network dynamicity. Analysis results show that our approach may have an equivalent level of attack resistance comparing with other defense mechanisms and overcome their limitations including NAT compatibility and network dynamicity.

• Journal of Korea Multimedia Society
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• v.9 no.11
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• pp.1381-1394
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• 2006

Generation methods of data cube have been studied for many years in data warehouse which supports decision making using stored data. There are two previous studies, one is multi-way array algorithm and the other is H-cubing algorithm which is based on the hyper-tree. The multi-way array algorithm stores all aggregation data in arrays, so if the base data is increased, the size of memory is also grow. The H-cubing algorithm which is based on the hyper-tree stores all tuples in one tree so the construction cost is increased. In this paper, we present an efficient data cube generation method based on hash table using weight mapping table and record hash table. Because the proposed method uses a hash table, the generation cost of data cube is decreased and the memory usage is also decreased. In the performance study, we shows that the proposed method provides faster search operation time and make data cube generation operate more efficiently.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.10a
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• pp.236-239
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• 2021

With the growth of AI technology, the scale of Knowledge Graphs continues to be expanded. Knowledge Graphs are mainly expressed as RDF representations that consist of connected triples. Many RDF storages compress and transform RDF triples into the condensed IDs. However, if we try to transform a large scale of RDF triples, it occurs the high processing time and memory overhead because it needs to search the large ID mapping table. In this paper, we propose the method of converting RDF triples using Hash-based ID mapping tables with MapReduce, which is the software framework with a parallel, distributed algorithm. Our proposed method not only transforms RDF triples into Integer-based IDs, but also improves the conversion speed and memory overhead. As a result of our experiment with the proposed method for LUBM, the size of the dataset is reduced by about 3.8 times and the conversion time was spent about 106 seconds.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10a
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• pp.46-48
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• 2004

Distributed Hash Table(DHT)를 기반으로 하는 structured P2P에서 복잡 질의를 통친 원하는 자료를 찾는 것은 쉽지 않다. 이와 같은 것들 중 하나가 범위 값을 이용하여 원하는 값을 찾는 range query이다. 본 논문에서는 full binary tree의 특징을 이용하여 structured P2P에서 range query를 수행할 수 있는 mapping 함수와, load balance를 지원하기 위한 방법을 제안한다 또한 실험을 통해서 이 방법들이 어느 정도의 성능을 보여주는 지도 살펴본다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.11
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• pp.967-969
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• 2013

In this paper, we propose an efficient mult-signature scheme based on a bilinear mapping for shared data in the cloud and prove the security of the proposed scheme using the difficulty of the computational Diffie-Hellman problem. For verification, the scheme is using the sum of the hash values of stored data rather than the entire data, which makes it feasible to reduce the size of the downloaded data.

• Journal of the Society of Disaster Information
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• v.17 no.1
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• pp.176-183
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• 2021

Purpose: The introduction of smart factories that reflect the 4th industrial revolution technologies such as AI, IoT, and VR, has been actively promoted in Korea. However, in order to solve various problems arising from existing file-based operating systems, this research will focus on identifying and verifying non-file system-based data protection technology. Method: The research will measure security storage that cannot be identified or controlled by the operating system. How to activate secure storage based on the input of digital key values. Establish a control unit that provides input and output information based on BIOS activation. Observe non-file-type structure so that mapping behavior using second meta-data can be performed according to the activation of the secure storage. Result: First, the creation of non-file system-based secure storage's data input/output were found to match the hash function value of the sample data with the hash function value of the normal storage and data. Second, the data protection performance experiments in secure storage were compared to the hash function value of the original file with the hash function value of the secure storage after ransomware activity to verify data protection performance against malicious ransomware. Conclusion: Smart factory technology is a nationally promoted technology that is being introduced to the public and this research implemented and experimented on a new concept of data protection technology to protect crucial data within the information system. In order to protect sensitive data, implementation of non-file-type secure storage technology that is non-dependent on file system is highly recommended. This research has proven the security and safety of such technology and verified its purpose.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.550-552
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• 2004

분산 해시 테이블 (Distributed Hash Table) 을 사용한 P2P 시스템에서는 해시함수를 사용하며 파일과 노드의 ID를 정의하고 파일의 ID와 매핑 (mapping) 되는 ID를 가진 노드에 파일을 저장함으로써 시스템 전체에 파일을 완전히 분산시킨다. 이러한 시스템에서는 파일을 찾을 때 해시된 파일 ID로 찾기 때문에 정확한 매치 (exact match) 만 가능하다. 하지만 현재 P2P 파일 공유 시스템에서는 파일의 전체 이름을 정확히 알지 못하더라도 부분적인 키워드로 파일을 검색할 수 있도록 하는 키워드 검색 (keyword search) 이 요구된다. 본 논문에서는 분산 해시 테이블을 기반으로 하는 P2P 시스템에서 키워드 검색이 가능하도록 하는 방안을 제안한다.