• Journal of KIISE:Computer Systems and Theory
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• v.36 no.4
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• pp.259-273
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• 2009

Most of large-scale distributed file systems decouple a metadata operation from read and write operations for a file. In the distributed file systems, a certain server named a metadata server (MDS) maintains metadata information in file system such as access information for a file, the position of a file in the repository, the namespace of the file system, and so on. But, the existing systems used restrictive metadata management schemes, because most of the distributed file systems designed to focus on the distributed management and the input/output performance of data rather than the metadata. Therefore, in the existing systems, the metadata throughput and expandability of the metadata server are limited. In this paper, we propose a new non-shared metadata management scheme in order to provide the high metadata throughput and scalability for a cluster of MDSs. First, we derive a dictionary partitioning scheme as a new metadata distribution technique. Then, we present a load balancing technique based on the distribution technique. It is shown through various experiments that our scheme outperforms existing metadata management schemes in terms of scalability and load balancing.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.6
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• pp.1311-1326
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• 2010

Peer-to-peer (P2P) networks consume the most bandwidth in the current Internet and file sharing accounts for the majority of the P2P traffic. Thus it is important for a P2P file sharing application to be efficient in bandwidth consumption. Bandwidth consumption as much as downloaded file sizes is inevitable, but those in file search and bad downloads, e.g. wrong, corrupted, or malicious file downloads, are overheads. In this paper, we target to reduce these overheads even in the presence of high volume of malicious users and their bad files. Sybil attacks are the example of such hostile environment. Sybil attacker creates a large number of identities (Sybil nodes) and unfairly influences the system. When a large portion of the system is subverted, either in terms of the number of users or the number of files shared in the system, the overheads due to the bad downloads rapidly increase. We propose ELiSyR, a file search protocol that can tolerate such a hostile environment. ELiSyR uses social networks for P2P file search and finds benign files in 71% of searches even when more than half of the users are malicious. Furthermore, ELiSyR provides similar success with less bandwidth than other general efforts against Sybil attacks. We compare our algorithm to SybilGuard, SybilLimit and EigenTrust in terms of bandwidth consumption and the likelihood of bad downloads. Our algorithm shows lower bandwidth consumption, similar chances of bad downloads and fairer distribution of computation loads than these general efforts. In return, our algorithm takes more rounds of search than them. However the time required for search is usually much less than the time required for downloads, so the delay in search is justifiable compared to the cost of bad downloads and subsequent re-search and downloads.

• Journal of Communications and Networks
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• v.15 no.2
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• pp.228-239
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• 2013

Peer-to-peer (P2P) systems have proved the most effective and popular file sharing applications in recent years. Previous studies mainly focused on equal service and differentiated service strategies when peers have no initial data before their downloads. For an upload-constrained P2P file sharing system, we model both the equal service process and the differentiated service process when the initial data distribution of peers satisfies some special conditions. Moreover, we show how to minimize the time required to distribute the file to any number of peers. The proposed fluid-based models can reveal the intrinsic relations among the initial data amount, the peer set size, and the minimum last finish time. The closed-form expressions derived from the extended models can closely approximate chunk-based models and systems, especially for relatively large files. As an application of the extended models, we show how to provide differentiated service efficiently to multiple peer sets. Since no limits are imposed on the upload bandwidth of peers or the size of each peer set, we believe that our analytic process and the results achieved can provide not only fundamental insights into bandwidth allocation and data scheduling but also a helpful reference for both improving system performance and building an effective incentive mechanism for P2P file sharing systems.

• Journal of Electrical Engineering and information Science
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• v.2 no.4
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• pp.37-45
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• 1997

With rapid increase of information requirements from various application areas, there has been much research on dynamic information storage structures that effectively support insertions, deletions and updates. In this appear we evaluate the performance of he existing dynamic signature file methods such as the S-tree, Quick Filter and HS file and provide guidelines for the most effective usage to a given operational environment. We derive analytic performance evaluation models of the storage structures based on retrieval time, storage overhead and insertion time. We also perform extensive experiments with various data distributions such as uniform, normal and exponential distributions. The relationships among various performance parameters are throughly investigated. We show through performance comparison based on analytic models and experiments that regardless of data distribution, the HS file significantly improves performance in both the retreival time and the storage overhead over S-tree and Quick Filter.

• Journal of Digital Forensics
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• v.12 no.3
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• pp.97-108
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• 2018

Computer technology and Internet advances enable easy massive file transfer by messenger, email, and web hard service users this means that a child pornography file owner who is illegally possessing itself can quickly transfer that to other users However there are currently no specific ways to prevent or block the distribution of child pornography between messenger, email, and web hard service users. in this paper, we propose a method to prevent the distribution of child pornography using the MD5, SHA-1 hash value stored in the 'police Child pornography Profiling system' and to identify the child pornography suspects using the subscriber information. the user extracts the hash value of the file before distributing the file, compared it with police system, and if it has the same value, blocks the transmission of the file and sends warning to the owner. the service provider sends the subscriber information to investigation agency child pornography owners can conduct a quick and accurate investigation.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.1 no.1
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• pp.38-46
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• 1991

This paper pro poses a ley distribution system based on identification information. The system uses an indivdual user's identification instead of the public file used in the Diffie-Hellman sustem. It does not require any services of a center to distribute work keys and users to keep directory public file. We propose an identity-based key distribution system for generating a commom secret conference kdy for two or more users. We assume users are connected in a ring network. Message among users authenticated using each user's identification informa-tion. The security of the our proposed system is based on the difficulty of both factoring large numbers and computing discrete logarithms over large finite fields.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.26 no.2
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• pp.201-210
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• 1996

There is increasing attention about radiology teaching files on the Internet in the field of diagnostic radiology. The purpose of this study was to aid in the creation of new radiology teaching file by analysing the present radiology teaching file sites on the Internet with many aspects and evaluating images on those sites, using Macintosh IIci computer, 28.8kbps TelePort Fax/Modem, Netscape Navigator 2.0 software The results were as follow : 1. Analysis of radiology teaching file sites (l) Country distribution was the highest in USA(57.5％). (2) Average number of cases was 186 cases and radiology teaching file sites with search engine were 9 sites (22.5％). (3) At the method of case arrangement, anatomic area type and diagnosis type were found at the 10 sites(25％) each, question & answer type was found at the 9 sites(22.5％). (4) Radiology teaching file sites with oro-maxillofacial disorder were 9 sites(22.5％). (5) At the image format, GIF format was found at the 14 sites(35％). and ]pEG format found at the 14 sites(35％). (6) Created year was the highest in 1995(43.7％). (7) Continuing case upload was found at the 35 sites(87.5％). 2. Evaluation of images on the radiology teaching files (l) Average file size of GIF format (71 Kbyte) was greater than that of JPEG format(24 Kbyte). (p<0.001) (2) Image quality of GIF format was better than that of JPEG format. (p<0.001).

• Proceedings of the Korean Society of Computer Information Conference
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• 2017.07a
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• pp.5-6
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• 2017

본 논문은 데이터를 보다 적은 소비전력으로 보관하기 위한 에너지 효율적인 파일 분산배치 정책을 제안한다. 이 정책은 개별 하드디스크 용량을 빠르게 가득 채우도록 분산 스토리지의 쓰기 동작을 처리하고, 가득 찬 하드디스크의 모터를 정지시켜 에너지 효율을 향상시킨다. Ceph 분산 스토리지를 수정하여 제안하는 파일 분산배치 정책을 적용하였으며 시뮬레이션을 통하여 제안하는 파일 분산배치 정책이 에너지 효율적임을 확인하였다.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06c
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• pp.245-247
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• 2012

We know that JPEG image format is one of the most popular image formats in the digital area and distribution of digital photographic drawing it is interested frequently in certain types of forensic investigation. In most case, corrupted images are shown gaudiness with the boundary of the corrupted parts. In the paper, we propose a technique to carve correct JPEG images using transformation method and the approach can be used for JPEG image file carving tool development.

• Journal of Information Processing Systems
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• v.16 no.2
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• pp.301-317
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• 2020

An enterprise patch-management system (PMS) typically supplies a single point of failure (SPOF) of centralization structure. However, a Blockchain system offers features of decentralization, transaction integrity, user certification, and a smart chaincode. This study proposes a Hyperledger Fabric Blockchain-based distributed patch-management system and verifies its technological feasibility through prototyping, so that all participating users can be protected from various threats. In particular, by adopting a private chain for patch file set management, it is designed as a Blockchain system that can enhance security, log management, latest status supervision and monitoring functions. In addition, it uses a Hyperledger Fabric that owns a practical Byzantine fault tolerant consensus algorithm, and implements the functions of upload patch file set, download patch file set, and audit patch file history, which are major features of PMS, as a smart contract (chaincode), and verified this operation. The distributed ledger structure of Blockchain-based PMS can be a solution for distributor and client authentication and forgery problems, SPOF problem, and distribution record reliability problem. It not only presents an alternative to dealing with central management server loads and failures, but it also provides a higher level of security and availability.