• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권6호
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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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• 제15권2호
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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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• 제2권4호
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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.

• 디지털포렌식연구
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• 제12권3호
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• pp.97-108
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• 2018

컴퓨터기술 및 네트워크의 발전은 메신저, 이메일, 웹하드, 토렌트등 서비스 사용자의 손쉬운 대용량 파일 전송을 가능하게 하였다. 이는 소지자체가 불법인 아동음란물파일 소지자가 빠르게 다른 사용자에게 아동음란물을 전송 할 수 있다는 것을 의미한다. 하지만 현재는 메신저, 이메일, 웹하드, 토렌트 사용자간의 아동음란물을 배포를 예방하거나 차단하는 구체적인 방법에 대해 제안된 것은 없다. 본 논문에서는 '경찰청 아동음란물프로파일링시스템'의 보관되어 있는 MD5, SHA-1 해시값을 이용하여 아동음란물의 배포를 차단하고 소지자의 가입자 정보를 이용하여 아동음란물 소지 피의자를 특정할 수 있는 방법을 제안한다. 사용자가 파일을 배포하기 전 파일의 해시값을 추출하여 경찰청 아동음란물프로파일링시스템과 비교한 후 동일 값이 있을 경우 파일의 전송을 차단하고 해당 소지자에게 경고를 보내게 되며 서비스제공 기업은 가입자 정보를 수사기관에게 보내 아동음란물 소지자에 대한 수사를 신속하고 정확한 수사를 진행할 수 있다.

• 정보보호학회논문지
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• 제1권1호
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• pp.38-46
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• 1991

본 논문에서는 ID 정보를 이용한 키 분배방식을 제안했다. 이 방식에서는 Diffie-Hellman 방식에서 사용하는 공개 화일의 불법 변경 등의 공격에 대한 위험이 제거되는 장점을 가지고 있는 방식이다. 또한, 본 논문에서는 2명 이상의 회의용 키를 생성하는 ID 정보를 이용한 회의용 키 분배방식을 제안하였다. 가입자들은 링 네트워크(ring network)를 구성하고 있다고 가정하였다. 각 가입자들간의 전송정보들은 각 가입자의 ID 정보를 이용하여 인증된다. 제안한 방식의 안정성은 큰 수의 소인수 분해 및 이산대수 계산 문제에 근거한다.

• 치과방사선
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• 제26권2호
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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).

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2017년도 제56차 하계학술대회논문집 25권2호
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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.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2012년도 한국컴퓨터종합학술대회논문집 Vol.39 No.1(C)
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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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• 제16권2호
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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.

• 한국융합학회논문지
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• 제10권3호
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• pp.7-14
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• 2019

정보통신 기술의 발전으로 우리는 사무실에서 개인용 컴퓨터를 이용한 방식의 회사업무처리에서 벗어나 스마트 기기를 이용하여 언제 어디서나 편리하게 업무를 처리하는 스마트워크 환경을 경험하고 있다. 오피스 프로그램을 이용하여 작성한 문서를 이메일 서비스를 이용하여 주고받던 것을 스마트 기기를 이용하여 사진을 찍고 모바일 메신저로 전송하는 것으로 대신할 수 있다. 제조현장에서는 보안문서인 작업지시서를 스마트 기기를 이용하여 사진을 찍고 공유하는 것을 쉽게 볼 수 있다. 본 논문에서는 제조현장에서 근로자의 스마트 기기에 남겨지는 보안문서 이미지 파일을 찾아내고 삭제 처리하는 시스템을 제안한다. 제안한 시스템은 광학문자인식 기술을 이용하여 이미지의 글씨를 인식한 후 키워드화 시켜 일치하는 비율을 통해 보안문서 이미지 파일을 검색해내고 삭제 처리한다. 본 논문에서 제안한 시스템을 이용할 경우 중소기업에서도 효율성 높은 시스템을 구축하여 보안인식이 낮은 제조현장의 작업자들도 편리하게 보안문서 파일을 관리할 수 있다.