• 한국컴퓨터정보학회논문지
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• 제19권10호
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• pp.81-89
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• 2014

본 논문에서는 서버로의 중복파일을 업로드 방지를 위하여 SA 해쉬 알고리즘을 제안하고 이를 이용하여 서버 시스템을 설계한다. SA 해쉬 값으로 동일한 파일이 서버에 있는 지 검사하고 존재한다면 클라이언트에게 업로드를 받지 않고 기존 파일을 이용하는 방법으로 효율적인 시스템 설계를 할 수 있게 되는 것이다. 중복파일 검사를 할 수 있는 SA 해쉬 알고리즘은 출력하고자 하는 비트 수 n을 한 블록으로 하고 원본 파일을 블록 단위로 나누게 된다. 원본 파일의 mod i 비트와 출력 해쉬 값의 i 비트를 XOR 연산을 하게 된다. 이렇게 반복적으로 원본 파일 길이까지 XOR연산을 하는 것이 SA 해쉬 알고리즘의 메인 루틴이다. 기존 해쉬 함수인 MD5, SHA-1, SHA-2보다 중복파일 업로드 방지 서버 시스템에 적합한 해쉬 함수인 SA 해쉬 알고리즘을 통해 시간 및 서버 스토리지 용량의 절약을 도모할 수 있다.

• 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.

• 한국정보통신학회논문지
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• 제22권3호
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• pp.557-567
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• 2018

현재 디스크에 파일을 암호화하여 저장하기 위한 다양한 파일 암호화 솔루션이 존재한다. 하지만 기존의 파일 암호화 솔루션은 암호화 및 복호화를 파일 혹은 디렉터리 단위로 일괄되게 처리한다. 본 논문에서는 파일의 부분 암호화를 지원하는 시스템 호출을 제안한다. 파일 데이터의 암호화를 원하는 부분에서 사용자는 시스템 호출 인터페이스로 암호화 정보를 설정한다. 그다음 파일 데이터를 쓰면 설정된 내용으로 데이터가 암호화되어 저장된다. 또한 복호화 정보를 설정한 뒤 파일 데이터를 읽어오면, 설정된 정보가 적용되어 필요한 부분만을 복호화 한다. 제안된 시스템 호출을 위해 검사, 관리, 암호화, 복호화, HMAC 모듈이 필요한 시스템 호출에 따라 구성되며, 이는 리눅스 환경에서 구현되었다. 또한 구현된 시스템 호출의 동작을 개발 보드에서 검증하였으며, 그 수행 속도를 측정하여 성능을 분석하였다.

• Restorative Dentistry and Endodontics
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• 제28권1호
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• pp.64-71
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• 2003

The purpose of this study was to compare the initial apical file(IAF) first Ole that fits to the apex in each canal before and after early flaring to analyze if the size of file to fit to the apex would increase after flaring. Eighty anterior teeth with complete apical formation and patent foramens were selected. The samples were randomly divided into 4 groups(GG, OS, GT, PT Group) of 20 teeth each. A file was fit to the apex in each canal and that size recorded. Radicular flaring were completed using different types of instruments. After flaring a file was again fit to the apex in the same manner as before and its size recorded. The results of this study were as follows : 1. The mean diameter of IAF before flaring(file diameters in $mm{\times}10^{-2}$) was $19.81{\pm}8.32$ before and $25.94{\pm}9.21$ after(p<0.05). 2. The increase in diameter of IAF was approximately one file size for all groups. 3. Ranking of increasing diameter of IAF were GG>CT>OS>PT group. There was a statistically significant difference between before and after flaring(p<0.05). 4 Ranking of the time for flaring were GG>GT>OS>PT group. There was a statistically significant difference between GG group and other groups(p<0.05). 5. In the case without change of IAF diameter, they showed decrease in force after flaring when IAF was pulled out from root canal(p<0.05). This study suggested that early radicular flaring increases the file size that is snug at the apex, and awareness of that difference gives the clinician a better sense of canal size. Early flaring of the canal provides better apical size information and with this awareness, a better decision can be made concerning the appropriate final diameter needed for complete apical shaping.

• 정보보호학회논문지
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• 제24권2호
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• pp.319-325
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• 2014

스마트폰이나 태블릿 PC 사용이 보급화 되면서 장소에 구애받지 않고 실시간으로 문서의 생성과 편집이 일어나고 있다. 이처럼 학교나 회사에서 업무처리 방법의 한 부분을 차지하고 있는 문서 파일들을 분석하여 데이터가 입력되거나 편집된 흐름을 추적할 수 있다면 디지털 포렌식 수사에서 증거 자료로 활용될 수 있을 것이다. 대표적인 문서 프로그램으로 Microsoft 사의 Office 시리즈를 꼽을 수 있다. MS Office 프로그램은 복합 문서 파일 형식(Compound Document File Format)을 사용하는 97-2003 버전, OOXML 파일 형식(Office Open XML File Format)을 사용하는 2007-현재 버전까지 두 가지 파일 형식으로 구성된다. 지금까지 연구된 MS 파일에 대한 디지털 포렌식 분석 방법은 파일에 은닉된 정보를 탐지하거나 문서의 속성 정보를 통해 위변조 여부를 판단하는 것이었다. 본 논문에서는 디지털 포렌식 관점에서 MS 엑셀 파일에 텍스트 셀이 입력된 순서를 분석하여 문서의 입력 순서와 마지막으로 수정한 셀을 파악하는 방법을 연구하였다.

• Restorative Dentistry and Endodontics
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• 제38권4호
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• pp.222-226
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• 2013

Objectives: The aim of this study was to assess the influence of operator experience level on the lifespan of the WaveOne Primary file (Dentsply Maillefer, Ballaigues, Switzerland) in extracted teeth. Materials and Methods: Moderately curved canals of extracted maxillary and mandibular molars were randomly distributed into 2 groups: experienced and inexperienced operators. Ten files were allocated to each group (n = 10). Each canal was prepared until the working length was reached, and the same file was used to prepare additional canals until it separated. The number of canals prepared before file separation was recorded. The fragment length of each file was measured, and the location of the fragment in the canal was determined. Data were statistically analysed using the independent 2-sample t-test. Results: The 2 operators prepared a total of 324 moderately curved canals of maxillary and mandibular molars. There was no significant intergroup difference in the mean number of canals prepared (p = 0.27). The average lifespan of the WaveOne Primary file was 17.1 and 15.3 canals, and the longest lifespan was 25 and 20 canals, when used by experienced and inexperienced operators, respectively. There were no statistically significant intergroup differences in separated fragment length and location. Conclusions: Within the limitations of this study, operator experience level appears to have no effect on the lifespan of the WaveOne Primary file in preparation of moderately curved canals. Single teeth with multiple canals can be prepared safely even by a novice operator by using a single file.

• 정보보호학회논문지
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• 제27권6호
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• pp.1271-1280
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• 2017

런타임 실행 압축 기술을 이용하는 안드로이드 패커(packer) 서비스는 덱스클래스로더(DexClassLoader)를 이용하여 원본 어플리케이션으로 전환한다. 하지만 덱스클래스로더의 API 인터페이스는 로드할 덱스(Dalvik EXcutable)의 경로와 컴파일 된 파일의 경로를 입력 받으므로 원본이 파일시스템에 드러나는 문제점이 있다. 따라서 해당 API를 패커 서비스에 그대로 사용하는 것은 안전하지 않다. 본 논문에서는 이 문제를 해결하기 위해 덱스클래스로더 API의 컴파일 흐름과 로드 흐름을 변경하여 해결하였다. 이 변경된 실행 흐름으로 인해 컴파일 된 파일을 암호화하여 파일 시스템에 두거나 메모리에만 존재하도록 하고, 이후 로드할 때 복호화 또는 치환을 하여 원본 앱 전환을 가능하게 한다. 제안하는 기법을 통해 원본 파일이 파일시스템에 노출되지 않음으로써 패커의 안정성이 올라갈 것이라 예상한다.

• Restorative Dentistry and Endodontics
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• 제40권2호
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• pp.123-127
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• 2015

Objectives: Glide path preparation is recommended to reduce torsional failure of nickel-titanium (NiTi) rotary instruments and to prevent root canal transportation. This study evaluated whether the repetitive insertions of G-files to the working length maintain the apical size as well as provide sufficient lumen as a glide path for subsequent instrumentation. Materials and Methods: The G-file system (Micro-Mega) composed of G1 and G2 files for glide path preparation was used with the J-shaped, simulated resin canals. After inserting a G1 file twice, a G2 file was inserted to the working length 1, 4, 7, or 10 times for four each experimental group, respectively (n = 10). Then the canals were cleaned by copious irrigation, and lubricated with a separating gel medium. Canal replicas were made using silicone impression material, and the diameter of the replicas was measured at working length (D0) and 1 mm level (D1) under a scanning electron microscope. Data was analysed by one-way ANOVA and post-hoc tests (p = 0.05). Results: The diameter at D0 level did not show any significant difference between the 1, 2, 4, and 10 times of repetitive pecking insertions of G2 files at working length. However, 10 times of pecking motion with G2 file resulted in significantly larger canal diameter at D1 (p < 0.05). Conclusions: Under the limitations of this study, the repetitive insertion of a G2 file up to 10 times at working length created an adequate lumen for subsequent apical shaping with other rotary files bigger than International Organization for Standardization (ISO) size 20, without apical transportation at D0 level.

• Journal of Information Processing Systems
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• 제2권3호
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• pp.147-152
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• 2006

NAND flash memory-based embedded systems are becoming increasingly common. These embedded systems have to provide a fast boot time. In this paper, we have designed and proposed a flash file system for embedded systems that require fast booting. By using a Flash Image Area, which keeps the latest flash memory information such as types and status of all blocks, the file system mounting time can be reduced significantly. We have shown by experiments that our file system outperforms YAFFS and RFFS.

• ETRI Journal
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• 제39권6호
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• pp.820-831
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• 2017

File systems and applications try to implement their own update protocols to guarantee data consistency, which is one of the most crucial aspects of computing systems. However, we found that the storage devices are substantially under-utilized when preserving data consistency because they generate massive storage write traffic with many disk cache flush operations and force-unit-access (FUA) commands. In this paper, we present DJFS (Delta-Journaling File System) that provides both a high level of performance and data consistency for different applications. We made three technical contributions to achieve our goal. First, to remove all storage accesses with disk cache flush operations and FUA commands, DJFS uses small-sized NVRAM for a file system journal. Second, to reduce the access latency and space requirements of NVRAM, DJFS attempts to journal compress the differences in the modified blocks. Finally, to relieve explicit checkpointing overhead, DJFS aggressively reflects the checkpoint transactions to file system area in the unit of the specified region. Our evaluation on TPC-C SQLite benchmark shows that, using our novel optimization schemes, DJFS outperforms Ext4 by up to 64.2 times with only 128 MB of NVRAM.