• The KIPS Transactions:PartA
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• v.17A no.2
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• pp.63-72
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• 2010

Recently, the need for multimedia devices, such as digital TV, and camcorder has increased. These devices provide many services on multimedia files such as playing, recording, and editing. Throughout these services, in case of storing edited large-scaled multimedia files, existing file system have several capability problems that are taking too much time and requiring disk I/O. In this paper, we propose the use of Linux Ext2 file system based 'Block-Link file (BL-file) system' in order to solve these problems. For the BL-file system, when editing and storing large-scaled files, there is no data input or output but only modification of the metadata. Additionally, by sharing data blocks between multimedia files, we can save disk spaces. Moreover, because the managing of data block sharing information is more convenient than the existing FWAE technique, we can lessen system overhead. The BL-file system is based on Ext2 file system and implemented in a Linux environment, and the usefulness of the proposed technique is validated by applying the Linux multimedia file-editing tool 'Avidemux'.

• KIPS Transactions on Computer and Communication Systems
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• v.2 no.8
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• pp.349-356
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• 2013

As various features of the smartphone have been used, a lot of information have been stored in the smartphone, including the user's personal information. However, a frequent update of the operating system and applications may cause a loss of data and a risk of missing important personal data. Thus, the importance of data backup is significantly increasing. Many users employ the backup feature to store their data securely. However, in the point of forensic view these backup files are considered as important objects for investigation when issued hiding of smartphone or intentional deletion on data of smartphone. Therefore, in this paper we propose a scheme that analyze structure and restore data for Kies backup files of Samsung smartphone which has the highest share of the smartphone in the world. As the experimental results, the suggested scheme shows that the various types of files are analyzed and extracted from those backup files compared to other tools.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.1
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• pp.205-214
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• 2019

Android uses app cache files to improve app execution performance. However, this optimization technique may raise security issues that need to be examined. In this paper, we present a practical design of "Android app cache manipulation attack" to intentionally modify the cache files of a target app, which can be misused for stealing personal information and performing malicious activities on target apps. Even though the Android framework uses a checksum-based integrity check to protect app cache files, we found that attackers can effectively bypass such checks via the modification of checksum of the target cache files. To demonstrate the feasibility of our attack design, we implemented an attack tool, and performed experiments with real-world Android apps. The experiment results show that 25 apps (86.2%) out of 29 are vulnerable to our attacks. To mitigate app cache manipulation attacks, we suggest two possible defense mechanisms: (1) checking the integrity of app cache files; and (2) applying anti-decompilation techniques.

• The Journal of the Korea Contents Association
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• v.21 no.5
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• pp.129-138
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• 2021

Today we are getting a lot of information and various activities on our website through the internet. These websites are maintained by individuals or by website specialists. The basic method is to change the files that make up the running website. Changing the entire file in this process takes a long time and changes the files that do not need to be changed, so the efficiency is greatly reduced. When only the files that need to be changed are changed, it takes a lot of effort as a person must manually search each path to check the files and change the files one by one. To solve this problem, automatic distribution systems were developed. Additional resources and learning are required, resulting in additional cost, time and labor. Therefore, in this paper, we propose an automatic update system to minimize resource consumption by using the resources and technologies of the existing website. The proposed system does not require learning new skills. This aims to improve reliability and reduce time compared to human work.

• KIPS Transactions on Computer and Communication Systems
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• v.11 no.12
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• pp.429-436
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• 2022

Temporary files are generated when the Hash Join is performed on tables larger than the memory. During the join process, each temporary file is deleted sequentially after it completes the I/O operations. This paper reveals for that the fallocate system call and file deletion-related trim options significantly impact the hash join performance when temporary files are managed on SSDs rather than hard disks. The experiment was conducted on various commercial and research SSDs using PostgreSQL, a representative open-source database. We find that it is possible to improve the join performance up to 3 to 5 times compared to the default combination depending on whether fallocate and trim options are used for temporary files. In addition, we investigate the write amplification and trim command overhead in the SSD according to the combination of the two options for temporary files.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.34 no.1
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• pp.71-82
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• 2024

With the advancement of information and communication technology (ICT), the use of electronic document types such as PDF, MS Office, and HWP files has increased. Such trend has led the cyber attackers increasingly try to spread malicious documents through e-mails and messengers. To counter such attacks, AI-based methodologies have been actively employed in order to detect malicious document files. The main challenge in detecting malicious HWP(Hangul Word Processor) files is the lack of quality dataset due to its usage is limited in Korea, compared to PDF and MS-Office files that are highly being utilized worldwide. To address this limitation, data augmentation have been proposed to diversify training data by transforming existing dataset, but as the usefulness of the augmented data is not evaluated, augmented data could end up harming model's performance. In this paper, we propose an effective semi-supervised learning technique in detecting malicious HWP document files, which improves overall AI model performance via quantifying the utility of augmented data and filtering out useless training data.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.34 no.2
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• pp.193-206
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• 2024

In tandem with the advancements in the digital era, the significance of digital data has escalated, necessitating an increased focus on digital forensics investigations. However, the process of collecting and analyzing digital evidence faces significant challenges, such as the unidentifiability of damaged files due to issues like media corruption and anti-forensic techniques. Moreover, the technological limitations of existing tools hinder the recovery of damaged files, posing difficulties in the evidence collection process. This paper aims to propose solutions for the recovery of corrupted MS Office files commonly used in digital data creation. To achieve this, we analyze the structure of MS Office files in the OOXML format and present a novel approach to overcome the limitations of current recovery tools. Through these efforts, we aim to contribute to enhancing the quality of evidence collection in the field of digital forensics by efficiently recovering and identifying damaged data.

• IEMEK Journal of Embedded Systems and Applications
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• v.7 no.6
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• pp.345-351
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• 2012

In traditional target-based data deduplication system, all of the files should be chunked and compared for reducing duplicated data blocks. One of the critical problem of this system arises as the number of files are increasing. The system suffers from computational delay for calculating hash value and processing metadata for handling each file. To overcome this problem, in this paper, we propose a novel data deduplication system using logical partition of storage system. The system applies data deduplication scheme to each logical partition not each file. Experiment result shows that the proposed system is more efficient compared with traditional deduplication scheme where the logical partition is full of files by 50% in terms of deduplication capacity and processing time.

• Journal of the Korean Operations Research and Management Science Society
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• v.21 no.1
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• pp.31-50
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• 1996

In this paper we prescribe a replication server scheme with an algorithm DRF (Differential Refresh File) to refresh multiple materialized views and replicas in distributed environments. Before sending relevant tuples in server sites to client sites, an effective tuple reduction scheme is developed as a preprocessor to reduce the transmission cost. Because it utilizes differential files with out touching base relations, the DRF scheme can help to minimize the number of locks, which enhances the system's performance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.5 s.248
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• pp.488-495
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• 2006

The demand for the use of 3D CAD data over the Internet environment has been increased. However, transmission of 3D CAD data has delayed the communication effectiveness because of the CAD data size. Lightweight CAD file design methodology is required for rapid transmission in the distributed environment. In this paper, to derive lightweight CAD files from commercial CAD systems, a file translation system producing a native file is constructed first by using the InterOp and API of the ACIS kernel. Using the B-rep model and mesh data extracted from the native file, the lightweight CAD file with topological information is constructed as a binary file. Since the lightweight CAD file retains topological information, it is applied to the dimensional verification, digital mock-ups and visualization of CAD files. Effectiveness of the proposed lightweight CAD file is confirmed through various case studies.