• Journal of Korea Society of Industrial Information Systems
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• v.10 no.2
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• pp.59-66
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• 2005

Recently, Ku and Chen(Ku-Chen) showed some problems in the password based remote user authentication scheme using smartcards proposed by Chien et al. and proposed an improvement from it. This paper shows some weaknesses in the Ku-Chen's scheme, especially the replay attacks, and proposes two authentication protocols to solve the problems in it. First of all, an authentication protocol using synchronized timestamps is proposed to solve the problem in the Ku-Chen's protocol. Then, a nonce-based authentication protocol is proposed to solve the inherent problems in the synchronized timestamp-based authentication protocols. The proposed authentication protocols support the advantages in the previous password-based authentication protocols and solve the problems in them effectively.

• The Transactions of the Korea Information Processing Society
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• v.6 no.5
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• pp.1143-1152
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• 1999

A Mobile computing environment is a new paradigm which provides users with the access to information irrespective of users' location. A transaction scheduling method for the mobile computing environment must be designed so that database consistency is maintained with considering the limited performance of mobile hosts and the narrow bandwidth of a wireless network. The scheduling method using a lock has some problems: the high message overhead between a server and a mobile host for maintaining a lock and the high abort ratio of the mobile transactions owing to violating the serializability when a mobile host uses a cache. So, in this paper, we propose an efficient transaction management method using timestamp to resolve these problems. The proposed method is used in the environment under which a mobile host uses a cache having two versions for each cached data item and a server maintains several versions for each data item. So, even though a mobile transaction is executed during several broadcasting interval, can be committed. As a result, the proposed method can improve the commit ratio of the mobile transactions by maintaining multiversion for each data item and does not require the additional message exchange to schedule transactions by using timestamp.

• Journal of Korea Multimedia Society
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• v.7 no.5
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• pp.633-639
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• 2004

The performance of optimistic concurrency control schemes which are generally used for Mobile computing is very sensitive to the transaction abort rate. Even if the abort probability can be reduced by back-shifting the timestamp from the time of requesting a commit, some transactions continuously perform unnecessary operations after the transactions accessed write-write conflicting data. In this paper, we propose an optimistic protocol that can abort the transactions during the execution phase by using the write notification approach. The proposed protocol enhances the performance of the optimistic concurrency control by reducing the unnecessary operations. In addition, we present a simulation study that compares our schemes with the timestamp based certification scheme. This study shows that our scheme outperforms the timestamp based certification scheme.

• Journal of information and communication convergence engineering
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• v.17 no.3
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• pp.174-184
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• 2019

In this study, we present a new scheme for smart education utilizing the concept of a blockchain for question sharing. A two-phase encryption technique for encrypting question papers (QSPs) is proposed. In the first phase, QSPs are encrypted using a timestamp, and in the second phase, previously encrypted QSPs are encrypted again using a timestamp, salt hash, and hash from the previous QSPs. These encrypted QSPs are stored in a blockchain along with a smart contract that helps the user to unlock the selected QSP. An algorithm is also proposed for selecting a QSP for the exam that randomly picks a QSP. Moreover, a timestamp-based lock is imposed on the scheme so that no one can decrypt the QSP before the allowed time. Security analysis is conducted to demonstrate the feasibility of the proposed scheme against different attacks. Finally, the effectiveness of the proposed scheme is demonstrated through implementation, and the superiority of the proposed scheme over existing schemes is proven through a comparative study based on different features.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.667-669
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• 2005

TCP Vegas나 FAST TCP는 RTT(Round Trip Time) 동안 실제 처리량(actual throughput)이 기대 처리량 (expected throughput)보다 특정 임계값보다 더 작으면 혼잡 상황으로 판단하고 송신측에서 내보내는 데이터 양을 감소시킴으로써 혼잡을 제어한다. 그러나 RTT 기반의 처리량(Throughput) 측정은 송수신 경로가 다를 경우 양방향 경로의 혼잡 상황을 구분하지 않는 문제점을 가지고 있다. 따라서 본 논문에서는 TCP Timestamp를 이용하여 양방향 혼잡 상황을 구분하여 혼잡을 제어하는 메커니즘을 제안한다. 그리고 제안한 방식에 대한 성능 분석을 위해 NS-2의 TCP Vegas를 수정하여 시뮬레이션한 결과를 제시한다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.1
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• pp.26-33
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• 2001

The proposed system was composed of pre-processor which was executing binary/high-pass filtering and post-processor which ranged from statistic data to prediction. In post-processor work, step one was filter process of image, step two was image recognition, and step three was destruction degree/time prediction. After these processing, we could predict image of the last destruction timestamp. This research was produced variation value according to growth of tree pattern. This result showed improved correction, when this research was applied image Processing. Pre-processing step of original image had good result binary work after high pas- filter execution. In the case of using partial discharge of the image, our research could predict the last destruction timestamp. By means of experimental data, this prediction system was acquired $\pm$3.2% error range.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.319-322
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• 2001

The proposed system was composed of pre-processor which was executing binary/high-pass filtering and post-processor which ranged from statistic data to prediction. In post-processor work, step one was filter process of image, step two was image recognition, and step three was destruction degree/time prediction. After these processing, we could predict image of the last destruction timestamp. This research was produced variation value according to growth of tree pattern. This result showed improved correction, when this research was applied image Processing. Pre-processing step of original image had good result binary work after high pass- filter execution. In the case of using partial discharge of the image, our research could predict the last destruction timestamp. By means of experimental data, this Prediction system was acquired ${\pm}$3.2% error range.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.2
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• pp.323-336
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• 2000

In order to achieve the deployment of B-ISDN services in a short time, B-ISDN is being combined with terrestrial ATM network and satellite network which covers a widespread service range. This paper analyzes and investigates several previously existent CDV compensation methods in order to compensate CDV arising from interfacing satellite TDMA and ATM. Specifically to supplement the problems of timestamp and cell number counting methods, new Partial Timestamp mechanism for CDV compensation is proposed. The CDV compensating efficiency of the proposed mechanism is analyzed and evaluated by simulations. It goes to show that Partial timestamps mechanism has many advantages in the aspect of the CDV compensation.

• Proceedings of the Korean Society of Computer Information Conference
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• 2019.07a
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• pp.391-392
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• 2019

본 논문에서는 타임스탬프의 위변조를 위한 안티포렌식의 도구로 사용되는 타임스탬프 변경도구들에 기능에 대하여 디지털 포렌식 관점에서 분석을 수행한다. 타임스탬프 변경도구들로써 수행할 수 있는 타임스탬프 변경작업의 범위와 특징을 찾아본다. NTFS파일시스템에서 사용하는 타임스탬프 변경도구들의 기능상의 분류는 그것들이 변경할 수 있는 타임스탬프 종류와 정밀도를 기준으로 정하고 그 도구들을 사용한 후에 기록된 타임스탬프의 특징들을 디지털 포렌식 관점에서 분석을 수행하기로 한다. 이 연구에서의 분류 형태 중 타입 I은 FileTouch.exe, SKTimeStamp, BulkFileChanger류의 도구들과 타입 II는 timestomp, 타입 III은 SetMACE로 분류하고 각 도구들을 사용한 후에 변경된 타임스탬프들의 특징을 살펴보기로 한다.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.5
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• pp.439-444
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• 2016

This paper proposes the technique to protect the privacy of those who uses Smart Tourism Service based on location. The proposed privacy protection technique (1) generates a shared private key, OTK(One Time Key) without information exchanging Users with a Tourism Server and provides Users and a Tourism Server with message confidentiality by encrypting data with the key, (2) concatenates users' ID, login time(timestamp), and randomly-generated nonce, generates OTK by hashing with a hash function, encrypts users' location information and query by using the operation of OTK and XOR and provides Users and a Tourism Server with message confidentiality by sending the encrypted result. (3) protects a message replay attack by adding OTK and timestamp. Therefore, this paper not only provides data confidentiality and users' privacy protection but also guarantees the safety of location information and behavior pattern data.