• 한국정보과학회논문지:데이타베이스
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• 제28권2호
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• pp.253-265
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• 2001

본 논문은 이동 컴퓨팅 환경에서 연속 부분 질의의 효과적인 처리를 위한 캐시 관리 방안을 제안한다. 연속 부분 부합 질의란 질의의 결과가 클라이언트의 메모리에 일관성을 유지하면서 지속되는 부분 부합 질의이다. 기존의 이동 환경을 위한 캐시 관리 기법은 레코드 식별자를 기반으로 하는 방법들이다. 하지만, 부분 부합 질의는 데이터의 내용을 기반으로 탐색하는 질의이기 때문에 이러한 레코드 식별자를 기반으로 하는 방법들은 캐시 관리를 효율적으로 할 수 없다. 제안하는 캐시 관리 방안에서는, 이동 클라이언트의 캐시 상태를 프레디킷(predicate)으로 기술하고, 서버가 캐시 관리를 위해 클라이언트에게 방송하는 캐시 무효화 정보, 즉 Cache Invalidation Reports(CIR)을 프레디킷으로 구성한다. 이러한 프레디킷 표현을 사용하여, 일련의 캐시 관리 기법-억지 방법(the brute-force method), 빼기 방법(the subtraction method), 교차 방법(the intersection method)-들을 제안한다. 그리고, 제안하는 방법의 계산 복잡도를 계산한다.

• 한국콘텐츠학회논문지
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• 제17권7호
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• pp.571-578
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• 2017

사용자가 스마트 기기 및 개인 PC를 통해 정보 시스템에 접근하기 위해서는 사용자 인증을 통한 정당한 사용자임을 증명해야한다. 이때 사용되는 사용자 인증 기술에는 ID/PW 기반 인증기술, OTP(One-Time-Password), 인증서, 보안카드, 지문인식 등 다양하다. 그 중에서 ID/PW 기반 인증기술은 사용자에게 익숙하지만 무작위 대입공격, 키로깅, 사전공격 등의 패스워드 공격에 취약하며 이러한 공격에 대응하기 위해 사용자는 복잡한 패스워드 조합 규정에 따라 주기적으로 패스워드를 변경해야한다. 본 논문에서는 기존 ID/PW 기반 인증 기술보다 보안성을 높이면서 패스워드를 사용하지 않고 스마트폰의 USIM 정보를 이용한 사용자 인증 시스템을 설계 및 구현하였다.

• International Journal of Internet, Broadcasting and Communication
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• 제8권1호
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• pp.7-18
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• 2016

Several authentication methods have been developed to make use of tokens in the mobile networks and smart payment systems. Token used in smart payment system is genearated in place of Primary Account Number. The use of token in each payment transaction is advantageous because the token authentication prevents enemy from intercepting credit card number over the network. Existing token authentication methods work together with the cryptogram, which is computed using the shared key that is provisioned by the token service provider. Long lifetime and repeated use of shared key cause potential brawback related to its vulnerability against the brute-force attack. This paper proposes a per-transaction shared key mechanism, where the per-transaction key is agreed between the mobile device and token service provider for each smart payment transaction. From server viewpoint, per-transaction key list is easy to handle because the per-transaction key has short lifetime below a couple of seconds and the server does not need to maintain the state for the mobile device. We analyze the optimum size of the per-transaction shared key which satisfy the requirements for transaction latency and security strength for secure payment transactions.

• 디지털산업정보학회논문지
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• 제7권3호
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• pp.85-95
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• 2011

Smart phones, greatly expanding in the recent mobile market, are equipped with various features compared to existing feature phones and provide the conveniences to in several ways. The camera, one of the features of a smartphone, creates the digital contents, such photos and videos, and plays a role for the media which transmits information, such as video calls and bar code reader. QR-Code recognition is also one of the camera features. It contains a variety of information in two-dimensional bar code type in matrix format, and makes it possible to obtain the information by using smart phones. This paper analyzes the method of QR-Code recognition, password method-the existing user-authentication technique, smart card, biometrics and voice recognition and so on and thenn designs a new user-authentication technique. The proposed user-authentication technique is the technique in which QR-Code, which can be simply granted is read by smart phones and transmitted to a server, for authentication. It has the advantages in view that it will simply the process of authentication and conteract the disadvantages, such as brute force attack, man-inthe-middle attack, and keyboard hacking, which may occur in other authentication techniques.

• 한국인터넷방송통신학회논문지
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• 제12권1호
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• pp.123-132
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• 2012

이 논문은 콘콜릭 테스팅을 특화한 목적 지향 테스트 데이터 생성 방법을 제안한다. GCT(Goal-oriented Concolic Testing)라 불리는 제안된한 특정 목표를 실행하는 테스트 입력을 생성한다. 콘콜릭 테스팅은 요구되는 테스트 입력을 발견할 때 까지 모든 가능한 경로 공간을 탐색하는 브루트 포스 방식으로 간주할 수 있다. 대조적으로 GCT는 자료 흐름 정보를 활용하여 목표가 실행되기 위해 먼저 수행되어야 하는 문장들을 식별하여 탐색되는 프로그램 경로의 수를 제한한다. 플래그 변수가 있는 실험을 통해 GCT의 효과성을 보인다.

• ETRI Journal
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• 제33권6호
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• pp.935-944
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• 2011

As a growing number of individuals are exposed to surveillance cameras, the need to prevent captured videos from being used inappropriately has increased. Privacy-related information can be protected through video encryption during transmission or storage, and several algorithms have been proposed for such purposes. However, the simple way of evaluating the security by counting the number of brute-force trials is not proper for measuring the security of video encryption algorithms, considering that attackers can devise specially crafted attacks for specific purposes by exploiting the characteristics of the target video codec. In this paper, we introduce a new attack for recovering contour information from encrypted H.264 video. The attack can thus be used to extract face outlines for the purpose of personal identification. We analyze the security of previous video encryption schemes against the proposed attack and show that the security of these schemes is lower than expected in terms of privacy protection. To enhance security, an advanced block shuffling method is proposed, an analysis of which shows that it is more secure than the previous method and can be an improvement against the proposed attack.

• 대한의용생체공학회:의공학회지
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• 제26권1호
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• pp.23-30
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• 2005

3D virtual endoscopy has been used as an alternative non-invasive procedure for visualization of hollow organs. However, due to computational complexity, this is a time-consuming procedure. In this paper, we propose a fast volume rendering algorithm based on perspective ray casting for virtual endoscopy. As a pre-processing step, the algorithm divides a volume into hierarchical blocks and classifies them into opaque or transparent blocks. Then, in the first step, we perform ray casting only for sub-sampled pixels on the image plane, and determine their pixel values and depth information. In the next step, by reducing the sub-sampling factor by half, we repeat ray casting for newly added pixels, and their pixel values and depth information are determined. Here, the previously obtained depth information is utilized to reduce the processing time. This step is recursively performed until a full-size rendering image is acquired. Experiments conducted on a PC show that the proposed algorithm can reduce the rendering time by 70- 80% for bronchus and colon endoscopy, compared with the brute-force ray casting scheme. Using the proposed algorithm, interactive volume rendering becomes more realizable in a PC environment without any specific hardware.

• Journal of Multimedia Information System
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• 제8권3호
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• pp.147-158
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• 2021

Versatile Video Coding (VVC) is the latest video coding standard developed by Joint Video Exploration Team (JVET). In VVC, the quadtree plus multi-type tree (QT+MTT) structure of coding unit (CU) partition is adopted, and its computational complexity is considerably high due to the brute-force search for recursive rate-distortion (RD) optimization. In this paper, we aim to reduce the time complexity of inter-picture prediction mode since the inter prediction accounts for a large portion of the total encoding time. The problem can be defined as classifying the split mode of each CU. To classify the split mode effectively, a novel convolutional neural network (CNN) called multi-level tree (MLT-CNN) architecture is introduced. For boosting classification performance, we utilize additional information including inter-picture information while training the CNN. The overall algorithm including the MLT-CNN inference process is implemented on VVC Test Model (VTM) 11.0. The CUs of size 128×128 can be the inputs of the CNN. The sequences are encoded at the random access (RA) configuration with five QP values {22, 27, 32, 37, 42}. The experimental results show that the proposed algorithm can reduce the computational complexity by 11.53% on average, and 26.14% for the maximum with an average 1.01% of the increase in Bjøntegaard delta bit rate (BDBR). Especially, the proposed method shows higher performance on the sequences of the A and B classes, reducing 9.81%~26.14% of encoding time with 0.95%~3.28% of the BDBR increase.

• 한국멀티미디어학회논문지
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• 제22권6호
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• pp.676-683
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• 2019

Wireless Sensor Networks (WSNs) consist of multiple tiny and power constrained sensors which use radio frequencies to carry out sensing in a designated sensor area. To effectively design and implement reliable WSN, it is critical to consider models, protocols, and algorithms that can optimize energy consumption of all the sensor nodes with optimal amount of packet delivery. It has been observed that deploying a single sink node comes with numerous challenges especially in a situation with high node density and congestion. Sensor nodes close to a single sink node receive more transmission traffic load compared to other sensors, thus causing quick depletion of energy which finally leads to an energy hole and sink hole problems. In this paper, we proposed the use of multiple energy efficient sink nodes with brute force technique under optimized parameters to improve on the number of packets delivered within a given time. Simulation results not only depict that, deploying N sink nodes in a sensor area has a maximum limit to offer a justifiable improvement in terms of packet delivery ratio but also offers a reduction in End to End delay and reliability in case of failure of a single sink node, and an improvement in the network lifetime rather than deploying a single static sink node.

• 한국컴퓨터정보학회논문지
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• 제24권1호
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• pp.137-143
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• 2019

As the performance of computers increases, the use of deep learning, which has faced technical limitations in the past, is becoming more diverse. In many fields, deep learning has contributed to the creation of added value and used on the bases of more data as the application become more divers. The process for obtaining a better performance model will require a longer time than before, and therefore it will be necessary to find an optimal model that shows the best performance more quickly. In the artificial neural network modeling a tuning process that changes various elements of the neural network model is used to improve the model performance. Except Gride Search and Manual Search, which are widely used as tuning methods, most methodologies have been developed focusing on heuristic algorithms. The heuristic algorithm can get the results in a short time, but the results are likely to be the local optimal solution. Obtaining a global optimal solution eliminates the possibility of a local optimal solution. Although the Brute Force Method is commonly used to find the global optimal solution, it is not applicable because of an infinite number of hyper parameter combinations. In this paper, we use a statistical technique to reduce the number of possible cases, so that we can find the global optimal solution.