• Journal of Welding and Joining
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• 제18권2호
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• pp.105-111
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• 2000

The hydrogen attack characteristics of 3Cr-1Mo-V steel as simulated weld heat affected state were studied in this paper. The hydrogen attack susceptibility was evaluated by the ratios of Charpy impact absorbed energy at 0℃({TEX}$vE_{0} {HA}_/vE_{0}${/TEX}) and reduction of area by tensile test({TEX}$RA_{HA}/RA${/TEX}) before and after exposure to hydrogen at 600℃ under 450kgf/㎠ for 300hr. The values of {TEX}$vE_{0} {HA}_/vE_{0}${/TEX} and {TEX}$RA_{HA}/RA${/TEX} were aggravated as the peak temperature of the simulated heat affected zone(HAZ) raised. These results were due to the increase of the possession of bubbles along the grain boundaries, which were resulted in the reduction of grain boundary area to be precipitated carbides due to grain coarsening and the carbon dissolved in the martensite-austenite constituent near by the prior austenite grain boundary. The possession ratio of methane bubbles formed along prior austenite grain boundaries were increased with raising the peak temperature.

• 한국멀티미디어학회논문지
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• 제17권8호
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• pp.988-994
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• 2014

Software Defined Network (SDN) is a new technology in computer network area which enables user to centralize control plane. The security issue is important in computer network to protect system from attackers. SYN flooding attack is one of Distributed Denial of Service attack methods which are popular to degrade availability of targeted service on Internet. There are many methods to protect system from attackers, i.e. firewall and IDS. Even though firewall is designed to protect network system, but it cannot mitigate DDoS attack well because it is not designed to do so. To improve performance of DDOS mitigation we utilize another mechanism by using SDN technology such as OpenFlow and sFlow. The methodology of sFlow to detect attacker is by capturing and sum cumulative traffic from each agent to send to sFlow collector to analyze. When sFlow collector detect some traffics as attacker, OpenFlow controller will modify the rule in OpenFlow table to mitigate attacks by blocking attack traffic. Hence, by combining sum cumulative traffic use sFlow and blocking traffic use OpenFlow we can detect and mitigate SYN flooding attack quickly and cheaply.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권4호
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• pp.805-821
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• 2011

Wireless Sensor Networks (WSNs) are rapidly emerging because of their potential applications available in military and civilian environments. Due to unattended and hostile deployment environments, shared wireless links, and inherent resource constraints, providing high level security services is challenging in WSNs. In this paper, we revisit various security attack models and analyze them by using a well-known standard notation, Unified Modeling Language (UML). We provide a set of UML collaboration diagram and sequence diagrams of attack models witnessed in different network layers: physical, data/link, network, and transport. The proposed UML-based analysis not only can facilitate understanding of attack strategies, but can also provide a deep insight into designing/developing countermeasures in WSNs.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.132-137
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• 2008

A failure analysis of ammonia converter which suffered hydrogen attack in two years since its initial operating time was presented. It is constructed from 2.25 Cr.1 Mo steel. Analysis showed that the failure on closing seam weld joint was due to local improper post weld heat treatment (PWHT). Improper PWHT can introduce high residual stresses in thick-walled pressure vessel. High residual stress level in weld joint is very prone to hydrogen attack for any components which are operating in hydrogen gas environment. The repair procedures based on the principle to decrease the residual stress then proposed. The repair was controlled very carefully by applying several nondestructive tests in the each stage of repair. To assure the successful of the proposed repair, after one year since repair time, high temperature ultrasonic and TOFD methods were applied on-stream to this equipment in order to evaluate its post repair condition. The two methods showed good results on the repaired area.

• 한국통신학회논문지
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• 제37권4C호
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• pp.290-296
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• 2012

본 논문에서는 U-헬스케어 의료 정보 환경을 위한 무선 인체 영역 네트워크(WBAN) 기반의 실용적인 인증 시스템을 제안한다. 제안한 인증 시스템은 AES와 같은 대칭키 암호 시스템을 기반으로 동작하며 데이터 기밀성, 데이터 인증, 데이터 무결성 등의 보안성을 보장할 뿐만 아니라 타임스탬프 기술을 적용하여 재전송 공격 방지 및 센서 노드, 마스터 노드, 베이스 스테이션, 의료 서버 사이에 안전한 인증을 수행하도록 설계하였다.

• 정보보호학회논문지
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• 제20권2호
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• pp.145-156
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• 2010

최근에 TV와 인터넷 등의 통신 기술의 발달로 인하여 인터넷망에 멀티미디어 콘텐츠를 융합한 IPTV 서비스가 증가하고 있다. 그러나 사용자가 임의의 장소에서 서비스를 제공받을 때 기존 IPTV 서비스는 이동 사용자의 가입 유 무 및 인증 과정이 복잡하여 불법적인 사용자의 증가와 서비스 지연 등의 통신 장애가 발생하는 문제점이 있다. 이 논문에서는 IPTV 서비스를 불법적으로 도용하는 사용자를 효율적으로 추출하여 무선 구간에서 많이 발생하는 복제 공격을 예방하기 위한 통신 보안 메커니즘을 제안한다. 제안 메커니즘은 사용자들이 사용하는 RFID 태그에 스마트 카드를 융합하여 플러그 앤 플레이 기능을 수행할 수 있도록 RFID-USB 장비에 보안 에이전트를 두어 키 초기화 과정, 상호 인증과정, 키 분배과정 등을 수행한다. 또한, 제안 메커니즘은 사용자가 RFID-USB 범위안에 접근할 때마다 RFID-USB에서 생성한 랜덤수와 이동 사용자의 ID를 해쉬 함수에 적용하여 해쉬된 토근값을 업데이트함으로써 무선 구간에서 자주 발생하는 재사용 공격과 man-in-the-middle 공격을 예방하고 있다.

• 한국전산유체공학회지
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• 제11권3호
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• pp.22-27
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• 2006

Flow around a guided missile in high maneuver, i.e. at a high angle of attack, shows complex phenomena. It is well known that even in geometrically symmetric conditions the flow around a missile at high angles of attack can generate unexpected large side forces and yaw moments due to asymmetric vortices. In this paper, a CFD code (FLUENT) based on the Navier-Stokes equations was used for the numerical analysis to find a suitable numerical mechanism for generation of asymmetric vortices. It is shown that a numerical technique of applying different surface roughness to a specific area of the missile nose surface gives the best fit in comparison with the experimental results. In addition, a numerical investigation of variations of side forces and pressure distributions with angle of attack and roll angle was conducted for the purpose of identifying the source of vortex asymmetries.

• International Journal of Computer Science & Network Security
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• 제23권9호
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• pp.111-119
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• 2023

Mobile Ad-hoc Network (MANET) is an infrastructure-less network that can configure itself without any centralized management. The topology of MANET changes dynamically which makes it open for new nodes to join it easily. The openness area of MANET makes it very vulnerable to different types of attacks. One of the most dangerous attacks is the Resource Consumption Attack (RCA). In this type of attack, the attacker consumes the normal node energy by flooding it with bogus packets. Routing in MANET is susceptible to RCA and this is a crucial issue that deserves to be studied and solved. Therefore, the main objective of this paper is to study the impact of RCA on two routing protocols namely, Ad hoc On-Demand Distance Vector (AODV) and Dynamic Source Routing (DSR); as a try to find the most resistant routing protocol to such attack. The contribution of this paper is a new RCA model (RCAM) which applies RCA on the two chosen routing protocols using the NS-2 simulator.

• 한국컴퓨터정보학회논문지
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• 제22권9호
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• pp.65-71
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• 2017

This paper proposes a smart phone authentication method based on user's behavior and habit that is an authentication method against shoulder surfing attack and brute force attack. As smart phones evolve not only storage of personal data but also a key means of financial services, the importance of personal information security in smart phones is growing. When user authentication of smart phone, pattern authentication method is simple to use and memorize, but it is prone to leak and vulnerable to attack. Using the features of the smart phone pattern method of the user, the pressure applied when touching the touch pad with the finger, the size of the area touching the finger, and the time of completing the pattern are used as feature vectors and applied to user authentication security. First, a smart phone user models and stores three parameter values as prototypes for each section of the pattern. Then, when a new authentication request is made, the feature vector of the input pattern is obtained and compared with the stored model to decide whether to approve the access to the smart phone. The experimental results confirm that the proposed technique shows a robust authentication security using subjective data of smart phone user based on habits and behaviors.

• 정보처리학회논문지:컴퓨터 및 통신 시스템
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• 제11권1호
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• pp.23-34
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• 2022

네트워크 기술의 발달로 그 적용 영역 또한 다양해지면서 다양한 목적의 프로토콜이 개발되고 트래픽의 양이 폭발적으로 증가하게 되었다. 따라서 기존의 전통적인 스위칭, 라우팅 방식으로는 네트워크 관리자가 망의 안정성과 보안 기준을 충족하기 어렵다. 소프트웨어 정의 네트워킹(SDN)은 이러한 문제를 해결하기 위해 제시된 새로운 네트워킹 패러다임이다. SDN은 네트워크 동작을 프로그래밍하여 효율적으로 네트워크를 관리할 수 있도록 한다. 이는 네트워크 관리자가 다양한 여러 양상의 공격에 대해서 유연한 대응을 할 수 있는 장점을 가진다. 본 논문에서는 SDN의 이러한 특성을 활용하여 SDN 구성 요소인 컨트롤러와 스위치를 통해 공격 정보를 수집하고 이를 기반으로 공격을 탐지하는 위협 레벨 관리 모듈, 공격 탐지 모듈, 패킷 통계 모듈, 플로우 규칙 생성기를 설계하여 프로그래밍하고 허니팟을 적용하여 지능형 공격자의 서비스 거부 공격(DoS)을 차단하는 방법을 제시한다. 제안 시스템에서 공격 패킷은 수정 가능한 플로우 규칙에 의해 허니팟으로 빠르게 전달될 수 있도록 하였으며, 공격 패킷을 전달받은 허니팟은 이를 기반으로 지능적 공격의 패턴을 분석하도록 하였다. 분석 결과에 따라 지능적 공격에 대응할 수 있도록 공격 탐지 모듈과 위협 레벨 관리 모듈을 조정한다. 제안 시스템을 실제로 구현하고 공격 패턴 및 공격 수준을 다양화한 지능적 공격을 수행하고 기존 시스템과 비교하여 공격 탐지율을 확인함으로써 제안 시스템의 성능과 실현 가능성을 보였다.