• Journal of Digital Convergence
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• v.13 no.9
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• pp.297-302
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• 2015

The increase in applying IT to vehicles has given birth to smart cars or connected cars. As smarts cars become connected with external network systems, threats to communication security are on the rise. With simulation test results supporting such threats to Convergence security in vehicular communication, concerns are raised over relevant vulnerabilities, while an increasing number of studies on secure vehicular communication are published. Hacking attacks against vehicles are more dangerous than other types of hacking attempts because such attacks may threaten drivers' lives and cause social instability. This paper designed a Convergence security protocol for inter-vehicle and intra-vehicle communication using a hash function, nonce, public keys, time stamps and passwords. The proposed protocol was tested with a formal verification tool, Casper/FDR, and found secure and safe against external attacks.

• Journal of the Korea Society of Computer and Information
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• v.16 no.3
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• pp.251-260
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• 2011

In this paper, we proposed a scheme that it safely exchanges encrypted keys without Trust Third Party (TTP) and Pre-distributing keys in multi-hop clustering sensor networks. Existing research assume that it exists a TTP or already it was pre-distributed a encrypted key between nodes. However, existing methods are not sufficient for USN environment without infrastructure. Some existing studies using a random number Diffie-Hellman algorithm to solve the problem. but the method was vulnerable to Replay and Man-in-the-middle attack from the malicious nodes. Therefore, authentication problem between nodes is solved by adding a ��TESLA. In this paper, we propose a modified Diffie-Hellman algorithm that it is safe, lightweight, and robust pair-wise agreement algorithm by adding One Time Password (OTP) with timestamp. Lastly, authentication, confidentiality, integrity, non-impersonation, backward secrecy, and forward secrecy to verify that it is safe.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.274-281
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• 2006

Sensor network applications need synchronized time extremely such as object tracking, consistent state updates, duplicate detection, and temporal order delivery. This paper describes reliable time synchronization protocol (RTSP) for wireless sensor networks. In the proposed method, synchronization error is decreased by creating hierarchical tree with lower depth and reliability is improved by maintaining and updating information of candidate parent nodes. The RTSP reduces recovery time and communication overheads comparing to TPSN when there are topology changes owing to moving of nodes, running out of energy and physical crashes. Simulation results show that RTSP has about 20% better performance than TPSN in synchronization accuracy. And the number of message in the RTSP is $20%{\sim}60%$ lower than that in the TPSN when nodes are failed in the network. In case of different transmission range of nodes, the communication overhead in the RTSP is reduced up to 40% than that in the TPSN at the maximum.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.2
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• pp.165-176
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• 2015

Clock or time synchronization protocol is one of the crucial factors that could determine the quality of the communication. With the rapid development of the network technology, more robust clock synchronization algorithm is required. IEEE 1588 is one of the possible solutions for a robust clock synchronization algorithm; however, there are still some challenges that need to be concerned in IEEE 1588 in term of reducing and stabilizing the PDV value. This survey paper shows several solutions that could improve the performance of IEEE 1588, including modifying the PTP message transmission, optimizing PTP method, filtering techniques, and using the hardware timestamp instead of application layer timestamp, and so on. Despite the improvement that is created with these techniques, the clock synchronization algorithm is still an open issue in the network communication.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.10
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• pp.1004-1010
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• 2012

In this paper, we propose the algorithm which considers applying recently proposed clock synchronization techniques with quite high accuracy in a few wireless sensor networks researches to time synchronization algorithm for multi-static radar system and especially overcomes the limitation of previous theory, cannot be applied between nodes in non-line of sight (NLOS). Proposed scheme estimates clock skew and clock offset using recursive robust least M-estimator with information of time stamp observations. And we improve the performance of algorithm by tracking and suppressing the time delays difference caused by NLOS system. Futhermore, this paper derive the mean square error (MSE) to present the performance of the proposed estimator and comparative analysis with previous methods.

• The Transactions of the Korea Information Processing Society
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• v.3 no.3
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• pp.512-522
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• 1996

To provide broadband ISDN service for the users in scattered locations, the application of satellite communications network is seriously considered. To trans mit ATM cells efficiently in satellite communications, it is effective to use TDM A method. However, it is necessary to have a method to compensate the cell delayvari-ation caused by the difference between TDMA and ATM. This paper optimized the cell control time(Tc) when traffic inputs have poisson or markov modulated poisson process by applying cell delay variation characteristics of time stamp method, which has the most advantages among compensation methods or cell delay variation. This paper also intorduces a method of reducing the cell clumping phenomena by adapting discrete time stamp method, including the analysis and evalutation of the range of required quality of CDV distribution by ATM transmission.The result of the experiment shows that CDV distribution-range can be controlled to 1.2$\times$Tc which reduces overall cell delay variation by discrrete time stamp method.

• The KIPS Transactions:PartD
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• v.11D no.2
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• pp.339-350
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• 2004

A broadcast method in mobile computing environments which have very large client populations solves the problem of low bandwidth. But most of previous proposed concurrency control protocols are restricted to read-only transactions from mobile client. In this paper, we propose the UTSM-ARM method which uses caching and broadcast method, and allows update transactions in mobile client. The UTSM-ARM decides the validation of cache data consistency with the dynamic update pattern ratio of accessed cached data. Also, the timestamps of accessed cached data and transaction in mobile client guarantee the serializable execution of mobile transactions. As a result, UTSM-ARM makes efficiently use of the asymmetric bandwidth of broadcast environment and can Increase the transaction throughput.

• Polymer(Korea)
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• v.28 no.4
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• pp.305-313
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• 2004

A vacuum pressure-difference technique for making a nano-precision replica is investigated for various applications. Master patterns for replication were fabricated using a nano-replication printing (nRP) process. In the nRP process, any picture and pattern can be replicated from a bitmap figure file in the range of several micrometers with resolution of 200nm. A liquid-state monomer is solidified by two-photon absorption (TPA) induced by a femto-second laser according to a voxel matrix scanning. After polymerization, the remaining monomers were removed simply by using ethanol droplets. And then, a gold metal layer of about 30nm thickness was deposited on the fabricated master patterns prior to polydimethylsiloxane molding for preventing bonding between the master and the polydimethylsiloxane mold. A few gold particles attached on the polydimethylsiloxane stamp during detaching process were removed by a gold selecting etchant. After fabricating the polydimethylsiloxane mold, a nano-precision polydimethylsiloxane replica was reproduced. More precise replica was produced by the vacuum pressure-difference technique that is proposed in this paper. Through this study, direct patterning on a glass plate, replicating a polydimethylsiloxane mold, and reproducing polydimethylsiloxane replica are demonstrated with a vacuum pressure-difference technique for various micro/nano-applications.

• Korean Journal of Materials Research
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• v.15 no.9
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• pp.589-593
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• 2005

Nanoimprinting lithography (NIL) is known as a suitable technique for fabricating nano and micro structures of high definition. Hot embossing is one of NIL techniques and can imprint on thin films and bulk polymers. Key issues of hot embossing are time and expense needed to produce a stamp withstanding a high temperature and pressure. Fabrication of a metal stamp such as an electroplated nickel is cost intensive and time consuming. A ceramic stamp made by silicon is easy to break when the pressure is applied. In this paper, a plastic stamp using a high temperature epoxy was fabricated and tested. The plastic stamp was relatively inexpensive, rapid to produce and durable enough to withstanding multiple hot embossing cycles. The merits of low viscosity epoxy solutions were a fast degassing and a rapid filling the microstructures. The hot embossing process with plastic stamp was performed on PMMA substrates. The hot embossing was conducted at 12.6 bar, $120^{\circ}C$ and 10 minutes. An imprinted PMMA wafer was almost same value of the plastic stamp after 10 times embossing. Entire fabrication process from silicon master to plastic stamp was completed within 12 hours.

• Journal of Internet Computing and Services
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• v.10 no.6
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• pp.229-239
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• 2009

To solve user authentication problem, many remote user authentication schemes using password and smart card at the same time have been proposed. Due to the increasing of interest in personal privacy, there were some recent researches to provide user anonymity. In 2004, Das et al. firstly proposed an authentication scheme that guarantees user anonymity using a dynamic ID. In 2005, Chien et al. pointed out that Das et al.'s scheme has a vulnerability for guaranteing user anonymity and proposed an improved scheme. However their authentication scheme was found some weaknesses about insider attack, DoS attack, and restricted replay attack. In this paper, we propose an enhanced scheme which can remove vulnerabilities of Chien et al.'s scheme. The proposed authentication protocol prevented insider attack by using user's Nonce value and removed the restricted replay attack by replacing time stamp with random number. Furthermore, we improved computational efficiency by eliminating the exponentiation operation.