• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.9
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• pp.1100-1106
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• 2012

This paper has presented the analysis of the micro-Doppler signatures scattered from the blades of the rotating propeller using the modified HHT method, one of the joint time-frequency analysis methods. The field scattered from the blade edge of the propeller was calculated using equivalent current method(ECM). After the acquisition of the scattered field data in the time domain, the modified HHT method was applied to analyze the micro-Doppler signature. The analysis results showed not only a good agreement with the realistic dynamic characteristic of the blade but also sinusoidally varing characteristics of the micro-Doppler signatures generated from rotating objects. It could be concluded that the joint time-frequency analysis via the modified HHT provided the discriminative characteristics for recognizing a small aircraft target with small RCS value.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.237.1-237.1
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• 2014

Etching is one of the most important steps in semiconductor manufacturing. In etch process control a critical task is to stop the etch process when the layer to be etched has been removed. If the etch process is allowed to continue beyond this time, the material gets over-etched and the lower layer is partially removed. On the other hand if the etch process is stopped too early, part of the layer to be etched still remains, called under-etched. Endpoint detection (EPD) is used to detect the most accurate time to stop the etch process in order to avoid over or under etch. The goal of this research is to develop a hardware and software system for EPD. The hardware consists of an Optical Plasma Monitor (OPM) sensor which is used to continuously monitor the plasma optical emission intensity during the etch process. The OPM software was developed to acquire and analyze the data to perform EPD. Our EPD algorithm is based on the following theory. As the etch process starts the plasma generated in the vacuum is added with the by-products from the etch reactions on the layer being etched. As the endpoint reaches and the layer gets completely removed the plasma constituents change gradually changing the optical intensity of the plasma. Although the change in optical intensity is not apparent, the difference in the plasma constituents when the endpoint has reached leaves a unique signature in the data gathered. Though not detectable in time domain, this signature could be obscured in the frequency spectrum of the data. By filtering and analysis of the changes in the frequency spectrum before and after the endpoint we could extract this signature. In order to do that, first, the EPD algorithm converts the time series signal into frequency domain. Next the noise in the frequency spectrum is removed to look for the useful frequency constituents of the data. Once these useful frequencies have been selected, they are monitored continuously in time and using a sub-algorithm the endpoint is detected when significant changes are observed in those signals. The experiment consisted of three kinds of etch processes; ashing, SiO2 on Si etch and metal on Si etch to develop and evaluate the EPD system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.8
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• pp.2827-2848
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• 2021

Mobile Crowdsourcing (MCS) has become an emerging paradigm evolved from crowdsourcing by employing advanced features of mobile devices such as smartphones to perform more complicated, especially spatial tasks. One of the key procedures in MCS is to collect answers from mobile users (workers), which may face several security issues. First, authentication is required to ensure that answers are from authorized workers. In addition, MCS tasks are usually location-dependent, so the collected answers could disclose workers' location privacy, which may discourage workers to participate in the tasks. Finally, the overhead occurred by authentication and privacy protection should be minimized since mobile devices are resource-constrained. Considering all the above concerns, in this paper, we propose a lightweight and privacy-preserving answer collection scheme for MCS. In the proposed scheme, we achieve anonymous authentication based on traceable ring signature, which provides authentication, anonymity, as well as traceability by enabling malicious workers tracing. In order to balance user location privacy and data availability, we propose a new concept named current location privacy, which means the location of the worker cannot be disclosed to anyone until a specified time. Since the leakage of current location will seriously threaten workers' personal safety, causing such as absence or presence disclosure attacks, it is necessary to pay attention to the current location privacy of workers in MCS. We encrypt the collected answers based on timed-release encryption, ensuring the secure transmission and high availability of data, as well as preserving the current location privacy of workers. Finally, we analyze the security and performance of the proposed scheme. The experimental results show that the computation costs of a worker depend on the number of ring signature members, which indicates the flexibility for a worker to choose an appropriate size of the group under considerations of privacy and efficiency.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.3
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• pp.1502-1522
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• 2019

Leakage of secret keys may be the most devastating problem in public key cryptosystems because it means that all security guarantees are missing. The forward security mechanism allows users to update secret keys frequently without updating public keys. Meanwhile, it ensures that an attacker is unable to derive a user's secret keys for any past time, even if it compromises the user's current secret key. Therefore, it offers an effective cryptographic approach to address the private key leakage problem. As an extension of the forward security mechanism in certificate-based public key cryptography, forward-secure certificate-based signature (FS-CBS) has many appealing merits, such as no key escrow, no secure channel and implicit authentication. Until now, there is only one FS-CBS scheme that does not employ the random oracles. Unfortunately, our cryptanalysis indicates that the scheme is subject to the security vulnerability due to the existential forgery attack from the malicious CA. Our attack demonstrates that a CA can destroy its existential unforgeability by implanting trapdoors in system parameters without knowing the target user's secret key. Therefore, it is fair to say that to design a FS-CBS scheme secure against malicious CAs without lying random oracles is still an unsolved issue. To address this problem, we put forward an enhanced FS-CBS scheme without random oracles. Our FS-CBS scheme not only fixes the security weakness in the original scheme, but also significantly optimizes the scheme efficiency. In the standard model, we formally prove its security under the complexity assumption of the square computational Diffie-Hellman problem. In addition, the comparison with the original FS-CBS scheme shows that our scheme offers stronger security guarantee and enjoys better performance.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.34
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• pp.157-185
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• 2007

The purpose of this thesis is to contribute to the activation of e-contract service for one stop e-trade by analyzing the problems and its solutions in e-contract service at home and abroad. In order to achieve the purpose of this thesis, case studies are done on e-contract service providers such as CECTRUST service of NTT DATA in Japan and HanCM.com of Haansoft in Korea and user companies such as Taisei Corporation using CECTRUST service and Hyundai Card using HanCM.com. The problems in the e-contract service are the lack of e-contract service providers, rare publicity of e-contract service, limited use of e-contract service at only home, higher pricing for e-contract service, short time management of e-contract documents by service providers, no application of newly developed security technology to e-contract service, unsatisfaction of requirements of e-contract service provider as trusted third party, absence of lower pricing e-contract service by service provider, authorizing key error in electronic signature under recognized authentication system in case of fail in renewal of digital certificate and reproduction of digital certificate. The solutions of these problems are the upbringing of e-contract service providers, broad publicity of e-contract service, development of e-contract service on a global basis, establishment of lower pricing for e-contract service, long time management of e-contract documents by service providers, application of newly developed security technology such as bio technology to e-contract service, satisfaction of requirements of e-contract service provider as trusted third party by designation of recognized e-document repository, development of lower e-contract service by way of application service provider(ASP), introduction of time stamping of e-contract document and signature key value. The limitation of this thesis is that the problems and its solutions could not meet with the broad recognition as they are conferred by intuition because of few e-contract service provider.

• Journal of Korean Society of Transportation
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• v.27 no.1
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• pp.179-190
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• 2009

Travel time is one of the most important traffic parameters to evaluate operational performance of freeways. A variety of methods have been proposed to estimate travel times. One feasible solution to estimating travel times is to utilize existing loop detector-based infrastructure since the loops are the most widely deployed detection system in the world. This study proposed a new approach to estimate travel times for freeways. Inductive vehicle signatures extracted from the loop detectors were used to match vehicles from upstream and downstream stations. Ground-truthing was also conducted to systematically evaluate the performance of the proposed algorithm by recognizing individual vehicles captured by video cameras placed at upstream and downstream detection stations. A lexicographic optimization method vehicle reidentification algorithm was developed. Vehicle features representing the characteristics of individual vehicles such as vehicle length and interpolations extracted from the signature were used as inputs of the algorithm. Parameters associated with the signature matching algorithm were calibrated in terms of maximizing correct matching rates. It is expected that the algorithm would be a useful method to estimate freeway link travel times.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2007.02a
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• pp.154-157
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• 2007

It has been widely believed that one can obtain $\iota$-Hierarchical Identity Based Encryption (HIBE) scheme secure against chosen ciphetext attacks from ($\iota$+1)-HIBE scheme secure against chosen plaintext attacks. In this paper, however, we show that when applying two concrete HIBE schemes that Boneh et al. [1, 2] proposed, chosen ciphertext secure $\iota$-HIBE schemes are directly derived from chosen plaintext secure $\iota$-HIBE schemes. Our constructions are based on a one-time signature-based transformation that Canetti et at.[3] proposed. The security of our schemes is proved in the selective-ID suity model without using random oracles.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.752-757
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• 1994

Very often, one would like to have visual image of mechanical or acoustical events such as musical sound and transient vibrations. Conventional methods to visualize the signal, such as power spectrum, do not normally allow to cultivate the signal of interests due to their inherent limitation on transient signals. Other than the conventional method, one could use an instantaneous frequency which can reveal the variation of frequency in terms of time. Nevertheless it is quite sensitive to noise and can not resolve the frequency components of signals; normally produces additional components other than those of the signals. In this paper, we introduce the Wigner-Ville spectrum to see the transient characteristics of signal, especially musical sound and transient mechanical vibration signatures. For musical sound, several popular western classic music have been selected for the analysis. For the transient mechanical signature, the signals obtained from the car door experiment and the beam experiment are interpreted in terms of Wigner-Ville spectrum. Results demonstrate the visual expressions of transient signals; musical sound and vibrations.

• 중국학논총
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• no.61
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• pp.181-202
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• 2019

Huangying-er黃鶯兒 is regarded as one of Feng Menglong's folk song books such as Guazhi-er掛枝兒, Shange山歌, and Jiazhutao夾竹桃. However, preceding researches criticized Huangying-er as 'a fly in the ointment' for laughing at pitiable female entertainers and harming the spirit of edification. In response, there has not been a detailed research on basic items such as editions, compiler, and written time. Thus, this study tried to shed new light on bibliographic information of Huangying-er. To discuss the bibliographic information of Huangying-er, this study organized and supplemented the 8 editions featuring Huangying-er in Ming Dynasty and Qing Dynasty periods. Most of these editions have signature of 'Fubaizhuren浮白主人' or 'Fubaizhaizhuren浮白齋主人'. After organizing the existing theories, this study came to support the theory claiming that the complier is Feng Menglong himself. Also, in reference to the works related to Huangying-er, this study concluded that Huangying-er was complied before compilation of Guazhi-er and Shange, the middle of the Wanli萬曆 reign period.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.11
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• pp.5527-5545
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• 2019

Through-wall ultra-wide band (UWB) radar has been considered as one of the preferred and non-contact technologies for the targets detection owing to the better time resolution and stronger penetration. The high time resolution is a result of a larger of bandwidth of the employed UWB pulses from the radar system, which is a useful tool to separate multiple targets in complex environment. The article emphasised on human subject localization and detection. Human subject usually can be detected via extracting the weak respiratory signals of human subjects remotely. Meanwhile, the range between the detection object and radar is also acquired from the 2D range-frequency matrix. However, it is a challenging task to extract human respiratory signals owing to the low signal to clutter ratio. To improve the feasibility of human respiratory signals detection, a new method is developed via analysing the standard deviation based kurtosis of the collected pulses, which are modulated by human respiratory movements in slow time. The range between radar and the detection target is estimated using joint time-frequency analysis (JTFA) of the analysed characteristics, which provides a novel preliminary signature for life detection. The breathing rates are obtained using the proposed accumulation method in time and frequency domain, respectively. The proposed method is validated and proved numerically and experimentally.