• The Journal of Korean Association of Computer Education
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• v.9 no.2
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• pp.111-124
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• 2006

Multicast services are provided on the Internet in fast increasing. Therefore it is important to keep security for multicast communication. If a member of the group is removed, new group key has to be generated and distributed to all remaining members of group. Minimizing number of messages and operation cost for generation of the composite keys to be used to encrypting group key are important evaluating criteria of multicast key management scheme since generation and distribution of new keys for rekeying require expensive operation. Periodic batch rekeying can reduce these important parameters rather than rekeying sequentially in fashion one after another. In this paper, Hamming distance is calculated between every members to be removed. In batch rekeying the members with Hamming distance less than threshold are selected for rekeying procedure. With running the round assignment algorithm in the case of removing several members simultaneously, our scheme has advantages of reducing messages and operation cost for generation of the composite keys and eliminating possibility of collusion attack for rekeying. We evaluate performance of round assignment algorithm through simulation and show that our scheme is excellent after performance comparison of existent schemes and our scheme.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.2
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• pp.167-174
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• 2014

In this paper, we address a task allocation problem for a robot team that performs a search and attack mission. The robots are limited in sensing and communication capabilities, and carry different types of resources that are used to attack a target. The environment is uncertain and dynamic where no prior information about targets is given and dynamic events unpredictably happen. The goal of robot team is to collect total utilities as much as possible by destroying targets in a mission horizon. To solve the problem, we propose a distributed task allocation framework incorporated with effective resource management based on resource welfare. The framework we propose enables the robot team to retain more robots available by balancing resources among robots, and respond smoothly to dynamic events, which results in system performance improvement.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2006.06a
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• pp.164-168
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• 2006

전력 공격은 암호화 연산 과정 중 발생하는 소비 전력의 파형을 측정하여 비밀 정보를 알아내는 공격 방식이다. 이러한 전력 공격에 대한 취약성을 막기 위하여 message blinding, exponent blinding과 같은 기법들이 적용되어 왔다. 본 고에서는 $ECC^{[1]}$암호화 연산 과정에서, r이 임의의 정수일 때, dP=(d-r)P+rP인 관계를 이용하는 exponent blinding기법$^{[2]}$에 대하여 언급하고, 위 기법을 전력 공격의 대응책으로 적용 시 적절히 구현되지 않으면 power attack에 대하여 매우 취약하다는 것을 보인다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.1
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• pp.115-120
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• 2013

There are lots of vulnerability and chance to be attacked in wireless sensor networks, which has many applications. Among those attacks, sybil attack is to generate a lot of false node and to inject false information into networks. When a user uses such false information without recognizing the attack, there might be a disaster. Although authentication method can be used to protect such attack, the method is not a good choice in wireless sensor networks, where sensor nodes have a limited battery and low power. In this paper, we propose a novel method to detect sybil attack with a little extra overhead. The proposed method use the characteristics that there is a weak connection between a group of normal nodes and a group of false nodes. In addition, the method uses energy aware routing based on random routing and adds a little information into the routing. Experimental results show that the proposed method detects false node by more than 90% probability with a little energy overhead.

• Journal of Korean Neurosurgical Society
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• v.41 no.4
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• pp.224-229
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• 2007

Objective : Despite improvement of therapeutic regimen, incidence of stroke increases and it remains a leading cause of death. Our study aims at offering variable data on recurrent strokes. Methods : There were 59 patients who admitted from Jan. 2002 to Dec. 2004 due to recurrent strokes. A retrospective longitudinal cohort study was done. Results : Four-hundred-seventy five patients, diagnosed with acute stroke, experienced 491 strokes in 3 years, and there were 75 recurrent strokes [15.3%] in 59 patients. These 59 patients were included in the study. First hemorrhagic cases [H] were 19 [32%], and the first infarction cases [I] were 40 [68%]. Subsequent strokes after first stroke were as follows : $H{\to}H$ 14 [23.7%] cases, $H{\to}I$ 5 [8.5%], $I{\to}H$ 8 [13.6%], $I{\to}I$ 32 (54.2%]. A Cox regression analyses showed that the first type of stroke was a significant factor to the second stroke as follows : if one has had a hemorrhagic stroke, the possibility of second hemorrhagic attack ($H{\to}H$ attack) increase 3.2 times than ischemic type and in ischemic stroke [$I{\to}I$ attack] 3.6 times increased incidence of second ischemic attack. Conclusion : The recurrence rate of stroke was 12.4% [59 of 475 patients]. If the first stroke is hemorrhage or infarction, the next stroke would have high potentiality of hemorrhage, or infarction. The possibility of same type in second stroke Increase over 3 times. In $H{\to}H$ group, the time interval between first and second stroke was shorter and the age of onset was earlier than in $I{\to}I$ group. Moreover, the infarction was more frequent than hemorrhage in multiple strokes. There was a correlation in lacunar type infarction between first and second attack.

• Journal of Chest Surgery
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• v.25 no.5
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• pp.533-540
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• 1992

To evaluate the risk factors involving the recurrence of the spontaneous pneumothorax, 125 patients were reviewed. These patients were consecutively diagnosed and treated for the spontaneous pneumothorax at the Department of Thoracic and Cadiovascular Surgery, Yeungnam University Hospital, from Jun. 1986 to Apr. 1991. The patients were divided into two groups, control and recurrent. The control group, consisting of the 125 patients, did not have recurrences of the pneumothorax for a period of 2 years following the first attack. The recurrent group were the remaining 57 patients, who experienced at least one recurrence during the same period. The number of patients over the age of 50 was significantly higher in the recurrent group than the control group. Abnormal findings on chest X-ray[e.g., old tuberculous scar, emphysematous change, visible bullae of blebs] were observed more frepuently in the recurrent group. also, when the pneumothorax size was larger than 50%, and the air-leakage from the chest tube was longer than 3 days during the first attack the incidence of recurrence was significantly increased in the recurrent group. The recurrence occured more frequently in the afternoon, and in the same thoracic cavity. Exertion and smoking were not related to the risk factors in this clinical setting.

• Journal of Oriental Neuropsychiatry
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• v.25 no.4
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• pp.319-332
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• 2014

Objectives: This study was conducted to evaluate the clinical effects of group therapy for Panic disorder patients based on Mindfulness & Li-Gyeung-Byun-Qi therapy. Methods: The FFMQ, BDI, STAI, STAXI, Panic attack, Anticipatory anxiety and subjective improvement of three Panic disorder patients were compared pre- and post-treatment when given Mindfulness & Li-Gyeung-Byun-Qi therapy. Results: 1) After the patient in case 1 underwent 5 weeks of group therapy for Panic disorder, the Mindfulness meditation score was slightly improved, anxiety and depression were significantly decreased, and expression of anger was also improved. In addition, the Panic attack and Anticipatory anxiety became more stable in the objective evaluation, while 'Extreme improvement' was shown in the subjective evaluation. 2) After the patients in case 2 and 3 underwent 5 weeks of group therapy for Panic disorder, Mindfulness meditation scores were slightly improved, anxiety and depression were significantly decreased, and expression of anger was also improved. In addition, the Panic attack and Anticipatory anxiety became more stable in the objective evaluation, while 'Moderate improvements' were shown in the subjective evaluation. Conclusions: As per the results in these cases, it was shown that group therapy for Panic disorder utilizing Mindfulness & Li-Gyeung-Byun-Qi therapy was effective to maintain meditation and control the emotions of anxiety, depression, anger and so on. Therefore, it was considered that expansion of clinical utilization through the standardization of a group therapy program for Panic disorder is needed. Furthermore, it was also considered that a comparative study of the effects of previous cognitive programs for Panic disorder according to the objectified and standardized manual is needed in the future.

• Convergence Security Journal
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• v.12 no.6
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• pp.101-106
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• 2012

As the existing strategy of preventing DDoS(Distributed Denial of Service) attacks has limitations, this study is intended to suggest the more effective method of preventing DDoS attacks which reduces attack power and distributes attack targets. Currently, DDoS attacks have a wide range of targets such as individuals, businesses, labs, universities, major portal sites and financial institutions. In addition, types of attacks change from exhausting layer 3, network band to primarily targeting layer 7. In response to DDoS attacks, this study suggests how to distribute and decrease DDoS threats effectively and efficiently using Proxy Server Group and Dynamic DNS.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.1
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• pp.67-80
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• 2007

Nateon Messenger, which has the most number of users in Korea, supports many services such as E-mail, note, Cyworld, SMS, etc. In this paper, we will analyse the authentication traffic which is transmitted and received by the Nateon Messenger. Through performing the replay attack with the authentication information, we will show that an attacker can be authenticated illegally. Furthermore, we will show that other domestic messengers have similar security problems.

• Journal of Korean Neurosurgical Society
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• v.38 no.6
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• pp.425-430
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• 2005

Objective : Recently, the survival rate and prognosis of spontaneous intracerebral hemorrhage[S-ICH] has improved, and their enhanced survival has become associated with a consequent rise in the recurrence of S-ICH. The aim of this study is to improve the prevention of recurrent S-ICH. Methods : Between January 1999 and March 2004, we experienced 48 cases of recurrence. We classified the patients into the two groups; a double ICH group and a triple ICH group. We investigated their brain CTs, MRIs, cerebral angiographies, and medical records, retrospectively. Results : Majority of patients had the intervals at least 12 months, and most of patients underwent conservative treatment. The most common hemorrhage pattern of recurrence was ganglionic-ganglionic [basal ganglia - basal ganglia], and the second attack was contralateral side of the first attack in a large percentage of all patients. Prognosis of patients was worsened in recurrent attack. Nearly all patients had medical history of hypertension, and most patients have taken antihypertensive medication at the arrival of emergency room. Conclusion : In treating hypertension for S-ICH patients, we stress that blood pressure must be thoroughly controlled over a long period of time.