• Industrial Engineering and Management Systems
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• v.10 no.4
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• pp.272-278
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• 2011

Decision tree as a classification tool is being used successfully in many areas such as medical diagnosis, customer churn prediction, signal detection and so on. The main advantage of decision tree classifiers is their capability to break down a complex structure into a collection of simpler structures, thus providing a solution that is easy to interpret. Since decision tree is a top-down algorithm using a divide and conquer induction process, there is a risk of reaching a local optimal solution. This paper proposes a procedure of optimally determining thresholds of the chosen variables for a decision tree using an adaptive particle swarm optimization (APSO). The proposed algorithm consists of two phases. First, we construct a decision tree and choose the relevant variables. Second, we find the optimum thresholds simultaneously using an APSO for those selected variables. To validate the proposed algorithm, several artificial and real datasets are used. We compare our results with the original CART results and show that the proposed algorithm is promising for improving prediction accuracy.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.8
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• pp.1946-1963
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• 2012

Hummingbird is a lightweight encryption and message authentication primitive published in RISC'09 and WLC'10. In FSE'11, Markku-Juhani O.Saarinen presented a differential divide-and-conquer method which has complexity upper bounded by $2^{64}$ operations and requires processing of few megabytes of chosen messages under two related nonces (IVs). The improved version, Hummingbird-2, was presented in RFIDSec 2011. Based on the idea of differential collision, this paper discovers some weaknesses of the round function WD16. Combining with the simple key loading algorithm, a related-key chosen-IV attack which can recover the full secret key is proposed. Under 15 pairs of related keys, the 128 bit initial key can be recovered, requiring $2^{27}$ chosen IV and the computational complexity is $O(2^{27})$. In average, the attack needs several minutes to recover the full 128-bit secret key on a PC. The experimental result corroborates our attack. The result shows that the Hummingbird-2 cipher can't resist related key attack.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.974-979
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• 2008

A design process for the structure-borne noise in a passenger vehicle is presented. The proposed process is improved from the previous one. The major difference between the current and last ones is that most of the countermeasures should be developed before fixing a tool for structural parts. This is requested for QCDP(Quality, Cost, Delivery and Productivity) by the design engineers. The proposed one consists of 4 steps: Problem definition, Cause analysis, Development of counter-measure and Validation. Based on the general rule: divide and conquer, the complex problem can be simplified into a few critical sub-systems through the first step: Problem definition. Secondly, the critical causes can be identified for the critical sub-systems through the second step: Cause analysis. Thirdly, effective countermeasures are investigated and produced through the third step: Countermeasure development. The proposed countermeasures are finally validated in the forth step: Validation.

• 한국HCI학회:학술대회논문집
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• 2009.02a
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• pp.232-239
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• 2009

Emerging social networking services provide a new paradigm for human-to-human communication. However, these services are centralized and managed by single service provider. In this paper, we propose MicroPost, a decentralized event notification service architecture for social applications based on publish/subscribe model. In our design space, event brokers are structured as an overlay network which provides the substrate of distributed peer-to-peer lookup service for storing and retrieving subscriptions with hashed keys. Event clients interact with event brokers to publish or subscribe social messages over the wide-area network. Using XML standards, we present an efficient algorithm to forward events for rendezvous-based matching in this paper. In our design space, the cost of routing is O(${\omega}log_kN$), where N is the number of event brokers, ${\omega}$ is the number of meta-data obtained from event messages, and k is a constant, which is selected by our design, to divide the identifier space and to conquer the lookup of given key. Consequently, what we achieved is an asynchronous social messaging service architecture which is decentralized, efficient, scalable, and flexible.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.1
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• pp.147-169
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• 2024

In pace with the development of network technology at lightning speed, social networks have been extensively applied in our lives. However, as social networks retain a large number of users' sensitive information, the openness of this information makes social networks vulnerable to attacks by malicious attackers. To preserve the link privacy of individuals in social networks, an uncertain graph method based on node random response is devised, which satisfies differential privacy while maintaining expected data utility. In this method, to achieve privacy preserving, the random response is applied on nodes to achieve edge modification on an original graph and node differential privacy is introduced to inject uncertainty on the edges. Simultaneously, to keep data utility, a divide and conquer strategy is adopted to decompose the original graph into many sub-graphs and each sub-graph is dealt with separately. In particular, only some larger sub-graphs selected by the exponent mechanism are modified, which further reduces the perturbation to the original graph. The presented method is proven to satisfy differential privacy. The performances of experiments demonstrate that this uncertain graph method can effectively provide a strict privacy guarantee and maintain data utility.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.3 s.345
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• pp.33-39
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• 2006

In this paper we propose the Modified Karatsuba-Ofman algorithm for polynomial multiplication to polynomials of arbitrary degree. Leone proposed optimal stop condition for iteration of Karatsuba-Ofman algorithm(KO). In this paper, we propose a Non-Redundant Karatsuba-Ofman algorithm (NRKOA) with removing redundancy operations, and design a parallel hardware architecture based on the proposed algorithm. Comparing with existing related Karatsuba architectures with the same time complexity, the proposed architecture reduces the area complexity. Furthermore, the space complexity of the proposed multiplier is reduced by 43% in the best case.

• Korean Journal of Computational Design and Engineering
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• v.14 no.5
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• pp.297-305
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• 2009

Automatic generation of the mid-surfaces of a CAD model is becoming a useful function in that it can help increase the efficiency of engineering analysis as far as it does not affect the result seriously. Several methods had been proposed previously to automatically generate the mid-surfaces, but they often failed to generate the mid-surfaces of complex CAD models. Due to the inherent difficulty of this mid-surface generation problem, it may not be possible to come up with a complete and general method to solve this problem. Since a method that can handle a specific case may not work for different cases, it seems that developing case-specific methods ends up with solving only a fraction of the problem. In this paper, therefore, we propose a method to generate mid-surfaces based on a divide-and-conquer paradigm. This method first decomposes a complex CAD model into simple volumes. The mid-surfaces of the simple volumes are automatically generated by the existing methods, and then they are converted into the mid-surfaces of the original CAD model.

• The Transactions of the Korea Information Processing Society
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• v.7 no.3
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• pp.943-952
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• 2000

The surface reconstruction problem from a set of wire-frame contours is very important in diverse fields such as medical imaging or computer animation. In this paper, surface triangulation method is proposed for solving the problem. Generally, many optimal triangulation techniques suffer from the large computation time but heuristic approaches may produce very unnatural surface when contours are widely different in shape. To compensate the disadvantages of these approaches, we propose a new heuristic triangulation method which iteratively decomposes the surface generation problem from a band (a pair of vertices chain) into tow subproblems from two sub-bands. Generally, conventional greedy heuristic contour triangulation algorithm, suffer from the drastic error propagation during surface modeling when the adjacent contours are different in shape. Our divide-and-conquer algorithm, called band partitioning algorithm, processes eccentric parts of the contours first with more global information. Consequently, the resulting facet model becomes more stable and natural even though the shapes are widely different. An interesting property of our method is hat it supports multi-resolution capability in surface modeling time. According to experiments, it is proved to be very robust and efficient in many applications.

• The KIPS Transactions:PartC
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• v.19C no.3
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• pp.179-184
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• 2012

Due to the absence of an alternative algorithm SHA-2, NIST (National Institute of Standards and Technology) is proceeding to development project of SHA-3. NIST announced five candidates of the final round at the end of 2010. Side-channel attack scenarios of five candidates for SHA-3 final round have been proposed. In this paper, we prove the possibility of the analysis against 32-bit modular addition by 8-bit blocks from our experiment on ARM chip board with a register size of 32-bit. In total we required 9700 power traces to successfully recover the 128-bit secret key for the attack against.

• Proceedings of the Korea Information Processing Society Conference
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• 2017.04a
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• pp.83-86
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• 2017

단일 코어 프로세스의 성능 향상은 전력 소모, 발열 등의 이유로 한계에 달했다. 이에 대한 대안으로 멀티 코어가 등장했으며 매니 코어 기술에 대한 연구가 활발히 진행 중에 있다. 이렇듯 멀티 코어 환경이 보편화됨에 따라 병렬 프로그래밍의 중요성이 더욱 커졌다. 한편, 순수 함수형 언어 Haskell은 부수효과가 없고 다양한 병렬화 도구를 지원함으로써 다가오는 병렬 프로그래밍 시대에 적합한 언어라 할 수 있다. 이때 Haskell 병렬 프로그램의 성능은 메모리 재사용(Garbage Collection) 시간에 큰 영향을 받는다. 그래서 Haskell 병렬 프로그램의 성능 향상, 분석을 위한 메모리 프로파일링 도구가 필요하다. 이미 Haskell이 제공하는 메모리 프로파일링 도구로 ghc-gc-tune이 있지만 실행 속도 측면에서 개선이 필요하다. 본 연구에서는 분할 정복법을 이용해서 매 단계마다 탐색 영역을 4분의 1로 줄이도록 ghc-gc-tune을 개선했다. 개선된 ghc-gc-tune을 극대 독립 집합 프로그램과 K-means 프로그램에 적용한 결과, 평균 98%의 정확도로 실행 시간을 평균 7.78배 단축했다.