• The Mathematical Education
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• v.52 no.3
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• pp.271-301
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• 2013

The purpose of the study was to investigate how students generalize and prove the factoring of $x^n-1$ using a Computer Algebra System application and the role of CAS in this process. The theoretical framework consists of the anthropological and the instrumental approach. In particular, the basis of the Task-Technique-Theorization(T-T-T) frame adapted form Chevallard's anthropological approach of Didactics is utilized. We found that Technique-Theorization emerges in mutual interaction between paper-and-pencil techniques and computer algebra techniques. And this interaction led to the students' theoretical reflection and conceptual understanding. In this process, we could identify three epistemic role of CAS : the role of checking the result, the role of cognitive stimulation and the role of extending thinking. Therefore CAS plays on a epistemic role of checking the result of a task, stimulating the student' cognition and extending their thinking as well as pragmatic role of producing the result of a input.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.23 no.6
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• pp.1111-1120
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• 2013

CAS used in IPTV or DTV has an environment of sending single type of contents through single streaming. But it can be improved to support users' various video applications through single streaming by combining with SVC. For such an environment, efficiency should be firstly considered, and hierarchical key management methods for billing policy by service levels should be applied. This study aims to look into considerations to apply SVC to CAS and propose SVC encryption in CAS environment. The security of the proposed scheme is based on the safety of CAS and oneway hash function. If the proposed scheme is applied, scalability can be efficiently provided even in the encrypted contents and it is possible to bill users according to picture quality. In addition, the test results show that SVC contents given by streaming service with the average less than 10%overhead can be safely protected against illegal uses.

• Annual Conference of KIPS
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• 2011.11a
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• pp.907-910
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• 2011

IPTV나 DTV에서 사용하는 CAS는 하나의 스트리밍으로 하나의 콘텐츠만을 전송하는 환경이지만 SVC와의 결합을 통해 사용자의 다양한 비디오 어플리케이션을 단일 스트리밍으로 지원하도록 개선할 수 있다. 이러한 환경에서는 효율성을 우선적으로 설계하여야 하며, 서비스 등급별 과금 정책을 위해 계층적 키 관리 기법의 적용이 필요하다. 본 논문에서는 CAS에 SVC를 적용함에 있어 발생할 수 있는 문제점들에 대해 살펴보고 CAS환경에서의 SVC 암호화기법에 대해 제안한다. 제안하는 기법의 안전성은 기존 CAS와 단방향 해시 함수의 안전성에 기반하며, 기존 CAS에 비교적 적은 오버헤드로 적용이 가능하다는 장점이 있다.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.6
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• pp.55-65
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• 2003

To perform the certificate validation processing on the user-side application induces the very considerable overhead because of the complex and time-consuming characteristic of the validation processing. Especially, the verification for digital signature over a certificate can be the major reason of the overhead, since the verification accompanies with the cryptographic calculation over each certificate on the certificate path. In this paper, we propose a new certificate validation scheme can reduce the overhead caused by user-side certificate validation processing and improve the utilization of CAs. As the result, our proposed scheme can not only reduces the overhead for the validation processing by decreasing the cryptographic calculation but also improves the utilization of CAs by employing them to the validation processing.

• The KIPS Transactions:PartC
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• v.11C no.1
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• pp.21-30
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• 2004

Most applications using the PKI allows a user to execute the certificate validation processing. The efficiency of user system can be declined by the user-side processing resulting the overhead and low speed of the validation processing. Therefore, in this paper, we propose a new certificate validation processing method can decrease the overhead on user by allowing CAs of the hierarchical PKI to participate in the validation processing. Therefore, our proposed scheme can not only reduce the considerable overhead caused by the user-side whole processing without a new implementation of the delegated server but also improve the time spent for the processing by the reduction of the validation processing job on user.

• Journal of Internet Computing and Services
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• v.4 no.4
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• pp.53-64
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• 2003

To perform the certificate validation on the user-side application induces the very considerable overhead on the user-side system because of the complex and time-consuming characteristic of the validation processing. Most of the time spend for performing the validation processing is required for the digital signature verification, since the verification accompanies with the cryptographic calculation over each certificate on the certificate path. In this paper, we propose a new certificate validation scheme using DSVP(Delegated Signature Validation Protocol) which can reduce the overhead for the user-side certificate validation processing. It is achieved by delegating the digital signature verification to CAs of the PKI domain. As the proposed DSVP is the protocol performed between a user and CAs, it is applied to the hierarchical PKI efficiently and used for delegating the digital signature verification reliably and safely, our proposed scheme can not only reduces the overhead for the validation processing by decreasing the cryptographic calculation but also improves the utilization of CAs by employing them to the validation processing.

• The KIPS Transactions:PartC
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• v.16C no.1
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• pp.21-26
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• 2009

Presently, the demand for IPTV, to satisfy a variety of goals, is exploding. IPTV is coming into the spotlight as a killer application in upcoming IP convergence networks such as triple play which is the delivery of voice, internet, and video service to a subscriber. IPTV utilizes CAS, which controls the subscriber access to content for a profit. Although the current CAS scheme provides access control via subscriber authentication, there is no authentication scheme for the content transmitted from service providers. Thus, there is a vulnerability of security, through which an adversary can forge content between the service provider and subscribers and distribute malicious content to subscribers. In this paper, based on a hash tree scheme, we proposed efficient and strong source authentication protocols which remove the vulnerability of the current IPTV system. We also evaluate our protocol from a view of IPTV requirements.

• Annual Conference of KIPS
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• 2011.04a
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• pp.897-900
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• 2011

최근 새로운 소프트웨어 배포 방식인 SaaS가 주목을 받고 있다. SaaS는 원활하고 효율적인 서비스 제공을 위하여 소프트웨어 서비스를 제공하는 SaaS 어플리케이션과 과금, 사용자 인증과 같은 공통 서비스들을 제공하는 SaaS 플랫폼으로 역할이 분리되어 있다. 이런 배경을 바탕으로 본논문에서는 효율적인 사용자인증을 위한 SaaS 플랫폼의 사용자인증 서비스인 Multi-Authentication Server를 설계 한다. 본논문에서 설계되는 Multi-Authentication Server는 OpenID, OAuth, CAS, X.509 프로토콜을 통합하여 웹기반의 사용자인증 서비스를 구현한다. 마지막으로 웹기반 사용자 인증의 보안성 한계 극복과, 최근 하드웨어 보안기능을 이용하여 RADIUS 프로토콜과 TPM칩을 통합한 하드웨어 기반 네트워크 인증서비스를 제공한다.