• Journal of Korea Multimedia Society
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• v.6 no.2
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• pp.288-300
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• 2003

As the importance of information security gets recognized seriously, ciphers technology gets used more. Particularly, since public key ciphers are easier to control the key than symmetric key ciphers and also digital signature is easily implemented, public key ciphers are increased used. Nowadays, public key infrastructure is established and operated to use efficiently and securely the public key ciphers. In the public key infrastructure, the user registers at the certificate authority to generate the private key and public key pair and the certificate authority issues the certificate on the public key generated. Through this certificate, key establishment between users is implemented and encryption communication becomes possible. But, control function of session key established in the public key infrastructure is not provided. In this thesis, the certificate issuing protocol to support the key recovery of the session key established during the wireless authentication and key establishment is proposed.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10c
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• pp.673-675
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• 2002

기존의 SET은 전자서명(digital signature), 데이터 암호화(data encryption), 전자 봉투(digital envelope)로 구성되어 있으며, RSA, SHA, DES를 사용하여 프로토콜을 구현하는데, 본 논문은 ECC의 공개키와 개인키를 이용하여 암호 강도가 강화된 대칭키 알고리즘을 제안하고 SET의 전자 봉투를 생략한 SSET를 제안하고 있다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.5
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• pp.410-415
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• 2013

Recently, as Internet enters WEB 2.0, many social network services through such as Facebook, Twitter and Youtube appeared. In these social network sites, users can easily make friends, join groups and access others personal information. Therefore, a malicious user can easily gather information of others. In order to protect user's personal information from the unauthenticated users, we propose privacy protection mechanism based on key assignment and user's trust level. A master-key is generated for each users and is segmented into a core-key and several sub-key. The master-key stores at the information owner's side and the sub-key will be distributed to requestor according to the relation and trust level. At last, in order to proof the efficiency, the performance of our proposed mechanism is compared with those of existing mechanisms.

• The Journal of Information Technology
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• v.6 no.4
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• pp.59-68
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• 2003

In this paper, a public key kanpsack cryptosystem algorithm is based on the security to a difficulty of polynomial factorization in computer communication is proposed. For the proposed public key kanpsack cryptosystem, a polynomial vector B(x,y,z) is formed by transform of superincreasing vector A, a polynomial f(x,y,z) is selected. Next then, the two polynomials B(x,y,z) and f(x,y,z) is decided on the public key. Therefore a public key knapsack cryptosystem is based on the security to a difficulty of factorization of a polynomial f(x,y,z)=0 with three variables. In this paper, a public key encryption algorithm for data security of computer network is proposed. This is based on the security to a difficulty of factorization. For the proposed public key encryption, the public key generation algorithm selects two polynomials f(x,y,z) and g(x,y,z). The propriety of the proposed public key cryptosystem algorithm is verified with the computer simulation.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.15 no.2
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• pp.23-36
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• 2005

The main obstacle hindering the wide deployment of identity-based cryptosystem is that the entity responsible for creating the private key has too much power. As a result, private keys are no longer private. One obvious solution to this problem is to apply the threshold technique. However, this increases the authentication computation, and communication cost during the key issuing phase. In this paper, we propose a new effi ient model for issuing multiple private keys in identity-based encryption schemes based on the Weil pairing that also alleviates the key escrow problem. In our system, the private key of a user is divided into two components, KGK (Key Description Key) and KUD(Key Usage Desscriptor), which are issued separately by different parties. The KGK is issued in a threshold manner by KIC (Key Issuing Center), whereas the KW is issued by a single authority called KUM (Key Usage Manager). Changing KW results in a different private key. As a result, a user can efficiently obtain a new private key by interacting with KUM. We can also adapt Gentry's time-slot based private key revocation approach to our scheme more efficiently than others. We also show the security of the system and its efficiency by analyzing the existing systems.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.5
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• pp.1071-1078
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• 2018

Recently, a family of lightweight block ciphers CHAM that has effective performance on resource-constrained devices is proposed. The CHAM uses a stateless-on-the-fly key schedule method which can reduce the key storage areas. Furthermore, the core design of CHAM is based on ARX(Addition, Rotation and XOR) operations which can enhance the computational performance. Nevertheless, we point out that the CHAM algorithm may be vulnerable to the fault injection attack which can reveal 4 round keys and derive the secret key from them. As a simulation result, the proposed fault injection attack can extract the secret key of CHAM-128/128 block cipher using about 24 correct-faulty cipher text pairs.

• Proceedings of the Korea Information Assurance Society Conference
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• 2004.05a
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• pp.77-82
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• 2004

The notion of a certificate was introduced by Kohnfelder in his 1978 MIT bachelor's thesis. The idea, now common, was that a certificate is a digitally signed statement binding the key-holder's name to a public key. With the increasing acceptance of digital certificate, there has been a gaining impetus for methods to nullify the compromised digital certificates and enable the end user to receive this information before be trusts a revoked certificate. The problem of certificate revocation is getting more and more crucial with the development of wide spread PKIs. In this paper, we investigate recent trend of certificate revocation mechanism.

• Proceedings of the Korean Information Science Society Conference
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• 2010.06d
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• pp.95-100
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• 2010

높은 이동성 및 휴대성을 갖는 모바일 디바이스의 기술적 발전은 사용자로 하여금 보다 높은 수준의 통합된 편의 기능 제공이 요구되고 있다. 이러한 예로 기존 물리적 지갑에 보관하던 플라스틱 신용카드, 멤버쉽 카드, 신분증 등의 개인정보를 모바일 디바이스 안에 저장 관리하는 모바일 지갑 서비스가 현실화되고 있다. 모바일 지갑을 통한 상거래 서비스를 이용할 시 디바이스에 저장된 각종 개인정보가 근거리 무선통신 기술을 통해 다른 모바일 기기나 지불서버에 전달되는 데, 이 무선전송 구간은 근원적으로 많은 보안 취약점을 갖고 있다. 따라서 본 논문에서는 모바일 지갑 응용 서비스에 모바일 기기간 안전한 키 설정 시 공개키 인증서를 활용하지 않고 두 기기간 공유키 검증을 할 수 있는 세션 키 검증 기술들을 분석하고, 해당기술들을 구현하여 모바일 지갑 결제 테스트베드에 포팅한 실험 결과를 통한 성능분석 결과를 제시한다. 본 성능평가를 통해 향후 다양한 모바일 기기 특성에 따른 최적의 세션 키 공유 키 검증 방법 선택 시 유용한 근거자료로 활용할 수 있을 것으로 기대된다.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.1 no.1
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• pp.47-65
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• 1991

An ID-based scheme provides a very efficient solution to the key distribution problem, since it can solve bothe the authentication problem and the communication complexity problem in a public key scheme. Especilly, and ID-Based ndninterative key distribution system plays an crucial roie in the one-way communication environment such as secure electronic mail, owing to its noninteractiveness. This paper aims at analyzing the previously proposed scheme s and providing possible improvements. It also demonstraes that the Maurey-Yacobi's scheme presented in Eurocry'91 is not secure, and provikdes an countemeasure to overcome the security problem.

• Proceedings of the Korea Multimedia Society Conference
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• 2003.11a
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• pp.40-43
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• 2003

브로드캐스트 암호화 기법은 공개된 네트워크 상에서 멀티미디어, 소프트웨어, 유료 TV 등의 디지털 정보들을 전송하는데 적용되고 있다. 브로드캐스트 암호화 기법에서 중요한 것은 오직 사전에 허가된 사용자만이 디지털 정보를 얻을 수 있어야 한다는 것이다. 브로드캐스트 메시지가 전송되면 권한이 있는 사용자들은 자신이 사전에 부여받은 개인키를 이용하여 먼저 세션키를 복호화하고 이 세션키를 통하여 디지털 정보를 얻게 된다. 이와 같이 사용자는 브로드캐스터가 전송하는 키를 이용하여 메시지나 세션키를 획득하게 되는데, 이러한 과정에서 브로드캐스터가 키를 생성하고 분배하는 과정이 필요하다. 하지만 브로드캐스트 암호화는 단지 일방향으로 전달되고 있을뿐 양방향성을 지니지 못하는 단점을 가지고 있다. 이에 본 논문에서는 T-commerce 상에서 적용하여 컨텐츠를 제공하거나 사용자가 컨텐츠에 대한 구매의사가 발생하는 상황을 고려한 키 분배에 관하여 제안한다.