• Journal of Internet Computing and Services
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• v.7 no.1
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• pp.59-64
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• 2006

Harn al proposed a GKRS(Global Key Recovery System) that combines the functions of the key recovery authorities and the public key certification authorities(CA), Among other features, user dominance(i.e, a user is allowed to select his own public-private key pair and especially a public element for verifying the validity of the public-private key pair)is proposed by [1] for wide acceptance of GKRS. In this paper, we attack the RSA version of GKRS by showing that its user-dominance feature and the corresponding key verification scheme employed by the CA allow for fraud by users against CA. We propose more secure GKPS than original GKPS, The proposed system makes the probability of user fraud negligible small.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.5
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• pp.1687-1707
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• 2022

With the development of multiuser online meetings, more group-oriented technologies and applications for instance collaborative work are becoming increasingly important. Authenticated Group Key Agreement (AGKA) schemes provide a shared group key for users with after their identities are confirmed to guarantee the confidentiality and integrity of group communications. On the basis of the Public Key Cryptography (PKC) system used, AGKA can be classified as Public Key Infrastructure-based, Identity-based, and Certificateless. Because the latter type can solve the certificate management overhead and the key escrow problems of the first two types, Certificateless-AGKA (CL-AGKA) protocols have become a popular area of research. However, most CL-AGKA protocols are vulnerable to Public Key Replacement Attacks (PKRA) due to the lack of public key authentication. In the present work, we present a CL-AGKA scheme that can resist PKRA in order to solve impersonation attacks caused by those attacks. Beyond security, improving scheme efficiency is another direction for AGKA research. To reduce the communication and computation cost, we present a scheme with only one round of information interaction and construct a CL-AGKA scheme replacing the bilinear pairing with elliptic curve cryptography. Therefore, our scheme has good applicability to communication environments with limited bandwidth and computing capabilities.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.6
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• pp.1480-1491
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• 2013

Certificate-based cryptography is a new cryptographic primitive which eliminates the necessity of certificates in the traditional public key cryptography and simultaneously overcomes the inherent key escrow problem suffered in identity-based cryptography. However, to the best of our knowledge, all existed constructions of certificate-based encryption so far have to be based on the bilinear pairings. The pairing calculation is perceived to be expensive compared with normal operations such as modular exponentiations in finite fields. The costly pairing computation prevents it from wide application, especially for the computation limited wireless sensor networks. In order to improve efficiency, we propose a new certificate-based encryption scheme that does not depend on the pairing computation. Based on the decision Diffie-Hellman problem assumption, the scheme's security is proved to be against the chosen ciphertext attack in the random oracle. Performance comparisons show that our scheme outperforms the existing schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.7
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• pp.2554-2571
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• 2014

Certificate-based cryptography is a new cryptographic paradigm that provides an interesting balance between identity-based cryptography and traditional public key cryptography. It not only simplifies the complicated certificate management problem in traditional public key cryptography, but also eliminates the key escrow problem in identity-based cryptography. As an extension of the signcryption in certificate-based cryptography, certificate-based signcryption provides the functionalities of certificate-based encryption and certificate-based signature simultaneously. However, to the best of our knowledge, all constructions of certificate-based signcryption in the literature so far have to be based on the costly bilinear pairings. In this paper, we propose a certificate-based signcryption scheme that does not depend on the bilinear pairings. The proposed scheme is provably secure in the random oracle model. Due to avoiding the computationally-heavy paring operations, the proposed scheme significantly reduces the cost of computation and outperforms the previous certificate-based signcryption schemes.

• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.247-249
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• 2005

신원(ID) 기반 암호시스템은 인증서 관리의 복잡함이 없는 좋은 장점이 있는 반면, KGC(Key Generator Center)가 사용자의 비일 키를 발행해 주기 때문에 안전하게 개인키를 사용자에게 전송해야 하는 문제와 KGC가 모든 사용자의 비밀 키 값을 얻을 수 있는 키 복구(key escrow) 문제가 나타난다. 이 성질을 제한하기 위해 제안된 여러 기법 중 가장 널리 사용되는 것으로는 다수의 KGC들이 threshold 기법을 이용하여 사용자의 개인키를 발행해 주는 방법이 있으나, 이것은 모든 KGC들이 개인의 신원을 각각 확인해야되는 비효율성이 있다. AISW`04에서 Lee등은, 하나의 KGC에서 요청자의 신원을 확인하며 다른 신뢰기관들은 개인키 보안을 협조해 주는 방식으로 개인키를 발행하고 발행한 개인키는 은닉방법에 의해 안전하게 전송할 수 있는 장정을 가진 키 발급 기법을 제안하였다. 그러나 그들의 방법은 키 복구 권한 제한 부분이 취약하여 또한 서비스 거부 공격에 안전하지 못한 단점을 갖고 있는데 본 논문에서는 이러한 취약성을 분석하며 이를 보완하여 키 복구 권한을 제한하면서 동시에 서비스 거부 공격에도 안전한 개선된 키 발행 기법을 제안한다.

• Journal of Information Processing Systems
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• v.13 no.4
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• pp.970-986
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• 2017

Certificateless public key cryptography (CL-PKC) is a new benchmark in modern cryptography. It not only simplifies the certificate management problem of PKC, but also avoids the key escrow problem of the identity based cryptosystem (ID-PKC). In this article, we propose a certificateless blind signature protocol which is based on elliptic curve cryptography (CLB-ECC). The scheme is suitable for the wireless communication environment because of smaller parameter size. The proposed scheme is proven to be secure against attacks by two different kinds of adversaries. CLB-ECC is efficient in terms of computation compared to the other existing conventional schemes. CLB-ECC can withstand forgery attack, key only attack, and known message attack. An e-cash framework, which is based on CLB-ECC, has also been proposed. As a result, the proposed CLB-ECC scheme seems to be more effective for applying to real life applications like e-shopping, e-voting, etc., in handheld devices.

• Journal of the Korea Computer Industry Society
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• v.3 no.8
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• pp.1105-1116
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• 2002

This paper has presented three types of key recovery methods, which are known as key escrow, key encapsulation, and trusted third party scheme. we have analyzed the existing key recovery products, which have been developed by the advanced nations for electronic commerce and electronic government. we have also analyzed the key recovery policies proposed by the advanced nations, such as The United States of America, Great Britain, and Japan. In this paper, several key recovery policies are proposed for the e-commerce and e-government system. And we have proposed key recovery scheme for the e-commerce system utilizing the on-line secret sharing scheme based on the Internet and public bulletin board.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.6
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• pp.17-22
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• 2009

Certificateless cryptography eliminates the need of certificacates in the public key crytosystems and solves the inherent key escrow problem in identity-based cryptosystems. This paper demonstrates that two certificateless signature schemes proposed by Guo et al. and Wang et al. respectively are insecure against key replacement attacks by a type I adversary. We show that the adversary who can replace a signer's public key can forge signatures under the replaced public key. We then make a suggestion to prevent the attacks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.11
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• pp.5625-5641
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• 2017

Certificateless public key cryptography resolves the certificate management problem in traditional public key cryptography and the key escrow problem in identity-based cryptography. In recent years, some good results have been achieved in speeding up the computation of bilinear pairing. However, the computation cost of the pairing is much higher than that of the scalar multiplication over the elliptic curve group. Therefore, it is still significant to design cryptosystem without pairing operations. A multi-signer universal designated multi-verifier signature scheme allows a set of signers to cooperatively generate a public verifiable signature, the signature holder then can propose a new signature such that only the designated set of verifiers can verify it. Multi-signer universal designated multi-verifier signatures are suitable in many different practical applications such as electronic tenders, electronic voting and electronic auctions. In this paper, we propose a certificateless multi-signer universal designated multi-verifier signature scheme and prove the security in the random oracle model. Our scheme does not use pairing operation. To the best of our knowledge, our scheme is the first certificateless multi-signer universal designated multi-verifier signature scheme.

• Proceedings of the Korea Information Processing Society Conference
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• 2017.11a
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• pp.203-206
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• 2017

사용자 인증 및 키 합의 프로토콜은 두 사용자의 안전한 통신에 필수적인 세션키를 생성하는 프로토콜이다. 전자서명과 디피-헬만(Diffie-Hellman) 키 합의 프로토콜을 이용하여 인증 및 키 합의를 수행할 수 있으나, 각각의 파라미터 정보를 모두 공유해야한다는 단점이 있다. 이에 ID 기반 서명을 이용하여 인증과 키 합의를 동시에 수행할 수 있는 프로토콜이 제안되었는데, 기본적으로 ID 기반 서명은 키 위탁(key escrow) 문제가 있다. 본 논문에서는 이러한 문제를 해결하기 위해 상호 인증과 키 합의를 동시에 수행할 수 있는 무인증서 (certificateless, CL) 서명 기법을 설계하고, 이를 이용한 인증 및 키 합의 프로토콜을 제안한다.