• 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.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.4
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• pp.744-752
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• 2017

ECQV implicit certificate reconstructs the public key from the certificate without validation of the signature unlike the explicit certificate. Like this, the certificate and the public key is implicitly validated when a public key is reconstructed from a certificate. Hence, ECQV implicit certificate is shorter than the explicit certificate due to be only comprised of the public key reconstruction data instead of the signature and the public key, and faster to reconstruct the public key from the certificate than validating the signature. Furthermore, ECQV is well suited for environments and application that resources such as memory and bandwidth are limited because it is shorter the key length, and faster the performance than other cipher cryptography due to be run on ECC. In this paper, we describe prerequisites of ECQV specified in the SECG SEC 4 and issuance of an implicit certificate, reconstruction of the public key from an implicit certificate. Also we designed and implemented ECQV, and measured the performance of it.

• ETRI Journal
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• v.38 no.4
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• pp.724-734
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• 2016

To achieve confidentiality, integrity, authentication, and non-repudiation simultaneously, the concept of signcryption was introduced by combining encryption and a signature in a single scheme. Certificate-based encryption schemes are designed to resolve the key escrow problem of identity-based encryption, as well as to simplify the certificate management problem in traditional public key cryptosystems. In this paper, we propose a new certificate-based signcryption scheme that has been proved to be secure against adaptive chosen ciphertext attacks and existentially unforgeable against chosen-message attacks in the random oracle model. Our scheme is not based on pairing and thus is efficient and practical. Furthermore, it allows a signcrypted message to be immediately verified by the public key of the sender. This means that verification and decryption of the signcrypted message are decoupled. To the best of our knowledge, this is the first signcryption scheme without pairing to have this feature.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.2
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• pp.881-896
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• 2016

Certificate-based cryptography is a useful public key cryptographic primitive that combines the merits of traditional public key cryptography and identity-based cryptography. It not only solves the key escrow problem inherent in identity-based cryptography, but also simplifies the cumbersome certificate management problem in traditional public key cryptography. In this paper, by giving a concrete attack, we first show that the certificate-based encryption scheme without bilinear pairings proposed by Yao et al. does not achieve either the chosen-ciphertext security or the weaker chosen-plaintext security. To overcome the security weakness in Yao et al.'s scheme, we propose an enhanced certificate-based encryption scheme that does not use the bilinear pairings. In the random oracle model, we formally prove it to be chosen-ciphertext secure under the computational Diffie-Hellman assumption. The experimental results show that the proposed scheme enjoys obvious advantage in the computation efficiency compared with the previous certificate-based encryption schemes. Without costly pairing operations, it is suitable to be employed on the computation-limited or power-constrained devices.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.7
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• pp.2703-2718
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• 2015

Nowadays, public cloud storage is gaining popularity and a growing number of users are beginning to use the public cloud storage for online data storing and sharing. However, how the encrypted data stored in public clouds can be effectively shared becomes a new challenge. Proxy re-encryption is a public-key primitive that can delegate the decryption right from one user to another. In a proxy re-encryption system, a semi-trusted proxy authorized by a data owner is allowed to transform an encrypted data under the data owner's public key into a re-encrypted data under an authorized recipient's public key without seeing the underlying plaintext. Hence, the paradigm of proxy re-encryption provides a promising solution to effectively share encrypted data. In this paper, we propose a new certificate-based proxy re-encryption scheme for encrypted data sharing in public clouds. In the random oracle model, we formally prove that the proposed scheme achieves chosen-ciphertext security. The simulation results show that it is more efficient than the previous certificate-based proxy re-encryption 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.

• Journal of the Korean Data and Information Science Society
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• v.28 no.1
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• pp.163-171
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• 2017

With the advance of function of smart phone system and internet services, mobile trade grows more popular in the area of e-business or banking. These environmental changes, it makes the needs of authorized certificates. Authorized certificate is not only important in these days but also future society. In 2015, 27 millions of Korean people used public key certificate, but most of them does not know the details on the public key certificate. Therefore, in this paper, we explain and investigate the characteristics on the public certificate and explain the relation ship between authorized certificate and public key encrytion. By investigating several papers, internet data, newspapers and books, we found the historical changes, substantial aspects, the encryption systems on the authorized certificate. Also we study the pros and cons of authorized certificate. Finally we predict the number of issued authorized certificate for the future society based on nonparametric statistical method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3629-3647
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• 2017

Certificate-based cryptography is a useful public key cryptographic primitive that combines the merits of traditional public key cryptography and identity-based cryptography. It not only solves the key escrow problem inherent in identity-based cryptography, but also simplifies the cumbersome certificate management problem in traditional public key cryptography. So far, four short certificate-based signature schemes have been proposed. However, three of them fail in achieving the existential unforgeability under adaptive chosen-message attacks and the remaining one was not constructed in the normal framework of certificate-based signature. In this paper, we put forward a new short certificate-based signature scheme. The proposed scheme is devised in the normal framework of certificate-based signature and overcomes the security weaknesses in the previous short certificate-based signature schemes. In the random oracle model, we formally prove that it achieves the existential unforgeability against adaptive chosen-message attacks. Performance comparison shows that it is efficient and practical.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2002.11a
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• pp.385-388
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• 2002

본 논문에서는 기본 데이터베이스의 보안적인 취약점에 대해서 알아보고 보안적인 취약점을 해결할 수 있는 방법으로써 Public Key Certificate와 Attribute Certificate를 이용한 서비스 모델을 제시한다. 즉 Public Key Certificate를 이용해서 인증 강도를 높이고 Attribute Certificate를 이용해서 데이터베이스를 사용하는 사용자들에게 Role 기반 권한을 제공해서 사용자들이 데이터베이스를 사용할 수 있는 권한을 손쉽게 세분화 할 수 있는 방법을 제안한다. 또한 공개키 기반 암호화를 사용해서 사용자가 특정 자료를 암호화해서 데이터베이스에 저장함으로써 비도덕적인 데이터베이스 관리자나 혹은 데이터베이스 시스템 내부의 침입자에 의해서 사용자의 데이터가 유출되는 것을 방지하는 방법을 제안한다.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.11 no.5
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• pp.75-84
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• 2001

Existent public key certificates provide authentication information through some information on user\`s public key. However, an attribute certificate which stores and manage user\`s attribute information, provides various privilege information such as position, privilege and role. In recent, international organizations establishes standards on attribute certificate, and the researches and developments on attribute certificate have been widely made. In addition it may be expected to be used many real application area requiring for authorization information as well as authentication information. Therefore, this paper considers background and standardization trends of attribute certificate and describes the profile and related techniques of attribute certificate currently established by IETF. In addition, it introduces and access control system using attribute certificate and specifies applications of attribute certificate.