• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권2호
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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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• 제9권7호
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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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• 제7권6호
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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.

• ETRI Journal
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• 제38권4호
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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.

• 한국정보통신학회논문지
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• 제11권12호
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• pp.2271-2279
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• 2007

본 논문에서는 다중수신자 환경에서 신원기반 암호 기법의 키 위탁 문제를 해결함과 동시에 묵시적인 공개키 인증을 유지하기 위하여 인증서기반 (certificate-based) 다중수신자 암호 기법을 소개한다. 제안 기법은 다중수신자에 대하여 메시지를 암호화하는 단계에서 Pairing 연산을 제거하였을 뿐만 아니라 복호화 단계에서 단 한번의 Pairing 연산만을 요구한다. 또한, Baek등에 의해 제안되었던 다중수신자 환경에서 가장 효율적인 신원기반 암호 기법[1]과의 계산량 비교를 통하여 제안 기법이 보다 효율적임을 보인다. 마지막으로 제안 기법을 이용하여 Subset-Cover 프레임워크 기반의 새로운 스테이트리스 공개키 브로드캐 스트 암호 기법을 제시한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권7호
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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.

• 정보보호학회논문지
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• 제17권1호
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• pp.3-10
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• 2007

본 논문에서는 ICISC 2004에 제안된 status certificate-based encryption(SCBE) 기법과 EUC Workshops 2006에 제안된 certificateless signature(CLS) 기법의 취약성을 제시한다. 이 두 기법은 ID 기반 암호시스템이 가지는 키 위탁 성질을 없애기 위해 사용자와 관리서버(CA또는 KGC)가 함께 사용자 키(SCBE: 복호용 키, CLS: 서명용 키)를 생성하게 되어 있고, 이들 중 한쪽만을 제어할 수 있는 공격자는 암호시스템에 위해를 가할 수 있는 어떠한 이점도 가질 수 없다고 알려져 있다. 그러나, 본 논문에서는 각 기법의 공격모델에서 허용하는 공격자가 공개키 변조를 통해 독자적으로 사용자 키를 생성하여 사용할 수 있음을 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권4호
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• pp.2254-2275
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• 2017

In this paper, we present an IND-CCA2 secure certificateless proxy re-encryption scheme in the random oracle model. A certificateless public key cryptography simplifies the certificate management in a traditional public key infrastructure and the built-in key escrow feature in an identity-based public key cryptography. Our scheme shares the merits of certificateless public key encryption cryptosystems and proxy re-encryption cryptosystems. Our certificateless proxy re-encryption scheme has several practical and useful properties - namely, multi-use, unidirectionality, non-interactivity, non-transitivity and so on. The security of our scheme bases on the standard bilinear Diffie-Hellman and the decisional Bilinear Diffie-Hellman assumptions.

• ETRI Journal
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• 제39권1호
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• pp.135-144
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• 2017

Recently, mobile phones have been recognized as the most convenient type of mobile payment device. However, they have some security problems; therefore, mobile devices cannot be used for unauthorized transactions using anonymous data by unauthenticated users in a cloud environment. This paper suggests a mobile payment system that uses a certificate mode in which a user receives a paperless receipt of a product purchase in a cloud environment. To address mobile payment system security, we propose the transaction certificate mode (TCM), which supports mutual authentication and key management for transaction parties. TCM provides a software token, the transaction certificate token (TCT), which interacts with a cloud self-proxy server (CSPS). The CSPS shares key management with the TCT and provides simple data authentication without complex encryption. The proposed self-creating protocol supports TCM, which can interactively communicate with the transaction parties without accessing a user's personal information. Therefore, the system can support verification for anonymous data and transaction parties and provides user-based mobile payments with a paperless receipt.

• Journal of the Korean Data and Information Science Society
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• 제28권1호
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• pp.163-171
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• 2017

인터넷 뿐만 아니라 휴대용 컴퓨터라고도 불리고 있는 스마트폰의 기능이 향상되면서 인터넷상거래나 금융기관거래에서 인터넷이나 스마트폰을 이용한 거래가 활성화 되고 있다. 인터넷이나 스마트폰을 이용한 상거래나 금융기관 거래 (banking)에는 공인인증서 (authorized certificate, certificate)가 반드시 필요하다. 공인인증서는 지금도 중요시 되지만 미래사회에도 계속 중요하게 다루어질 중요한 안전장치이다. 공인인증서는 2015년 3월 현재 우리나라 국민 2,841만명이 이용할 정도로 생활 필수품에 가까운 위치를 점했다. 그러나 공인인증서의 사용자들이 상상이상으로 공인인증서에 대해 알고 있지 못하다는 점을 파악하여 본 논문에서는 공인인증서에 대한 중요사항들을 정리하고 암호학과 관련된 내용들을 설명하고자 한다. 각종 논문과 인터넷 자료 및 신문기사, 그리고 서적을 통하여 공인인증서의 본질적인 모습과 공인인증서가 어떤 암호체계를 기반으로 발전해 왔는지, 또 과거의 모습부터 근래의 모습에는 어떤 변화를 거쳐왔는지 살펴보고 다양하게 쓰이는 공인인증서의 장점과 그 속에 공존하는 단점, 그리고 취약점들에 대하여 언급하였다. 또한 앞으로 공인인증서가 어떻게 발전해 나갈지에 대해 비모수적 통계적 방법으로 예측하였다.