• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권7호
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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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권5호
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• pp.2792-2810
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• 2017

Forward-secure signature is a specific type of signature, which can mitigate the damage caused by the signing key exposure. Most of the existing forward-secure (identity-based) signature schemes can update users' secret keys at each time period, achieve the existential unforgeability, and resist against classical computer attacks. In this paper, we first revisit the framework of forward-secure identity-based signatures, and aim at supporting flexible key update at multi time period. Then we propose a post-quantum forward-secure identity-based signature scheme from lattices and use the basis delegation technique to provide flexible key update. Finally, we prove that the proposed scheme is strongly unforgeable under the short integer solution (SIS) hardness assumption in the random oracle model.

• 융합보안논문지
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• 제21권1호
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• pp.33-44
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• 2021

클라우드 컴퓨팅 기술을 활용한 데이터의 아웃소싱은 제공된 데이터에 대한 제 자 노출3,변조 , 연산위임 결과의 신뢰성 등이 문제가 되고 있다. 이러한 보안 이슈들를 해결하기 위해 데이터를 암호화 한 후 연산 및 분석을 수행하는 준동형 암호가 큰 각광을 받고 있으며, 최근에는 준동형 암호에 인증 기능을 보강한 준동형 인증 암호들이 제안되었다. 이 암호를 활용하면 정보의 유출과 민감한 개인정보에 대한 침해 문제없이 데이터의 분석이 가능함과 동시에 위임된 연산에 대한 신뢰성을 보장받을 수 있기 때문이다. 그러나 준동형 인증 암호 설계에 대한 연구는 아직 초기 단계이다. 제시된 준동형 인증 암호들 중 실용적인 스킴들은 그 안전성이 매우 낮거나, 반대로 안전성이 높은 경우에는 실용적이지 못하다. 또한 준동형 메시지 인증 스킴과 준동형 암호를 바탕으로 준동형 인증 암호를 설계하는 기법에 대한 분석이 부재한 실정이다. 본 논문에서는 준동형 메시지 인증 스킴과 준동형 암호를 결합하여 설계하는 기법에 대한 안전성 분석하였다. 분석 결과 위조 불가능한 준동형 메시지 인증 스킴을 이용하여 준동형 인증 암호를 구성하면 준동형 인증 암호 역시 위조불가능성을 갖지만 강한 위조 불가능성의 경우는 그렇지 않았다. 한편 구별불가능성을 갖는 준동형 암호를 이용하여 준동형 인증 암호를 설계하더라도 구별불가능성에 대한 안전성을 만족하지 못함을 확인하였다.

• 정보보호학회논문지
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• 제14권5호
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• pp.165-176
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• 2004

Al-Riyami 와 Paterson$^{[1]}$ 은 Certificateless 공개키 시스템이라 부르는 새로운 공개키 패러다임을 제안하였다. 이 시스템은 공개키 암호기법과 ID-기반 암호기법 각각의 장점을 가지고 있다. 즉, 기존의 공개키 기반 구조상의 인증서를 필요로 하지 않으면서도 ID기반 암호 시스템의 본질적 성질인 키위탁(key escrow) 관련 파생문제를 가지지 않는다. 본 논문에서 우리는 양방향 사용자 인증을 만족하는 인증서를 사용하지 않는 효율적 암호 스킴을 제안한다. 제안하는 스킴의 안전성은 computational Diffie-Hellman 문제(CDHP)와 bilinear Diffie-Hellman 문제(BDHP)의 어려움에 기반한다. 기밀성과 위조 불가능성을 위한 안전성을 증명하기 위하여 모델을 설정하고 제안된 스킴이 랜덤한 오라클(random oracle) 모델에서 안전함을 증명한다.

• Journal of Information Processing Systems
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• 제12권2호
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• pp.249-262
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• 2016

In 2004, Yang et al. proposed a threshold proxy signature scheme that efficiently reduced the computational complexity of previous schemes. In 2009, Hu and Zhang presented some security leakages of Yang's scheme and proposed an improvement to eliminate the security leakages that had been pointed out. In this paper, we will point out that both Yang and Hu's schemes still have some security weaknesses, which cannot resist warrant attacks where an adversary can forge valid proxy signatures by changing the warrant $m_w$. We also propose two secure improvements for these schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권12호
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• pp.3261-3273
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• 2013

In the paper, we propose a novel adaptively secure hierarchical identity-based signature scheme from lattices. The size of signatures in our scheme is shortest among the existing hierarchical identity-based signature schemes from lattices. Our scheme is motivated by Gentry et al.'s signature scheme and Agrawal et al.'s hierarchical identity-based encryption scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권3호
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• pp.1502-1522
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• 2019

Leakage of secret keys may be the most devastating problem in public key cryptosystems because it means that all security guarantees are missing. The forward security mechanism allows users to update secret keys frequently without updating public keys. Meanwhile, it ensures that an attacker is unable to derive a user's secret keys for any past time, even if it compromises the user's current secret key. Therefore, it offers an effective cryptographic approach to address the private key leakage problem. As an extension of the forward security mechanism in certificate-based public key cryptography, forward-secure certificate-based signature (FS-CBS) has many appealing merits, such as no key escrow, no secure channel and implicit authentication. Until now, there is only one FS-CBS scheme that does not employ the random oracles. Unfortunately, our cryptanalysis indicates that the scheme is subject to the security vulnerability due to the existential forgery attack from the malicious CA. Our attack demonstrates that a CA can destroy its existential unforgeability by implanting trapdoors in system parameters without knowing the target user's secret key. Therefore, it is fair to say that to design a FS-CBS scheme secure against malicious CAs without lying random oracles is still an unsolved issue. To address this problem, we put forward an enhanced FS-CBS scheme without random oracles. Our FS-CBS scheme not only fixes the security weakness in the original scheme, but also significantly optimizes the scheme efficiency. In the standard model, we formally prove its security under the complexity assumption of the square computational Diffie-Hellman problem. In addition, the comparison with the original FS-CBS scheme shows that our scheme offers stronger security guarantee and enjoys better performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권4호
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• pp.2219-2236
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• 2017

With cloud storage services, users can handle an enormous amount of data in an efficient manner. However, due to the widespread popularization of cloud storage, users have raised concerns about the integrity of outsourced data, since they no longer possess the data locally. To address these concerns, many auditing schemes have been proposed that allow users to check the integrity of their outsourced data without retrieving it in full. Yuan and Yu proposed a public auditing scheme with a deduplication property where the cloud server does not store the duplicated data between users. In this paper, we analyze the weakness of the Yuan and Yu's scheme as well as present modifications which could improve the security of the scheme. We also define two types of adversaries and prove that our proposed scheme is secure against these adversaries under formal security models.

• ETRI Journal
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• 제38권2호
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• pp.397-404
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• 2016

In group-oriented applications, it is often required to verify a group of signatures/messages. The individual verification of signed messages in such applications comes at a high cost in terms of computations and time. To improve computational efficiency and to speed up the verification process, a batch verification technique is a good alternative to individual verification. Such a technique is useful in many real-world applications, such as mail servers, e-commerce, banking transactions, and so on. In this work, we propose a new, efficient identity-based signature (IDS) scheme supporting batch verifications. We prove that the proposed IDS scheme and its various types of batch verifications is tightly related to the Computational Diffie.Hellman problem under a random oracle paradigm. We compare the efficiency of the proposed scheme with related schemes that support batch verifications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권12호
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• pp.5553-5571
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• 2016

In this paper, we introduce a new concept called generalized ring signcryption (GRSC), which can achieve ring signature and ring signcryption functions with only one key pair and one algorithm. It is very useful for a system which has a large number of users, or has limited storage space, or whose function requirements may be changed later. We give a formal definition and a security model of GRSC and propose a concrete scheme based on bilinear pairings. In the random oracle model, the scheme's confidentiality can be proved under the GBDH assumption, and its unforgeability can be proved under GDH' assumption, and what is more, this scheme also allows unconditional anonymity. Compared with other identity-based ring signcryption schemes that use bilinear pairings as well, our scheme is a highly efficient one.