• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.3
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• pp.1157-1177
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• 2014

Convertible authenticated encryption (CAE) schemes enable the signer to send a confidential message and its corresponding signature to the designated recipient. The recipient can also convert the signature into a conventional one which can be verified by anyone. Integrating the properties of self-certified public key systems, this paper presents efficient and computationally indistinguishable self-certified CAE schemes for strengthening the security of E-Commerce applications. Additionally, we also adapt the proposed schemes to elliptic curve systems for facilitating the applications of limited computing power and insufficient storage space. The proposed schemes are secure against known existential active attacks, satisfy the semantic security requirement, and have the following advantages: (i) No extra certificate is required since the tasks of authenticating the public key and verifying the signature can be simultaneously carried out within one step, which helps reducing computation efforts and communication overheads. (ii) In case of a later dispute, the recipient can convert the signature into an ordinary one for the public arbitration. (iii) The signature conversion can be solely performed by the recipient without additional computation efforts or communication overheads. (iv) The recipient of the signature can prove himself, if needed, to anyone that he is actually the designated recipient.

• Bulletin of the Korean Mathematical Society
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• v.53 no.4
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• pp.1051-1069
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• 2016

Combining the concept of self-certified public key and message recovery, Li-Zhang-Zhu (LZZ) gives the proxy signature scheme with message recovery using self-certified public key. The security of the proposed scheme is based on the discrete logarithm problem (DLP) and one-way hash function (OWHF). Their scheme accomplishes the tasks of public key verification, proxy signature verification, and message recovery in a logically single step. In addition, their scheme satisfies all properties of strong proxy signature and does not use secure channel in the communication between the original signer and the proxy signer. In this paper, it is shown that in their signature scheme a malicious signer can cheat the system authority (SA), by obtaining a proxy signature key without the permission of the original signer. At the same time malicious original signer can also cheat the SA, he can also obtain a proxy signature key without the permission of the proxy signer. An improved signature scheme is being proposed, which involves the remedial measures to get rid of security flaws of the LZZ et al.'s. The security and performance analysis shows that the proposed signature scheme is maintaining higher level of security, with little bit of computational complexity.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.15 no.3
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• pp.109-114
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• 2005

On the research for constructing secure group-oriented proxy signature schemes, there are several proposals of threshold proxy signature schemes which combine the notions of proxy signature with threshold signature. Recently, Hsu and Wu proposed a threshold proxy signature scheme which uses a self-certified public key based on discrete logarithm problem. In this paper, we show that this scheme is vulnerable to original signer's forgery attack. So our attack provides the evidence that this scheme does not satisfy nonrepudiation property.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.9 no.4
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• pp.61-70
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• 1999

In this paper we propose the verifiable self-certified schemes(key distribution scheme identification scheme digital signature scheme) based on ${\gamma}$th -residuosity which make up for defects of Girault's self-certified schemes allow the authenticity of public keys to be verified during the use of the keys. The security of our schemes is based on the difficulty of ${\gamma}$th -residuosity problem and discrete logarithm problem simultaneously.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.4
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• pp.71-84
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• 2003

Self-certified public keys need not be accompanied with a separate certificate to be authenticated by other users because the public keys are computed by both the authority and the user. At this point, verifiable self-certified public keys are proposed that can determine which is wrong signatures or public keys if public keys are used in signature scheme and then verification of signatures does not succeed. To verify these public keys, key generation center's public key trusted by users is required. If all users trust same key generation center, public keys can be verified simply. But among users in different domains, rusty relationship between two key generation centers must be accomplished. In this paper we propose inter-domain verifiable self-certified public keys that can be verified without certificate between users under key generation centers whose trusty relationship is accomplished. Also we present the execution of signature and key distribution between users under key generation centers use different public key parameters.

• Journal of KIISE
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• v.43 no.4
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• pp.497-508
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• 2016

With a cloud storage service, data owners can easily access their outsourced data in cloud storage on different devices and at different locations, and can share their data with others. However, as the users no longer physically have possession of their outsourced data and the cloud still facing the existence of internal/external threats, the task of checking the data integrity is formidable. Over recent years, numerous schemes have been proposed to ensure data integrity in an untrusted cloud. However, the existing public auditing schemes use a third-party auditor(TPA) to execute high computation to check data integrity and may still face many security threats. In this paper, we first demonstrate that the scheme proposed by Zhang et al. is not secure against our two threat models, and then we propose a self-certified public auditing scheme to eliminate the security threats and guarantee a constant communication cost. Moreover, we prove the securities of our public auditing scheme under three security models.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.1
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• pp.3-13
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• 2004

E-Commerce is suddenly spreading in a daily life. A rights trading system is a system that circulates digital-tickets such as plane tickets, software license, coupon. There are two main approaches so far account-based and smart-card based systems. The NTT Proposed FlexToken, a new smart card based copy prevention scheme for digital rights. They Proposed using pseudonymous self certified keys of Petersen and Horster in order to ensure anonymity of users. However. Petersen and Holster's scheme should register a pseudonymous key pair at TTP (One-time) every time so that users create the signature which is satisfied with unlinkability property In this paper, we propose a new anonymous rights trading system using group signature. This paper has a meaning having applied to digital rights trading system an efficient smart card based group signature.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2006.06a
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• pp.79-82
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• 2006

다중 사용자 환경에서 안전한 대리서명을 설계하는 연구의 하나로, threshold 서명 방식을 대리서명에 적용한 threshold 대리서명 기법들이 최근 많이 제안되고 있다. Xue와 Cao가 2004년 발표한 threshold 대리서명 기법은 Hsu-Wu 자체인증 공개키 방식 (Self-certified public key)을 기반으로 설계된 것으로 WISA 2005, CISC 2005, ICCSA 2006에서 각각 다른 취약성이 밝혀진 바 있다. 특히 CISC 2005, ICCSA 2006에서는 각각의 공격방법에 내성을 가질 수 있도록 Xue-Cao 기법을 개선하는 방안을 같이 제시하였다. 본 논문에서는 이러한 개선안이 적용된 Xue-Cao 기법에 대해 두 가지 종류의 원서명자 위조 공격이 가능함을 보인다. 하나는 Hsu-Wu 자체인증 공개키 방식의 취약성을 이용하는 것이고 다른 하나는 Xue-Cao 기법의 서명 생성 방식의 취약성에 기반한 것이다. 이러한 공격을 통해 개선된 Xue-Cao 기법 또한 대리자 보호, 부인방지와 같은 안전성 조건을 만족하지 않음을 확인한다.