• Convergence Security Journal
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• v.4 no.2
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• pp.35-41
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• 2004

Proxy signature scheme based on delegation of warrant is studied in these days. Proxy signature Is a signature scheme that the original signer delegates his signing warrant to the proxy signer, and the proxy signer creates a signature on behalf of the original signer. For using this scheme, the security for protecting from the forgeability or misuse is necessary. There are several security requirements for using the proxy signature schemes. In this paper we suggest the proxy-register protocol scheme that original signer registers to the verifier about the proxy related information. In our scheme, verifier verifies the signature that original signer creates about the proxy information and sets the warrant of proxy signer, validity period for proxy signature and some limitation. Finally, we will show the advantages of our suggestion by comparing with the previous proxy signature schemes.

• Journal of KIISE:Computer Systems and Theory
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• v.31 no.8
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• pp.465-472
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• 2004

Proxy signatures is a signature scheme that an original signer delegates one's signature capability to a proxy signer, and then the proxy signer creates a signature on behalf of the original signer. Delegation of authority is a common practice in the real world, in particular, it happens naturally in hierarchical groups such as company, bank and army, etc. In this paper, we propose a new dynamic multi-proxy signature scheme allowing repetitive delegations in a hierarchical group. We adopt multi-proxy signatures to enhance the security of proxy signature. In multi-proxy signatures, plural proxy signers can generate a valid proxy signature collectively on behalf of one original signer. In our scheme, the proxy group is not fixed but constructed dynamically according to some situations. Delegations are processed from higher level to lower level in the hierarchy using delegation tickets. When the original signer wants to delegate one's signature authority, the original signer generates a delegation ticket based on secret sharing and Diffie-Hellman problems. The delegation ticket is shared among proxy signers and then all the proxy signers can generate a valid proxy signature collectively by reconstructing the original signer's delegation ticket. If a certain proxy signer can not attend the proxy signature generating protocol, the proxy signer can also delegate repetitively his partial signature authority to the lower level participants, and then the proxies are constructed dynamically.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 1997.11a
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• pp.26-33
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• 1997

Mambo, Usuda, Okamoto 등에 의하여 최초로 제안된 대리 서명방식은 원서명자가 지정한 대리 서명자가 원서명자를 대신하여 서명하는 것을 허용한다. 본 논문에서는 기존의 대리 서명방식에서 발생하는 대리 서명자의 유효 위임 서명기간과 위임을 한 원서명자의 탈법을 방지할 수 있는 새로운 보증 부분 위임에 의한 대리 서명방식을 제안하였다. 제안한 방식은 유효기간의 정보가 포함된 보증서를 해쉬 함수를 이용하여 대리 서명자에게 위임 정보로 제공하고 다시 대리 서명자는 원서명자로부터 받은 위임정보에 자신의 정보를 부가하여 대리 서명 생성 정보로 사용토록 하였다.

• Proceedings of the Korea Multimedia Society Conference
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• 2003.11a
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• pp.116-119
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• 2003

대리 서명은 디지털 서명 기술의 응용으로서 Mambo에 의하여 최초로 제안이 되었고, Araki에 의하여 다단계 대리 서명으로 확장되었다. 본 논문에서는 위임 인증서와 서명 검증자의 서명 생성 여부를 원 서명자가 추후 확인하는 프로토콜을 이용하여 부인 봉쇄 및 원 서명자의 보호가 이루어지는 효율적이고 안정적인 다단계 대리 서명 방식을 제안한다.

• Journal of KIISE:Information Networking
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• v.31 no.6
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• pp.545-555
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• 2004

Proxy signature scheme allow a designated proxy person to sign a message on behalf of the original signer. Partially blind signature scheme allows the signer to insert non-removable common information into his blind signature. Proxy signature and partially blind signature are very important technologies in secure e-commerce. In this paper we propose new proxy signature scheme and ID-based partially blind signature scheme using bilinear pairing. further combining them, we propose a proxy partially blind signature scheme. The security of our schemes relies on the hardness of Computational Diffie-Hellman Problem. If we removing common information form propose ID-based partially blind signature scheme and proxy partially blind signature scheme, then they become variants of ID-based blind signature scheme and proxy blind signature scheme of Zhangs respectively.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2002.11a
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• pp.571-574
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• 2002

Lenstra와 Verheul에 의해 주장된 XTR은 짧은 키 길이와 빠른 연산 속도의 장점을 가지고 있기 때문에 복잡한 연산에 유용하게 사용될 수 있다. 또한 본 서명자의 부재시 위임 서명자가 대신 서명할 수 있는 대리 서명은 본 서명자가 대리 서명시 사용 될 비밀 정보를 생성하여 대리 서명자에게 전송한다. 대리 서명자는 전송된 비밀 정보의 유용성을 판별한 후 유용하다면 이 정보를 사용하여 서명하게 된다. 이러한 대리 서명 과정에서 발생하는 연산들은 XTR을 이용하여 속도의 향상을 가져올 수 있고, 짧은 키 길이로 동일한 안정성을 가진다. 따라서 유선에서 뿐만 아니라 무선에서도 효율성을 가질 수 있다.

• Journal of KIISE:Information Networking
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• v.30 no.4
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• pp.484-493
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• 2003

Proxy signature scheme is a cryptographic protocol that an original signer delegates her signing capability to a proxy signer, and then the proxy signer is able to create signatures on behalf of the original signer. In general, there is time-limit for which the signing capability of the proxy signer is valid. One of methods to limit the valid delegation time is to make public delegation information contain the expiration date of the delegation. however, in this method we cannot prevent the proxy signer from signing after the valid delegation is expired because no one knows the exact time when the proxy signer signed a message. The validity of the past legal signatures cannot be preserved in case that the proxy singer´s key is compromised during the delegation period. In this paper, we propose a new scheme, time-limited forward-secure proxy signature protocol, which prevents the proxy singer from signing after the valid delegation is expired and which preserves the validity of the past legal signatures even if the signing key is compromised. The proposed scheme does not require the exact time-information by making an original signer control time-related parameters and satisfies the forward-security property in each update-period of the proxy signing key. The time-period is determined according to the application characteristics or security policies.

• Proceedings of the Korea Information Assurance Society Conference
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• 2004.05a
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• pp.91-96
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• 2004

Proxy signature scheme based on delegation of warrant is studied in these days. Proxy signature is a signature scheme that the original signer delegates his signing warrant to the proxy signer, and the proxy signer creates a signature on behalf of the original signer. For using this scheme, the security for protecting from the forgeability or misuse is necessary, There are several security requirements for using the proxy signature schemes. In this paper we suggest the proxy-register protocol scheme that original signer registers to the verifier about the proxy related information. In our scheme, verifier verifies the signature that original signer creates about the proxy information and sets the warrant of proxy signer, validity period for proxy signature and some limitation. Finally, we will show the advantages of our suggestion by comparing with the previous proxy signature schemes.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2002.11a
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• pp.253-256
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• 2002

법인에서 권한의 위임을 통한 대리 서명은 이미 오프라인에서 널리 사용되고 있다. 이러한 대리 서명을 온라인 상에서 사용하기 위해서는 법인은 위임자에게 위임 인증서를 발급하고 위임자는 그 인증서로 대리서명을 하여 온라인 상에서 업무를 수행할 수 있다. 그러나 이러한 기술을 사용하기 위해서는 위임자의 권한 위임장이 위 변조와 오남용의 위험으로부터 안전하게 보호되어야 한다는 요구 사항이 먼지 만족 되야 하는 필요성이 있다. 위임 인증서는 안전한 대리 서명을 효과적으로 달성하기 위해 등장하였으며 현재 여러 가지 응용 서비스가 제안되고 있다. 본 논문에서는 법인이라는 특수한 환경에서 위임 인증서를 이용하여 안전한 대리서명을 사용할 수 있는 기술과 방법을 제안한다.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.2
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• pp.3-11
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• 2003

Proxy signatures are signature schemes in which an original signer delegates her signing capability to a proxy entity, who signs a message on behalf of the original signer. In this paper we propose the ID-based proxy signature schemes using a bilinear map. In the previous R-based proxy signature scheme, the proxy signer can misuse the right of the signing capacity and the public key directory is required. However, by inserting the warrant information such as the identity of the proxy signer and the limit of the signing capacity to the proxy signature, our scheme can prevent the misuse of the proxy key pair by the proxy signer and does not require a public key certificate. Furthermore, our scheme dose not need a secure channel to deliver the warrant. Consequently, the proposed scheme is more efficient and useful than the previous proxy signature schemes.