• Journal of KIISE:Computer Systems and Theory
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• v.30 no.5_6
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• pp.239-249
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• 2003

The secret sharing is the basic concept of the threshold cryptosystem and has an important position in the modern cryptography. At 1995, Jarecki proposed the proactive secret sharing to be a solution of existing the mobile adversary and also proposed the share renewal scheme for (k, n) threshold scheme. For n participants in the protocol, his method needs $O(n^2)$ modular exponentiation per one participant. It is very high computational cost and is not fit for the scalable cryptosystem. In this paper, we propose the efficient share renewal scheme that need only O(n) modular exponentiation per participant. And we prove our scheme is secure if less than img ${\frac{1}{2}}$ n-1 adversaries exist and they are static adversary.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.769-771
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• 2002

임계 암호시스템은 현대 암호학에서 중요한 한 축을 이루는 암호학의 한 분야이다. 본 논문에서는 임계 암호시스템의 근간이 되는 비밀 분산(Secret Sharing)의 한 분야인 (k, n) threshold scheme에서 능동적 비밀 분산 (Proactive Secret Sharing)을 위한 공유(Share)갱신 방법을 개선한 새로운 공유 갱신 방법을 제안한다. 이전 방법은 각 참여자당 O(n$^2$)의 모듈라 멱승 연산을 수행하는데 비하여 제안 방법은 O(n)의 모듈라 멱승 연산만으로 공유갱신이 가능하다. 이와 함께 본 논문에서는 k ＜(1/2)n-1인 경우에 대하여 제안 방법의 안전함을 증명한다.

• Convergence Security Journal
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• v.20 no.4
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• pp.177-186
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• 2020

In current public blockchain, any node can see every blocks, so that public blockchain provider transparent property. However, some application requires the confidential information to be stored in the block. Therefore, this paper proposes a multi-layer blockchain that have the public block layer and the private block for confidential information. This paper suggests the requirement for encryption of private block. Also, this paper shows the t-of-n threshold cryptosystem without dealer who is trusted third party. Moreover, the delegated node who has key information can be withdraw the delegated node group or a new delegated node can join in the delegated node group. Therefore, the paper proposes an efficient key information resharing scheme for withdraw and join. Finally proposed scheme satisfies the requirements for encryption and fairness.