• Bulletin of the Korean Mathematical Society
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• v.46 no.2
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• pp.303-309
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• 2009

Cryptographic protocols depend on the hardness of some computational problems for their security. Joux briefly summarized known relations between assumptions related bilinear map in a sense that if one problem can be solved easily, then another problem can be solved within a polynomial time [6]. In this paper, we investigate additional relations between them. Firstly, we show that the computational Diffie-Hellman assumption implies the bilinear Diffie-Hellman assumption or the general inversion assumption. Secondly, we show that a cryptographic useful self-bilinear map does not exist. If a self-bilinear map exists, it might be used as a building block for several cryptographic applications such as a multilinear map. As a corollary, we show that a fixed inversion of a bilinear map with homomorphic property is impossible. Finally, we remark that a self-bilinear map proposed in [7] is not essentially self-bilinear.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7C
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• pp.1007-1014
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• 2004

In this paper, H.235 based security mechanism for H.323 multimedia applications was implemented in embedded environment. H.235 covers authentication using HMAC-SHAI -96, authenticated Diffie-Hellman key exchange, security capability exchange, session key management for voice encryption, and encryption functions such as DES, 3DES, RC2. H.235-based mechanisms were also analyzed in terms of its security and possible attacks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.4
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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.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2003.07a
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• pp.73-76
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• 2003

인터넷상에서 많은 상거래 및 개인 정보들이 전송되고 있다. 그러나 이런 정보들은 많은 위협에 노출되어 있다. 이를 해결하기 위해서 전자서명, 컨텐츠 암호 등 많은 방법들이 제안되고 있지만, 이런 기법들을 이용하기 위해서는 키의 생성, 분배, 전송을 위한 처리 모듈이 기본적으로 필요하다. 이런 모듈 중 전송 및 분배 시에 제3자를 이를 가로채어서 유용하는 문제점이 발생된다. 이에 본 연구는 기존의 키 교환 알고리즘인 Diffie-Hellman(DH)에 공개키 암호화 방법과 패스워드 방법을 추가하여 기존의 키 교환에서 발생된 문제점들에 대해서 해결 하고자 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.11
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• pp.967-969
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• 2013

In this paper, we propose an efficient mult-signature scheme based on a bilinear mapping for shared data in the cloud and prove the security of the proposed scheme using the difficulty of the computational Diffie-Hellman problem. For verification, the scheme is using the sum of the hash values of stored data rather than the entire data, which makes it feasible to reduce the size of the downloaded data.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.8
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• pp.1972-1988
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• 2013

In order to deal with key exposure problem, we introduce forward secure technique into certificateless proxy signature scheme, and propose the formal definition and security model of the forward secure certificateless proxy signature. Our security model takes into account the super adversary in certificateless signature. Furthermore, we present a construction of forward secure certificateless proxy signature scheme with bilinear maps. Based on the difficulty of computational Diffie-Hellman problem, we prove the scheme is secure against chosen message attack in the random oracle model. Finally, we analyze efficiency of the proposed scheme.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2008.10b
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• pp.445-448
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• 2008

The key establishment between nodes is one of the most important issues to secure the communication in wireless sensor networks. Some researcher used the probabilistic key sharing scheme with a pre-shared key pool to reduce the number of keys and the key disclosure possibility. However, there is a potential possibility that some nodes do not have a common share in the key pool. The purpose of this paper is to devise a peer to peer key sharing protocol (PPKP) based on Quorum system and Diffie-Hellman key exchange scheme (DHS). The PPKP establishes a session key by creating a shared key using the DHS and then scrambles it based on Quorum system to secure that. The protocol reduces the number of necessary keys than the previous schemes and could solve the non-common key sharing possibility problem in the probabilistic schemes.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2002.06a
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• pp.190-194
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• 2002

Multiplication in Galois Field GF(2/sup m/) is a primary operation for many applications, particularly for public key cryptography such as Diffie-Hellman key exchange, ElGamal. The current paper presents a new architecture that can process Montgomery multiplication over GF(2/sup m/) in m clock cycles based on cellular automata. It is possible to implement the modular exponentiation, division, inversion /sup 1)/architecture, etc. efficiently based on the Montgomery multiplication proposed in this paper. Since cellular automata architecture is simple, regular, modular and cascadable, it can be utilized efficiently for the implementation of VLSI.

• Journal of Communications and Networks
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• v.12 no.3
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• pp.201-208
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• 2010

We propose a new notion of metered signatures. Metered signature is an extension of k-times signatures in which a signer can generate only k signatures. However, the restriction of metered signatures can be more elaborate: It can be used k-times every day or to preserve the order of signed messages in some applications. Any violation of this regulation reveals a secret key or the signature on a predetermined message. The applications includes proxy signatures, limited free downloads, and the rating web site. We give two instances of metered signatures: One is based on the computational Diffie-Hellman problem (CDHP) using a bilinear map and the other is based on the RSA problem. In both schemes, the signature and certificate size and the verification cost are constant with respect to k. Further, we show that the proposed metered signatures admit batch verification of many signatures almost at one verification cost with small security loss.

• Journal of the Korea Society of Computer and Information
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• v.23 no.2
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• pp.53-61
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• 2018

In this paper, the author proposes an efficient group key agreement scheme in a mobile environment where group members frequently join and leave. This protocol consists of basic protocols and general ones and is expected to be suitable for communications between a mobile device with limited computing capability and a key distributing center (or base station) with sufficient computing capability. Compared with other schemes, the performance of the proposed protocol is a bit more efficient in the aspects of the overall cost for both communication and computation where the computational efficiency of the scheme is achieved by using exclusive or operations and a one-way hash function. Also, in the aspect of security, it guarantees both forward and backward secrecy based on the computational Diffie-Hellman (CDH) assumption so that secure group communication can be made possible. Furthermore, the author proves its security against a passive adversary in the random oracle model.