• KSII Transactions on Internet and Information Systems (TIIS)
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• v.2 no.6
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• pp.312-332
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• 2008

Password-based authentication key exchange (PAKE) protocols in the literature typically assume a password that is shared between a client and a server. PAKE has been applied in various environments, especially in the “client-server” applications of remotely accessed systems, such as e-banking. With the rapid developments in modern communication environments, such as ad-hoc networks and ubiquitous computing, it is customary to construct a secure peer-to-peer channel, which is quite a different paradigm from existing paradigms. In such a peer-to-peer channel, it would be much more common for users to not share a password with others. In this paper, we consider password-based authentication key exchange in the three-party setting, where two users do not share a password between themselves but only with one server. The users make a session-key by using their different passwords with the help of the server. We propose an efficient password-based authentication key exchange protocol with different passwords that achieves forward secrecy in the standard model. The protocol requires parties to only memorize human-memorable passwords; all other information that is necessary to run the protocol is made public. The protocol is also light-weighted, i.e., it requires only three rounds and four modular exponentiations per user. In fact, this amount of computation and the number of rounds are comparable to the most efficient password-based authentication key exchange protocol in the random-oracle model. The dispensation of random oracles in the protocol does not require the security of any expensive signature schemes or zero-knowlegde proofs.

• Journal of Information Processing Systems
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• v.6 no.1
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• pp.43-52
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• 2010

In the secure communication areas, three-party authenticated key exchange protocol is an important cryptographic technique. In this protocol, two clients will share a human-memorable password with a trusted server, in which two users can generate a secure session key. On the other hand the protocol should resist all types of password guessing attacks. Recently, STPKE' protocol has been proposed by Kim and Choi. An undetectable online password guessing attack on STPKE' protocol is presented in the current study. An alternative protocol to overcome undetectable online password guessing attacks is proposed. The results show that the proposed protocol can resist undetectable online password guessing attacks. Additionally, it achieves the same security level with reduced random numbers and without XOR operations. The computational efficiency is improved by $\approx$ 30% for problems of size $\approx$ 2048 bits. The proposed protocol is achieving better performance efficiency and withstands password guessing attacks. The results show that the proposed protocol is secure, efficient and practical.

• ETRI Journal
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• v.36 no.5
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• pp.856-864
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• 2014

Usually, key-establishment protocols are suggested in a security model. However, there exist several different security models in the literature defined by their respective security notions. In this paper, we study the relations between the security models of key establishment. For the chosen security models, we first show that some proven key-establishment protocols are not secure in the more restricted security models. We then suggest two compilers by which we can convert a key-establishment protocol that is secure in a specific security model into a key-establishment protocol that is still secure in a more restricted security model.

• 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.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.11a
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• pp.1083-1085
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• 2010

상호간의 보안 통신을 위해서는 서로간의 안전한 비밀키 교환이 이루어져야 한다. 이를 보장하기 위해서는 안전한 키교환 프로토콜이 사용되어야 한다. 키교환 프로토콜은 안전성을 보장함과 동시에 키의 신선도와 확신에 대한 요구사항을 모두 만족시켜야한다. 현재 대표적인 키교환 프로토콜인 Diffie-Hellman을 기본으로 하는 다양한 프로토콜이 연구 및 개발되고 있다. 최근에 연구된 EKE-E(Encrypted Key Exchange-Efficient) 프로토콜은 Diffie-Hellman 알고리즘을 통한 키교환을 제공하며 man-in-the-middle공격과 오프라인 사전공격에 대한 안정성을 보장한다. 하지만 재전송 공격에 취약성을 가진다. 본 논문에서는 최근에 제안된 키교환 프로토콜인 EKE-E의 안전성을 만족하며 재전송공격에 안전한 프로토콜을 제안한다. 동시에 연산을 줄여 보다 성능을 향상시킨다.

• Journal of Internet Computing and Services
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• v.9 no.2
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• pp.83-88
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• 2008

Session initiation protocol (SIP) is an application-layer prolocol to initiate and control multimedia client session. When client ask to use a SIP service, they need to be authenticated in order to get service from the server. Authentication in a SIP application is the process in which a client agent present credentials to another SIP element to establish a session or be granted access to the network service. In 2005, Yang et al. proposed a key exchange and authentication scheme for use in SIP applications, which is based on the Diffie-Hellman protocol. But, Yang et al.'s scheme is not suitable for the hardware-limited client and severs, since it requires the protocol participant to perform significant amount of computations (i.e., four modular exponentiations). Based on this observation. Huang and Wei have recently proposed a new efficient key exchange and authentication scheme thor improves on Yang et al.'s scheme. As for security, Huang and Wei claimed, among others, that their scheme is resistant to offline dictionary attacks. However, the claim turned out to be untrue. In this paper, we show thor Huang and Wei's key exchange and authentication scheme is vulnerable to on offline dictionary attack and forward secrecy.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.3
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• pp.13-25
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• 2004

The key exchange protocols are very crucial tools to provide the secure communication in the broadband satellite access network. They should be required to satisfy various requirements such as security, key confirmation, and key freshness. In this paper, we present the guideline of security functions in BSAN(Broadband Satellite Access Network), and analyze the specification of the security primitives and the hey exchange Protocols for the authenticated key agreement between RCST(Return Channel Satellite Terminal) and NCC(fretwork Control Centre). In addition, we propose the security specification for a domestic broad satellite network based on the analysis on the analysis profile of ETSI(European Telecommunications Standards Institute) standards. The key exchange protocols proposed in ETSI standard are vulnerable to man-in-the-middle attack and they don't provide key confirmation. To overcome this shortcoming, we propose the 4 types of the key exchange protocols which have the resistant to man-in-the-middle-attack, key freshness, and key confirmation, These proposed protocols can be used as a key exchange protocol between RCST and NCC in domestic BSAN. These proposed protocols are based on DH key exchange protocol, MTI(Matsumoto, Takashima, Imai) key exchange protocol, and ECDH(Elliptic Curve Diffie-Hellman).

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.10 s.340
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• pp.31-38
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• 2005

Ipsec is a security protocol suite that provides encryption and authentication services for IP messages at the network layer of the internet. Internet Key Exchange (IKE) is a protocol that is used to negotiate and provide authenticated keying materials in a protected manner for Security Associations (SAs). In this paper, we propose a dynamic key lifetime change algorithm for performance enhancement of virtual private networks using IPSec. The proposed algorithm changes the key lifetime according to the number of secure tunnels. The proposed algorithm is implemented with Linux 2.4.18 and FreeS/WAN 1.99. The system employing our proposed algorithm performs better than the original version in terms of network performance and security.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10c
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• pp.291-293
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• 1999

본 논문은 네트워크 인증시스템 AUTHSYS에서 사용하는 SNAKE 프로토콜에 관한 논문이다. SNAKE 프로토콜은 키 분배 센터를 사용하는 중재 방식의 프로토콜이며, 티켓을 활용하는 프로토콜이다. SNAKE 프로토콜은 대칭형 암호 알고리즘과 해시 알고리즘만을 사용하는 프로토콜이며, none 기반 기법을 사용하여 메시지의 최근성을 보장한다. 또한 시스템간에 클릭 동기화를 요구하지 않으며, 클라이언트의 연산부담을 최소화하여 이동 컴퓨팅 환경에서 효과적으로 사용할 수 있도록 설계한 프로토콜이다.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2003.12a
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• pp.211-220
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• 2003

본 논문은 신뢰 할 수 없는 네트워크를 통해서도 사용자를 인증하거나 키를 교환하는 것에 적합한 패스워드 인증 프로토콜을 제안한다. 기본 아이디어는 패스워드 검증정보의 램덤성(randomness)을 증가시키기 위하여, 패스워드를 분할한 후 이에 대한 각 패스워드 지식을 확대(amplification)하는 구조로 설계된다. 또한 서버측 파일을 암호화하여 보관함으로써 서버 파일 타협 공격에 강인하도록 구성하였다. 더불어 검증정보 및 서버의 암호화키가 다수의 서버들에게 분산되도록 설계된 방식을 제안한다.