• The KIPS Transactions:PartC
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• v.12C no.7 s.103
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• pp.949-958
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• 2005

In the paper we study key agreement schemes when a party needs to establish a session key with each of several parties, thus having multiple session keys. This situation can be represented by a graph, tailed a key graph, where a vertex represents a party and an edge represents a relation between two parties sharing a session key. graphs to establish all session keys corresponding to all edges in a key graph simultaneously in a single session. A key agreement protocol of a key graph is a natural extension of a two-party key agreement protocol. We propose a new key exchange model for key graphs which is an extension of a two-party key exchange model. using the so-called randomness re-use technique which re-uses random values to make session keys for different sessions, we suggest two efficient key agreement protocols for key graphs based on the decisional Diffie-Hellman assumption, and prove their securities in the key exchange model of key graphs. Our first scheme requires only a single round and provides key independence. Our second scheme requires two rounds and provides forward secrecy. Both are proven secure In the standard model. The suggested protocols are the first pairwise key agreement protocols and more efficient than a simple scheme which uses a two-party key exchange for each necessary key. Suppose that a user makes a session key with n other users, respectively. The simple scheme's computational cost and the length of the transmitted messages are increased by a factor of n. The suggested protocols's computational cost also depends on n, but the length of the transmitted messages are constant.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04a
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• pp.518-520
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• 2003

This paper proposes a new session key agreement scheme which is based on Station-to-station protocol, or STS shortly. We extend key agreement model of STS, to take into account smart cards. Besides, we modify STS to withstand message replaying attack. Security analysis shows our scheme is still secure.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.8
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• pp.4025-4042
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• 2017

Session initiation protocol (SIP) is a kind of powerful and common protocols applied for the voice over internet protocol. The security and efficiency are two urgent requirements and admired properties of SIP. Recently, Hamed et al. proposed an efficient authentication and key agreement scheme for SIP. However, we demonstrate that Hamed et al.'s scheme is vulnerable to de-synchronization attack and cannot provide anonymity for users. Furthermore, we propose an improved and efficient authentication and key agreement scheme by using elliptic curve cryptosystem. Besides, we prove that the proposed scheme is provably secure by using secure formal proof based on Burrows-Abadi-Needham logic. The comparison with the relevant schemes shows that our proposed scheme has lower computation costs and can provide stronger security.

• Journal of Internet Computing and Services
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• v.4 no.6
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• pp.95-102
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• 2003

The Diffle-Hellman Key Exchange scheme can produce a common session key between the two communicators, but its problem is that it makes a man-in-the middle attack possible. To solve problems like these, several protocols have been put forward, and the Simple Authenticated Key Agreement (SAKA) Protocol is among them. This protocol has been suggested by Seo-Sweeney, Tseng, and Ku-Wang, respectively, In this paper, we will put forward a new protocol that has been improved from all the original protocols mentioned above, but is still safe and quick to use, While the existing protocol divides the common session key production stage and the verification stage, the protocol suggested in this paper takes care of both of those stages simultaneously, therefore improving the processing performance.

• Journal of Communications and Networks
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• v.18 no.2
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• pp.190-200
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• 2016

In this paper, we consider some aspects of binding properties that bind an anonymous user with messages. According to whether all the messages or some part of the messages are bound with an anonymous user, the protocol is said to satisfy the full binding property or the partial binding property, respectively. We propose methods to combine binding properties and anonymity-based authenticated key agreement protocols. Our protocol with the full binding property guarantees that while no participant's identity is revealed, a participant completes a key agreement protocol confirming that all the received messages came from the other participant. Our main idea is to use an anonymous signature scheme with a signer-controlled yet partially enforced linkability. Our protocols can be modified to provide additional properties, such as revocable anonymity. We formally prove that the constructed protocols are secure.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.18 no.3
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• pp.3-8
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• 2008

Ephemeral data are easily revealed if state specific information is stored in insecure memory or a random number generator is corrupted. In this letter, we show that Nam et al.'s group key agreement scheme, which is an improvement of Bresson et al.'s scheme, is not secure against session-state reveal attacks. We then propose an improvement to fix the security flaw.

• International Journal of Internet, Broadcasting and Communication
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• v.8 no.3
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• pp.50-57
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• 2016

In 2013, Li et al. proposed an improved smart card-based remote user password authentication scheme, and claimed that their scheme not only overcomes security weaknesses of the Chen et al.'s scheme but also is a more user friendly scheme compared with other schemes. In this paper, we analyze the security of Li et al.'s authentication scheme and we show that Li et al.'s authentication scheme is still insecure against the various attacks, such as the off-line password guessing attack, the forgery attack, and the session key generation attack etc. Also, we propose an improved scheme that can resist these security drawbacks of Li et al.'s authentication, even if the secret information stored in the smart card is revealed. As a result of security analysis, the improved scheme is relatively more secure against several attacks than other related schemes in terms of the security.

• International Journal of Internet, Broadcasting and Communication
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• v.9 no.3
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• pp.35-43
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• 2017

In 2013, Lee-Lie proposed secure smart card based authentication scheme of Zhu's authentication for TMIS which is secure against the various attacks and efficient password change. In this paper, we discuss the security of Lee-Lie's smart card-based authentication scheme, and we have shown that Lee-Lie's authentication scheme is still insecure against the various attacks. Also, we proposed the improved scheme to overcome these security problems of Lee-Lie's authentication scheme, even if the secret information stored in the smart card is revealed. As a result, we can see that the improved smart card based user authentication scheme for TMIS is secure against the insider attack, the password guessing attack, the user impersonation attack, the server masquerading attack, the session key generation attack and provides mutual authentication between the user and the telecare system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.8
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• pp.1982-1997
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• 2012

Authenticated multiple key agreement protocols not only allow participants to agree the multiple session keys within one run of the protocol but also ensure the authenticity of the other party. In 2011, Dehkordi et al. proposed an identity-based authenticated multiple key agreement protocol. In this paper, we demonstrate that Dehkordi et al.'s protocol is vulnerable to impersonation attacks. Furthermore, we have found that their protocol cannot provide perfect forward security or mutual security. Then we propose an identity-based authenticated multiple key agreement protocol which removes the weaknesses of the Dehkordi et al.'s protocol. Compared with the multiple key agreement protocols in the literature, the proposed protocol is more efficient and holds stronger security.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.9
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• pp.555-560
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• 2014

Recently, there are many researches on sharing group session key for members in a group. Among them, Harn and Lin proposed a scheme based on the Shamir's group session key and Liu, Cheng, Cao, and Jiang improved it to reduce the specific weakness. Especially, these schemes are based on the finite integer ring to protest the insider attack, in which a valid member can derived another member's secret using known information. In this paper, it is shown that the finite integer ring implies the failure of the reconstruction of group session key depending on the adopted parameters. We fix this problem and propose new group session key transfer scheme using the Shamir's secret sharing.