• Journal of Korea Multimedia Society
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• v.21 no.4
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• pp.493-498
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• 2018

In this paper, we provide the performance analyses of a dual-hop amplify-and-forward(AF) relay transmission composed of asymmetric radio-frequence(RF) and free-space optical(FSO) links. In the mixed RF/FSO system, a relay is equipped with two receive antennas for RF signals and one additional transmit antenna for FSO signals. In order to improve a performance of RF link, a switch-and-stay (SSC) diversity technique is applied at the relay which can provide a proper link performance with a low complexity. Specifically, we offer the performance analyses of the proposed system in terms of outage probability and secrecy outage probability. In numerical examples, we compare the system performances with no diversity and selection combining systems and verify our analytical results via computer-based Monte-Carlo simulations.

• Journal of information and communication convergence engineering
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• v.7 no.3
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• pp.340-344
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• 2009

Multi-server password authentication schemes enable remote users to obtain service from multiple servers with single password without separately registering to each server. In 2007, Hu-Niu-Yang proposed an improved efficient password authenticated key agreement scheme for multi-server architecture based on Chang-Lee's scheme proposed in 2004. This scheme is claimed to be more efficient and is able to overcome a few existing deficiencies in Chang-Lee's scheme. However, we find false claim of forward secrecy property and some potential threats such as offline dictionary attack, key-compromise attack, and poor reparability in their scheme. In this paper, we will discuss these issues in depth.

• ETRI Journal
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• v.38 no.5
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• pp.934-940
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• 2016

In this paper, secure multicasting with the help of cooperative decode-and-forward relays is considered for the case in which a source securely sends a common message to multiple destinations in the presence of a single eavesdropper. We show that the secrecy rate maximization problem in the secure multicasting scenario under an overall power constraint can be solved using semidefinite programing with semidefinite relaxation and a bisection technique. Further, a suboptimal approach using zero-forcing beamforming and linear programming based power allocation is also proposed. Numerical results illustrate the secrecy rates achieved by the proposed schemes under secure multicasting scenarios.

• Journal of information and communication convergence engineering
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• v.9 no.4
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• pp.431-434
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• 2011

Password-based user-authentication schemes have been widely used when users access a server to avail internet services. Multiserver password-authentication schemes enable remote users to obtain service from multiple servers without separately registering with each server. In 2008, Jia-Lun Tsai proposed an improved and efficient password-authenticated key agreement scheme for a multiserver architecture based on Chang-Lee's scheme proposed in 2004. However, we found that Tsai's scheme does not provide forward secrecy and is weak to insider impersonation and denial of service attacks. In this article, we describe the drawbacks of Tsai's scheme and provide a countermeasure to satisfy the forward secrecy property.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.4
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• pp.29-36
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• 2003

In this paper, we propose a new Two-factor Authentication and Key Exchange(TAKE) protocol that can be applied to low-power PDAs in Public Wireless LAMs using two factor authentication and precomputation. This protocol provides mutual authentication session key establishment, identity privacy, and practical half forward-secrecy. The only computational complexity that the client must perform is one symmetric key encryption and five hash functions during the runtime of the protocol.

• Journal of the Korea Society of Computer and Information
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• v.16 no.3
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• pp.251-260
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• 2011

In this paper, we proposed a scheme that it safely exchanges encrypted keys without Trust Third Party (TTP) and Pre-distributing keys in multi-hop clustering sensor networks. Existing research assume that it exists a TTP or already it was pre-distributed a encrypted key between nodes. However, existing methods are not sufficient for USN environment without infrastructure. Some existing studies using a random number Diffie-Hellman algorithm to solve the problem. but the method was vulnerable to Replay and Man-in-the-middle attack from the malicious nodes. Therefore, authentication problem between nodes is solved by adding a ��TESLA. In this paper, we propose a modified Diffie-Hellman algorithm that it is safe, lightweight, and robust pair-wise agreement algorithm by adding One Time Password (OTP) with timestamp. Lastly, authentication, confidentiality, integrity, non-impersonation, backward secrecy, and forward secrecy to verify that it is safe.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.12 no.6
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• pp.93-112
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• 2002

Since the multicast group which is composed of various members is dynamic, members of the group frequently join or leave. So, for a new session, group keys are efficiently updated and distributed. In this paper, we describe very simple and new efficient logical key hierarchy(ELKH) protocol which is based on an one-way function. In the previous schemes, when the group controller distributes new created keys or updated keys to the members the information is usally encryted and then transmited over a multicast channel. But ELKH secretes the multicast message by using the one-way function and XOR operator instead of encrypting it. Hence our main construction improves the computational efficiency required from the group controller and group memebers while doesn't increase size of re-keying message when compared to $EHBT^{[12]}$. Assuming the security of an underlying one-way function, we prove that our scheme satisfies forward secrecy and backward secrecy.

• Journal of the Korea Society of Computer and Information
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• v.16 no.2
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• pp.183-191
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• 2011

Recently Wang-Li proposed the remote user authentication scheme using smart cards. But the proposed scheme has not been satisfied security requirements considering in the user authentication scheme using the password based smart card. In this paper, we described the Wang-Li and Yoon et al.'s authentication scheme simply, and we prove that the Wang-Li's scheme is vulnerable to a password guessing attack and impersonation attack in case that the attacker steals the user's smart card and extracts the information in the smart card. Accordingly, we propose the improved user authentication scheme based on the hash function and generalized ElGamal signature scheme that can withstand many possible attacks including a password guessing attack, impersonation attack and replay attack, and that can offer the function of forward secrecy. The result of comparative analysis, the our proposed scheme is much more secure and efficient than the Wang-Li and Yoon et al.'s scheme.

• Journal of Advanced Navigation Technology
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• v.17 no.6
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• pp.736-748
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• 2013

In this paper, we analyse the vulnerabilities of KL scheme which is an ID-based authentication scheme for AMI network, and propose two kinds of authentication schemes which satisfy forward secrecy as well as security requirements introduced in the previous works. In the first scheme, we use MDMS which is the supervising system located in an electrical company for a time-synchronizing server, in order to synchronize smart grid devices in home, and we process device authentication with a new secret value generated by OTP function every session. In the second scheme, we use a secret hash-chain mechanism for authentication process, so we can use a new secret value every session. The proposed two schemes have strong points and weak points respectively and those depend on the services area and its environment, so we can select one of them efficiently considering real aspects of AMI environment.

• KIPS Transactions on Computer and Communication Systems
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• v.2 no.12
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• pp.517-524
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• 2013

Although password-based authentication as known as knowledge-based authentication was commonly used but intrinsic problems such as dictionary attack remain unsolved. For that the study on possession-based authentication was required. User remote authentication using smartcard is proceeding actively since Lee et al. proposed user remote authentication using knowledge-based information(password) and possession-base information(smartcard) in 2002. in 2009, Xu et al. proposed a new protocol preserving user anonymity and Shin et al. proposed enhanced scheme with analysis of its vulnerabilities on user anonymity and masquerading attack in 2012. In this paper, we analyze Shin et al. scheme on forward secrecy and insider attack and present novel user authentication based on elliptic curve cryptosystem which is secure against forward secrecy, insider attack, user anonymity and masquerading attack.