• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.1
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• pp.84-90
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• 2011

In this paper, a VoIP-based voice secure telecommunication technology using the text-independent speaker authentication in the telematics environments is proposed. For the secure telecommunication, the sender's voice packets are encrypted by the public-key generated from the speaker's voice information and submitted to the receiver. It is constructed to resist against the man-in-the middle attack. At the receiver side, voice features extracted from the received voice packets are compared with the reference voice-key received from the sender side for the speaker authentication. To improve the accuracy of text-independent speaker authentication, Gaussian Mixture Model(GMM)-supervectors are applied to Support Vector Machine (SVM) kernel using Bayesian information criterion (BIC) and Mahalanobis distance (MD).

• Proceedings of the Korea Information Processing Society Conference
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• 2007.11a
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• pp.1010-1013
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• 2007

와이브로 서비스는 고속 이동 인터넷 환경 속에서 고속으로 무선 인터넷 서비스를 제공하는 기술이다. 기존의 무선인터넷 서비스와 달리 이동성을 제공한다는 점에서 차별화를 제공한다. 이렇게 이동하는 단말에게 양질의 데이터를 안전하게 전송하기 위해서는 보안기술이 중요한 요소로 작용한다. 서비스를 제공하기 전에 단말(Mobile Station)과 RAS(Radio Access Stations)간의 인증을 바탕으로 상호 키(TEK:Traffic Encryption Key)를 분배하고 TEK를 바탕으로 데이터를 암호화해서 전송하게 된다. 기존의 인증 프로토콜에서는 RAS에서 단독으로 키를 생성하는 방식이지만, 본 논문에서는 기존의 프로토콜의 문제점으로 지적된 Replay Attack에 대해 DH(Diffie-Hellman) 키 분배(Key Distribution) 방식을 적용하는 프로토콜을 제안함으로써 취약점에 대비 하였다. 이를 통해 RAS에 집중되는 키 생성에 대한 오버헤드를 단말에 분산 시킬 수 있다. 이로써 제안된 프로토콜을 사용해서 기존의 프로토콜을 사용했을 때보다 보안강도를 높일 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.3
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• pp.400-410
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• 2010

In an identity-based threshold broadcast encryption (IDTHBE) scheme, a broadcaster chooses a set of n recipients and a threshold value t, and the plaintext can be recovered only if at least t receivers cooperate. IDTHBE scheme is different from the standard threshold public key encryption schemes, where the set of receivers and the threshold value are decided from the beginning. This kind of scheme has wide applications in ad hoc networks. Previously proposed IDTHBE schemes have ciphertexts which contain at least n elements. In addition, the security of theses schemes relies on the random oracles. In this paper, we introduce two new constructions of IDTHBE for ad hoc networks. Our first scheme achieves S-size private keys while the modified scheme achieves constant size private keys. Both schemes achieve approximately (n-t)-size ciphertexts. Furthermore, we also show that they are provablesecurity under the decision bilinear Diffie-Hellman Exponent (BDHE) assumption in the standard model.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.9
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• pp.4624-4640
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• 2017

This paper mainly presents a secure and efficient e-Medical Record System via searchable encryption scheme from asymmetric pairings, which could provide privacy data search and encrypt function for patients and doctors in public platform. The core technique of this system is an extension public key encryption system with keyword search, which the server could test whether or not the files stored in platform contain the keyword without leaking the information about the encrypted file. Compared with former e-medical record systems, the system proposed here has several superior features: (1)Users could search the data stored in cloud server contains some keywords without leaking anything about the origin data. (2) We apply asymmetric pairings to achieve shorter key size scheme in the standard model, and adopt the dual system encryption technique to reduce the scheme's secure problem to the hard Symmetric External Diffie-Hellman assumption, which could against the variety of attacks in the future complex network environment. (3) In the last of paper, we analyze the scheme's efficiency and point out that our scheme is more efficient and secure than some other classical searchable encryption models.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.9
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• pp.4527-4547
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• 2018

Signcryption is a cryptographic primitive that provides authentication (signing) and confidentiality (encrypting) simultaneously at a lower computational cost and communication overhead. With the proposition of certificateless public key cryptography (CLPKC), certificateless signcryption (CLSC) scheme has gradually become a research hotspot and attracted extensive attentions. However, many of previous CLSC schemes are constructed based on time-consuming pairing operation, which is impractical for mobile devices with limited computation ability and battery capacity. Although researchers have proposed pairing-free CLSC schemes to solve the issue of efficiency, many of them are in fact still insecure. Therefore, the challenging problem is to keep the balance between efficiency and security in CLSC schemes. In this paper, several existing CLSC schemes are cryptanalyzed and a new CLSC scheme without pairing based on elliptic curve cryptosystem (ECC) is presented. The proposed CLSC scheme is provably secure against indistinguishability under adaptive chosen-ciphertext attack (IND-CCA2) and existential unforgeability under adaptive chosen-message attack (EUF-CMA) resting on Gap Diffie-Hellman (GDH) assumption and discrete logarithm problem in the random oracle model. Furthermore, the proposed scheme resists the ephemeral secret leakage (ESL) attack, public key replacement (PKR) attack, malicious but passive KGC (MPK) attack, and presents efficient computational overhead compared with the existing related CLSC schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.9
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• pp.4742-4770
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• 2019

Cloud computing provides a broad range of services like operating systems, hardware, software and resources. Availability of these services encourages data owners to outsource their intensive computations and massive data to the cloud. However, considering the untrusted nature of cloud server, it is essential to encrypt the data before outsourcing it to the cloud. Unfortunately, this leads to a challenge when it comes to providing search functionality for encrypted data located in the cloud. To address this challenge, this paper presents a public key encryption with equality test for heterogeneous systems (PKE-ET-HS). The PKE-ET-HS scheme simulates certificateless public encryption with equality test (CLE-ET) with the identity-based encryption with equality test (IBE-ET). This scheme provides the authorized cloud server the right to actuate the equivalence of two messages having their encryptions performed under heterogeneous systems. Basing on the random oracle model, we construct the security of our proposed scheme under the bilinear Diffie-Hellman (BDH) assumption. Eventually, we evaluate the size of storage, computation complexities, and properties with other related works and illustrations indicate good performance from our scheme.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.15 no.3
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• pp.77-89
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• 2005

As the ID-based public key cryptosystems become a very active research area, a number of ID-based key agreement protocols have been proposed, but unfortunately many of them were analyzed that there were some security flaws in the protocols. In addition to key agreement protocols, in recent, Liu et al. and Kim et al. proposed the key agreement protocols that multiple session keys are established at once among participated entities. In this paper, we propose an ID-based tripartite key agreement protocol that establishes 8 keys by improving the efficiency of the Liu et al's. Moreover, the proposed protocol can be used in the situation where multiple different private key generators(PKG) are involved. Therefore, because the private key issued by different PKGs belonging to each entity's domain can be used, our proposed scheme is more efficiently applicable to the practical applications.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.3
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• pp.101-110
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• 2003

Secure and reliable group communication is an increasingly active research area prompted by the growing popularity of many types of group-oriented and collaborative applications. The central challenge is secure and efficient group key management. While centralized methods are often appropriate for key distribution in large multicast-style groups, many collaborative group settings require distributed key agreement techniques. Most of prior group key agreement protocols have been focused on reducing the computational costs. One exception is STR protocol that optimizes communicational cost. On the other hand, it requires O(n) number of modular exponentiations. In this paper, we propose a new group key agreement protocol that modifies STR protocol by utilizing pairing based cryptography. The resulting protocol reduces computational cost of STR protocol while preserving the communication cost.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.3
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• pp.1502-1522
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• 2019

Leakage of secret keys may be the most devastating problem in public key cryptosystems because it means that all security guarantees are missing. The forward security mechanism allows users to update secret keys frequently without updating public keys. Meanwhile, it ensures that an attacker is unable to derive a user's secret keys for any past time, even if it compromises the user's current secret key. Therefore, it offers an effective cryptographic approach to address the private key leakage problem. As an extension of the forward security mechanism in certificate-based public key cryptography, forward-secure certificate-based signature (FS-CBS) has many appealing merits, such as no key escrow, no secure channel and implicit authentication. Until now, there is only one FS-CBS scheme that does not employ the random oracles. Unfortunately, our cryptanalysis indicates that the scheme is subject to the security vulnerability due to the existential forgery attack from the malicious CA. Our attack demonstrates that a CA can destroy its existential unforgeability by implanting trapdoors in system parameters without knowing the target user's secret key. Therefore, it is fair to say that to design a FS-CBS scheme secure against malicious CAs without lying random oracles is still an unsolved issue. To address this problem, we put forward an enhanced FS-CBS scheme without random oracles. Our FS-CBS scheme not only fixes the security weakness in the original scheme, but also significantly optimizes the scheme efficiency. In the standard model, we formally prove its security under the complexity assumption of the square computational Diffie-Hellman problem. In addition, the comparison with the original FS-CBS scheme shows that our scheme offers stronger security guarantee and enjoys better performance.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.12 no.3
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• pp.103-118
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• 2002

To provide the privacy of transmitted message over network the use of cryptographic system is increasing gradually. Because the security and reliability of the cryptographic system is totally rely on the key, the key management is the most important part of the cryptographic system. Although there are a lot of security products providing encryption, the security of the key exchange protocols used in the product are not mostly proved yet. Therefore, we have to study properties and operation of key agreement protocols based on elliptic curve in ANSI X9.63. furthermore, we analyze the security of their protocols under passive and active attacker models and propose the most suitable application field taking the feature of the protocols into account.