• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.11
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• pp.2928-2940
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• 2013

Key exposure is a major threat to secure cryptosystems. To mitigate the impact caused by key-compromise attacks, a key-insulated cryptographic mechanism is a better alternative. For securing the large message communication in peer-to-peer networks, in this paper, we propose the first novel identity-based key-insulated encryption (IB-KIE) scheme with message linkages. Our scheme has the properties of unbounded time periods and random-access key-updates. In the proposed scheme, each client can periodically update his private key while the corresponding public one remains unchanged. The essential security assumption of our proposed scheme is based on the well-known bilinear Diffie-Hellman problem (BDHP). To ensure the practical feasibility, we also formally prove that the proposed scheme achieves the security requirement of confidentiality against indistinguishability under adaptive chosen-ciphertext attacks (IND-CCA2) in the random oracle model.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.4
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• pp.822-839
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• 2011

Group key agreement protocols derive a shared secret key for a group of users to ensure data confidentiality or/and integrity among the users in the subsequent communications. In this paper, we inspect two group key agreement schemes which have been proposed by Shi et al. and Zheng et al. in 2005 and 2007 respectively. Although both schemes were claimed to be secure in a heuristic way, we reveal several flaws using the Bellare-Rogaway security model extended to multi-party setting by Bresson et al. These flaws are found to be originated from inappropriate selection of key derivation function, inadvertent exclusion of partners' identities from the protocol specification and insufficient consideration in preserving known temporary information security and key freshness properties. Furthermore, we suggest and discuss proper countermeasures to address such flaws.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.6
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• pp.629-639
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• 1992

This paper examines the security vulnerability, demanded service, layering consideration for local area networks(LANs), and proposes a new key distribution system suitable to local area networks. the new key distribution system Is applicable to time quantum in encrytion key and then the time used arid the quantity of encryption message using the encryption key are limited. A system suggested in this paper can achive some higher concurrency of key and authentication of the opposite party. Even through a encryption key expose by reason of wiretapping of a frame unit, It has achived some more security and safety, because the contens of all traffic messages are not known.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.18 no.5
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• pp.17-30
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• 2008

In the paper, we consider password-based authenticated key exchange with different passwords, where the users do not share a password between themselves, but only with the server. The users make a session key using their different passwords with the help of the server. We propose an efficient password-based authenticated key exchange protocol with different passwords which achieves forward secrecy without random oracles. In fact this amount of computation and the number of rounds are comparable to the most efficient password-based authenticated key exchange protocol in the random oracle model. The protocol requires a client only to memorize a human-memorable password, and all other information necessary to run the protocol is made public.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.18 no.4
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• pp.27-35
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• 2008

In this paper we show that the full-round SCO-1[12] is vulnerable to the related-key differential attack. The attack on the full-round SCO-1 requires $2^{61}$ related-key chosen ciphertexts and $2^{120.59}$ full-round SCO-1 decryptions. This work is the first known attack on SCO-1.

• Convergence Security Journal
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• v.21 no.1
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• pp.55-62
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• 2021

Recently, the use of sensor devices is gradually increasing. As various sensor device emerge and the related technologies advance, there has been a dramatic increase in the interest in heterogeneous wireless sensor networks (WSNs). While sensor device provide us many valuable benefits, automatically and remotely supported services offered and accessed remotely through WSNs also exposes us to many different types of security threats. Most security threats were just related to information leakage and the loss of authentication among the involved parties: users, sensors and gateways. An user authentication protocol for wireless sensor networks is designed to restrict access to the sensor data only to user. In 2019, Chen et al. proposed an efficient user authentication protocol. However, Ryu et al. show that it's scheme still unstable and inefficient. It cannot resist offline password guessing attack and session key attack. In this paper, we propose an improved protocol to overcome these security weaknesses by storing secret data in device. In addition, security properties like session-key security, perfect forward secrecy, known-key security and resistance against offline password attacks are implied by our protocol.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.6
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• pp.15-20
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• 2008

Provable security has widely been used to prove a cryptosystem's security formally in crpytography. In this paper, we analyze the Cramer-Shoup public key cryptosystem that has been known to be provable secure against adaptive chosen ciphertext attack and argue that its security proof is not complete in the generic sense of adaptive chosen ciphertext attack. Future research should be directed toward two directions: one is to make the security proof complete even against generic sense of adaptive chosen ciphertext attack, and another is to try finding counterexamples of successful adaptive chosen ciphertext attack on the Cramer-Shoup cryptosystem.

• ETRI Journal
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• v.22 no.4
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• pp.25-31
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• 2000

Design of secure and efficient public-key encryption schemes under weaker computational assumptions has been regarded as an important and challenging task. As far as ElGamal-type encryption schemes are concerned, some variants of the original ElGamal encryption scheme based on weaker computational assumption have been proposed: Although security of the ElGamal variant of Fujisaki-Okamoto public -key encryption scheme and Cramer and Shoup's encryption scheme is based on the Decisional Diffie-Hellman Assumption (DDH-A), security of the recent Pointcheval's ElGamal encryption variant is based on the Computational Diffie-Hellman Assumption (CDH-A), which is known to be weaker than DDH-A. In this paper, we propose new ElGamal encryption variants whose security is based on CDH-A and the Elliptic Curve Computational Diffie-Hellman Assumption (EC-CDH-A). Also, we show that the proposed variants are secure against the adaptive chosen-ciphertext attack in the random oracle model. An important feature of the proposed variants is length-efficiency which provides shorter ciphertexts than those of other schemes.

• Journal of Korea Multimedia Society
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• v.20 no.3
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• pp.500-510
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• 2017

Recently Lee et al. proposed an improved symmetric key-based remote user authentication scheme to eliminate the security weaknesses of Kumari et al.'s scheme. They hence claimed that their scheme is secure to various well-known attacks. However, we found that Lee et al.'s scheme is still insecure against outsider attack, smart card stolen and off-line password guessing attack. To overcome these security vulnerabilities, we propose an enhanced authentication scheme with key-agreement which is based on the fuzzy-extractor. Furthermore, we prove that the proposed scheme is more secure, and that it serves to gratify all of the required security properties. Finally, we compare the performance and functionality of the proposed scheme with those of previous schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.2
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• pp.1064-1079
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• 2019

Information security has become increasingly important with the rapid development of mobile devices and internet. An efficient encryption system is a key to this end. In this paper, we propose an image encryption method based on the cross diffusion of two chaotic maps. We use two chaotic sequences, namely the Logistic map and the Chebyshev map, for key generation which has larger security key space than single one. Moreover, we use these two sequences for further image encryption diffusion which decreases the correlation of neighboring pixels significantly. We conduct extensive experiments on several well-known images like Lena, Baboon, Koala, etc. Experimental results show that our algorithm has the characteristics of large key space, fast, robust to statistic attack, etc.