• Journal of the Institute of Electronics Engineers of Korea CI
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• v.46 no.1
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• pp.78-87
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• 2009

An attribute-based signature scheme is a signature scheme where a signer's private key is associate with an attribute set and a signature is associated with an access structure. Attribute-based signature schemes are useful to provide anonymity and access control for role-based systems and attribute-based systems where an identity of object is represented as a set of roles or attributes. In this paper, we formally define the definition of attribute-based signature schemes and propose the first efficient attribute-based signature scheme that requires constant number of pairing operations for verification where a policy is represented as a disjunctive normal form (DNF). To construct provably secure one, we introduce a new interactive assumption and prove that our construction is secure under the new interactive assumption and the random oracle model.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.1_2
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• pp.110-118
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• 2006

Cryptographic protocol design in a two-party setting has of tel ignored the possibility of simultaneous message transmission by each of the two parties (i.e., using a duplex channel). In particular, most protocols for two-party key exchange have been designed assuming that parties alternate sending their messages (i.e., assuming a bidirectional half-duplex channel). However, by taking advantage of the communication characteristics of the network it may be possible to design protocols with improved latency. This is the focus of the present work. We present three provably-secure protocols for two-party authenticated key exchange (AKE) which require only a single round. Our first, most efficient protocol provides key independence but not forward secrecy. Our second scheme additionally provides forward secrecy but requires some additional computation. Security of these two protocols is analyzed in the random oracle model. Our final protocol provides the same strong security guarantees as our second protocol, but is proven secure in the standard model. This scheme is only slightly less efficient (from a computational perspective) than the previous ones. Our work provides the first provably- secure one-round protocols for two-party AKE which achieve forward secrecy.

• The KIPS Transactions:PartC
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• v.12C no.2 s.98
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• pp.157-168
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• 2005

Group key agreement protocols are designed to provide a group of parties securely communicating over a public network with a session key. The mobile computing architecture is asymmetric in the sense of computational capabilities of participants. That is, the protocol participants consist of the stationary server(application servers) with sufficient computational Power and a cluster of mobile devices(clients) with limited computational resources. It is desirable to minimize the amount of computation performed by each group member in a group involving low-power mobile devices such as smart cards or personal digital assistants(PDAs). Furthermore we are required to update the group key with low computational costs when the members need to be excluded from the group or multiple new members need to be brought into an existing group. In this paper, we propose a dynamic group key protocol which offers computational efficiency to the clients with low-power mobile devices. We compare the total communicative and computational costs of our protocol with others and prove its suity against a passive adversary in the random oracle model.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.3
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• pp.75-84
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• 2004

In this paper, we present a related key differential attack on Full-round GOST Firstly, we present a distinguishing attack on full rounds of GOST, which can distinguish it from random oracle with probability 1- 64$2^{64}$ using a related key differential characteristic. We will also show that H. Seki et al.'s idea can be applied to attack on 31 rounds of GOST combining our related key differential characteristic. Lastly, we propose a related key differential attack on full rounds of GOST. In this attack we can recover 12 bits of the master key with $2^{35}$ chosen plaintexts and $2^{36}$ encryption times for the 91.7% expectation of success rate.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.4
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• pp.163-181
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• 2004

Group key agreement protocols are designed to solve the fundamental problem of securely establishing a session key among a group of parties communicating over a public channel. Although a number of protocols have been proposed to solve this problem over the years, they are not well suited for a high-delay wide area network; their communication overhead is significant in terms of the number of communication rounds or the number of exchanged messages, both of which are recognized as the dominant factors that slow down group key agreement over a networking environment with high communication latency. In this paper we present a communication-efficient group key agreement protocol and prove its security in the random oracle model under the factoring assumption. The proposed protocol provides perfect forward secrecy and requires only a constant number of communication rounds for my of group rekeying operations, while achieving optimal message complexity.

• Smart Media Journal
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• v.12 no.2
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• pp.76-82
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• 2023

In the 4th industrial revolution, the blockchain that distributes and manages data through a P2P network is used as a new decentralized networking paradigm in various fields such as manufacturing, culture, and public service. However, with the advent of quantum computers, quantum algorithms that are able to break existing cryptosystems such as hash function, symmetric key, and public key cryptography have been introduced. Currently, because most major blockchain systems use an elliptic curve cryptography to generate signatures for transactions, they are insecure against the quantum adversary. For this reason, the research on the quantum-resistant blockchain that utilizes lattice-based cryptography for transaction signatures is needed. Therefore, in this paper, we propose a blind signature scheme for the blockchain in which the contents of the signature can be verified later, as well as signing by hiding the contents to be signed using lattice-based cryptography with the property of quantum resistance. In addition, we prove the security of the proposed scheme using a random oracle model.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.6
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• pp.23-35
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• 2009

Password-Authenticated Key Exchange (PAKE) Protocol is a useful tool for secure communication conducted over open networks without sharing a common secret key or assuming the existence of the public key infrastructure (PKI). It seems difficult to design efficient PAKE protocols using RSA, and thus many PAKE protocols are designed based on the Diffie-Hellman key exchange (DH-PAKE). Therefore it is important to design an efficient PAKE based on RSA function since the function is suitable for designing a PAKE protocol for imbalanced communication environment. In this paper, we propose a computationally-efficient key exchange protocol based on the RSA function that is suitable for low-power devices in imbalanced environment. Our protocol is more efficient than previous RSA-PAKE protocols, required theoretical computation and experiment time in the same environment. Our protocol can provide that it is more 84% efficiency key exchange than secure and the most efficient RSA-PAKE protocol CEPEK. We can improve the performance of our protocol by computing some costly operations in offline step. We prove the security of our protocol under firmly formalized security model in the random oracle model.