• Journal of the Korea Institute of Information Security & Cryptology
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• v.11 no.1
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• pp.73-85
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• 2001

Electronic check schemes are more efficient than electronic coin scheme with respect to computational costs and the amount of information exchanged. In spite of these, difficulties in making a refund reusable and in representing the face value of a check have discouraged its development. In this paper, a new online electronic check system is presented, which solves the above problems. This system uses the partially blind signature to provide user anonymity and to represent the face value of a check. The partially blind signature enables us to make the format of refunds and initially withdrawn checks identical. Thus, it allows refunds to be reused to buy goods without any limitatiosn. Both initially withdrawn checks and refunds in our system guarantee untraceability as well as unlinkability. We also use a one-time secret key as the serial number of a check to increase the efficiency of payments. The presented check system also provides multiple offline shopping sessions to minimize the number of online messages handled by a bank. During the multiple offline shopping session, we use a one-way accumulator to provide non-repudiation service. We also analyze our new systems our new system\`s security, efficiency, and atomicity.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.2
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• pp.69-80
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• 2003

Verifiable encryption is an encryption technique with which one can verify what has been encrypted even if one can not decrypt the ciphertext. This technique can be used in fair exchange to convince the counterpart of his or her receiving an item by presenting an encrypted form in advance. In this paper, a method that can guarantee the payment atomicity is proposed by applying verifiable encryption to an electronic cash system based on the representation problem. With the new method, the process of dispute settlement is improved in the fact that the trusted third party do not have to interact with the bank to resolve disputes. This method is also flexible in a sense that clients and shops can request for dispute settlement regardless of any deadline constraint. However, additional proof is necessary to apply verifiable encryption during payment. We discuss the security and the atomicity of our method, and compare ours with others.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.11 no.6
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• pp.27-40
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• 2001

In an offline system, the bank does not participate in payments. As a result, it is difficult to make the refund spendable. Due to this, current offline systems do not provide spendable refunds. In these systems, a check consists of two parts: a spendable part and a refund part. A client uses the spendable part during the payment phase, and uses the refund part to get the refund for the remainder of the check. Therefore, a client cannot reuse the remaining and must always refund it. Moreover, the relationship between the spent amount and the refund amount can be used to guess which check the client used when the client refunds the remaining. To remedy these problems, we propose a new offline system which allow clients to reuse the remaining values of the check. This system provides unlinkability of the payments made by using a single check. It also provides mechanisms to detect and identify clients who perform misconduct such as double spending and over spending. The required overall computational cost to withdraw, spend and refund a check in our system is lower than using several checks in other offline systems.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.11 no.6
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• pp.41-51
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• 2001

Group signature schemes allow a group member to sign messages anonymously on behalf of the group. In case of dispute, only a designated group manager can reveal the identity of the member. During last decade, group signature schemes have been intensively investigated in the literature and applied to various applications. However, there has been no scheme properly handling the situation that a group member wants to leave a group or is excluded by a group manager. As noted in[3], the complexity of member deletion stands in the way of real world applications of group signatures and the member deletion problem has been a pressing open problem. In this paper we propose an efficient group signature scheme that allows member deletion. The length of the group public key and the size of signatures all independent of the size of the group and the security of the scheme relies on the RSA assumption. In addition, the method of tracing all signatures of a specific member is introduced.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.6
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• pp.37-47
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• 2009

In VANET, each vehicle can obtain traffic information from other vehicles or infrastructure, and they frequently exchange life-critical safety message. Therefore, it is necessary among vehicles to establish a secure channel for keeping the driver's safe and protecting the channel against several attack challenges. TSVC is a representative scheme which needs low communication and computation to be performed. But, there is a delay when verifying the messages because it is designed based on TESLA. Thus, it is not acceptable to use TSVC for sending the time-critical messages. In this paper, we propose a novel message authentication scheme which reduces a delay for the verification of messages. Therefore, the proposed scheme can be suitable to transmitting time-critical messages. Furthermore, the scheme supports to privacy preservation and can robust against DoS attacks.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.20 no.6
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• pp.195-208
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• 2010

As information communication technologies have highly advanced, a large amount of user sensitive information can be easily collected and unexpectedly distributed. For user-friendly services, a service provider requires and processes more user information. However known privacy protection models take on a passive attitude toward user information protection and often involve serious weaknesses. In reality, information exposure by unauthorised access and mistakenly disclosure occurs frequently. In this paper, we study on the applicability of anonymous authentication services for fine-grained user privacy protection. We analyze authentication schemes and classify them according to the level of privacy newly defined in this paper. In addition, we identify security requirements that a privacy protection scheme based on anonymous authentication can achieve within legal boundary.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.20 no.4
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• pp.75-87
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• 2010

Secure communication has been one of the main challenges in vehicular ad hoc networks(VANET) since broadcast messages from nearby vehicles contain life-critical information for drivers and passengers. So far various secure communication schemes have been proposed to secure the communication in VANET, and they satisfy most security requirements. However most of them need to put trust on roadside units(RSUs), which are usually deployed in unattended area and vulnerable to compromise. In this paper, we propose a secure communication scheme, which does not need to put trust on RSUs. And we adopt a grouping technique to averagely divide the huge burden in the server without jeopardizing the anonymity of users. Moreover we design a complete set of protocols to satisfy common security requirements with a relatively lower hardware requirement. At last, we evaluate the scheme with respect to security requirements, communication overhead, storage overhead and network performance.

• The Journal of the Korea Contents Association
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• v.20 no.12
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• pp.593-610
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• 2020

The purpose of this study is to explore how the collectivism of Koreans has changed or has not changed. Through in-depth interviews and FGI with the older and new generations, keywords that express Korean collectivism today were discovered. First, the collectivism of Koreans is defined as 'selective collectivism', which is based on a more compact group consisting of self-selected members rather than a given group as before. Second, with the development of technology, online collectivism, in contrast to offline collectivism, emerged. Online collectivism is based on communication using online technology, and is characterized by horizontal relationship based on anonymity and 24-hour connectivity that transcends time and space. Third, the most important factor that composes Korean collectivism was found to be 'Cheong', which was recognized as an unchanged aspect of collectivism. Lastly, for Koreans, the group is closely related to self-identity, and for this reason, Koreans are obsessed with the sense of belonging to the group membership and the relationship with the members. The implications and limitations of the study were discussed.

• The Journal of the Convergence on Culture Technology
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• v.8 no.1
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• pp.583-590
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• 2022

With the release of the Bitcoin source in 2009, cryptocurrencies are continuously developing and expanding the market. Recently, new applicability is expanding centered on NFT coin and metaverse payment service. In particular, the Central Cryptocurrency Exchange actively supports relay transactions between cryptocurrencies or between traditional fiat currencies and cryptocurrencies. The cryptocurrency trading market based on such a central exchange encouraged speculative factors of cryptocurrencies, strongly arousing speculation and futility of cryptocurrencies. In addition, the central cryptocurrency exchange induces the centralization of users and virtual assets, thereby hindering the decentralization and security enhancement strategies of the block chain. Therefore, this study describes the current status and problems of centrally controlled centralized cryptocurrency exchanges in service, and presents a distributed cryptocurrency exchange modeling strategy and major issues as a decentralization model of the exchange. This research can strengthen the anonymity, decentralization, and autonomy of cryptocurrency based on blockchain.

• The Journal of the Convergence on Culture Technology
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• v.7 no.2
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• pp.157-163
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• 2021

This study attempted to find individual reasons for inducing cybercrime. The survey was conducted targeting investigators and security experts on 11 types of cybercrime. There are 16 internal factors that cause crime and classified according to Maslow's 5 steps. As a result of the survey on a total of 176 items, the credibility of the Cronbach's Alpha coefficient was 0.925. The result of the factor analysis is as follows. Factor analysis results are maslow phase 1 physiological desire is commercial, sykes. Phase 2 safety desires are not punishable and crowd. The three-stage social desire is impulsiveness, indifference, etc. The fourth stage of respect is anonymity and honor. The desire for self-reality in stage 5 has been reduced to indesity, a loss of moderation, morality, and media effects. In conclusion, the physiological desire, the desire for respect for the crime of infringing on the information and communication network, the desire for menstruation, the desire for self-realization for the crime of using information and communication networks, the desire for self-actualization for the crime of illegal content. It was in the order of desire.