• Journal of KIISE:Information Networking
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• v.30 no.3
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• pp.355-370
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• 2003

In offline check systems, a client does not have to pay the exact amount. Instead, a client refunds the difference between the check value and the paid amount. In most offline systems, clients can not spend the remainder. But if the refund can be made spendable, it would provide a more convenient payment method. In this paper, we present a new offline system, which allows refunds to be reused as payments. In our system, the shop issues a new check using its private key for the difference. This new check, called the refund check, can be spent in the same way as checks issued by the bank. If the refund check is deposited to, or refunded at the bank, the bank charges the issuer of the check for the amount. The form of a check in this system is much simpler than previous check systems. It also uses a more flexible and efficient denomination method. The refund check is unlinkable to the check used in the payment where the refund check was issued. This system provides coin and owner tracing mechanisms to reinforce controls on illegal use of anonymous checks and was designed with consideration to the atomicity of transactions.

• 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.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.

• International Commerce and Information Review
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• v.5 no.2
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• pp.19-45
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• 2003

The main issues addressed in this paper are as follows : First, this paper makes a distinction among types of e-money, IC card type versus Network type, open-loop type versus closed-loop type, online type versus offline type and accountable type versus unaccountable type, and analysis the clear and accurate criterion. Second, generally speaking, e-money is a claim on originator of e-money and not legal tender, so, delivery of e-money by itself does not relieve of monetary obligation. Between it is not easy to define e-money, by now there are many definitions of e-money, there is a legal uncertainty accordingly and then it is not easy to find proper law applicable to resolve a particular issue. As a result. many problems relating to e-money would be solved through analogical application of the moot proper law among the laws that apply to the cash, check, credit card, or fund transfer after analyzing type of e-money at issue. This paper studies the methods on diffusion of the utilization of electronic money. To diffuse the usage of electronic money, it need; prerequisitely as a basic conditions independence of electronic money, non-reusability, and anonymity. And also as a additional conditions it need; usability in the offline commerce, transferability, divisibility. And now electronic money is used very actively, but still has many Jaw problems such as protections of consumer, law enforcement, supervisory, etc. So electronic money has called as money, but it is sure that electronic money is not a legal tender. So to facilitate the economic function of the electronic monel it is need to supplement the electronic money in the legal sides.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.8B
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• pp.939-946
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• 2011

The Internet banking service provides convenience than the traditional offline services. However, it still causes a number of security problems including hacking. In order to strengthen security, the financial institutions have provided such authentication methods as the official authentication certificate, the security token, the security card and OTP. However, the incidents related to hacking have continuously occurred. Especially, various weak points have been suggested for the authentication methods in regard to such types of hacking as the memory hacking or the MITM attack. So I needed was a new authentication method. In this study, the two-channel authentication method which provide two-way authentication on the user's PC and mobile device when executing the electronic financial transactions in the Internet banking environment is suggested. Also, by analyzing it in comparison with other existing methods, it is possible to check that the prospects of safety and credibility are strengthened.