• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.11 no.3
• /
• pp.33-44
• /
• 2001

E-commerce has various advantages such as saving the cost and no constraint on time and space, unlike real-world commerce. On the other hand, e-commerce has some important issues to solve since the commerce is conducted on the cyberspace. The issues are a mutual confidence of parties participating in the commerce as well as a method of payments. On early days, electronic cash was designed using blind digital signature to protect the personal information from being exposed and to provide the perfect anonymity for user. In this paper, a new blind signature scheme based on Feige-Fiat-Shamir digital signature is proposed, which is very efficient compared with the other schemes in terms of the computational complexity. Also, a traceable Electronic Cash System which is based on the proposed blind digital signature is designed, which has a nice feature of identifying the spender in case of using the money illegally.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.13 no.6
• /
• pp.149-161
• /
• 2003

Partially blind signature scheme allows the signer to insert non-removable common information into his blind signature. Blind signatures providing with both users privacy and data authenticity are one of key parts of information systems, such anonymous electronic cash and electronic voting as typical examples. Partially blind signature, with which all expired e-cash but for still-alive can be removed from the banks database, copes well with the problem of unlimited growth of the banks' database in an electronic cash system. In this paper we propose an efficient ID-based partially blind signature scheme using the Weil-pairing on Gap Diffie-Hellman group. The security of our scheme relies on the hardness of Computational Diffie-Hellman Problem. The proposed scheme provides higher efficiency than existing partially blind signature schemes by using three-pass protocol between two participants, the signer and requesters also by reducing the computation load. Thus it can be efficiently used in wireless environment.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.9 no.4
• /
• pp.23-36
• /
• 1999

As the blind signature(10) does not reveal any information about the message or its signature it has been used for preventing the information leakage and for providing the anonymity in secure electronic payment systems. Unfortunately this perfect anonymity could be misused by criminals as blind signatures prevent linking the withdrawal of money nd the payment made 표 the same customer. Therefore we should provide publicly verifiable mechanism if it is required for the judge to trace the blackmailed messages. In this paper we propose a modified blind signature scheme which additionally provides the role of message recovery after analyzing the existing meta-ELGamal scheme(12) suggested by Horster. And we suggest a new fair blind multi-signature scheme based on the oblivious transfer protocol with which a judge can publicly verify its fairness and correctness if needed. Proposed scheme can also applicable to the diverse electronic payment applications.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
• /
• 2003.07a
• /
• pp.37-42
• /
• 2003

Threshold signature and blind signature are playing important roles in cryptography as well as practical applications such as e-cash and e-voting systems. In this paper, we present a new threshold blind digital signature based on pairings without a trusted third party. Our scheme operates on Gap Diffie-Hellman group, where Computational Diffie-Hellman problems are hard but Decision Diffie-Hellman problems are easy. For example, we use pairings that could be built from Weil pairing or Tate pairing. To the best of our knowledge, we claim that our scheme is the first threshold blind signature using pairings with provable security in the random oracle model.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
• /
• 2003.07a
• /
• pp.21-25
• /
• 2003

Key exposure is the most devastating attacks in any crytographic scheme. In this paper, we investigate key exposure problem in blind signature. We then present a variant of Okamoto-Guillou-Quisquater (OGQ for short) blind signature scheme guaranteeing forward secrecy. Namely, even if current secret key is revealed, forging any signature valid in the past is impossible. Our proposed scheme exhibits an efficient key updating protocol and introduces no significant communication overhead.

• The KIPS Transactions:PartD
• /
• v.9D no.2
• /
• pp.307-312
• /
• 2002

In this paper we propose the efficient blind signature scheme based on Gap problem. We can find the short signature schemes for Weil pairing as the example of signature schemes based on Gap problem. Since short signature scheme is based on elliptic curve, our proposed signature scheme can be used in wireless PKI environment.

• Journal of the Korea Society of Computer and Information
• /
• v.5 no.3
• /
• pp.70-75
• /
• 2000

This paper first examines the problems of digital signatures concerning discrete logarithms and factorizations. Then the study introduces a blind signature that is based on digital signature. It also attempts to propose a new digital signature by excluding the use of inverse which has presumably caused problems in limited resources. Finally, the paper suggests a blind signature that can be offered by this new digital signature.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.13 no.1
• /
• pp.3-10
• /
• 2003

In this paper, a partially blind signature schemes baled on EC-KCDSA is proposed and we applied it to design an electronic check payment system. Because the proposed partially blind signature scheme uses elliptic curve cryptosystem, it has better performance than any existing schems using RSA cryptosystem. When issuing a refund check, one-time pad secret key is used between the bank and the customer to set up secure channel. So the symmetric key management is not required.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
• /
• 1997.11a
• /
• pp.354-367
• /
• 1997

Chaum's blind signature scheme is the typical withdrawal procedure of electronic cash. In blind signature scheme, a signer sign a document while he never knows the content of the signed document. Yung and Jakobsson presented new signature scheme with which the content of document can be unblinded if unusual activity is detected. This signature is referred to as the magic ink signature. In this paper, we analyze the magic ink signature, and present two new magic ink signature schemes using KCDSA and Schnorr signature algorithm. We propose two types of the efficient electonic cash system using these magic ink signature schemes. One is the electronic cash system with a single server magic init signature scheme, and the other is the electronic cash system with a distributed magic ink signature scheme.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2003.05a
• /
• pp.824-827
• /
• 2003

With a rapid development of Information Telecommunication technique, network communication environment has been greatly improved. People come to feel more convinient to purchase products through Internet. Accordingly, various kinds of electronic payment systems have been developed and used. In this paper, we propose an algorithm which not only can associate the broker system with an electronic cash user, but also regenerate all amount of money previously paid using technique such as Meta-Message recovery and a RSA Blind Signature based on discrete logarithm problem.