A Protocol for Fair Electronic Purchase Based on Concurrent Signatures

E-commerce protocols for the electronic purchase of goods are difficult to design and implement due to their complexity and high security demands. Fairness of such protocols in literature highly depends on an additional TTP（trusted third party）. However, it is difficult to find such a TTP in some situations. In addition, fairness for customers has been neither fully considered nor well satisfied in existing electronic purchasing protocols. In this paper, a new protocol FEP （fair electronic purchase） without a special TTP but an online bank is presented based on a concurrent digital signature scheme. The FEP protocol guarantees fair electronic purchase of goods via electronic payment between consumers, merchants and their online banks. The protocol is practical and the analysis based on the game logics shows that it achieves the properties of viability, fairness, and timeliness.

Generalization of perfect concurrent signatures

Recently, Susilo et al.＇s perfect concurrent signature scheme （PCS1） and Wang et al.＇s improved perfect concurrent signature scheme （iPCS1） are proposed, which are considered as good improvements on concurrent signatures, and they adopt the same algorithms. In this paper, we develop generic perfect concurrent signature algorithms of which Susilo et al. and Wang et al.＇s algorithms turn out to be a special instance. We also obtain numerous new, efficient variants from the generic algorithms which have not been proposed before. To display the advantage of these variants, a modified privacy-preserving PCS protocol is given. It shows that the new variants adapt to the protocol well and can form concrete privacy-preserving PCS schemes, while the original algorithms do not. Security proofs and efficiency analysis are also given.

Concurrent Signcryption Using Bilinear Pairings for E-commerce

Concurrent signature was introduced as an efficient approach to solving the problem of fair exchange of signatures. Almost all fair exchange e-commerce protocols based on concurrent signature that have been proposed until now either do not provide message privacy protection or adopt the sign-then-encrypt scheme to provide confidentiality. However,confidentiality is an important requirement of fair exchange e-commerce protocol. In this paper,a new concept called concurrent signcryption which combines the concepts of concurrent signature and signcryption together to resolve the confidentiality problem in e-commerce systems based on concurrent signature. We also propose a concurrent signcryption scheme using bilinear pairings and prove its security in the random oracle model. Compared with the sign-then-encrypt scheme using bilinear pairings,our scheme enjoys shorter message length and less operation cost. Moreover,in our scheme the two ambiguous signcryptions can be published in any order.

New concurrent digital signature scheme based on the computational Diffie-Hellman problem

Based on strong designated verifiers signatures,a new fair concurrent signature scheme is proposed. Compared with the previous concurrent signature schemes,even if a keystone must be chosen by the initial signer,the matching signer will easily get the keystone through an extraction algorithm. Due to the property of strong designate verifying,the initial signer couldn＇t make use of the keystone prepared carefully to deceive the matching signer. Then the matching signer is able to participate actively the signature scheme. Besides,there aren＇t bilinear operations in the keystone algorithm to deliver the keystone efficiently. Therefore the efficiency of our signature scheme is also improved.