Arnau VIVES-GUASCH †a) , Student Member, Maria-Magdalena PAYERAS-CAPELLÀ † †b) , Macià MUT-PUIGSERVER † †c) , Jordi CASTELLÀ-ROCA †d) , and Josep-Lluís FERRER-GOMILA † †e) , Nonmembers SUMMARY An electronic ticket is a contract, in digital format, between the user and the service provider, and reduces both economic costs and time in many services such as air travel industries or public transport. However, the security of the electronic ticket has to be strongly guaranteed, as well as the privacy of their users. We present an electronic ticketing system that considers these security requirements and includes the exculpability as a security requirement for these systems, i.e. users and the service provider can not falsely accuse each other of misbehavior. The system ensures that either both parties receive their desired data from other or neither does (fair exchange). Another interesting property is reusability. Thanks to reusability the tickets can be used a predefined number of times with the same security as single tickets. Furthermore, this scheme takes special care of the computational requirements on the users side by using light-weight cryptography. We show that the scheme is usable in practice by means of its implementation using mobile phones with Near Field Communication (NFC) capabilities.
The certified mail is a value-added service that is widely used in the paper world. However, the scientific community has not yet provided a solution for certified e-mail that has achieved widespread acceptance. This lack of a certified e-mail solution is not due to a lack of proposed approaches; because over the past 40 years, more than 100 protocols have been reported in journals and at conferences. The vast majority of these proposed protocols use a trusted third party (TTP) to achieve fairness. The few solutions without a TTP have not been successful due to their high computational and/or communication cost. Blockchain provides a new approach to develop the protocols without a TTP but without the prior drawbacks of the previous solutions without a TTP. Here, we present a new protocol for certified e-mail based on a blockchain without a conventional TTP that is integrated with the conventional e-mail infrastructure. The protocol is secure, efficient, and viable from a practical perspective.
Fair digital signature of contracts and agreements is an essential process in any electronic commerce scenario, and therefore also in data marketplaces, where the relationships and agreements among the different parties (consumers and providers) are more dynamic. In multi-party contract signing, N parties wish to sign a contract in a such a way that either all signatories obtain evidence of the signing or none obtains conflicting evidence regarding the honest signatories; the exchange must be fair. In this paper, we propose a blockchain-based multi-party contract signing protocol. This solution does not require the existence or potential intervention of a trusted third party (TTP), thus avoiding the difficulty of N signatories agreeing upon a TTP. In addition, this proposal meets the necessary requirements: fairness, timeliness, non-repudiation of origin, and non-repudiation of receipt. Furthermore, confidentiality can be easily achieved. To minimize costs associated with the use of blockchain, it should be invoked in the case of exception (analogous to optimistic solutions with a TTP) and by only one of the N signatories. However, when the use of blockchain is required, we show that its cost is within perfectly manageable margins.
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