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The development of new applications of electronic commerce (e-commerce) that require the payment of small amounts of money to purchase services or goods opens new challenges in the security and privacy fields. This kind of payments are called micropayments and they have to provide a tradeoff between efficiency and security requirements to pay low-value(More)
Automatic Fare Collection (AFC) systems calculate the fare that the users must pay depending on the time of service (time-based) or the points of entrance and exit of the system (distance-based). The progressive introduction of Information and Communication Technologies (ICT) allows the use of electronic tickets, which helps to reduce costs and improve the(More)
A group signature is a convenient cryptographic primitive to tackle with authentication and privacy problems. In the literature, it is used as an underlying black box by several theoretical proposals of secure applications and services, such as e-cash schemes, automatic fare collection systems and so on. However, there is a lack of implementations of group(More)
Certified e-mail is a particular case of fair exchange. TTPs play an important role in this kind of protocols and their reliability and security is a problem that needs to be addressed. In order to enhance the trust in non-repudiation services we propose TTPs that provide verifiable services, so users get evidence of the TTPs operations. In this paper we(More)
The development of new applications of electronic commerce (e-commerce) that require the payment of small amounts of money to purchase services or goods opens new challenges in the security and privacy fields. These payments are called micropayments and they provide a trade-off between efficiency and security requirements to pay low-value items. It is usual(More)
The new mobile devices can access data networks and they can also execute complex applications. In this work, we present the first micropayment system adapted to these devices, accomplishing the security properties that guarantees the privacy of users and avoids the financial risks. Moreover, the payment phase has been designed as a fair exchange, where the(More)
Great cities try to prevent from high levels of pollution and traffic jams by restricting the access of vehicles to centric zones, also known as Low-Emission Zones (LEZ). Depending on the topology of the city and also on the traffic patterns and contamination levels, the LEZ can be divided in multiple zones with different prices, obtaining a Multifare Low(More)
A wide variety of transport systems can benefit from the use of Electronic Ticketing (ET). ET systems are progressively introduced in transports systems, and produce a reduction of the associated economic costs and time intervals, and the control of the system is improved. However, the use of ET systems enables various privacy abuses both in real-time and(More)
A lot of new applications in the field of electronic commerce require customers to pay small amounts of money to purchase low-value services, goods or pieces of information. These kinds of payments, called micropayments, provide a trade-off between efficiency and security requirements. In a previous work, we presented an efficient and secure micropayment(More)